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So, with the moon now passing into the waning crescent phase, the Day-Night Band imagery is less operationally useful, at least for the detection of fog and other lower level cloud types.  That is, at least until the moon is back into the waxing gibbous phase.  Nevertheless, when cirrus clouds aren’t present, the Nighttime Microphysics RGB has proven to be a very valuable tool for the detection of fog and other low-level clouds.  Just this morning a forecaster at the Huntsville, AL WFO was able to use the imagery not only for the detection of fog, but also to aid in the issuance of a special weather statement about the fog.  The image below valid at ~724 UTC (0224 am CDT) 17 Oct shows the fog (whitish-aqua colors) lying across the valley areas of NE Alabama and adjacent areas of southern Tennessee and NW Georgia.

MODIS Nighttime Microphysics RGB 724 UTC 17 October 2014

 

Around the time of this image, the visibility in the foggy locations had decreased to ~1/4 – 1/2 SM or less.  Notice the fog in the DeKalb Valley is fainter than the fog in areas to the north and west.  Not only is the DeKalb Valley more narrow, but the fog was likely more shallow.  This feature of the imagery can also help to guide forecasters in assessing the longevity of the fog once sunrise breaks.  Over time, forecasters can develop a sense of pattern recognition with the varying degrees of color shading and tailor forecasts to better match the time of dissipation.  In this case, the fog in the DeKalb Valley began to dissipate significantly by about 1430 UTC, while  the deeper and more expansive fog to the north and west lasted about an hour longer.

We are in the third and final month of assessing SPoRT’s real-time version of LIS running the Noah land surface model. The assessment is being conducted at the NWS forecast offices in Huntsville, Houston, and Raleigh to determine the utility of SPoRT-LIS for monitoring drought and areal flooding potential. The past 1-2 weeks featured substantial rainfall that occurred over a large portion of the central and eastern U.S.  Much of this precipitation was associated with a deep trough that progressed from the Southern Plains to the U.S. East Coast from 13-16 October.  Fairly widespread rainfall amounts exceeding 5 inches occurred over portions of eastern Oklahoma, south-western Missouri, western Arkansas, and in a swath extending from southeastern Arkansas to the southern Appalachians (Fig. 1).

Fig 1.  Depiction of 7-day rainfall estimates from the Stage IV radar+gauge product, ending 1200 UTC 16 October 2014.

Figure 1. Depiction of 7-day rainfall estimates from the Stage IV radar+gauge product, ending 1200 UTC 16 October 2014.

One of the SPoRT-LIS fields that forecasters have found quite useful during the assessment is the one-week change in total column relative soil moisture (RSM, 0-2 m).  The RSM is the ratio of the current volumetric soil moisture between the wilting and saturation points for a given soil type, with values scaling between 0% (wilting) and 100% (saturation).  In response to the recent substantial rainfall over the Deep South, the LIS total column RSM increased by 8-24+% over a large area (Fig. 2) approximately corresponding to the areas that received 4 or more inches of rainfall in the past week given by the orange and red shading in Figure 1. This beneficial rainfall led to the improvement of the U.S. Drought Monitor classification by 1-2 classes over portions of Kansas, Oklahoma, Texas, extending into Alabama, Tennessee, and northern Georgia (Fig. 3).  The most recent U.S. Drought Monitor product issued on 14 October (Fig. 4) shows that all drought classes have been removed over northern Alabama, Tennessee, and Kentucky.

Fig 2.  SPoRT-LIS one-week change in total column (0-2 m) relative soil moisture valid 1200 UTC 16 October 2014.

Figure 2. SPoRT-LIS one-week change in total column (0-2 m) relative soil moisture valid 1200 UTC 16 October 2014.

Fig 4.  One-week change in the U.S. Drought Monitor classifications, from 7 to 14 October 2014.

Figure 3. One-week change in the U.S. Drought Monitor classifications, from 7 to 14 October 2014.

Fig 3.  U.S. Drought Monitor classification valid 14 October 2014.

Figure 4. U.S. Drought Monitor classification valid 14 October 2014.

