Low clouds and fog in the N. Gulf and Texas regions caused MVFR/IFR/LIFR conditions over a large area. The VIIRS Nighttime Microphysics RGB shows aqua to gray coloring to represent these features. In the RGB the scene is fairly complex with high and middle clouds (reds, blues, purples, tans …..). The RGB composite uses the traditional 11-3.9um difference (seen below) and combines other channels to better illustrate the low cloud features between the middle/high clouds. The RGB also improves the characterization of the thick, cold cloud tops associated with the cutoff low producing precipitation along the coast and southern states when compared to the simple 11-3.9um. Other “microphysical” RGBs are possible during the day or in a form that can be applied both day and night (i.e. 24hr product).
The MODIS RGB image below captured the dust event in portions of the Intermountain West today, April 14th, as strong winds lifted dust across the drought-stricken region. NWS offices in the region issued high wind warnings and dust storm warnings due to the conditions. Visibilities below one quarter mile in some instances were reported with portions of I 80 closed near Tooele, Utah. The dust is indicated by pinkish colored steaks across portions of Utah and Nevada in the Dust RGB below.
This pic was tweeted by Jed Boal of KSL5 TV in Salt Lake City.
Addendum… I just wanted to update with another image a little later on the 14th to show the evolution of the blowing dust. The area of dust ahead of the frontal boundary was diminishing by about 2030 UTC in Utah, while the large area of dust continued to impact portions of southern Nevada in strong northwesterly flow in the post-frontal airmass (image below).
On April 9, 2015 a powerful storm system moved through the Midwest, producing numerous severe thunderstorms and reports of damaging wind, large hail, and tornadoes. One of these thunderstorms produced a long-track tornado that moved through north central Illinois. The National Weather Service in Chicago has assigned a preliminary EF-4 rating to this tornado.
NASA SPoRT has established a collaboration with the USGS, National Weather Service, and NASA Applied Sciences: Disasters Program to provide Earth remote sensing imagery to supplement other data sets available during their storm damage assessments. Imagery is made available to the NOAA/NWS Damage Assessment Toolkit, a geographic information system (GIS) application operated on mobile devices and web browsers, which aids in the collection of photos and other damage indicators collected during a survey. Satellite imagery can be helpful in some cases, helping to identify affected areas where road networks are limited, or there are other access restrictions. Image sources include moderate spatial resolution (250-375 m) imagery from the NASA MODIS and NASA/NOAA VIIRS sensors, higher resolution (15-30 m) satellite imagery from NASA’s Landsat-7, Landsat-8, EO-1, and Terra ASTER, and fine-scale (1-4 m) imagery from commercial vendors that provide disaster support in collaboration with USGS and other federal agencies.
An upper level closed low near Baja and a backdoor front combined to bring considerable precipitation to New Mexico during the day and overnight period of March 19, 2015. Ample moisture surged northward over New Mexico ahead of the closed low, and precipitable water as measured by the soundings at Albuquerque, NM and El Paso, TX tied for the fourth highest value for March since 1950 (at both locations). Additional support for this event came in the form of a back door cold front which raced through the eastern plains of New Mexico during the day on March 19. Because of warm temperatures, Winter Storm Warnings (blue) and Advisories (yellow) were limited to the New Mexico northern high terrain including the Jemez Mountains, San Juan Mountains and Sangre de Cristo mountains, as shown in the figure below.
Two NESDIS Snowfall Rate (SFR) products were available for review the morning following the event. The first is from 0353Z on 20 March 2015, or about 10pm MDT on the evening of March 19, and is shown in the figure below with the 04Z surface observations. The east to northeast flow in the eastern half of the state indicates the progress of the back door front. Most locations in central and eastern New Mexico are reporting rain, including Raton (KRTN) just to the east of the active snow area in the SFR product. Angel Fire (KAXX) just to the south of the area is reporting snow. At this time, the SFR product appears to do a good job in distinguishing between rain and snow despite the fact the Angel Fire is just outside the SFR active area.
The 0.5 reflectivity mosaic at the same time illustrates beam blockage that impacts the area east of Albuquerque, but also the limited radar coverage in northern New Mexico, though there are weak echos associated with the snow report at KAXX as well as the rain at KRTN. Also note convection in western Texas – earlier in the evening one-inch hail was reported in eastern New Mexico. This is an example of the interesting regimes that can impact our CWA in that we can have winter weather warnings and severe weather at concurrent times.
