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.
Archive for the ‘VIIRS’ Category
The cold air outbreak over the eastern United States had impacts far and wide, including the development of snow showers all the way into northern Alabama. However, between unseasonably low 850 mb temperatures and northwesterly flow, the outbreak also caused a semi-persistent band of snow to develop along the Tennessee River (downwind of a reservoir known as “Lake Wheeler”).
While most of the river-effect monitoring occurred with radar, the late-morning MODIS overpass captured one of the narrow river-effect bands (and did so more effectively than the lower-resolution GOES-East Imagery).
Snowfall reports from underneath the band have indicated 2 to 3 inches of snow, compared to the 1-2 inches reported with heavy or persistent snow showers elsewhere. Unfortunately, orbit timing and cloud cover have not allowed us to view the snow swath using the Snow-Cloud RGB. However, the Snow-Cloud RGB from the edge of this morning’s MODIS pass still illustrated the river-effect band persistence.
Recently, I had the opportunity to travel to the Tucson NWS office and work with forecasters there concerning a number of experimental data sets transitioned by the SPoRT group. Primarily, this involved the SPoRT LIS, GPM Constellation and IMERG, and NESDIS QPE data sets. However, I also had the opportunity to see how other products were being utilized by forecasters. While taking a look at the Nighttime Microphysics RGB image, I was initially perplexed by the apparent presence of fog and low clouds in parts of the desert southwest. The first image below is a 4-panel image from AWIPS, showing the Longwave (LW) and Shortwave (SW) IR, the LW-SW IR channel difference, and the Nighttime Microphysics RGB from the VIIRS instrument on the morning of Sept 23rd.
The difference in brightness temperatures between the LW and SW IR channels in parts of SW Arizona, SE California and areas of NW Mexico around the Gulf of California, results in relatively large positive values. Notice the yellow colors that appear in these areas in the channel difference imagery (image 1, lower right), and the corresponding appearance of white-aqua colors in the Nighttime Microphysics RGB (the 10.8-3.9 channel difference represents the green color component of the RGB recipe). For a forecaster accustomed to looking at these imagery in other parts of the country (and those will less sandy surfaces), these channel difference values and colors in the RGB would suggest the presence of low stratus and/or fog. However, no clouds or fog were present in those locations during the morning. You can, however, see some low clouds in portions of central and eastern New Mexico, as indicated by the brighter white-aqua colors.
So, what is going on here? Well, as eluded to above, it’s the presence of dry sand. The image below (courtesy of COMET) shows the IR emissivity over several different surface features: tree leaves, red clay, dry sand, and water.
Notice that the emissivity over dry sand changes fairly substantially through portions of the SW and LW portion of the spectrum, and is lower at 3.9 µm than at 10.8 µm. The channel difference between 10.8 and 3.9 µm will result in positive values (given clear sky conditions of course) over dry sandy areas, thus mimicking the presence of low clouds and/or fog, as would be the interpretation in other areas. The next image below demonstrates the LW and SW IR brightness temperatures and differences, along with the Nighttime Microphysics RGB, as sampled over a clear, dry sandy area.
Notice the substantial resulting green color contribution in the Nighttime Microphysics RGB (lower right in above image). These colors are very similar to colors that would be indicative of fog and other low cloud features as they traditionally appear under similar temperature conditions in other areas outside of dry, sandy areas (image 4 below).
NWS Albuquerque recently began ingesting the updated SPoRT CONUS LIS products in our new AWIPS II system as part of our continued collaboration with SPoRT. These products have already peaked the interest of several local, state, and federal partners. Short-term drought conditions have improved steadily since late winter as more frequent and widespread precipitation events impacted the state. Overall, deep-layer soil moisture conditions have improved substantially compared to this time last year (Fig. 1).
The SPoRT LIS products have become a valuable tool for drought monitoring during our monthly drought workshops. Several state and federal partners noted on our most recent call in late July that these new products provided an additional layer of situational awareness and infuse more science into the drought monitoring process. These products have also peaked the interest of our fire weather community, in particular Incident Meteorologist Brent Wachter. New Mexico during late July is generally under the influence of higher humidity with periodic wetting rainfall events. The convective nature of the precipitation however tends to bring about a patchwork of “have’s and have-nots”. The Fort Craig wildfire broke out in a dry pocket of south central Socorro County within the middle Rio Grande Valley during the afternoon of 26 July 2015. The New Mexico State Climatologist, Dave DuBois, captured the wildfire on camera and posted the image to Twitter shortly thereafter (Fig. 2).
The SPoRT LIS 0-10cm volumetric soil moisture at 12Z 28 July 2015 showed the corresponding dry area where the wildfire developed (Fig. 3). Les Owen from the New Mexico Department of Agriculture also noted this area of drying within Socorro County in what he called his “windshield survey” in mid to late July. The Fort Craig fire grew to nearly 700 acres over the course of two days. The NASA SPoRT soil moisture imagery showed the dry area quite well and the fire was located smack dab in the middle of it.
