Observing the First Major Thundersnow Outbreak of the 2019-2020 Winter Season

Written by Sebastian Harkema and Emily Berndt

The first major heavy-banded snowfall event of the 2019-2020 winter season occurred from Oct. 9-12 and produced over two feet of snowfall in North Dakota. Throughout the event, the NESDIS merged snowfall rate (mSFR; Meng et al. 2017) product tracked the heaviest snowfall rates, including bands with snowfall rates greater than 2 in/hr. With a temporal resolution of 10 minutes, this product can be used in real-time to forecast the location and evolution of snowbands producing heavy snowfall, and even anticipate cloud-seeding. SPoRT has collaborated closely with NESDIS to experimentally transition and assess the passive microwave and merged snowfall rate products with NWS forecast offices (Ralph et al. 2018).  Therefore, this product is available in AWIPS and forecasters can select different snow-to-liquid ratio values to best fit the situation.

Figure 1: NESDIS mSFR product and GOES-EAST ABI (Ch. 13) on October 9, 2019.

Figure 1 demonstrates the mSFR product overlapping GOES-East ABI (channel 13) for October 9th as the snowband traversed across Montana. While the mSFR product provides a unique way to monitor snowfall, the phenomenon known as thundersnow captivated the attention of some operational forecasters as well as the general public, in part by the availability of Geostationary Lightning Mapper (GLM) observations. Recent work from NASA SPoRT has shown that the overlap of GLM and mSFR data can be used to objectively identify and characterize electrified snowfall (i.e., thundersnow; Harkema et al. 2019a). In fact, Harkema et al. 2019a demonstrated that thundersnow flashes identified by GLM contain on average more total optical energy per flash area than other flashes in the GLM field-of-view. Harkema et al. 2019a also demonstrate that thundersnow flashes observed by GLM are spatially larger compared to non-thundersnow flashes and is likely a result of weaker mesoscale updrafts and slower charging rates compared to severe summertime convection.

Figure 2: NESDIS mSFR product, GOES-EAST ABI (Ch. 13), and GLM flash extent density observations on October 10, 2019.

Figure 2 demonstrates the objective identification of thundersnow based on the overlap of mSFR and GLM flash extent density observations on October 10th around the Colorado/Nebraska/Wyoming border region. From the loop, this region experiences an enhancement of snowfall rates approximately 30-40 minutes after the first occurrence of thundersnow. Even though it appears as though thundersnow can be used as a precursor for enhancement of snowfall rates in the near future, thundersnow has a spatial offset of 131±65 km from the heaviest snowfall rates (Harkema et al. 2019b, In Review). This spatial offset is evident when examining the thundersnow that occurred along the Minnesota/Manitoba border between 12-15 UTC on October 11th (Fig. 3).

Figure 3: NESDIS mSFR product, GOES-EAST ABI (Ch. 13), and GLM flash extent density observations on October 11, 2019.

The thundersnow observed by GLM occurs on the northern extent of the heaviest snowfall rates (purples/whites). The separation of thundersnow and the heaviest snowfall rates is likely caused by hydrometeor lofting of the snowfall as it descends to the surface because of the low terminal fall speed of the ice crystals.

Winter is fast approaching and the NESDIS mSFR product and GLM can be used in tangent with each other to improve situation awareness. NASA SPoRT is at the forefront of understanding the operational implications of electrified snowfall and continues to investigate the thermodynamic and microphysical properties that are associated with it. See the official JPSS Quick Guide and a past JPSS Science Seminar for more product information.

References

Harkema, S. S., C. J. Schultz, E. B. Berndt, and P. M. Bitzer, 2019a: Geostationary Lightning Mapper Flash Characteristics of Electrified Snowfall Events. Wea. Forecasting, 43(5), 1571–1585, https://doi.org/10.1175/WAF-D-19-0082.1.

Harkema, S. S., E. B. Berndt, and C. J. Schultz, 2019b: Characterization of Snowfall Rates, Totals, and Snow-to-Liquid Ratios in Electrified Snowfall Events from a Geostationary Lightning Mapper Perspective. Wea. Forecasting. In Review.

