Archive for the ‘GOES Products’ Category

This was one of those storms that people will talk about for years, especially those that were directly affected by it.  It all started with three separate shortwaves that all phased together once off the Mid-Atlantic coast, far enough offshore to limit any direct effects save for some unusual late season snow and gusty winds the next day.  The highest impact area included Cape Cod, Nantucket, Nova Scotia, and New Foundland.  I’m sure any ships that were in the vicinity were not happy with this situation!

GOES-Sounder RGB Air Mass animation valid 03/24/14-03/26/14.

GOES-Sounder RGB Air Mass animation valid 03/24/14-03/26/14.

The evolution of the nor’easter can be seen in the GOES Sounder RGB Air Mass animation above.  A southern stream system originating in the Gulf of Mexico moved east of Florida while two other shortwaves dropped southeast out of Canada.  All of the pieces combined near the North Carolina coastline, but the explosive deepening took place as the combined system moved northeast away from the Mid-Atlantic.  There appears to be a few stratospheric intrusions, but the most impressive intrusion occurs with the final shortwave as noted by the dark oranges and reds that appear at the end of the day on 03/25.  When models are forecasting a phasing situation, this product can be quite useful in identifying the features and observing the stratospheric drying seemingly “bleed” from one shortwave to the other.

MODIS RGB Air Mass product valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product with ASCAT winds overlaid valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product with ASCAT winds overlaid valid at 1540 UTC on 03/26/14.

The two MODIS RGB Air Mass products above show the nor’easter near peak intensity.  Notice how distinct the gradient between oranges and greens is in this image, almost as though you can see the upper portion of the frontogenesis, well behind the actual front.  The intensity of the stratospheric intrusion is quite evident by the dark pinks near the center of the cyclone.  The second image shows the wind field overlaid from ASCATB.  Notice the large area of hurricane force winds (red wind barbs) near the bent-back front, in the comma-head of the cyclone.  This area of wind affected parts of Southeast Massachusetts, including Nantucket where winds gusted from 60-85 mph.  Nantucket recorded a wind gust of 82 mph and about 10″ of snow.  Meanwhile, Nova Scotia bore the brunt of this beast with wind gusts of 129 mph at the Bay of Fundy and 115 mph in Wreckhouse.  Waves were equally impressive with altimeter readings between 40-50 ft and a buoy report of 52.5 ft.

GOES-13 Infrared imagery with the GLD-360 30-minute lightning density product overlaid.

GOES-13 Infrared imagery with the GLD-360 30-minute lightning density product overlaid.

Another interesting aspect of this storm was the two distinct areas of thunderstorms that erupted.  I overlaid the OPC and TAFB offshore zones for reference.  Notice well east of the Bahamas there are possible supercell thunderstorms associated with the southern shortwave energy.  Meanwhile, as the strong northern stream shortwaves exit the NC coastline, two areas of thunderstorms developed with the easternmost storm exhibiting supercell characteristics.  Although the lightning was not as intense with this northern area, I would speculate that the storms were associated with very strong wind gusts due to the dry air associated with the stratospheric intrusion.

VIIRS Visible image valid at 1719 UTC on 03/26/14.

VIIRS Visible image valid at 1719 UTC on 03/26/14.

VIIRS Visible image with the 18 UTC OPC surface analysis overlaid.

VIIRS Visible image with the 18 UTC OPC surface analysis overlaid.

I’ll finish this entry with two VIIRS Visible images above showing the majestic beauty of this nor’easter.  The 18 UTC OPC surface analysis depicts the storm at a maximum intensity of 955 mb, after a 45 mb drop in 24 hours!  This qualifies as one of the most explosive cyclones on record.  Another tidbit. . .this was the strongest storm in this part of the Atlantic since Hurricane Sandy (2012).

Thanks for reading!