I wanted to follow up with this sooner, but I’ve been rather busy preparing for the NWA conference.  Yep, I tend to be one of those “last-minute” people.  Anyway, just last week I posted an example showcasing the advantage of the VIIRS Day-Night Band Radiance RGB in detecting fog through cirrus clouds.  The next day, SPoRT collaborator Doug Schneider (Morristown WFO), followed up with another great example that I wanted to share.  I’m just going to take an excerpt from an email he sent to the Morristown staff…

“I know I’ve been sending out quite a few emails lately about NASA SPoRT products, so please bear with me, but I thought this was a great example of how they can add value.

I’ve mentioned the MODIS/VIIRS Fog product before, but sometimes there are better products available for identifying fog, especially when thin cirrus are present. In the MODISVIIRS Fog product image that is attached, you can see that it is difficult to see the extent of fog. There’s clearly some in the Sequatchie Valley, but there is also some in the NE TN/SW VA area that can’t be easily seen.

The attached MODIS/VIIRS Nighttime Microphysics product also shows fog in the southern areas where it is clear (fog is light blue colors), but cirrus obscures NE sections.

The VIIRS Day/Night Band Radiance RGB product does the best job showing the extent of fog. Fog is clearly identified in the valleys of SW VA and NE TN, despite the presence of cirrus. The extent of fog is also more easily seen in the central and southern valley areas.

The attached menu image shows where you can find the Day/Night Band Radiance RGB product under the Satellite -> NASA SPoRT -> Polar Imager -> MODIS/VIIRS -> SR East menus.

Remember that these products are from a polar-orbiting satellite, and may only be available once a night, usually between 07z and 10z.”

I’ve included the images he referenced below, and circled the specific area of fog in NE Tennessee / SW Virginia that he was mentioning.

Suomi-NPP VIIRS Day-Night Band Radiance RGB, 0724 UTC 10 Oct 2014.  Circled area shows valley fog not detectable in subsequent GOES or VIIRS NT Microphysics images.

Suomi-NPP VIIRS Day-Night Band Radiance RGB, 0724 UTC 10 Oct 2014. Circled area shows valley fog not detectable in subsequent GOES or VIIRS NT Microphysics images.

Suomi-NPP VIIRS 11-3.9 um image, 0724 UTC 10 Oct 2014.  Notice that high cirrus clouds (blue colors) obscure the fog below.

Suomi-NPP VIIRS 11-3.9 um image, 0724 UTC 10 Oct 2014. Notice that high cirrus clouds (blue colors) obscure the fog below.

Suomi-NPP VIIRS Nighttime Microphysics RGB, 0724 UTC 10 Oct 2014.  Fog can be seen in other areas to the south/southwest, but not beneath the cold, cirrus clouds (under the yellow circle) since this RGB recipe contains multi-spectral IR components.

Suomi-NPP VIIRS Nighttime Microphysics RGB, 0724 UTC 10 Oct 2014. Fog can be seen in other areas to the south/southwest, but not beneath the cold, cirrus clouds (under the yellow circle) since this RGB recipe contains multi-spectral IR components.

This is exactly the kind of inter-office sharing SPoRT is looking for from our close partners.  We greatly thank Doug and the Morristown office for their collaborative efforts!

I’ve blogged about this particular use of VIIRS Day-Night Band imagery before, but wanted to take a moment to showcase this excellent example from last night.  In the early morning hours of Thursday, Oct 9th, fog began developing in the valleys of Jackson County, AL (denoted by the yellow circle), as it often does on nights with high relative humidity and light winds.  Of course, save for a scant observation or two, a forecaster would not have known because of the presence of high, thin cirrus clouds that obscured the fog below.  Take a look at this GOES-IR image from early that morning (Image 1).

Image.  GOES-IR image over northern Alabama and surrounding areas, valid 0745 UTC 9 October 2014

Since this is an IR image, temperatures from the colder cirrus clouds saturate the instrument signal across northeastern portions of Alabama, where the fog occurred.  Clearly, fog could not be discerned in this type of imagery due to the presence of cirrus.  Next, let’s take a look at a Nighttime Microphysics RGB image from the Suomi-NPP VIIRS instrument valid at about the same time (Image 2).

Image 2. Nighttime Microphysics RGB from the Suomi-NPP VIIRS instrument, valid 0743 UTC 9 October 2014

Even here (in what has become favorite imagery of mine) the fog is not clearly detectable.  Perhaps a faint hint of fog, indicated by a narrow sliver of whitish-gray can be seen in the far northwest corner of Jackson County.  Nevertheless, since this RGB recipe utilizes different IR components, the cirrus once again obscures the fog below.  Now, let’s take a look at SPoRT”s Day-Night Band Radiance RGB valid at the same time (Image 3).

