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With an unseasonably strong upper low approaching New Mexico,  forecasters at NWS Albuquerque anticipated high elevation snow and widespread rain with relatively high QFP values for the period of 26-27 April 2015.  A winter storm watch was issued at 400 am MDT on Saturday, April 25.  Snow was forecast for the highest terrain across the northern and central New Mexico, but significant snow accumulations were expected late Sunday, April 26 through early Monday, April 26.  Additionally, rain amounts in excess of an inch were expected across the eastern plains.

The GFE storm total snow from mid-day Saturday, April 25 is shown below.  The forecast called for the most significant snow accumulations, just over a foot across the highest peaks, to occur over the Sangre de Cristo Mountains (just to the west of Interstate 25) and the higher elevations along the Colorado border north of Raton, NM. The watch was upgraded to a warning at 4am MDT on Sunday, April 26.

GFEsnowforecast_from20150425

Widespread precipitation was reported during the overnight hours, with 3-.6in of rain in the Albuquerque metro area. The position of the closed low early on the morning of Monday, April 27 is shown below.  Snow was still being reported at Angel Fire in the Sangre de Cristo Mountains, but the big story by this point was rain across the eastern plains.

dkpattern0

Two Snowfall Rate products were received during the overnight hours around 3am MDT (09Z). The date/time stamp was not included on the images – the first shows SFR at 0838Z and the second at 0913Z.  Both include metar observations from 09Z.  Angel Fire is reporting snow, though in both images the SFR ends just north of the site. Raton is reporting rain and the SFR products both show the eastern edge of snow accumulations ending just to the west of Raton. Based on very high accumulations south of Angel Fire, the SFR product may be underestimating the area of active snow.

NESDIS_SFR_20150427_0838Z

NESDIS_SFR_20150427_0913Z

As is often the case, radar cover across the north central mountains is limited. The 0.5 reflectivity mosaic below is from 09Z, between the two SFR products above. Angel Fire is marked by the purple circle. Radar returns over the Sangre de Cristo mountains are greater north of Angel Fire. In eastern New Mexico, Tucumcari (blue circle) is reporting rain associated with the strongest radar returns. Rain continued through the daytime hours with numerous rainfall reports of over one inch.  In fact, Tucumcari Aiport reported 1.50″ of rain, the 3rd largest 1-day total in April since 1941!

0_5ref_mosaic_20150427_0900Zannot

Snow accumulation reports did verify our forecast of over a foot of snow for this late season event. Determining snow records is more difficult since routine snow observations are few.  Highest totals were received in the Sangres, with 18 inches observed at Black Lake, just south of Angel Fire. Smaller accumulations were noted over the San Juan and Jemez Mountains, areas which did not have a Winter Storm Warning in effect.  The RGS Snow-Cloud product from April 28 shows new snow cover across much of the north central high terrain. Snow over the San Juan and Jemez Mountains (west of the Sangres) likely accumulated prior to the SFR products above.

snowfallreports SnowCloudRGB_20150418_1726Z

 

20150417_0817_sport_viirs_seregion_ntmicro2015041708_metars_abi

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).

20150417_0817_sport_viirs_seregion_fog

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.

MODIS Dust RGB showing blowing areas of dust (pink streaks) over portions of Utah and Nevada,

MODIS Dust RGB showing blowing areas of dust (pink streaks) over portions of Utah and Nevada, 1852 UTC 14 Apr 2015

picture of dust affecting travel in the Salt Lake City area, 14 Apr 2015...picture tweeted by Jed Boal of KSL5 TV.

picture of dust affecting travel in the Salt Lake City area, 14 Apr 2015…picture tweeted by Jed Boal of KSL5 TV.

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).

MODIS image showing blowing dust (pinkish areas) in the Great Basin and central Utah, ~20 UTC 14 Apr 2015

MODIS image showing blowing dust (pinkish areas) in the Great Basin and central Utah, ~2030 UTC 14 Apr 2015

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.