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Late yesterday evening (Dec 17th) fog began forming along coastal areas of Lousiana and Texas.  By 10 pm CST, visibilities at some locations along the coast had already dropped to less than 1 SM.  The fog continued to intensify, with visibilities falling to around 1/4 SM or less at many locations during the early morning hours this morning (Dec 18th).   By 2 am CST (0800 UTC), the visibility had fallen to near 0 SM in portions of SW Louisiana as noted by the observation at Jennings (3R7, near Fenton in the image, image 1).

GOES 11-3.9 Spectral Difference Image, with Ceiling (AGL) and Visibility (SM) observations 18 Dec 2013 0800/0815 UTC

Image 1.  GOES 11-3.9 Spectral Difference Image, with Ceiling (AGL) and Visibility (SM) observations 18 Dec 2013 0800/0815 UTC

In this standard GOES spectral difference imagery however, the fog is very diffcult to visually discern, likely due to it’s very shallow depth.   There is some indication of the fog, with slightly brighter pixels in areas of southern LA and SE Texas.  However, notice the better (albeit slightly) detection of the fog in the Nighttime Microphysics RGB products from the VIIRS and MODIS instruments below (images 2 and 3, respectively).  The fog in these images appears as a pinkish-gray color.

Image 2.  Suomi NPP VIIRS Nighttime Microphysics RGB 18 Dec 2013 0808 UTC

Image 2. Suomi NPP VIIRS Nighttime Microphysics RGB 18 Dec 2013 0808 UTC

Image 3.  Aqua MODIS Nighttime Microphysics RGB 18 Dec 2013 0804 UTC

Image 3. Aqua MODIS Nighttime Microphysics RGB 18 Dec 2013 0804 UTC

I think the fog is a little easier to see in the MODIS image, which may be due to higher resolution and small differences in channel wavelengths between the VIIRS and MODIS instruments.  Nevertheless, the fog in all of the imagery is rather subtle and will require development of pattern recognition by forecasters.  Sampling the color contributions, I found that the primary changes between areas of fog and areas without occurred in the green color (assigned the ~10.8-3.9/3.7 channel difference), which would be expected.  For example, when taking a color sample from the pinkish-gray band of fog in SW Louisiana (near Jennings) from the MODIS image, I came up with: Red-180, Green-137, Blue-165.  Meanwhile, sampling of a pixel in central Louisiana without fog: Red-167, Green-99, Blue-150.

So, how did the fog appear in the Day-Night Band RGBs?  Not very well at all, as you can see in the next couple of images…

Image 4.  Suomi NPP VIIRS Day-Night Band Radiance RGB 18 Dec 2013 0808 UTC

Image 4. Suomi NPP VIIRS Day-Night Band Radiance RGB 18 Dec 2013 0808 UTC

Image 5.  Suomi NPP Day-Night Band Reflectance RGB 18 Dec 2013 0808 UTC

Image 5. Suomi NPP Day-Night Band Reflectance RGB 18 Dec 2013 0808 UTC

I wasn’t able to detect any fog at all in the Day-Night Band RGB imagery.  However, there is still potentially important information to glean from all of this.  If the fog is evident (even slightly) in the NT Microphysics RGB imagery mainly due to the 10.8-3.7/3.9 channel difference, but is essentially translucent in the visible spectrum (Day-Night Band), then it is likely very shallow.  This could be helpful for determining the duration of the fog during a change of conditions, such as the development of mixing after sunrise (i.e. shallow fog dissipation will be quicker than thick fog dissipation).

Notice in the GOES visible loop below (images at 0445 UTC and 0601 UTC) that the fog dissipated very quickly after sunrise (click the expanded image to obtain the loop).

Loop of GOES visible images at 1445 and 1601 UTC with observations of

Loop of GOES visible images at 1445 and 1601 UTC with ceiling (AGL) and visibility (SM) observations  oat 1500 and 1600 UTC

The Corpus Christi, Houston and Slidell offices all issued Dense Fog Advisories or Special Weather Statements concerning the fog in their respective County Warning/Forecast Areas during the early morning hours.

