Feeds:
Posts
Comments

Archive for the ‘JPSS Proving Ground’ 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!

Read Full Post »

Well, it’s February and it’s the East Pacific off of California, so the short answer is no.  But. . .what an amazing structure, right?  We haven’t seen anything this good looking in the tropical Atlantic in years!  But I digress. . .

MODIS RGB Air Mass product valid at 0621 UTC on 02/28/14.  The blue lines are the boundaries of OPC (north), TAFB (south), and Hawaii (west)

MODIS RGB Air Mass product valid at 0621 UTC on 02/28/14. The blue lines are the boundaries of OPC (north), TAFB (south), and Hawaii (west)

MODIS RGB Air Mass product valid at 1032 UTC on 02/28/14.

MODIS RGB Air Mass product valid at 1032 UTC on 02/28/14.

The first image was collected four hours before the second image and you can see how the center of the intense storm developed an “eye-like” feature (images courtesy of NASA SPoRT).  Notice the distribution of the pinks and reds in both images as well.  That is dry, stratospheric air filling the center of the strong upper-level low (~300-500 mb).  The second area shows an additional area of pink approaching the southern California coast.  This area is associated with strong instability that has led to rare California thunderstorms.

So, how do we know if there is stratospheric air?

AIRS Total Column Ozone product valid at 2200 UTC on 02/27/14.

AIRS Total Column Ozone product valid at 2200 UTC on 02/27/14.

AIRS Ozone Anomaly Product valid at 2200 UTC on 02/27/14.

AIRS Ozone Anomaly Product valid at 2200 UTC on 02/27/14.

The first image above is the AIRS Total Column Ozone product developed at NASA SPoRT.  The color bar on the left is not correct.  The main idea is that the warmer (cooler) the colors, the more (less) ozone is in the atmospheric column.  The green colors indicate ozone levels above 200 Dobson Units (ozone unit of measurement) with the magenta areas indicating ~500 Dobson Units.  The second image shows the AIRS Ozone Anomaly product with the first level of blue indicating 125% of normal, while the yellow region indicates >200% of normal ozone at that latitude and geographic location.  Stratospheric air is associated with high levels of ozone and potential vorticity which can help identify the strength of the upper-level low.  These images show the connection of this ozone pocket with the “reservoir” of ozone located in the northern latitudes at this time of year.

AIRS Total Column Ozone Product valid at 1000 UTC on 02/28/14.

AIRS Total Column Ozone Product valid at 1000 UTC on 02/28/14.

AIRS Ozone Anomaly valid at 1000 UTC on 02/28/14.

AIRS Ozone Anomaly valid at 1000 UTC on 02/28/14.

As the upper-low cut off and became stacked over the surface low (~971 mb), you can see how the high concentration of ozone becomes more focused over the storm.  Once again, the magenta coloring indicates ozone levels >500 Dobson Units.  The anomalies are more incredible with a large area of >200% of normal directly west of southern California.

I will continue to work with forecasters at OPC, TAFB, SAB, and WPC on discovering ways to use these products in conjunction with the RGB Air Mass products to gauge storm strength and look for signals upstream of developing tropopause folds and stratospheric intrusions.

GOES-15 Visible imagery with the GLD-360 30-minute lightning density product overlaid.

GOES-15 Visible imagery with the GLD-360 30-minute lightning density product overlaid.

The ozone isn’t the only impressive part of this storm.  Notice the occasional bursts of lightning within the spiral bands of the parent storm.  Although not completely unusual, this is a great indicator of how much energy is available to this storm.

GOES-Sounder RGB Air Mass product with GLD-360 lightning strikes overlaid.

GOES-Sounder RGB Air Mass product with GLD-360 lightning strikes overlaid.

I put together a longer animation of the GOES-Sounder RGB Air Mass product with the GLD-360 lightning strikes overlaid.  Note the first system that came ashore in California earlier this week, then moved over the four-corners regions with plenty of lightning, especially for this time of year.  The current storm is seen lurking offshore with more lightning developing in a band of thunderstorms that moved from Los Angeles to just north of San Diego.  This system will be responsible for the next bought of winter weather for the Midwest to the Mid-Atlantic next week.