Similar graphics are shown for 0855Z, or 3am MDT, on the morning March 20th. Activity has weakened considerably and the WSW is about to be cancelled. Still, light snowfall rates are depicted by the SFR over the northern high terrain. The metar observation at Angel Fire, KAXX, is still reporting snow.
The 0.5 reflectivity mosaic illustrates that the only isolated precipitation continues over western and central New Mexico, with no returns over the northern high terrain.
In the image below, the 0855Z SFR product is combined with the awips hi-res topography map to illustrate the agreement with the SFR and the highest terrain of the southern San Juan and northern Sangre de Cristo Mountains in northern New Mexico.
One of the frustrations with evaluating the NESDIS SFR product is that consecutive products can be separated by long periods of time, in this case by 5 hours. However, substantial snow accumulations were reported in the Sangre de Cristo mountains – from 6 to 19 inches. Thus the area depicted by the SFR product seems to be fairly accurate, but the evaluation is rates is more difficult.
In addition to snow, widespread rainfall reports ranged from one quarter of an inch to one inch. Early this morning, the following DOT report was posted – the combination of rain and snow resulted in rock slides on at least two roads in northern New Mexico.
NWS Raleigh along with WFOs Houston and Huntsville have been participating in an assessment of several NASA SPoRT Land Information System (LIS) soil moisture products during the past year. During the winter, the same WFOs have been receiving two LIS soil temperature products as a part of an initial testbed. These soil temperature products are the 3-km average surface skin temperature and 0-10 cm soil temperature.
Past experience has shown that the temperature of the soil and ground surface can have an impact on snow and ice accumulation. It was hoped that the availability of the SPoRT 0-10 cm soil temperature and the skin temperature products would provide useful information to forecasters. In addition, the SPoRT analysis products would complement a network of mesonet point observations managed by the NC State Climate Office that provide 10cm soil temperatures.
The numerous winter weather precipitation events in central NC this year provided an opportunity to view and evaluate the SPoRT products. At WFO Raleigh, the SPoRT soil temperature data was informally viewed and consulted to evaluate its utility.
On Friday, January 9th, 2015, areas of freezing rain fell across the southern and central Coastal Plain of North Carolina during the pre-dawn hours. Surface air temperatures ranged in the mid to upper 20s at 10 UTC or 5 AM EST (Fig. 1). The precipitation was driven by convergent low level flow that resulted in a small region of ascent and saturation across portions of southeastern North Carolina. The precipitation followed a period of 24 to 36 consecutive hours of sub-freezing air temperatures.
Given the cold antecedent conditions, the ground across the area was very cold. The SPoRT 3-km average surface skin temperature as displayed in AWIPS 2 is shown in the top of Fig. 2. Skin temperatures in the region of freezing rain ranged between 20 and 25 degrees. In addition, the SPoRT 0-10 cm soil average temperature (bottom of Fig. 2) indicated that the average soil temperature in the layer from the surface to 10cm or 4 inches below the ground averaged between 25 and 30 degrees. This indicated that not only was the top of the soil column well below freezing but the soil immediately below the ground was below freezing and wouldn’t be providing significant heat to warm the ground near the surface.
Given this environment, the precipitation fell as an area of light freezing rain across the Coastal Plain which resulted in icy conditions on many roadways with numerous car accidents across Sampson, Bladen, Duplin and nearby counties during the morning (Fig. 3). While the amount and extent of precipitation was in question just hours prior to the event, the soil temperature data provided increased confidence that any precipitation that fell would have a significant impact.
In another event, during the early morning hours on Tuesday, January 27th, 2015, a short wave trough and the associated surface trough produced an area of precipitation that moved across central NC. The precipitation was in the form of snow and snow showers near the Virginia border across the northern Piedmont and northern Coastal Plain of North Carolina with air temperatures hovering near freezing (Fig. 4). Temperatures were warmer to the south where the precipitation fell as rain or mixed rain and snow.
The ground across northern NC was cool that morning but the soil was generally above freezing. The SPoRT 3-km average surface skin temperature as displayed via the web is shown in the top of Fig 5 with the skin temperatures in the region where precipitation was falling ranging around or a few degrees above freezing. Skin temperatures cooled to the west behind the surface trough and the precipitation, as cooler and drier air moved into the area. In addition, the SPoRT 0-10 cm average soil temperature (bottom of Fig.5) indicated that the average soil temperature in the layer from the surface down to 10cm below the ground averaged in the upper 30s to lower 40s. These values were consistent with the soil temperature observations from the NC State Climate Office’s ECNONET network (not shown) which reported 10 cm soil temperatures in the upper 30s to lower 40s.