Meng, H., Dong, J., Ferraro, R., Yan, B., Zhao, L., Kongoli, C., Wang, N.‐Y., and Zavodsky, B. ( 2017), A 1DVAR‐based snowfall rate retrieval algorithm for passive microwave radiometers, J. Geophys. Res. Atmos., 122, 6520– 6540, doi:10.1002/2016JD026325.

NASA SPoRT’s SST Composite Maps Capture Upwelling in the Wakes of Hurricanes Dorian and Humberto

NASA SPoRT’s SST Composite Maps Capture Upwelling in the Wakes of Hurricanes Dorian and Humberto

Written by Patrick Duran, Frank LaFontaine, and Erika Duran

Category 5 Hurricane Dorian passed over the Bahamas between September 1 and 3 2019, producing catastrophic destruction and causing at least 60 direct fatalities in the island nation. In addition to the impacts on human life, strong, slow-moving hurricanes like Dorian can leave lasting effects on the ocean over which they travel. Through a process known as upwelling, hurricanes bring colder water from below the surface up to the top layer of the ocean.  As a result, a trail of cooler sea surface temperatures (SSTs), also referred to as a “cold wake,” is often visible behind a passing storm. Meteorologists and oceanographers can monitor changes in SST and identify a cold wake following tropical cyclones using satellite data.

NASA SPoRT produces composite maps of SST twice daily using data from the VIIRS-NPP, MODIS-Aqua, and MODIS-Terra instruments, along with OSTIA-UKMO data obtained from the GHRSST archive at NASA’s Jet Propulsion Laboratory and the NESDIS GOES-POES SST product. The input data are weighted by latency and resolution to produce the composite, which is available at 2 km resolution.

Figure 1 shows a loop of the SPoRT SST composite from August 31 – September 23, 2019 over a region that includes the Bahamas and the Southeast United States. Two rounds of SST cooling are observed as Hurricanes Dorian and Humberto move through the region.

Figure 1: Animation of NASA SPoRT SST Composite Maps from August 21 through September 23, 2019. Daily images are displayed at 1800 UTC.

On August 31, very warm SSTs of around 29-30 deg Celsius (84-86 deg Fahrenheit) overspread the waters surrounding the Bahamas (Fig. 2).

Figure 2: SST Composite Map at 1800 UTC on August 31, 2019.

After Hurricane Dorian tracked through the region and made landfall in North Carolina on September 6, the waters north of the Bahamas were considerably cooler – in the 26–29 deg Celsius (79–84 deg Fahrenheit) range (Fig. 3).

Figure 3: As in Fig. 2, but for September 6, 2019.

Over the next week, the surface waters warmed a degree or two (Fig. 4), but did not fully recover to the same temperature observed on 31 August.

As in Figs. 2-3, but for September 13, 2019.

On September 13, Tropical Storm Humberto formed 210 km (130 miles) ESE of Great Abaco Island. As the storm tracked northeast past the Bahamas, it encountered the cold wake left by Hurricane Dorian the previous week. These cooler waters, combined with the influence of some dry air and vertical wind shear, inhibited the storm’s intensification as it passed by the Bahamas. On September 15, Humberto moved over the warmer waters of the Gulf Stream off the coast of North Florida (Fig. 5) intensified to hurricane strength.

Figure 5: As in Figs 2-4, but for September 15, 2019.

Humberto continued to strengthen, and attained a maximum sustained wind speed of 125 MPH as it passed by Bermuda on September 19. Its strong winds and associated waves overturned the same region of ocean that was previously affected by Hurricane Dorian, decreasing sea surface temperatures to as low as 25 deg Celsius (77 deg Fahrenheit) in some areas (Fig. 6).

Fig. 6: As in Figs. 2-5, but for September 19, 2019.

These images highlight the effect that tropical cyclones can have on SST, and how a hurricane can make it more difficult for any subsequent storms to intensify over the same region. Satellite analyses of SSTs (such as those produced by NASA SPoRT) allow forecasters to monitor SST across the globe, helping them to produce better forecasts of tropical cyclone intensity in all ocean basins.