Image 3.  Day-Night Band Radiance RGB from the Suomi-NPP VIIRS instrument, valid 0743 UTC 9 October 2014

The fog is much more clearly observed in this imagery since thin cirrus are mostly translucent in the VIIRS nighttime visible band.  This image, as stated, is an RGB and also employs a longwave IR channel (~11 µm), giving the cirrus a blue appearance.

Visibility observations are only available from one site in this area, at the Scottsboro, AL airport, which is located near the center of the circle.  At 0800 UTC, the visibility at the location was 7 SM, but dropped to 1/4 SM by 0900 UTC.  However, that is just one small point location.  Forecasters really need a better understanding of the extent of the fog for special weather statements or dense fog advisories that address the threat.  After viewing the Day-Night Band imagery for well over a year now, I think the ability to see fog and other phenomena through cirrus at night is one of the best applications of the DNB imagery, at least from an operational forecast perspective.

On the evening of Monday, October 6th, several severe thunderstorms producing large hail moved across the Tennessee Valley region.  I, along with another colleague, was on the radar desk for severe weather operations at the Huntsville, AL Weather Forecast Office.  Some thunderstorms in the region had already produced large hail up to the size of golf balls to our north.  As a vigorous short wave moved through the region, leading to increased lapse rates and deep layer shear, the threat for large hail was expected to continue into the early evening hours.  As usual here at the Huntsville WFO, total lightning data from the North Alabama Lightning Mapping Array (NALMA) were incorporated into our warning decision process.

At 548 pm CDT, my colleague  issued an initial severe thunderstorm warning for a storm cell located over northwestern portions of Jackson County, AL, primarily for the expectations of large hail.  Reflectivity from the KHTX radar and the initial polygon can be seen below in image 1.

Reflectivity0.5_JacksonCounty_Oct62014-7

Image 1.  KHTX 0.5 degree reflectivity (dBZ) with warning polygon issued at 2248 UTC (548 pm CDT) 6 Oct 2014. The black circle near the top center of the image is the KHTX “cone of silence”.

I had taken over warning responsibility for this severe thunderstorm by 6 pm and was having to decide whether or not to continue the warning when it expired at 615 pm CDT.  This storm was tracking very close to the KHTX radar (noted by the black circle) and it was difficult to make out some of its higher level features and characteristics (although the Advanced Radar for Meteorological and Operational Research (ARMOR) was also being utilized at this point).   The storm had wavered in intensity since the warning issuance and was only expected to be at the low-end of severe criteria.  Another factor complicating the warning decision was that this storm was tracking over an area with very low population density.  So, severe weather reports providing ground-truth were difficult to come by, and in fact, we had not received any yet allowing for verification of the warning.

Nevertheless, this is where the NALMA data came into play.  Just shortly after the severe thunderstorm issuance, source densities within the storm surged, with values reaching well over 400 sources (image 2) between 550 and 552 pm CDT.

Source density values from the North Alabama Lightning Mapping Array, 2-min period ending 552 pm CDT (2252 UTC) 6 October 2014.

Image 2. Source density values from the North Alabama Lightning Mapping Array, 2-min period ending 552 pm CDT (2252 UTC) 6 October 2014.

 

Over the next series of updates from the NALMA, source densities maintained relatively high values.  As late as 2302 UTC, when I was beginning to consider the continuance of the warning, source values were still around 400 or higher.  Afterward, values did gradually decrease.  However, with the understanding that hail production will take some time following the strengthening updraft and that severe weather may not manifest up to about 30 minutes (or longer in some cases) after sustained surges in total lightning, I decided to continue the warning (Image 3).  As the storm continued eastward, we finally received our first reports of one inch diameter hail in the town of Stevenson.  Interestingly, the hail accumulated to the depth of a few inches according to one report.

So, yet again, this was another case in which total lightning provided value-added data and significant help for an operational warning decision.

Stevenson

Image 3. KHTX 0.5 degree reflectivity with warning polygon (yellow), valid 617 pm CDT 6 October 2014. The town of Stevenson, AL is highlighted where one inch diameter hail was reported covering portions of Hwy 72.