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The RGB Imagery for Aviation and Cloud Analysis got underway on December 1st with SPoRT’s collaborative coastal NWS offices in Southern Region.  These offices include Corpus Christi, Houston, Slidell, Mobile, Melbourne, and Miami.  A separate evaluation with AK offices and CA/OR coastal offices has also begun recently.  The SR coastal office evaluation will run through the end of January, where offices will be evaluating the VIIRS and MODIS Nighttime Microsphysics RGB imagery, VIIRS Day-Night Band Reflectance and Radiance RGBs, in addition to the hybrid GOES/MODIS/VIIRS 11-3.9 um looped product.  SPoRT personnel have conducted training for the offices and will be helping during the evaluation with questions and/or technical issues.  Although RGBs have been used in the European forecast community for years, they are quite new to most U.S. forecasters.  However, and importantly, the imagery available from the Aqua/Terra satellites (MODIS imager) and the Suomi NPP satellite (VIIRS imager) are a part of GOES-R and JPSS Proving Ground activities and will serve as educational tools for forecasters before the GOES-R and JPSS eras.  As a part of the evaluation, forecasters will answer a short survey about the operational impact of these imagery on aviation forecasts in particular, but may of course include impacts for other operational products (i.e. advisories, fire weather, public, hydrologic, etc).

While many potential positive impacts to various forecast products have been related on this blog, I’ll be watching and posting those which forecasters at these offices (and myself) observe during the evaluation period (time permitting of course).  Take the following case from yesterday, December 9th, for example…

Image 1.  SUOMI NPP VIIRS Nighttime Microphysics RGB valid 9 DEC 2013 0736 UTC.

Image 1. SUOMI NPP VIIRS Nighttime Microphysics RGB valid 9 Dec 2013 0736 UTC.

In the image above, notice the swath of light purple colors that extend across a good portion of the TX Gulf Coast.  Further north, in north central and northeastern TX extending to include portions of Oklahoma, Missouri and Arkansas, an area of low clouds with colors closer to dull reds to greenish-white are apparent.  In Image 1, a small area near Corpus Christi, TX has been sampled, with the contributions from Red (183), Green (132) and Blue (209) included in the image (This was sampled in Microsoft Paint).  At about the same time, observations across this region of coastal TX were nearly uniform.  Ceilings were around 300-400 ft from Houston, to Port Lavaca and Corpus Christi, with visibilities ranging from 1.5 to 2.5 SM.

Image 2.  GEOES IR image (730 UTC) with Ceiling (AGL) and Visibility observations (0800 UTC) 9 Dec 2013.

Image 2. GEOES IR image (730 UTC) with Ceiling (AGL) and Visibility observations (0800 UTC) 9 Dec 2013.

Thus, the colors represented by the shades of light purple represented an extensive low stratus/fog deck encompassing the area.  Notice that a swath of this color/cloud type also extended into northern Louisiana and Mississippi.  Low visibilities ranging from 2.5 to 3 SM and low ceilings around 400 ft were observed in both areas.

Herein lies the power of the RGB imagery.  Since the combination of colors are related to several physical characteristics (i.e. red – optical depth, green – particle phase and size, blue – temperature), then it is easier to make assessments about cloud homogeneity or inhomogeneity.   While other satellite observations generally just relate one physical characteristic (usually temperature), or in the case of the standard 11-3.9 channel (particle phase/size), they don’t have the ability to tie together several physical characteristics together in one image like the RGBs can.  It is thus much easier, with RGB imagery, to assess locations where cloud characteristics are the same and make inferences about the similarity of ceilings and visibility in areas without direct observations.

This next image shows a sample of the color taken from the Texarkana site in NE Texas at the same time, underneath the area of low stratus containing more dull red colors.

Image 3.  Suomi NPP VIIRS Nighttime Microphysics RGB valid Dec 9 2013 0736 UTC.

Image 3. Suomi NPP VIIRS Nighttime Microphysics RGB valid 9 Dec 2013 0736 UTC.