Snowfall Rate Provides Guidance for New Mexico Snow Event

Forecaster Jennifer Palucki from Albuquerque, New Mexico submitted a nice case study to our online evaluation form being used during the current 2016 NESDIS Snowfall Rate Evaluation.  Here are some of her discussion and impressions of using the product:

A very well defined band of snow developed along a frontal boundary extending from the southern Sangre de Cristo Mountains, toward Las Vegas, and continued southeastward toward Melrose. Initially the southeast part of the band was rain, but as temps dropped it changed to snow. At 0052z (552pm MST; see image below) the merged SFR likely did very well distinguishing where there was snow and no snow, however, in areas that there was snow, amounts were way underdone. At 545pm, approximately 4″ of snow had fallen in Sapello in the southern Sangre de Cristo Mtns. Snow likely started around 1 or 2pm, which is an average of about 1″/hr compared to the 0.3″/hr the SFR product was showing with an 18:1 ratio. Thus, the amounts via the SFR product were largely underdone. It was still snowing heavily according to the spotter at 545pm. At 645pm, approximately 1.5 inches of snow was reported in Las Vegas. The SFR product was showing around 0.1″/hr for this area.

ABQ_160203_0052Z_annotated_zoom

NESDIS SFR Product at 0052 UTC on 03 February 2016 showing light snow over Las Vegas, NM.

Another pass at 0330z (830pm MST; see image below), the SFR product missed the southeastern extent of the snowfall, and again had amounts that were likely underdone. A report of 0.5 inches of snow in the last hour was reported at 841pm in Taos. The SFR product showed around 0.02 liquid equivalent, or around 0.3″/hr snowfall rate given 18:1 ratio (which should be close to the snow ratios in that area).

ABQ_160203_0330Z_annotated

NESDIS SFR Product at 0330 UTC on 03 February 2016 showing some heavier snow over Taos, NM.

Really like using this product to gather intel on where it is snowing in areas without radar coverage. Do have some concerns about the amounts, especially in these scenarios where the heavier amounts are likely isolated. In this case, the band was very narrow, likely no more than 10 to 15 miles wide.

Life of Winter Storm Jonas as seen by the NESDIS Snowfall Rate Product

Winter Storm Jonas tracked across the eastern United States this past weekend dropping near-record amounts of snowfall in a track from West Virginia through southern New York.  Two things about this storm are particularly interesting:  1) the heavy amounts of snow that fell for long periods of time and 2) the relatively narrow swath of the heaviest snows.  Below is the 48-hour snow accumulations from the National Weather Service ending Sunday, January 24.  It is striking that New York City received on the order of 30 inches of snow, while areas less than 100 miles to the north received little if any snow.

NWS_SnowTotals

48-hour snowfall totals ending Sunday, January 24, 2016 (from NWS Central Region).  Contours are every 3″ with the darkest reds indicating 30″ of snow.

Select Eastern Region WFOs are currently evaluating the NESDIS Snowfall Rate product, which uses passive microwave observations from 5 sensors, to observe total column snowfall rates.  Below is a series of images from this past weekend showing the SFR product displayed as a 10:1 solid/liquid conversion.  The darkest greens indicate snowfall rates at the top of the sensor detection range at approximately 2″/hr.  Depending on the actual solid/liquid ratio in individual areas, rates may have been higher.

SFR_Collage_first4

SFR_Collage_second4

NESDIS SFR Product showing the evolution of Winter Storm Jonas from late on Friday through early Sunday.  The darkest greens indicate solid snowfall rates of around 2″/hr.

In the images, the NESDIS SFR product shows very good agreement with the location and track of the heaviest snows (greens) compared to the heaviest totals in the ground reports.  Additionally, the SFR product does well in picking up the abrupt northern edge of the snowfall (especially across southern New York).

UPDATE:  The Sterling, VA WFO included mention of the SFR product in a forecast discussion to confirm snowfall rates that would cause white out conditions:

Sterling_AFD

NESDIS Snowfall Product Captures Unfolding Winter Weather in the South

Beginning in the morning hours of 22 January 2016, rain began to change to snow across Mississippi, Tennessee, and Alabama.  The NESDIS Snowfall Rate, which is currently being evaluated by a handful of Weather Forecast Offices, has the ability to differentiate rain from snow.  This ability was particularly important for the large winter storm impacting much of the eastern half of the United States.  The animation below shows the 10:1 Solid SFR Product with METAR station observations indicating temperatures and precipitation.