In locations where snow was falling, air temperatures fell to around 32 degrees, the surface skin temperatures were near or just above freezing, and soil temperatures deeper in the ground at 10 cm were in the upper 30s to lower 40s. Given these conditions, it’s possible to conclude that the snow would not accumulate efficiently or much at all. However, the snow fell steadily for at least short periods of time with radar reflectivities in the 25-35 dBZ range. The snow rates were significant enough to produce accumulations of a quarter to a half inch with a few locations reporting an inch or more of snow with some accumulations noted on roadways (Fig. 6).
Snow accumulation forecasting, especially in the South, can be very problematic. In our region, snow accumulation events require so many variables to come together just right and even the slightest accumulation can have a significant impact. Forecasters have many variables to consider including the amount of precipitation expected to fall, the rate, the air temperature, the moisture profile, the soil and skin temperatures, solar impact, and more. In this case, the precipitation rate overcame the other marginal factors for accumulating snow, and more snow accumulated than was anticipated (Fig. 7).
The NASA SPoRT 0-10 cm soil temperature and skin temperature products were examined this winter at WFO Raleigh. The initial results were generally favorable and the additional information was fairly well received. It is important however, that the soil temperature information is used in good context of other observational or forecast information and is used as part of the process. In short, the soil temperature data is one piece of the puzzle, its importance should not be overvalued. There is also some feedback on some technical and delivery issues we noted at Raleigh that we have shared with the developers.
Yet another bout of snow, sleet and ice recently affected much of the Tennessee and Ohio Valley regions. Although clouds were clearing in western portions of this region, allowing for a broad scale satellite view of the newly laid snow/ice field, eastern portions remained cloud-covered until sunset. While ground reports contain valuable information about the depth of snow and/or ice, they’re only point measurements, so assumptions often have to be made about the spatial extent of the snow, until satellite observations are available (unless clouds obscure). So, those observations would have to wait until the next day, during visible sunlight hours…or would they? Well, not exactly…which is the point of this blog post.
The image below (Image 1) is a Snow/Cloud RGB produced by SPoRT and disseminated to collaborative NWS field offices. The green colors represent the background surface (grass, trees, cities, etc.), while the deeper reds represent snow/ice cover. White colors depict clouds, while reddish-white represents very cold clouds containing ice crystal clouds. Notice the swath of snow that is visible from NE Texas into the Midwest. Meanwhile, clouds obscure any snow/ice in eastern areas.
Clouds had pushed eastward by sunset, but did still not move far enough to provide a clear indication of the eastward extent of the snow/ice field that had just fallen. However, once the VIIRS Day-Night Band imagery became available later that night, the spatial extent of the snow and ice could be fairly easily observed. Notice in the next image (Image 2) the snow and ice cover that was apparent over portions of the Tennessee and Ohio Valley region.
This type of imagery can be helpful for operational forecasters when trying to assess the potential societal impacts of lingering snow and ice, and also the impacts on sensible parameters such as temperatures and relative humidity, which can help improve weather forecasts.
NASA SPoRT has developed a real-time application of the NASA Land Information System (LIS) that runs over much of the central and eastern United States. The LIS produces several products, including a suite of soil moisture products that can be used to help assess drought and flooding potential. There are four LIS soil moisture products that are being assessed by WFO Raleigh forecasters in AWIPS-2. The products are also available online at http://weather.msfc.nasa.gov/sport/case_studies/lis_SEUS.html for the Southeast and http://weather.msfc.nasa.gov/sport/case_studies/lis_NC.html for North Carolina.
After a dry start to the month, multiple rainfall events occurred across central NC during the middle and latter portion of December 2014. During the afternoon of 22 December, forecasters were analyzing rainfall from the previous 24 hours which ranged from a tenth of an inch in the Northwest Piedmont to an inch or more across the eastern Piedmont and Coastal Plain regions. This event was the 3rd fairly significant rainfall event (>0.5 inches) over the central NC since 10 December. Forecasters became concerned as another storm system would impact the Carolinas during the next few days and was expected to produce between 1.25 to 2.0 inches of rain from 22 to 25 December (see Fig. 1). This additional rain had the potential to produce some flooding on main stem rivers, especially across the Coastal Plain.