As the difference in colors suggests, the cloud characteristics are different here than in SE coastal TX.  Referring to image 2, the ceiling and visibility at Texarkana were 1100 ft and 6 SM, respectively.  Ceilings were still relatively low, but were higher than in coastal TX, as was the visibility.  Essentially, this was a slightly higher stratus deck.  The red color contibutions were very similar in each location, suggesting clouds of similar depth.  However, differences in green and blue are clearly discernible.  The cloud deck near the coast certainly contained more blue, indicating warmer temperatures, which makes physical sense.  The clouds in NE TX contained more green however, which would suggest smaller water particle size. But, emssions in the 3.9 channel from the surface beneath the low/thin cloud deck near the coast may also be contributing to less green color there.  Taking a look at proximity soundings in this area of clouds from Forth Worth (FWD) and Little Rock (LZK), cloud tops decreased during the 00-12 UTC period, but contained super-cooled water droplets by the 12 UTC sounding.

As an aside, forecasters have expressed the desire (including myself) to have the specific values from the red, green, blue color contributions available in AWIPS when sampling the imagery.  This is a valuable part of the feedback and evaluation process.  Unfortunately, this is not possible in AWIPS I, but will be in AWIPS II.

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With the RGB Imagery for Aviation and Cloudy Analysis evaluation underway, we’re already getting some good feedback from our end-users.  From WFO Morristown – “I looked at the Nighttime Microphysics product in hindsight to see how fog around TRI was depicted this morning.  The (RGB) product did an outstanding job of clearly showing areas of fog vs. clouds, even though there were some thin midlevel clouds over the fog areas.”  Below is a loop of the available MODIS (Aqua and Terra) and Suomi NPP VIIRS images from the southern Appalachain region early from late last evening through early this morning (click the image to see the loop).

Image 1.  Loop of Nighttime Microphysics RGB images: Terra MODIS (0359 UTC, Sep 20), Suomi NPP VIIRS (0736 UTC, Sep 20) and Aqua MODIS (0810 UTC, Sep 20).

Image 1. Loop of Nighttime Microphysics RGB images: Terra MODIS (0359 UTC, Sep 20), Suomi NPP VIIRS (0736 UTC, Sep 20) and Aqua MODIS (0810 UTC, Sep 20).

The image shows the early production of fog (ligher, aqua colors) in the Cumberland and Allegheny Plateau region of eastern Kentucky and SW Virginia by the time of the first MODIS pass at 0359 UTC.  Notice how the fog spreads to include other valley locations in East Tennessee by the time of the last images at 0736 UTC and 0810 UTC.

Meanwhile, the fog is clearly not as apparent using the standard 11-3.9 µm imagery (and standard color curve) even with the 1km Aqua MODIS image inserted (image 2, ~0810 – 0815 UTC).

Image 2.  Aqua MODIS and GOES-East hybrid 11-3.9 µm image valid ~0810-0815 UTC, Sep 20 2013

Image 2. Aqua MODIS and GOES-East hybrid 11-3.9 µm image valid ~0810-0815 UTC, Sep 20 2013

…and is even less noticable in the 4km GOES-East image alone a little later at 0832 UTC (image 3).

GOES-East 11-3.9 µm image valid 0832 UTC, Sep 20 2013

Image 3.  GOES-East 11-3.9 µm image valid 0832 UTC, Sep 20 2013

Fog in the narrow valleys in the region shows up quite well in the VIIRS Day/Night Band Radiance RGB, developed by SPoRT (image 4).  The forecaster noted that, “the DNB Radiance RGB showed fog clearly as well, but maybe not quite as well as the Nighttime Microphysics product.”  I would agree, however I was encouraged by the detail and the relative ease with which fog was discernible in the image.

Image 4.  Soumi NPP VIIRS Day/Night band Radiance RGB valid 0736 UTC, Sep 20 2013

Image 4. Soumi NPP VIIRS Day/Night band Radiance RGB valid 0736 UTC, Sep 20 2013

The typical issues with the timeliness of the polar-orbiting imagery, for opertional considerations, appears to be the largest concern for forecasters at this point in the survey process.  Of course, this won’t be an issue in the GOES-R era, and acquanting forecaters with these types of imagery before the next generation of GOES satellites is launched is an important step in the learning process.