AL_TN_SFR_Example_20160122_07-19Z_slower

The animation shows the evolution of snow across the area beginning with snow in Western Tennessee and Eastern Mississippi at around 1200 UTC (6:00a local time).  Also of note at that same time is that the SFR Product indicates relatively heavy snow (~1.5 in./hr. solid snow) directly over the Nashville area; however, the METAR site at the airport is still reporting rain.  In the following hour (1300 UTC; not shown in the loop here because there was no SFR product valid near 1300 UTC) Nashville was reporting snow.  Thus, the SFR product was seeing in-cloud snow in that area that began to reach the ground within an hour of the observation.  This is one way forecasters can use the product to view in-cloud snow to determine the potential for snow to reach the ground.

Later in the period, a similar set up appears in the Huntsville area at the Madison County Executive Airport (KMDQ).  The 1853 UTC SFR product shows light snow over Madison County, but the 1900 UTC METAR was not yet reporting any snow.  However, the 2000 UTC METAR showed snow beginning to fall across the Huntsville area.  The change over to snow falling across Western Madison county into Central Madison county was between 1830 and 1900 UTC, verified as I drove home from work.

The NESDIS SFR product will continue to be evaluated as blizzard conditions begin to set up along parts of the East Coast.

SFR Product Verifies Snow Coverage over Four Corners

The NESDIS Snowfall Rate (SFR) product assessment is in full swing at NWS Albuquerque and forecasters are already capturing some good cases over data sparse regions. The first week of January 2016 was very active across New Mexico as back to back winter storm systems crossed the area. The second system in the series crossed over the Four Corners region on 4 January 2016, producing light to moderate snowfall rates for several hours. The forecaster on shift noted the observation at Farmington, NM (KFMN) indicated light snow with a visibility of 5 statute miles. A quick glance at the SFR procedure used in Figure 1a shows the extent of any precipitation echoes well to the east of KFMN at 0000 UTC 5 January 2016. The nearest radar (KABX, not shown) is located roughly 150 miles southeast of KFMN near Albuquerque, NM. The arrival of a SFR product at 0010 UTC 5 January 2016 showed the extent of the precipitation was much greater with the merged POES image overlaid on the radar data (Figure 1b). Sampled liquid equivalent values in the light green areas to the east of KFMN were near 0.03″/hour.

Figure 1a. Liquid equivalent values of the merged SFR product valid 0000 UTC 5 January 2016. KFMN is denoted by the white circle. Note the extent of the radar coverage is well east of KFMN.

Figure 1b. Liquid equivalent values of the merged SFR product valid 0010 UTC 5 January 2016. KFMN is denoted by the white circle. Note the extent of the snowfall coverage is much greater with the addition of the POES image.

The Terminal Aerodrome Forecast (TAF) issued for KFMN shortly before the receipt of this image indicated temporary fluctuations in the visibility to 1 statute mile with light snow and an overcast ceiling near 1,200 ft between 0000 UTC and 0400 UTC (Instrument Flight Rules, IFR). It is not clear whether any operational changes occurred based on the receipt of the merged SFR product or whether the product increased confidence on the IFR forecast. However, it is entirely possible given the improvement in product latency compared to the 2015 assessment that the imagery could be used in this way.

The webcam available at San Juan College just a short distance from the KFMN observation showed significant decreases in the visibility between 330pm and shortly after sunset (Figure 2a and 2b). The two images below show the decrease in surface visibility as well as notable accumulations on grassy surfaces in front of the college. An observer 3 miles southeast of Farmington did report a total accumulation of 1″ from this event. The merged SFR product did in fact show higher rates immediately to the east of KFMN. The last image in the series shows the impact on travel conditions noted by the NM Department of Transportation web page (Figure 3). The areal coverage of the difficult travel impacts (yellow highlights) was greater than that depicted by what can be seen based on poor radar coverage.

Figure 2a. Webcam at San Juan College around 330pm. Note the light snowfall beginning to develop over the distant mesas behind the college.

Figure 2a. Webcam at San Juan College around 330pm. Note the light snowfall beginning to develop over the distant mesas behind the college.

Figure 2b. Webcam at San Juan College shortly after sunset. Note the dramatic decrease in visibility and light snow accumulations on grassy surfaces in front of the college.

Figure 2b. Webcam at San Juan College shortly after sunset. Note the dramatic decrease in visibility and light snow accumulations on grassy surfaces in front of the college.