Thanks for reading and as always, feel free to contact me with questions and feedback!

Read Full Post »

SPoRT is conducting an assessment of RGB imagery for Aviation and Cloud Analysis with Alaska WFO partners.  A 17 minute training module for high-latitude application of nighttime RGBs with an Alaska example was created by SPoRT to support this assessment (see SPoRT training page to download or launch module). The Juneau WFO provided feedback for 1/24/14.  Here is a part of their feedback regarding the value of the Nighttime Microphysics RGB imagery from MODIS and VIIRS and an example image from AWIPS/D2d.

WFO Juneau feedback:
“… the microphysics image was very helpful in picking out where the fog and low clouds were in the complex terrain that is the SE panhandle. most of the fog this morning was confined to the narrower valleys and channels while the wider channels were mostly clear. This is possibly due to higher winds still present in the wider channels limiting fog formation there. It also showed little or no fog and low clouds out in the gulf. The microphysics image was very helpful with figuring out fog for zone and marine forecasts. It also helped out with the TAFs with seeing if there were any higher clouds layers above the fog layer.”

AJK_Ntmicro_assess_feedback_for_blog_20140124_0736_annotated

Read Full Post »

Just thought I’d make a short post to mention a myriad of features observed in the early morning hours of the 12th from the VIIRS instrument aboard the Suomi NPP satellite.  In image 1 below, a faint surface snow field can be seen stretching across parts of northwestern Missouri into Iowa, deep convective clouds and even a couple of flashes of lightning were present in the western Atlantic off the North Carolina coast, and rippling wave clouds can be seen in the lee of the Appalachians.  These were among several features I wanted to showcase, and importantly, the surface snow field and lightning are two features observable only in the Day-Night Band.  However, I also wanted to point out an unusual and rather sharp reflectance that appeared in the near coastal waters of Louisiana.  In fact, it’s probably the most prominent feature in the image.  In image 1 below, notice the bright yellow colors that appear in the Gulf waters just south of Louisiana.

Image 1.  Soumi NPP VIIRS Day-Night Band Radiance RGB, valid 12 Jan 2014 0700 UTC

Image 1. Soumi NPP VIIRS Day-Night Band Radiance RGB, valid 12 Jan 2014 0700 UTC

This image is the Radiance RGB produced from the raw image of emitted and reflected light.  There is likely no source emitting that much light south of Louisiana, so this is largely reflected light.  But, what is doing the reflecting?  Also, why was there such a sharp gradient in the reflected light?  At the time of the Suomi NPP passage, the moon was at an elevation of about 35.5 degrees above the western horizon (at New Orleans, courtesy of the U.S. Naval Observatory).  So, the moon wasn’t behind the satellite during its passage, resulting in some glare from directly reflected light, but was relatively low on the horizon to its left (from the point of view facing Earth).  I don’t really have any answers, but wanted to point out this odd feature in case someone else had any good ideas.

For the previous day, I noticed that winds in the region had been southwesterly, but then shifted from the west to northwest by the aftenoon as a cold front crossed the area.  Offshore winds dominated for the rest of the day and were gusty at times before calm winds prevailed late that night.  Perhaps some material of a more reflective property upwelled during the afternoon and evening?  Or perhaps there was something about the thermal properties of the water that resulted in refraction of light into the sensor?  Without a more thorough analysis I can’t be sure.  I don’t recall seeing anything like this in the Day-Night Band imagery before.  Notice the area of brightness appears in the Day-Night Band Reflectance product quite well too (image 2).

12Jan2014_VIIRS_DNBReflectance_GulfReflectance

Image 2. Soumi NPP VIIRS Day-Night Band Reflectance image, valid 12 Jan 2014 0700 UTC

Read Full Post »

A well defined TROWAL feature that set up over the high plains from eastern NM into western TX and KS on December 21, 2013 was captured very well by the NESDIS snowfall rate product.   A composite radar reflectivity loop in the first image below summarizes the overall evolution of this feature between 12 UTC on December 21st and 00 UTC on the 22nd (click image to loop and enlarge).  Initially temperatures were too warm for snow across much of the area however as a potent cold front shifted south over the region rain changed over to snow.  In the area of greatest instability the snow became heavy at times from near Tucumcari, NM (KTCC) to Dalhart, TX (KDHT).