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Showers and thunderstorms developed over the northern half of PR Sat Sep 14 and produced localized areas of  2 to 4 inches of rain that resulted in urban flooding and a new daily rainfall record at the San Juan (SJU) LMM Int’l Airport.  A total of 2.88 inches fell at the SJU airport on Sat Sep 14 with 2.52 inches falling in less than 2 hours between 1145 AM and 130 PM. These showers and thunderstorms developed as a result of upper level diffluence ahead of an upper level low over the central Caribbean Sea aided by surface convergence due to sea breeze interaction and abundant moisture.  Figure 1 below shows a four panel display of various water vapor channels from the GOES-Sounder and GOES imager overlaid with ECMWF model height fields and 15/00Z RAOB data.  Figure 2 below shows the 12Z Sat Sep 14 Skew-T for SJU. Note the 20-35-kt south southwest flow at 300 and 200 mb on both the four panel display and the 12Z Skew-T respectively.



Animation of GOES-IR imagery (Fig. 3 below) with increased temporal resolution due to Rapid Scan Operations (RSO) in effect shows the development of showers and thunderstorms first over the San Juan area around 1445 UTC and then over north central and northwest PR through 2015 UTC. The imagery shows cold cloud tops ranging from -50C to -70C that were displaced to the north due to 20-35 kt south southwest flow aloft seen on the 12Z SJU RAOB data.


As part of GOES-R Proving Ground activities, WFO SJU continues to evaluate the NESDIS QPE product which uses mainly GOES-IR channel to estimate rainfall rates.  Satellite based rainfall estimates for the 24-hr period ending 12 UTC Sun Sep 15 (Fig 4 below) showed up to an inch of rain fell just offshore of San Juan due to the coldest cloud tops being displaced to the north due to 20-35 kt south southwest flow seen on the 12Z upper air data.


Gauge data (Fig. 5 below) and Dual-Pol radar estimates (Fig. 6 below) indicate that in general between 1 to a little over 3 inches fell over parts of northern PR. This clearly indicates the need to continue to improve the GOES-R QPE algorithm to estimate rainfall and also to account for shear and cloud storm motions.

24-hr rainfall


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An evaluation of the GOES-R CI product, which was created by researchers at the University of Alabama-Huntsville (UAH), is currently being conducted at several offices in the Southern Region of the NWS, including here at WFO Huntsville.  SPoRT has worked with the UAH team to transition the GOES-R CI product into the Advanced Weather Interactive Processing System (AWIPS) at some of our collaborative offices.  Importantly, this allows for the overlay of other data sets, including radar, satellite and surface or upper-air analyses, which can add context to the CI data.  The evaluation period officially kicked off Monday, August 19th and will continue through the end of September.  During that time, forecasters at NWS offices in Albuquerque, Melbourne, Miami, Corpus Christi, in addition to Huntsville will be providing analysis of the GOES-R CI product and filling out surveys pertaining to its operational utility.  Huntsville is unique in this assessment, in that we are the only office with AWIPS II participating in the evaluation.

The GOES-R CI product is intended to provide forecasters with probabilities of 0-2 hour convective intiation of cloud objects observed in the visible and IR bands of the GOES-East and GOES-West satellites, and serves as a proxy to future GOES-R capabilities.  This product has undergone improvements in recent years based on user feedback, and now incorporates NWP model data (RAP), while outputting a probabilistic value, rather than the binary or strength-of-signal values from prior years.  The product is expected to show operational benefit, in particular, for assessing downstream locations most susceptible to convective activity, and allowing timely forecast updates for airports and/or outdoor venues.

The HUN WFO is glad to be a part of this evaluation and we hope to provide valuable feedback for the GOES-R CI product developers.

UAH GOES-R CI and GOES-East visible imagery, regional view in AWIPS II at WFO Huntsville.  Product valid 1402 to 1445 UTC August 21, 2013.