Figure 3. Screen capture of NM DOT web page showing areal coverage of difficult travel conditions (yellow highlights) and some text summaries detailing the impacts.

Post Frontal Orographic Snowfall Impacts NM

A slow-moving upper level storm system tracked east across northern NM and southern CO on 14-15 December 2015. A weak tap of subtropical moisture ahead of this system provided light to moderate snowfall mainly along the Continental Divide of western NM and the higher terrain running north-south through central and northern NM. Snow accumulations of 3 to 8 inches were reported ahead of and immediately behind the surface front and the mid level trough passage. A classic westerly,upslope flow event developed behind the upper wave as moist, unstable flow interacted with the north-south oriented higher terrain. Winter weather advisories and winter storm warnings were in effect over much of northern NM for the expectation of storm total snowfall of 8 to 12″ with locally higher amounts. Figure 1 depicts the distribution of advisories and warnings over northern NM on the Albuquerque National Weather Service public page.

Advisory and warning map for the ABQ CWA valid 15 December 2015.

Figure 1. Advisory and warning map for the ABQ County Warning Area valid 15 December 2015.

Poor radar coverage over northern and western NM makes it a challenge for assessing winter precipitation patterns and snowfall rates. Figure 2 shows a radar mosaic valid 1800 UTC 15 December 2015 utilizing an enhanced color curve to identify areas of lighter snowfall. Automated surface observations are sparse in this area however there are at least a few observations reporting snow where nothing is present in the radar reflectivity. Webcams at ski resorts serve as an excellent near real-time proxy for visualizing active snow accumulations in these poor radar coverage regions. Additionally, once daily snow accumulation reports from ski resorts aid the verification process following the winter event.

Figure 2. Winter radar mosaic from KABX valid 1800 UTC 15 December 2015. Note the orange circle depicting a large area of poor radar coverage.

The integration of satellite data allows forecasters to supplement these data void areas. The most recent interation of the NESDIS snowfall rate products available at WFO Albuquerque illustrate the snowfall rate derived from radar (Figure 3a) and the snowfall rate available from merging the POES satellite data with the radar data (Figure 3b). Note the grey areas overlaid on the map in Figure 3a indicate areas of reliable radar coverage. The snowfall rate derived from satellite data in Figure 3b clearly shows coverage outside of the area with reliable radar coverage. A very cold and unstable airmass in association with this precipitation suggested snowfall rates in the higher terrain would average between 20-30:1. The 18:1 image in the lower right of Figure 3b indicated rates around 0.4/hr.

FIgure 3a. Radar derived snowfall rate product over northern NM valid 1750 UTC 15 December 2015.

Figure 3a. Radar derived snowfall rate product over northern NM valid 1750 UTC 15 December 2015. Note the grey areas overlaid on the map indicating where reliable radar coverage exists. Upper left (liquid equivalent), upper right (10:1), lower right (18:1), lower left (36:1).

NESDIS snowfall rate product filling in the radar gaps over northern NM valid 1750 UTC 15 December 2015. Note the circles in the upper left image are the location of the webcams in Figure 4.

Although there is sparse coverage of automated surface observations around the higher terrain, webcams from ski resorts can verify the existence of moderate to heavy snowfall. Visibilities in the webcams below suggest snowfall rates higher than those depicted in the NESDIS products – visually, rates look closer to perhaps 1″/hr in the upper right and lower right images (Figure 4). One of our goals of this assessment is to combine information from the webcams with the more quantitative snowfall rate product to better estimate snowfall in data void areas. Snowfall reports from the Chama Railyard indicated 8.5″, Taos Ski Valley 6″, Ski Santa Fe 12″, and Pajarito Mountain 10″.

 

Figure 4. Webcams from across northern NM. Top left (Chama Railyard, yellow circle), Top right (Taos Ski Valley, white circle), Bottom right (Ski Santa Fe, red circle), Bottom left (Pajarito Mt, orange circle).