Composite Radar Reflectivity Loop December 21, 2013.  Click to enlarge.

Composite Radar Reflectivity Loop December 21, 2013. Click to loop and enlarge.

The following series of images compare hourly precipitation reports at several sites across western TX and KS with the NESDIS snowfall rate product.  The first image was captured at 2040UTC and the AWIPS cursor readout at KDUX (Dumas, TX) is shown.  Note the observation is reporting an hourly precipitation accumulation of 0.05 (P0005) with moderate snowfall and a visibility of 1/2SM.  The cursor readout comparison with the QPE product is 0.0544 in/hr.  The following sample point valid for KPYX (Perryton, TX)  is reporting a visibility of 1/4SM however no weather or precipitation is available since it is only an AWOS.  However, the QPE product is sampling a precipitation rate of 0.1064 in/hr which converting with a simple 10:1 snow ratio would equate to heavy snow at 1″ per hour.  The next image was captured at 2236UTC and the cursor readout at KDDC (Dodge City, KS) is shown.  Note the observation is reporting an hourly precipitation accumulation of 0.07 (P0007) with moderate snowfall and a visibility of 1/2SM.  The QPE comparison in the readout shows a rate of 0.092 in/hr.  These values are exceptionally representative of the current conditions and the latency is less than 30 minutes.

NESDIS QPE valid 2040 UTC December 21, 2013.  Note the sample point comparison for the observation at KDUX (Dumas, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KDUX (Dumas, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KPYX (Perryton, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KPYX (Perryton, TX).

NESDIS QPE valid 2236 UTC December 21, 2013. Note the sample point comparison for the observation at KDDC (Dodge City, KS).

NESDIS QPE valid 2236 UTC December 21, 2013. Note the sample point comparison for the observation at KDDC (Dodge City, KS).

After the storm system pulled out of the region the Snow-Cloud RGB product provided a stellar view of this mesoscale band of snowfall.  Modifying temperatures over the following days significantly eroded snowpack in most areas except where the heaviest snow fell.  Local storm reports obtained from the Iowa State website indicated between 6 and 11 inches of snow impacted the area within the central axis of the TROWAL feature.

Snow-Cloud RGB valid at 1704 UTC December 22, 2013.

Snow-Cloud RGB valid at 1704 UTC December 22, 2013.

Snow-Cloud RGB valid at 2014 UTC December 24, 2013.

Snow-Cloud RGB valid at 2014 UTC December 24, 2013.

Read Full Post »

I’ve posted about this a few times, but this morning offered another good example of the ability of the Suomi NPP VIIRS Day-Night Band RGB imagery to show low clouds beneath thin cirrus.  First, take a look at the 11-3.9 µm imagery (with the standard color curve) from the VIIRS instrument, valid this morning at approx 0749 UTC.  Focus your attention mainly over southern Texas.

Suomi NPP VIIRS 11-3.9 µm image valid 19 Dec 2013 0749 UTC

Image 1.  Suomi NPP VIIRS 11-3.9 µm image valid 19 Dec 2013 0749 UTC

In the image above, high, cirrus clouds will appear as blue colors, while lower clouds appear yellow.  Notice the bank of low clouds in the northern Gulf extending into portions of extreme SE Texas and southern Louisiana.  Notice that some low clouds can also be observed in and around the thin cirrus to the southwest in southern Texas.  These cloud features show up arguably better in the VIIRS Day-Night Band image from the same time (image 2).

Image 2.  Soumi NPP VIIRS Nighttime Microphysics RGB 19 Dec 0749 UTC

Image 2. Soumi NPP VIIRS Nighttime Microphysics RGB 19 Dec 0749 UTC

With the Nighttime Microphysics RGB, the low clouds appear as an off-white, while the high thin cirrus are the deep reds and blues spreading across much of the CONUS in the image.  Notice the low clouds in southern Texas still cannot be observed very well beneath the cirrus canopy, as the cirrus are mostly opaque to the longer IR wavelengths.  Now, let’s take a look at the VIIRS Day-Night Band imagery.  I like the Day-Night Band Radiance RGB best for this particular situation (image 3).