UAH GOES-R CI and GOES-East visible imagery, regional view in AWIPS II at WFO Huntsville. Product loop valid 1402 to 1445 UTC August 21, 2013.

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A tropical wave moved across Puerto Rico on Thu July 18, 2013 and brought historic rains to the San Juan metro area dumping between 8 to 10 inches of rain in a 24-hr period with most of these rains (8.91 inches) falling in a 6-hr period between 11AM to 430PM. These rains had significant impacts across the San Juan area causing significant flash flooding in area streams and rivers and greatly disrupting ground and air traffic. At one time, over 12 flights scheduled to arrive at the San Juan Luis Muñoz Marin Int’l Airport (SJU LMM) were diverted to the Borinquen airport in northwest PR and the Charlotte Amalie airport in St. Thomas. The 9.23 inches of rain that fell at the SJU LMM Int’l Airport was the second highest 24-hr total ever observed in any single day since records began in 1898.  To read more about other climate records broken with this event, click here.


This 36-hr animation loop (click above for animation) of total water vapor content product from CIRA starting from 18Z Wed July 17 through 03Z Fri July 19 shows the progression of the tropical wave from east of the Lesser Antilles across PR. Values of 60 mm (2.36 inches) were observed over PR with this wave. These values were near the 99th percentile for mid-July according to a precipitable water climatology study done by the Rapid City SD Forecast Office.


Composite Reflectivity animation loop (click above for animation)  from the TDWR from 1239Z through 1609Z shows several clusters of showers and thunderstorms moving over the San Juan area and northeast PR. Just after 1609Z, the TDWR failed likely due to intense lightning activity cutting out power at the radar site.


GOES 4-km infrared imagery animation (click above for animation) shows very cold and intense convection with a large area of tops colder than -70C with tops as cold as -82C at 1710 UTC just north of San Juan.

As part of an evaluation project between WFO SJU and NASA SPoRT, the WFO SJU is evaluating the NESDIS Quantitative Precipitation Estimate (QPE), a satellite-based precipitation estimation product that is derived from both Infrared and microwave data. The image below shows a maximum of 3.14 inches right over the San Juan area during the 24-hr period ending 8AM Fri July 19. Because of the coarse resolution of GOES-IR channel (currently 4km), the satellite is going to miss some of the smaller-scale extremes that will show up in individual gauge reports since the satellite represents an average value over the entire pixel. Even taking that into consideration, satellite based estimates were greatly underestimated for this event. Another factor that may have contributed to the underestimation of precipitation by GOES was the temporal resolution. Rain rates are currently derived every 15 minutes and that didn’t seem to keep up with the rapid evolution and explosiveness of the convection. At one time during the event, 15-minute rain rates were 0.75 inches with 1-hr rain rates of 3.10 inches. However, in the future GOES-R era, both the spatial and temporal resolution will be improved by a factor of 2 with the resolution of the infrared channel at 2km and routine imagery available every 5 minutes.


Image Credit: Bob Kuligowski – NESDIS Center for Satellite Applications and Research (STAR)

The 24-hr rainfall total (image below) precipitation ending for the same period described above shows widespread rainfall amounts of 1-3 inches of rain across all of PR. Over the western half of PR, the satellite-based estimates appeared to have overestimated the amount of rain. This is because the satellite can’t see through thick cirrus clouds and incorrectly assigns a rain rate because the cirrus appear to be a cold cloud. This is a well-known limitation of the current algorithm to derive rain rates from current GOES.