A SPoRT-LIS field that forecasters have found useful 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). The one-week change product valid at 15 UTC on 22 December, just prior to the rain event, is shown in Fig. 2 with the NWS CWAs outlined in yellow. Note that multiple significant rainfall events occurred across central NC during the previous two weeks. Not surprisingly, this product indicated that much of central NC had experienced a relative soil moisture increase from the previous week.
Another SPoRT-LIS field that forecasters found useful is the SPoRT LIS 0-200 cm Relative Soil Moisture (%) analysis product. The LIS 0-200 cm Relative Soil Moisture (RSOIM) analysis from 15 UTC on 22 December is shown in Fig. 3. The RSOM values in the area outlined by the red box across the northern and central portions of the Coastal Plain are highlighted in the deeper and darker green shading and generally exceed 55% and in many locations exceed 60%. Subjective analysis of the RSOIM product by previously by WFO Huntsville AL during several synoptic rainfall events suggests that when the 0-200 cm RSOIM values exceed 55%, the risk of flooding on larger rivers increases substantially.
Significant rain did fall across central NC during the days leading up to Christmas. An analysis of precipitation across central NC from 23 to 25 December shown in Fig. 4 indicates a large area of 2.0 to 2.5 inches of rain fell across the Coastal Plain of NC with an average of around 2.0 to 2.25 inches across the Tar and Neuse River basins. These same locations were noted in Fig. 2 with RSOIM values that exceeded 55%.
The significant rain combined with the wet antecedent conditions did result in flooding at several forecast points across central NC with a few locations in the Coastal Plain reaching moderate flooding. The observed hydrograph and multiple forecast traces for Smithfield NC (SMFN7) on the Neuse River is shown in Fig. 5. The observed stage is noted by the nearly continuous red dots surrounded by blue circles that exceed the orange horizontal line (flood stage) and the red horizontal line (moderate flood stage). The river exceeded flood stage at Smithfield during the afternoon of 24 December and reached moderate flooding less than 24 hours later.
Several days prior to flooding, the hydrologic situation was discussed in the NWS Raleigh Area Forecast Discussion (AFD) issued at 230 PM EST on Monday, 22 December (text shown below). In the AFD, the antecedent conditions were discussed with multiple SPoRT LIS products referenced. While the rainfall during the following few days exceeded the initial forecast and the anticipated impacts, the availability of the SPoRT LIS products lead to increased awareness of the flooding potential which proved especially helpful as the observed rainfall amounts increased and river levels rose.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
AS OF 230 PM MONDAY…
ANTECEDENT RAINFALL OVER THE PAST 24 HOURS RANGED FROM A MINIMA OF ABOUT A TENTH OF AN INCH IN THE NORTHWEST PIEDMONT (THE UPPER YADKIN/PEE DEE AND UPPER HAW RIVER BASINS) TO A STRIPE OF 1 INCH PLUS ACROSS THE SOUTHEAST (THE CENTRAL NEUSE AND CENTRAL CAPE FEAR BASINS). WILL SEE ONLY MINOR RISES ON THE MAINSTEM RIVERS IN RESPONSE…BUT THIS IS THE 3RD FAIRLY SIGNIFICANT RAINFALL EVENT (>0.5 INCHES) OVER THE AREA SINCE 12/10. RELATIVE SOIL MOISTURE PERCENTAGES IN THE 0-200 CM COLUMN HAVE BEEN INCREASING…WITH HIGHER PERCENTILES NEARER THE SURFACE…SO QUICKER RUNOFF IS EXPECTED FROM OUR UPCOMING RAIN EVENT.
CURRENT QUANTITATIVE PRECIP FORECASTS FROM THE GEFS AND NAEFS ENSEMBLES ARE IN LOCKSTEP AGREEMENT AT PRESENT…WITH HEAVIEST RAIN (~1.3-1.5 INCHES) FROM TOMORROW NIGHT THROUGH CHRISTMAS MORNING. RAINFALL AMOUNTS IN THIS RANGE COULD POTENTIALLY CAUSE SOME MINOR FLOODING ON THE NEUSE RIVER AND TAR RIVER LATE ON CHRISTMAS DAY…BUT IT WOULD BE LOW IMPACT WITH THOSE RIVERS BARELY REACHING MINOR FLOOD STAGE. THE UPSHOT…RIVER FLOODING WILL ONLY BE AN ISSUE IF RAINFALL FORECASTS BEGIN TRENDING HIGHER…INTO THE 2 INCH PLUS RANGE.