Landsat-8 Panchromatic Band at 15 m resolution showing portion of the EF-4 tornado track northwest of Rochelle, Ill.

Landsat-8 Panchromatic Band at 15 m resolution showing a portion of the EF-4 tornado track northwest of Rochelle, Ill. Image acquired on April 10, 2015.

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.

Landsat-8 True Color image at 30 m resolution showing a portion of the EF-4 tornado track northwest of Rochelle, Ill.

Landsat-8 True Color image at 30 m resolution showing a portion of the EF-4 tornado track northwest of Rochelle, Ill. Image acquired on April 10, 2015.

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.

WSW

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.

NESDIS_SFR_20150320_0353Z_obs

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.

0_5reflectivity_20150320_0400Z_obs

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.

NESDIS_SFR_20150320_0855Z_obs

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.

0_5reflectivity_20150320_0854Z_obs

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.

SFR_0855Z_withTerrain

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.

DOTinfo

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.

Fig 1. AWIPS 2 display of surface METAR data and composite regional radar reflectivity from 1000 UTC on 09 January, 2015.

Fig 1. AWIPS 2 display of surface METAR data and composite regional radar reflectivity from 1000 UTC on 09 January, 2015.

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.

Fig 2. AWIPS 2 display of NASA SPoRT 3-km average surface skin temperature (top) and the NASA SPoRT 0-10 cm soil temperature (bottom) valid at 0900 UTC on 09 January, 2015.

Fig 2. AWIPS 2 display of NASA SPoRT 3-km average surface skin temperature (top) and the NASA SPoRT 0-10 cm soil temperature (bottom) valid at 0900 UTC on 09 January, 2015.

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.

Fig 3. Snapshot of a WECT-TV news story on the car accidents resulting from the freezing rain on 09 January, 2015.

Fig 3. Snapshot of a WECT-TV news story on the car accidents resulting from the freezing rain on 09 January, 2015.

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.

Fig 4. NC State Climate Office CRONOS display of surface temperatures and composite regional radar reflectivity from 1000 UTC on 27 January, 2015.

Fig 4. NC State Climate Office CRONOS display of surface temperatures and composite regional radar reflectivity from 1000 UTC on 27 January, 2015.

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.

Fig 5. Web page display of the NASA SPoRT 3-km average surface skin temperature (top) and the NASA SPoRT 0-10 cm soil temperature (bottom) valid at 1000 UTC on 27 January, 2015.

Fig 5. Web page display of the NASA SPoRT 3-km average surface skin temperature (top) and the NASA SPoRT 0-10 cm soil temperature (bottom) valid at 1000 UTC on 27 January, 2015.

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.

Fig 6. Snapshot of a WRAL-TV photo taken near Henderson, NC at around 0630 UTC on 27 January, 2015.

Fig 6. Snapshot of a WRAL-TV photo taken near Henderson, NC at around 0630 UTC on 27 January, 2015.

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).

Fig 7. Subjective analysis of accumulated snow in inches from the 26-27 January, 2015 winter storm.

Fig 7. Subjective analysis of accumulated snow in inches from the 26-27 January, 2015 winter storm.

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.

Image 1.  MODIS  Snow/Cloud RGB 1631 UTC 5 March 2015

Image 1. MODIS Snow/Cloud RGB 1631 UTC 5 March 2015

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.

Image 2.  Suomi-NPP VIIRS Day-Night Band Radiance RGB, 0805 UTC 6 March 2015.  The solid white line indicates the extent of the snow/ice cover.  Clouds are also in the image over portions of the southern Appalachians and the Gulf into the Atlantic Coastal Plain.

Image 2. Suomi-NPP VIIRS Day-Night Band Radiance RGB, 0805 UTC 6 March 2015. The solid white line indicates the extent of the snow/ice cover. Clouds are also in the image over portions of the southern Appalachians and the Gulf into the Atlantic Coastal Plain.

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.

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