 

 

From September 20 through September 23, 2014, the Ocean Prediction Center (OPC) was monitoring the development of the season’s first hurricane-force extratropical storm in the East Pacific.  Models were suggesting a marginal hurricane-force wind event would unfold well west of the Pacific Northwest, near 140W longitude, north of 40N latitude.  OPC is routinely using satellite data to monitor and forecast these strong ocean storms.  On this particular event, OPC forecaster James Kells collaborated with Michael Rowland and David Kosier on if and when to pull the trigger on the hurricane-force warning.

GOES-15 6.5 um water vapor animation showing the evolution of the hurricane-force low.

GOES-15 6.5 um water vapor animation showing the evolution of the hurricane-force low.

The above animation shows the evolution of the hurricane-force low, with an eye-like feature evident near the end of the loop.  By 1200 UTC on the 23rd, it was forecast to develop hurricane force winds (64 knots or greater) just west of Oregon near 140W.  During the production of the 1200 UTC OPC Surface Analysis, there was question of whether or not the winds had reached hurricane force intensity. The ASCAT pass from ~0600 UTC showed a large area of 50-55 knot winds in the strong cold advection south of the low center, and the GFS model indicated that the system was still developing.  The GFS 0-30m boundary layer winds also indicated a very small area with hurricane force intensity.

Advanced Scatterometers A and B overlaid on GOES-15 Infrared imagery showing storm force winds at ~0600 UTC on 09/23/14.

Advanced Scatterometers A and B overlaid on GOES-15 Infrared imagery showing storm force winds at ~0600 UTC on 09/23/14.

The 1130 UTC MODIS RGB Air Mass product was timelier, and it showed an area of downward momentum south of the low with the deep purple shading. The corresponding water vapor image was less clear with upper level moisture obscuring the downward motion just beneath it.   In addition, there were no surface reports south of the low center as there were no buoys moored nor drifting in that vicinity.  Furthermore, most ships were aware of the danger and navigated away from the region neglecting the possibility of a surface report in the area of question.

Aqua MODIS RGB Air Mass image from 1130 UTC on 09/23/14.

Aqua MODIS RGB Air Mass image from 1130 UTC on 09/23/14.

A cross-section of the 1200 UTC 09/23/14 GFS model potential temperature and dew point temperature was taken through the low center in order to analyze the depth of the stratospheric intrusion, and also to gauge the magnitude of the downward momentum.  It showed a deep stratospheric intrusion to roughly 500 hPa, and it corroborated the strong downward momentum indicated by the imagery.  The RGB Air Mass image showed the intensity of the downward momentum through the red/purple coloring and gave a good indication of the stronger winds aloft mixing down toward the surface.  The imagery increased confidence with classifying the system as a hurricane force low.

The 1200 UTC 09/23/14 GFS vertical cross-section of potential temperature and dewpoint showing the downward transport of drier air associated with the tropopause fold.

The 1200 UTC 09/23/14 GFS vertical cross-section of potential temperature and dewpoint showing the downward transport of drier air associated with the tropopause fold.

The 1200 UTC 09/23/14 OPC surface analysis.

The 1200 UTC 09/23/14 OPC surface analysis.

~ Guest blogger, James Kells (OPC)

The North Carolina Drought Management Advisory Council (NCDMAC, which consists of multi-agency representatives from local through federal level) has a weekly videoconference to assess drought conditions across North Carolina and provide guidance/suggestions for the U.S. Drought Monitor (http://www.drought.gov/drought) product. Many factors are considered, including agricultural reports, stream levels, and rainfall distribution/deficit, to name but a few. The National Weather Service Office in Raleigh introduced and began to present SPoRT’s 0-200cm relative soil moisture products to the council in July. Soil moisture data, especially near-real-time data, is almost always difficult to find, and the NCDMAC typically relied on a rather sparse network of monitored wells and rainfall deficits as a proxy for quantitative analysis of a quality dataset. The data has been very well received and this week played a role in the council’s decision to recommend expansion of D0 across a major portion of the NC piedmont. The sub-county resolution was especially useful in determining where to ‘draw the line’, so to speak.

SoilMoisture
0-200 centimeter relative soil moisture. Values generally below 25 percent were used to highlight potential D0 area.

SoilMoistureChg
0-200 centimeter relative soil moisture – weekly change.

usdmsep23
U.S. Drought Monitor – resulting expansion of D0 across central NC.

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