Several storms then impacted the area late on the 28th and the 29th leading to some natural fire suppression and reduction in active fire behavior. The follow-up SPoRT imagery at 12Z 30 July 2015 showed the increase in 0-10cm relative soil moisture over the same area (Fig. 4). The high resolution imagery could be useful in determining fuel dryness for potential fire starts from human activities, cloud to ground lightning ignitions, as well as highlight potential active fire behavior areas. We will continue to assess the possible applications of the SPoRT LIS products as we move through the remainder of the 2015 monsoon season.
The Albuquerque NWS recently began receiving an updated NESDIS snowfall rate (SFR) product from NASA SPoRT. We were anxious to see how the updated product performed during our most recent winter storm. A fast moving upper level trough and associated Pacific Front blasted into western New Mexico on the afternoon of Saturday, December 13. The upper low deepened and closed off over New Mexico with wrap around snow impacting northeast New Mexico through mid-day Sunday, December 14. Ahead of the system, temperatures were very warm with Albuquerque reporting a high of 61 and Santa Fe reporting a high of 57 on Saturday. The RGB snow-cloud product from 2045Z on Sunday depicts snow cover following the event. Four areas in the state were impacted – the western high terrain, the San Juan and Sangre de Cristo Mountains (mainly west slopes) in north central New Mexico, and extreme northeastern corner of New Mexico. Four yellow ovals mark areas to be discussed in this blog entry. Strong westerly, downslope flow on the backside of this storm system resulted in the snow-free region along the eastern slopes between Taos and Raton.
In the loop below, the 0.5 reflectivity mosaic and surface observations show the surface front moving into western New Mexico (left most oval in the snow-cloud product) during the period from 1942Z to 2318Z. In the first image, the winds have shifted to the northwest in Farmington (FMN) and rain is reported as temperatures are too warm to support snow. Note that throughout the loop the Farmington area, especially west and north of the site, there are no radar returns. The Four Corners area has poor to no radar coverage and it is an area where we hope the SFR product will help us. Snow was reported at Gallup (GUP) by 2030Z.
The SFR product was limited during this initial period, with only one swath covering New Mexico at 2034Z (shown below). This image (obtained from the SPoRT product page) shows that snow is detected in northeast Utah and northwest Colorado, but not in northwest New Mexico. The Gallup area ended up with about one inch of snow while higher terrain south of Gallup reported two to three inches. While only rain was reported at the Farmington ASOS, the snow-cloud product shows some snow just to the east of Farmington where reports of one-half to an inch of snow was reported.
The next SFR product with coverage over New Mexico had a timestamp of 0338Z (14 December 2014), and is compared to the composite reflectivity image of 0336Z in the image below. Reflectivity is strongest just west and northwest of the Albuquerque ASOS (ABQ), which is reporting rain. The cold front however was moving quickly from west to east toward the ABQ metro area. The strong reflectivity returns to the northwest of Albuqurque are actually bright banding as rain began changing over to snow. The dual polarization hydrometeor classification algorithm showed the rain/snow line shifting quickly eastward. Fifteen minutes prior to this image, rain transition to snow was reported in Rio Rancho, just northwest of Albuquerque. The higher terrain just east of Albuquerque, the Sandia and Manzano Mountains, did receive snow accumulations of two to four inches and the SFR product highlights that area with light rates (blue) of about .02 inches/hour. The Santa Fe area (SAF) is not reporting snow at this time, but is highlighted with the max values of SFR, though snow reports in the Santa Fe area were generally less than 2 inches. Recall that afternoon temperature were quite warm, making it difficult for snow to accumulate. The SFR product also depicts rates up to .05 inches/hour over the Sangre de Cristo mountains north and east of Santa Fe, where accumulations of 4 to 8 inches were reported. Interestingly, the SFR product is estimating precipitation around Santa Fe when the radar reflectivity pattern and observation do not indicate rain or snow. A portion of this area to the immediate northeast and east of ABQ is beam-blocked by the Sandia Mountains (yellow oval southwest of SAF).
A similar comparison is shown for 13 hours later, or around 1655Z on December 15. (Another image was available around 08Z, but is not discussed in the post.) Note that the SFR product depicts accumulating snow, albeit light, from eastern Taos through all but extreme southern Colfax County. Two stations (KAXX and KRTN) are reporting snow, but radar composite reflectivities do not extend over either location. Snow did accumulate at KAXX, but not at Raton (KRTN) where temperatures hovered right above freezing.
Snow that is evident in extreme northeast New Mexico occurred after mainly 16Z and was associated with persistent wrap around precipitation (a SFR product was not available). The SFR product was not used in near real time for this event but was re-examined only a short time thereafter. However, the product did validate that we will indeed be able to complement radar void coverage areas in an operational forecast environment using polar-orbiting satellite imagery. This example will also serve to highlight potential product applications, advantages, and disadvantages for forecaster training prior to the upcoming NESDIS evaluation period.
