Anomalously-deep upper low brings light snow to northwestern Alaska

July 19th, 2022 |

GOES-18 Mid-level (6.9 µm) Water Vapor images, with plots of hourly surface weather type [click to play animated GIF | MP4]

GOES-18 images shown in this blog post are preliminary and non-operational

GOES-18 Mid-level Water Vapor (6.9 µm) images during the 18 July – 19 July 2022 period (above) showed a series of impulses rotating within the broader circulation of an anomalously-deep low pressure system that meandered over the Bering Strait region. Anomalously-cold air associated with this deep low helped to produce brief periods of unusual July snow at some locations across the Seward Peninsula and northwestern Alaska.

In GOES-18 Air Mass RGB images created using Geo2Grid (below), brighter shades of red highlighted the core of this broad low pressure system, where high-altitude ozone levels were elevated (due to an unusually low tropopause).

GOES-18 Air Mass RGB images [click to play animated GIF | MP4]


Plots of rawinsonde data at Nome, Alaska at 00 UTC and 12 UTC on 19 July 2022 [click to enlarge]

In fact, at 12 UTC on 19 July the low 500 hPa geopotential height value of 5269.3 meters from the Nome, Alaska rawinsonde report (above) established a new July record for that site. The 12 UTC sounding also suggested that the tropopause was located at an unusually low pressure level of 483 hPa — such a low tropopause height was supported by NOAA-20 Gridded NUCAPS data from the SPoRT site (below).

NOAA-20 Gridded NUCAPS Tropopause Height at 1236 UTC on 19 July [click to enlarge]

Blowing snow across the North Slope of Alaska

April 15th, 2022 |

Suomi-NPP VIIRS Visible (0.64 µm) and Shortwave Infrared (3.74 µm) images [click to play animated GIF | MP4]

A sequence of Suomi-NPP VIIRS Visible (0.64 µm) and Shortwave Infrared (3.74 µm) images (above) revealed a long east-to-west oriented swath of horizontal convective roll (HCR) clouds associated with blowing snow and blizzard conditions across parts of the North Slope of Alaska on 15 April 2022. The plume of supercooled water droplet HCR clouds appeared warmer — lighter shades of cyan — due to enhanced reflection of incoming solar radiation   At reporting sites within the northern portion of the HCR clouds and blowing snow, winds were gusting in the 35-40 knot range and the visibility was often 1/2 to 1/4 mile.

A Suomi-NPP VIIRS SnowCloud RGB image at 1624 UTC (below) showed that this plume of HCR cloud features — which was mixed with blowing snow — crossed the coast of northwestern Alaska and extended several miles westward  across nearshore waters of the Chukchi Sea.

Suomi-NPP VIIRS SnowCloud RGB image at 1624 UTC (credit: Jason Ahsenmacher, NWS Fairbanks) [click to enlarge]

GOES-17 Near-Infrared Snow/Ice (1.61 µm) images created using Geo2Grid (below) showed how the HCR cloud plume evolved during the day.

GOES-17 Near-Infrared Snow/Ice (1.61 µm) images [click to play animated GIF | MP4]

Thanks to Jason Ahsenmacher, NWS Fairbanks, for bringing this interesting case to our attention!

Blowing dust, wildfires and severe weather in the southern Plains — with blizzard conditions in the northern Plains

April 12th, 2022 |

GOES-16 True Color RGB images [click to play animated GIF | MP4]

5-minute GOES-16 {GOES-East) True Color RGB images created using Geo2Grid (below) showed widespread blowing dust (shades of tan) and wildfire smoke plumes (brighter shades of white) across much of the central/southern Plains on 12 April 2022. Wind speeds were anomalously strong behind a dryline within the warm sector of an anomalously-deep surface low, which were responsible for the spread of wildfires and blowing dust.

In southeastern Colorado, 1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images along with 5-minute Fire Power and Fire Temperature products (below) displayed a smoke plume and thermal signatures of 2 grass fires that rapidly intensified between La Junta (where the peak wind gust was 53 knots) and Lamar. The Fire Temperature and Fire Power derived products are components of the GOES Fire Detection and Characterization Algorithm FDCA.