 

Latest Version of NESDIS Snowfall Rate Product in AWIPS

Researchers at the National Environmental Satellite and Information Service (NESDIS) have recently wrapped up development of the latest iteration of their Snowfall Rate (SFR) product to aid WFOs in situational awareness of snowfall events and snowfall forecasting.  The developers within NESDIS have teamed up with SPoRT, utilizing SPoRT’s unique transition, training, and evaluation capabilities to deliver the SFR products to several WFOs in the CONUS and Alaska.  During the evaluation period this winter, I will be evaluating the SFR and merged SFR products for use mainly here in the Tennessee Valley (provided the atmosphere obliges), but I will also be looking at the product CONUS-wide (and perhaps AK too, as the opportunity affords).

The SFR products are being delivered in two main versions: a merged snowfall rate product (merged polar-orbiter and radar data) and a product that contains only data from polar orbiters.  Through collaboration with researchers and forecasters (especially at the Boulder NWS office), SPoRT is including SFR data with liquid to snow ratios of 10:1, 18:1, and 35:1.  These data are being ported in AWIPS II workstations at the NWS offices.  In the merged product, the polar swath data are complimented with NSSL’s Multi-Radar/Multi-Sensor (MRMS) precipitation data, and update much more frequently (every 10 minutes).  Swaths containing polar orbiter data of course come in as associated polar orbiter swaths cross a region, with updates from about every 30 minutes to as long as ~4-5 hours over any location.

A look at the products the past several days has brought the opportunity for some initial evaluation.  So far, the SFR product looks rather promising.  Here’s a quick look at the product as a snowstorm was ongoing yesterday evening (Dec 15th) across the northern/central Rockies and the Northern Plains.  The loop below (Image 1) shows data from 0110Z through 0410Z 16 Dec 2015.

NESDIS Merged Snowfall Rate Product (showing 10:1 liquid to snow ratio) 0110Z to 0410Z 16 Dec 2015

Image 1.  NESDIS Merged Snowfall Rate Product (showing 10:1 liquid to snow ratio) 0110Z to 0410Z 16 Dec 2015

The loop above shows the Merged Snowfall Rate product (displaying 10:1 liquid to snow ratio).  Most of what you see is the MRMS precipitation during the loop.  At the end of the loop however, you will notice a sudden expansion of the apparent snowfall over the region as an insertion of snowfall rate derived from a polar orbiter swath is incorporated into the product.  So, let’s take a closer look at that single image containing the polar orbiter data (Image 2).

 

NESDIS Merged Snowfall Rate product (10:1 ratio) with polar orbiter data insertion, 0410Z 16 Dec 2015

Image 2.  NESDIS Merged Snowfall Rate product (10:1 ratio) with polar orbiter data insertion, 0410Z 16 Dec 2015

In the image above, you will notice that MRMS data remain and replace satellite retrievals where these data are available.  That is, the MRMS data take precedence over the satellite data in the merged SFR product.  However, data are inserted for locations where snowfall is detected by satellite instruments and radar (MRMS) data are not available.  For large areas of Wyoming and Colorado, where radar coverage is certainly more limited, notice that the insertion of polar-orbiter data allowed for a more thorough and proper analysis of locations likely experiencing snowfall.  Many of the surface observations (in yellow) likewise corroborate the snow that was occurring, particularly for locations in Wyoming, where coverage from radar data alone was very lacking.  However, there are some surface observations that do not corroborate where the SFR product is indicating snowfall.  Multiple reasons for this apparent discrepancy may exist, but it’s important to remember that the polar orbiting satellite instruments are detecting snowfall in the clouds.  Some of this snowfall may not be reaching the surface due to sublimation aloft.  Also, the snowfall could be very light and patchy in some instances with detection issues at some of the automated ground observation sites.

Now, let’s take a quick look at the polar orbiting data alone (Image 3).

NESDIS SFR product (liquid to snow ratio 10:1) 0345 UTC 16 Dec 2015

Image 3.  NESDIS SFR product (liquid to snow ratio 10:1) 0345 UTC 16 Dec 2015

The resolution of the polar orbiting data still allowed for the detection of banded structures across parts of the Dakotas that were evident in the MRMS data.

Further evaluations and posts about this product will be forthcoming as we progress through the winter.  Perhaps I’ll have the chance at some point to evaluate the product here in the Tennessee Valley…that is, if the current mild Eastern U.S. pattern changes.

 

Spring Snow in New Mexico

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

 

Spring High Terrain New Mexico Snow Event

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