Image 3.  Suomi NPP VIIRS Day-Night Band Radiance RGB 19 Dec 2013 0749 UTC

Image 3. Suomi NPP VIIRS Day-Night Band Radiance RGB 19 Dec 2013 0749 UTC

Since the cirrus are mostly translucent in the visible portion of the spectrum, the low clouds can be seen beneath.  Also, given that the Day-Night Band Radiance RGB has an IR component, this results in better delineation between high and low clouds.  In this situation, forecasters would have a much better idea of the extent of the low cloud deck.  Observations from 0800Z indicated the cloud bases were around 1-2 kft in that area of southern Texas, which could have significant impacts on sensible weather and forecasts, especially for aviation.

Read Full Post »

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.

Read Full Post »

Well, of course the moon didn’t disappear, but it’s now back at a position where reflected moonlight will be available during the Suomi NPP passes each night…for about the next two weeks anyway.  Yesterday, the VIIRS Day-Night Band imagery didn’t show much as the moon was just over the horizon in the east when the Suomi NPP satellite and VIIRS instrument passed overhead (image 1).

Image 1.  Suomi NPP VIIRS Day-Night Band Radiance RGB image 11 Dec 2013

Image 1. Suomi NPP VIIRS Day-Night Band Radiance RGB image 11 Dec 2013 0659 UTC

Notice that just a faint hint of reflected moonlight was available in the far western portion of the image when the VIIRS instrument passed overhead around 0700 UTC.  However, this morning, with the moon in a better position and at 77% phase (notice it was 67% yesterday), more reflected moonlight was available to make out some cloud features (image 2).

Image 2.  Suomi NPP VIIRS Day-Night Band Radiance RGB 12 Dec 2013

Image 2. Suomi NPP VIIRS Day-Night Band Radiance RGB image 12 Dec 2013 0641 UTC

Low clouds in the Gulf region showed up better this morning, with more visible light available.  Interestingly, if you look closely, you can see a shadow cast by the low/mid cloud deck in the north central part of the Gulf, on a rough line running generally south of the Pensacola/Destin FL area.  Observations at the time showed the base of this cloud deck was at about 7-9 kft.  So, it would have cast a shadow with a low moon angle!

Observations with the VIIRS Day-Night Band imagery will continue to improve over the next few days as the moon approches full phase.

 

 

Read Full Post »

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.

Read Full Post »

A ridge of high pressure moved into the desert southwest in the wake of a strong winter storm system that impacted the region last weekend.  Strong low level inversions beneath the ridge and melting snow cover increased the potential for an extended period of low clouds and freezing fog.  The MODIS Nighttime Micropyhsics product valid at 0501 UTC November 29, 2013 showed low clouds and possible areas of freezing fog along the I-70 corridor over and west of Grand Junction.  Observations at Grand Junction verified IFR low clouds at 900′ with visibilities above 6 miles.  The following VIIRS Nighttime Microphysics product at 0904 UTC November 29, 2013 showed low clouds and freezing fog expanding eastward into the Colorado, Gunnison, and Uncompahgre River Basins and the Grande Valley south of Grand Junction.  Visibilities have been significantly reduced to 1/4 mile at Montrose and farther south at Cortez.  The ceiling at Montrose is 200′ with visibility at 3/4 mile.  The nighttime microphysics product shows exceptional detail within the narrow valleys along Roan Creek to the northeast of Grand Junction.  Notice the fog and low cloud deck is very close to Rifle at 0904 UTC but the observation still suggests clear skies.  31 minutes later at 0935 UTC  the observation at Rifle dropped to LIFR at 400′ however visibilities remained at or above 6 miles.

MODIS NT Microphysics product valid at 0501 UTC November 29, 2013.

MODIS NT Microphysics product valid at 0501 UTC November 29, 2013.

VIIRS NT Microphysics product valid at 0904 UTC November 29, 2013.

VIIRS NT Microphysics product valid at 0904 UTC November 29, 2013.

Read Full Post »

Older Posts »

Follow

Get every new post delivered to your Inbox.

Join 91 other followers