Image Credit: Anita LeRoy – NASA SPoRT

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As part of its GOES-R Proving Ground activities, SPoRT is partnering with Bob Kuligowski (NESDIS) and Alaska WFOs and RFC to assess the Quantitative Precipitation Estimate (QPE) product suite at high latitudes.  The intensive evaluation period will begin July 15 and go until September 15.  The QPE product has been developed in preparation for GOES-R. The QPE algorithm uses the current GOES longwave IR and water vapor channels and is calibrated in near-realtime using microwave sounding retrievals from a variety of satellites (TRMM, NOAA 18 & 19, METOP-A and B). In the GOES-R era, an additional 3 IR channels will be incorporated with the improved resolution to 2km. While the QPE product is better suited to convective type precipitation, this assessment with Alaska operational users is looking at the value of the product at high latitude and what adjustments might be made to improve its use in regimes with more stratiform, low-top precipitation.  Below is a comparison of the QPE to the AK RFC post analysis of the 24-hour precipitation ending on July 7 at 1200Z.  While fairly good agreement exists in some areas, the question is how well the QPE product can provide guidance in low density observation areas at high latitude.

To see a web display of product suite over several domains go to the SPoRT Real-Time Data page for QPE.


QPE 24-hour accumulation ending July 10, 2013 at 1200Z over Alaska domain. Product created by NOAA/NESDIS, transitioned via NASA/SPoRT for use in AWIPS by NWS users.


Web graphic of 24-hour precipitation estimate from the Alaska River Forecast Center ending July 10, 2013 at 1200Z.

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Evaluations of the NESDIS Quantitative Precipitation Estimate (QPE) and CIRA Layered Precipitable Water (LPW) products have been ongoing for a portion of March at three of SPoRT’s collaborative West Coast NWS offices (Monterey, Eureka, and Medford).  The GOES-R QPE is an experimental satellite-based precipitation estimation algorithm using both IR and microwave data from the GOES-East and West satellites.  A suite of products are currently being generated and ported into AWIPS I, including a 15-minute rainrate product and several accumulation products on timescales of 1-hour, 3-hours, 6-hours, 1-day, 3-days and 7-days.  The IR and microwave data used to generate the QPE have different timescale resolutions, about 15 minutes and 1+ hours, respectively.  IR data are used to infer cloud top temperatures and heights, and rainfall rates are derived from this information.  Further calibration with microwave data from the TRMM and NOAA 18/19 helps to fine-time the precipitation accumulations.  However, calibration with tropical environments does not always necessarily translate well in mid-latitude environments, even coastal marine environments.  As a result, precipitation in areas with relatively think cirrus clouds can be overestimated, while the QPE product is thought to perform better in convective situations for operational purposes.

Unfortunately, during the evaluation period, precipitation has generally been below normal, but a couple of events have allowed for a few evaluations of these products so far.

First, the good…

On March 16th, one forecaster noted that the QPE and LPW data were useful for helping to “comfirm that heavy precipitation was not going to be a factor with the incoming front.  QPE was small offshore, and TPW matched model TPW pretty well.”  Below are images of the QPE (Image 1) and LPW (Image 2) as viewed through AWIPS at that time.

Figure 1.  NESDIS QPE 6-hour accumulation product valid 0600-1200 UTC 16 March

Figure 1. NESDIS QPE 6-hour accumulation (inches) product valid 0600-1200 UTC 16 March

Image 2.  CIRA Layered TPW product valid 1500 UTC 16 March.  From upper left clockwise: Total precipitable water, surface-850mb LPW, 700-500mb LPW, 850-700mb LPW

Image 2. CIRA Layered TPW product valid 1500 UTC 16 March. From upper left, clockwise: Total precipitable water, surface-850mb LPW, 700-500mb LPW, 850-700mb LPW

Although relating that the impacts of the LPW product to the forecast process were small, the forecaster did express high confidence in the values and asserted that the value of the layered PW product over a standard total column product was large.  With increased forecaster confidence, details about the incoming storm moisture were noted in the Area Forecast Discussion that morning.

I am eager to evaluate this product over the upcoming weeks, especially during strong moisture advection events concurrent with low or mid-level jets.  It will be interesting to see if having satellite-based information about the vertical distribution of moisture and determining intersecting regions of isentropic lift within these vertical layers will provide better assessments of precipitation.