GOES-16 “Red” Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), Fire Power (bottom left) and Fire Temperature (bottom right) [click to play animated GIF | MP4]

Farther to the south, 1-minute GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (below) include plots of time-matched SPC Storm Reports for severe thunderstorms in central Texas — which produced tornadoes and hail as large as 5.50 inches in diameter. Note that 2 of these storms exhibited Above-Anvil Cirrus Plumes (AACP: reference | VISIT training) in the Visible imagery; however, the corresponding “warm AACP” signature was not evident in the Infrared images, as is frequently the case.

GOES-16 “Red” Visible (0.64 µm, top) and “Clean” Infrared Window (10.35 µm, bottom) images, with time-matched SPC Storm Reports plotted in red/cyan [click to play animated GIF | MP4]

The lack of a “warm AACP ” infrared signature was explained by 2000 UTC rawinsonde data (source) from Fort Worth, Texas (below), which indicated that stratospheric temperatures continued to cool with height.

Plot of 2000 UTC rawinsonde data from Fort Worth, Texas [click to enlarge]

 

GOES-16 Mid-level (6.9 um) Water Vapor images, with hourly surface precipitation type plotted in red [click to play animated GIF | MP4]

Finally, across the northern Plains within the cold sector of the large surface low, blizzard conditions spread across much of North Dakota (and adjacent portions of eastern Montana, northern South Dakota and northwestern Minnesota) — as shown in 5-minute GOES-16 Mid-level Water Vapor (6.9 um) images with plots of precipitation type (above) and wind barbs/gusts (below).

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

===== 14 April Update =====

GOES-16 Mid-level (6.9 um) Water Vapor images, with hourly surface precipitation type plotted in red [click to play animated GIF | MP4]

As the Northern Plains blizzard persisted into its third day on 14 April, longer animations of GOES-16 Water Vapor images are shown with plots of precipitation type (above) and wind barbs/gusts (below). Storm total snowfall accumulations included 36 inches in North Dakota, with peak wind gusts of 72 mph in South Dakota (WPC Storm Summary). The 3-day total of 18.3 inches was Bismarck’s largest April snowfall on record.

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

===== 15 April Update =====

GOES-16 Day Snow Fog RGB images [click to play animated GIF | MP4]

On the morning of 15 April, GOES-16 Day Snow Fog RGB images (above) revealed the partial extent of new snow cover from the 3-day blizzard (darker shades of red), along with narrow plumes of “river effect snow” (shades of white) streaming southeastward from unfrozen reservoirs along the Missouri River in North Dakota and South Dakota. At one point, a plume passing directly over Hazen, North Dakota (downwind of Lake Sakakawea) was producing light snow that reduced the surface visibility to 4 miles.  

NUCAPS Profiles before an historic snow in Portland Oregon

April 11th, 2022 |
GOES-16 Band 13 infrared (10.3 µm) imagery, 0941-1346 UTC on 11 April 2022 (Click to enlarge)

April 11 2022 saw the first measurable snowfall ever in April at the Portland OR airport (WFO Portland Tweet), where records have been kept since 1940. The GOES-16 animation above shows the weather system responsible for the weather.

NOAA-20 overflew the west coast shortly after 1000 UTC (map of the orbit, from this website), and NUCAPS profiles derived from the CrIS and ATMS instruments on board helped define the cold airmass just offshore. The toggle below shows two soundings (green suggesting that the retrieval converged to a solution) just along the shoreline; 850-mb temperatures are -5oC and -4oC at the northern and southern profiles, respectively; the diagnosed freezing levels at both locations are higher than 2000′.

NUCAPS profiles from NOAA-20 at two locations off the west coast of the United States, 1019 UTC on 11 April 2022 (Click to enlarge)

The toggle below shows Sounding Availability points (zoomed in) and diagnosed freezing levels farther offshore, suggesting colder air out over the open ocean.

Sounding Availability points, and diagnosed freezing levels, ca. 1020 UTC on 11 April 2022 (click to enlarge)

Gridded NUCAPS are available in AWIPS — and also at this site created by NASA SPoRT (and at RealEarth). The toggle below shows gridded 850- and 700-mb temperatures from the NOAA-20 overpass. The coldest air is shown over the Pacific Ocean at 1017 UTC.

Gridded 850- and 700-mg temperatures, 1017 UTC on 11 April 2022 (Click to enlarge)

NUCAPS profiles and gridded NUCAPS fields can give timely observations over large data voids (such as the Pacific Ocean) in advance of high-impact weather events.