A potent winter storm system impacted portions of New Mexico on March 26, 2016, ending an extended stretch of very dry weather. Snowfall amounts of 3 to 9 inches were reported from the Sangre de Cristo Mountains eastward across the northeast plains. The MODIS and VIIRS satellite products proved useful for illustrating the extent of snow cover in both the daytime and nighttime scenes. The images below are graphical briefings posted to the NWS Albuquerque web page and shared via Twitter after this much needed snowfall 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.
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).
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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″.
Over the last few days Himawari-8 AHI Air Mass RGB imagery has captured an impressive view of Severe Tropical Storm Choi-wan near Japan. The storm began as a tropical depression near Wake Island and the Japan Meteorological Agency upgraded the depression to a tropical storm on October 2nd. The tropical storm continued to move north-northwest toward Japan and the Sea of Okhotsh but weakened as it evolved. Yesterday and today (October 8th) the storm began to take on more extratropical characteristics and look like a strong mid-latitude low pressure system (click on Fig. 1 animation).
Currently, SPoRT is investigating the utility of NOAA Unique CrIS/ATMS Processing System (NUCAPS) satellite retrieved soundings for hurricane tropical to extratropical transition events. Soundings are typically used to anticipate severe weather and analyze the pre-convective environment; however, they can be just as valuable for analyzing and understanding the environment surrounding complex extratropical transition events, especially over data sparse oceanic regions. National Center forecasters at the National Hurricane Center and Ocean Prediction Center routinely use the Air Mass RGB for forecasting such events, especially for identifying the influence of warm, dry stratospheric air during extratropical transition. Although the Air Mass RGB provides a wealth of information about the upper-level horizontal distribution of temperature and moisture characteristics surrounding a storm, it does not provide insight about the vertical distribution of thermodynamic characteristics. With Next-Generation S-NPP/JPSS NUCAPS Soundings now available in AWIPS-II, they can be used in conjunction with the Air Mass RGB to anticipate extratropical transition events.
Here are a few examples of NUCAPS Soundings compared to the Air Mass RGB. Let’s take a look at NUCAPS Soundings in three locations in the environment surrounding Severe Tropical Storm Choi-wan (Fig. 2).
Location 1, red/orange coloring, represents upper-level dry air on the Air Mass RGB. To no surprise, the NUCAPS Sounding (Fig. 3) reveals dry upper-levels and dry conditions throughout the atmospheric column.
Now Location 2 is also in an orange colored region and representative of upper-level dry air, but take note the coloring is not as “red tinted” as Location 1 and there are more mid-level clouds. Mid-level clouds tend to be light tan or ocher colored in the Air Mass RGB. The NUCAPS Sounding (Fig. 3) does confirm a mid-level moisture layer from about 800-600 mb. Seeing ocher clouds in the RGB only means that qualitatively mid-level clouds are present (one can’t get a quantitative height from the RGB), but inspection of the NUCAPS Sounding would give a quantitative height estimate of the mid-level clouds. Although this sounding is in the region right over the mid-level cloud, looking at more soundings in the same orange region (but not right over a cloud) do show the atmospheric column is not completely dry (like Location 1) but there is low- to mid-level moisture present throughout the region surrounding Location 2. Just by looking at the RGB one may not realize a mid- to low-level moisture layer is present since the interpretation of the orange coloring in the Air Mass RGB is upper-level dry air.
Location 3 is the most interesting (at least to me since the sounding gives more information about the atmosphere than one could extrapolate from just looking at the Air Mass RGB). The green coloring around Location 3 represents a warm, moist air mass. The NUCAPS Sounding (Fig. 4) does reveal a more moist sounding about 300 mb and above, but note there is mid-level dry air present and a low level moist layer. Again the NUCAPS Soundings provide more information about mid- and low- level characteristics that one can’t infer from the RGB imagery. This is just one example that highlights the utility of analyzing Next-Generation satellite data sets for complex weather events in data sparse regions.