Now, for the not so good…

The QPE product has tended to overestimate precipitation where cold, thick cirrus clouds are present, making it difficult or impossible to infer reasonable precipitation amounts from the QPE product alone.  On March 20th, a survey respondent noted that “with so much high-level cold cloud tops, the QPE product was virtually unusable.”  In this particuar case, of mostly stratiform precipitation ahead of a frontal boundary, the QPE product far overestimated precipitation east of the Cascades in southern Oregon and underestimated the rainfall near and along the coast.  Notice the swaths of heavy rainfall across northern CA and SE Oregon in the QPE product in Image 3.  However, notice the general lack of precipitation in these areas per the Stage-III product in Image 4 below.

Image 3.  NESDIS 24-Hr QPE product for Oregon and sourrounding areas, valid period ending 12 UTC 20 March

Image 3. NESDIS 24-Hr QPE product for Oregon and sourrounding areas, valid for the period ending 1200 UTC 20 March

Stage-III 24-Hour precipitation for the period ending 12 UTC 20 March

Image 4.  Stage-III 24-Hour precipitation totals for the period ending 1200 UTC 20 March

The forecaster went on to state that “perhaps [the QPE] will be better in the summer with convection…or perhaps in the next few days with the colder NW flow showery regime.”  Indeed, this product is expected to perform better in such situations.

Despite some of the limitations discussed so far, these products do show potential for assessing atmospheric moisture content and precipitation.  The SPoRT team and our collaborative offices will be conducting further evaluations of both stratiform and convective precipitation cases on the West Coast and elsewhere to provide input about these potentially valuable products.

Thanks to Anita LeRoy, Geoffrey Stano and Kevin Fuell for help in providing imagery for this post.

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On Wednesday, February 29th, I trained three HPC forecasters on using the GOES-Sounder RGB Airmass product in operations with model overlays to identify model weaknesses/strengths. The forecasters seemed to grasp this method of training well and one of them included it in the HPC Map Discussion on Friday to show just how well the PV anomaly showed up in this product when compared to conventional water vapor imagery. Below are some sample images as the event unfolded in the Tennessee and Ohio Valleys.

The GOES-Sounder RGB Airmass product valid at 21z on 03/02/12.

Figure 1: The above image shows the severe event unfolding in the Ohio Valley around 21z on 03/02/12. The red circle highlights the tail end of a squall line with discrete cells on the southwest flank. The red circle highlights drying behind the frontal band, but no stratospheric air is evident in this image. The yellow circles highlight three PV anomalies evidenced with the pinks of the dry stratospheric air acting as a tracer.

The MODIS (Aqua) RGB Airmass product valid at 1910z on 03/02/12.

Figure 2: This MODIS (Aqua) RGB Airmass image is two hours earlier (1910z on 03/02/12) and shows greater detail in regards to the drying behind the frontal band. This dry air looks to be part of a larger dry punch that originates from lower in the atmosphere, but may also contain some dry stratospheric air (highlighted in the larger red area). Note the extra dry surge that precedes the frontal band (smaller red area) that was associated with earlier supercells that caused significant tornado damage in parts of southern TN and northern AL. Although we only get a few MODIS passes a day, this product is definitely showing much more detail than the GOES-Sounder product.

The GOES-13 water vapor image valid at 2115z on 03/02/12.

Figure 3: This final image shows the GOES-13 water vapor image at 2115z on 03/02/12 with the CIMSS water vapor table. The red circle highlights the drier air behind the frontal band, indicating drying around 400 mb, which could have aided in the discrete appearance of the southern supercells along with the excellent environmental instability and shear. The yellow circle highlights the earlier disturbance that initiated the supercells in northern AL and southern TN. Although you can identify the drying, it is hard to decipher the origin of that drying from water vapor imagery alone.

This is only one case of how the airmass products could provide additional information to forecasters in identifying subtle features within the synoptic flow. I hope to collect more cases like this to give HPC forecasters and SAB analysts more confidence in isolating a particular region that would be at high risk for heavy rainfall. This could also prove useful to SPC forecasters for identifying heightened risk areas for severe weather.

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