Developing winter storm over Colorado

March 19th, 2020 |

GOES-16 Mid-level Water Vapor (6.9 um) images, with hourly plots of surface wind barbs and gusts (knots) [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 um) images, with hourly plots of surface wind barbs and gusts (knots) [click to play animation | MP4]

As a winter storm began to organize over Colorado on 19 March 2020, GOES-16 (GOES-East) Mid-level Water Vapor (6.9 um) images (above) showed the developing  middle tropospheric cyclonic circulation across the Colorado/Kansas/Nebraska border area. Peak wind gusts included 60 mph in Colorado and Nebraska, and 62 mph in Kansas (WPC Storm Summary).

As a result of the strong winds, several areas of blowing dust were seen in GOES-16 “Red” Visible (0.64 um), Split Window Difference (10.3-12.3 um) and Dust Red-Green-Blue (RGB) images (below): (1) a well-defined plume that originated in southeastern Colorado and moved northeastward across western Kansas, (2) a smaller plume originating north/northwest of Lamar, Colorado which moved eastward toward the Colorado/Kansas border, (3) a small plume that originated over the burn scar from the 07 March “Beaver Fire” in the Oklahoma Panhandle, and (4) multiple narrow plumes of dust in the wake of a cold front that moved southeastward across the region late in the day (which reduced the surface visiblity to 2 miles in southwestern Kansas).

GOES-16

GOES-16 “Red” Visible (0.64 um), Split Window Difference (10.3-12.3 um) and Dust RGB images [click to play animation | MP4]

A NOAA-20 True Color RGB image as viewed using RealEarth (below) provided a more detailed view of the dust plume north of Lamar, Colorado as well as the longer plume which stretched from southeastern Colorado into western Kansas.

NOAA-20 True Color RGB image at 18:40 UTC [click to enlarge]

NOAA-20 True Color RGB image at 18:40 UTC [click to enlarge]

GOES-16 Visible images with plots of GLM Groups (below) revealed a few clusters of lightning associated with convective elements that were likely producing thundersnow across northeastern Colorado and near the Colorado/Nebraska border. Where warmer air was still present near the Colorado/Kansas border, a more longer-lived thunderstorm was producing rainfall at the surface.

GOES-16

GOES-16 “Red” Visible (0.64 um) images, with GLM Groups plotted in red and hourly surface weather type plotted in yellow [click to play animation | MP4]



===== 20 March Update =====

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

On the following day, GOES-16 Day Cloud Phase Distinction RGB images (above) showed the large swath of fresh snow cover (shades of green) produced by this storm as it moved northeastward across the Upper Midwest. Clouds persisted over much of eastern Colorado, masking the extent of the snow cover there.

===== 21 March Update =====

Landsat-8 False Color RGB image, with and without labels [click to enlarge]

Landsat-8 False Color RGB image at 1724 UTC, with and without labels [click to enlarge]

On 21 March, a decrease in cloudiness over eastern Colorado allowed much of the snow cover (shades of cyan) to be seen in a swath of 30-meter resolution Landsat-8 False Color imagery as viewed using RealEarth (above). The effects of terrain were evident, with a lack of snow cover seen in areas where downslope flow was prevalent during the winter storm.

The effect of snow cover on boundary layer cloud development

March 15th, 2020 |

GOES-16 Snow/Cloud Discrimination RGB images [click to play animation]

GOES-16 Snow/Cloud Discrimination RGB images, with hourly plots of surface wind barbs (knots) [click to play animation]

GOES-16 (GOES-East) “Snow/Cloud Discrimination” Red-Green-Blue (RGB) images (above) revealed a west-to-east oriented band of fresh snow cover (1-4 inches, shades of red) across central Illinois on 15 March 2020. With a low-level northeasterly flow of cold air across the region, boundary layer cumulus clouds began to develop as solar heating warmed the surface — but this cloud development was suppressed over deeper portions of the snow cover. These RGB images use “Red” Visible (0.64 µm) data as the Red component, and Near-Infrared “Snow/Ice” (1.61 µm) data as the Green and Blue components; bare ground appears as shades of cyan, with supercooled water droplet clouds appearing as brighter shades of white.

A sequence of VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP (below) showed a closer look at the band of snow cover and its effect on modulating the afternoon development of cumulus clouds.

VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP [click to enlarge]

A 30-meter resolution Landsat-8 False Color RGB image viewed using RealEarth (below) provided a detailed view of the band of snow cover (shades of cyan) at 1622 UTC.

Landsat-8 False Color RGB image, with and without labels [click to enlarge]

Landsat-8 False Color RGB image, with and without labels [click to enlarge]

Gridded NUCAPS over the southeast United States

February 21st, 2020 |

Analyzed snow depth at 0600 UTC on 21 February 2020 from the NOHRSC (Click to enlarge)

Snow fell over the southeastern United States, principally North and South Carolina, late on 20 February/early on 21 February 2020. This blog post, one in a series, investigates how gridded NUCAPS thermal fields perform in analyzing the rain/snow line. The snow totals are shown above, an image that was taken from this website at the National Operational Hydrologic Remote Sensing Center (NOHRSC).