I’ve written about the operational utility of Day-Night Band (DNB) RGB imagery several times in the SPoRT blog, and here I’m going to take the chance to do that again. First, just some brief background information in case you’re not familiar with this type of imagery. The DNB RGB is composed of a long wave IR channel (~10.8 µm), which is assigned to the blue color component of the RGB recipe, while the DNB channel (0.7 µm) is assigned equally to the red/green colors of the RGB. SPoRT produces two DNB RGB products: Radiance and Reflectance. I typically prefer the Radiance RGB for operational uses since it is composed of the raw data (emitted and reflected light) from the sensor. Sure, cities are quite bright in the imagery, but the cloud features also stand out better compared to the reflectance product, where the data are normalized by the available amount of moonlight. Below are a few observations from the Suomi-NPP VIIRS instrument during this most recent full moon cycle.
First, take a look at the images below from the SE half of the CONUS on the early morning of December 7th. The top image (Image 1) is a Nighttime Microphysics RGB at approx. 0736 UTC, while Image 2 is a DNB Radiance RGB valid at the same time. While this type of imagery is far superior to legacy IR imagery (even enhanced with fanciful color curves), there are proper operational forecasting/analysis applications that one has to consider. The Nighttime Microphysics RGB is generally more useful for distinguishing different cloud types (e.g., low stratus vs fog, thin cirrus vs thick cirrus, etc). After at least a year of viewing the DNB imagery, I think perhaps the best application of these types of imagery (at least with respect to operational forecasting) lies in the ability to view low clouds through cirrus at night. No other imagery available to forecasters offers this capability currently. Take for example these first two images below and pay close attention to the cloudy regions stretching from the central Plains into the lower Mississippi Valley.
Notice that in the Nighttime Microphysics RGB the expansive deck of low stratus across much of Kansas, southwestern Missouri and Oklahoma is almost entirely obscured by the cold cirrus clouds. Of course, this is only realized upon looking at the DNB imagery. Details in the low stratus can also be observed in the DNB imagery, such as the cloud banding stretching SW-NE across much of northern Louisiana and Mississippi. Since the cloud bases in this imagery were mostly at MVFR and IFR levels with respect to aviation forecast concerns, knowledge about the details and characteristics of the low clouds are very important.
The next series of images from the New England region in the early morning hours of December 9th again demonstrates this application of the DNB imagery.
In the images above, notice that the extensive low cloud deck across the region that spans from Maine to at least as far south as northeastern North Carolina cannot readily be observed either in the legacy IR (10.8 µm ) imagery or in the Nighttime Microphysics RGB. However, more details about the low clouds can be discerned from the DNB imagery. Sure, cirrus clouds are optically thick enough to prevent viewing of any low clouds in the NY metro area. Nevertheless, the advantages of the DNB imagery for detecting low clouds beneath thin cirrus can clearly be seen. Again, as expressed earlier, this type of imagery certainly offers application for aviation forecasting, in particular.
Lastly, here are some observations from just this morning (Dec 10th) over the Rio Grande Valley region.
In the VIIRS IR image (Image 6) just as in previous IR imagery the cirrus clouds obscure the presence of any clouds beneath. However, the patchy low clouds in eastern New Mexico can be much more easily seen in the DNB imagery. In the area between Midland, TX (KMAF) and Fort Stockton (KFST), a forecaster might have made the assumption that the low clouds were continuous based on the observations alone and without the aid of the DNB imagery. Yet, what becomes noticeable in the DNB imagery is that a gap exists in the low cloud deck.
Of course, with all of this said, the availability of the imagery severely limits its application for operational forecasting and analysis. Generally, only one or two passes are available over a given location on any night. Also, due to moonlight limitations, the imagery are only available for about half of the month…at best. I can only lament that the DNB imagery will not be available on a geo-stationary platform (at least anytime soon). Nevertheless, understanding the limitations of the imagery while also appreciating its advantages can offer operational utility when applied properly to a forecast challenge.
Starting around 07Z last night, we noticed a station in the far northeast corner of Colorado reporting some reduction in visibility, with no other stations nearby reporting any reduction. We couldn’t see any indication in the 11u-3.9u IR satellite imagery. Once the VIIRS DNB imagery came in of the 09:04UTC imagery set, it was definitely evident in the Nighttime Microphysics channel, slightly in the Dust RGB channel, but not at all in the other DNB channels. Good to know the sensor was reporting correctly!
Seen above, top to bottom: VIIRS DNB Reflectance RGB, IR Longwave, Dust RGB, Nighttime Microphysics imagery. The latter definitely shows the small patch of fog clearly with the whiter (lower) clouds.