NOAA-20 overflew the Carolinas shortly after 0700 UTC on 21 February, and gridded values of 950-mb, 900-mb and 850-mb Temperatures are shown below. (Note how the 950-mb field intersects the ground at the western edge of the Piedmont).  The 0º C isotherm at 850 and 900 mb is close to the coast;  it is sub-freezing over most of the land at those levels.  The analysis from 950-mb shows cold air stretching southwestward from southeastern Virginia, and that region is also where the accumulating snow was focused.  This is an argument in favor of the temperature fields in NUCAPS giving useful information about the rain/snow line.

850-mb, 900-mb, and 950-mb analyses of temperature derived from NUCAPS vertical profiles of temperature, 0723 UTC on 21 February 2020. The same color enhancement is used for each level, spanning -40º C to 30º C; 0º C is highlighted by the black line (Click to enlarge)

One of the gridded NUCAPS fields available in AWIPS via the Product Browser (there are many!) is the binary probability of a temperature occurring.  The 850-mb binary probability of 0º C is close to the coast, at 900-mb, just slightly inland.  The 950-mb values also suggest cold air is more likely over the region where snow fell.  There are also some embedded cold pockets at 950 mb over interior North/South Carolina.

Conditional Probability of 0 C at 850, 900 and 950 mb, 0723 UTC on 21 February 2020 (Click to enlarge)

Note that gridded NUCAPS fields include data from infrared retrievals, microwave-only retrievals, and from retrievals that do not converge. The gridding can mask behavior in the vertical profiles that might not necessarily engender confidence in a meteorological analyst. The plot below shows NUCAPS points (Green points are infrared retrievals that successfully converged, yellow points are microwave-only retrievals, and red points occur where the microwave-only and infrared retrievals failed to converge; this is typically where precipitation is falling) plotted on top of the 850-mb temperature analysis.  Note, however, that values do show up everywhere!  Users of the gridded data should keep in mind the quality of the data that goes into the analysis when they use it.  Two vertical soundings from which gridded data are derived are shown at bottom.  Users can decide if they would use those vertical soundings in isolation.

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020 (Click to enlarge)

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020. Two soundings are also shown, from a green point and from a yellow point.  Note that the plot also shows the binary probability of a temperature at 0º C (Click to enlarge)

Bore-like feature over Lower Michigan

February 13th, 2020 |

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm), 1435 – 1840 UTC on 13 February 2020 (Click to enlarge)

TJ Turnage, the Science and Operations Officer (SOO) at the National Weather Service forecast office in Grand Rapids, noted today the presence of smooth, curving bands over Lake Michigan. The animation above shows their development — and the smooth appearance of the bands (just offshore of Ottawa Co, and curving into Allegan Co) is in marked contrast to the north-south oriented lake-effect bands over central Lake Michigan. This falls into the “What the Heck is this?” Blog Category.

An hourly animation that includes surface conditions sheds little light. The bore-like feature seems to arise out of an interaction of the atmospheric flow with Big and Little Sable Points, and surface winds at Muskegon (just north of Ottawa Co) and Holland (in Allegan Co) change as the feature moves over — but no snow is observed at those stations during the bore passage.

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm) and surface METARS hourly from 1300 – 2100 UTC on 13 February 2020 (Click to enlarge)

Radar imagery (from the College of Dupage) also shows little return associated with the bore-like features.  (Click to see images from 1720 and 1800 UTC, when the bands were on shore).

NEXRAD Composite Radar Imagery (Composite Reflectivity) centered on MI, 1655-1820 UTC on 13 february 2020 (Click to enlarge)

 

Water vapor imagery, below, suggests that the stable layer that is trapping the energy and causing the bore-like feature originated near Big and Little Sable Points, around 1600 UTC.  The enhancement also suggests the bore-like feature is higher than the tops of lake-effect bands in the middle of Lake Michigan.  (Click here for a rocking animation of the water vapor imagery;  the rocking allows for better tracking of the impulse back to the source near the Sables, its earliest hint is at 1610 UTC — vs. about 1635 UTC in visible imagery).

GOES-16 ABI Band 10 (7.34 µm, low-level water vapor) infrared imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

GOES-16 ABI Band 2 (0.64 µm) visible imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

Bore-like features require stable layers.  The Gaylord Michigan sounding at 1200 UTC — upstream from the region out of which the bore emerged — shows several inversion layers.  The weighting function for the sounding (from this site) shows peak contributions for 7.34 µm (indeed, from all water vapor channels) from above 500 mb.  The coldest brightness temperature in the bands is -28 º C;  based on the Gaylord sounding, that’s a pressure level near 560 mb.  These Bore-like features are not Lake-Effect snow bands, despite having the correct aspect ratio — their width and length both suggest Lake-effect bands, but their height suggests otherwise.

NOAA-20 overflew this region shortly after 1700 UTC, and a NUCAPS sounding is close to the Michigan shoreline, just east of Holland, where the cloud band is coming onshore. The sounding from NUCAPS at that point/time is below.  The very smooth sounding does bear a passing resemblance to the Gaylord Sounding, but the smoothness of the NUCAPS profile — sampling a volume of air that in this case is about as wide as a county, makes identification of sharp inversions difficult.

NOAA-20 NUCAPS Profile points over Lake Michigan and lower Michigan, ca. 1730 UTC on 13 February 2020 (Click to enlarge)

NUCAPS Profile of temperature and moisture, 17 UTC on 13 February 2020 (Click to enlarge)