VIIRS True Color and False Color RGB images from Suomi-NPP and NOAA-20 (above) revealed narrow swaths of lake effect snow cover — which appeared as shades of cyan in the False Color images — downwind of Milford Lake (located NW of Junction City) and Turtle Creek Lake (located NNW of Manhattan) in northeastern Kansas on 22 February 2022.

A sequence of Tulsa radar 0.5-degree base reflectivity images at 30-minute intervals (from 0700-1800 UTC) showed the lake effect bands streaming southeastward from those 2 lakes — followed by a toggle between Suomi-NPP VIIRS True Color and False Color RGB images at 1903 UTC (below). A northwesterly flow of cold arctic air (in the teens to single digits F) across the still-unfrozen water of the lakes picked up enough moisture to create narrow cloud bands that produced the accumulating snowfall.

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NUCAPS profiles from NOAA-20 provide a widespread swath of thermodynamic information that occurs (over CONUS) when normal radiosondes are not available (for example, around 1800 UTC as above). In addition, NUCAPS provides information in regions away from the sparse radiosonde network. The image above shows NUCAPS sounding availability points over Wisconsin; southern Wisconsin is forecast to receive freezing rain and ice pellets overnight. What do NUCAPS soundings, and gridded NUCAPS fields show?

Gridded NUCAPS temperature fields (at 850 mb and 925 mb) are shown below. The color enhancement has been altered so that values around the melting point (0^o C) are black. The NUCAPS fields are capably capturing the strength and location of the low-level inversion: note how much farther north the warm air is at 850 mb compared to 925 mb! This information might be useful is diagnosing regions most at risk to accumulating freezing rain. (One might look at gridded dewpoint depressions fields as well to determine where evaporative cooling might occur).

And individual NUCAPS profile near 43 N, 89 W, shown below, shows a very strong surface inversion.

How does the NUCAPS profiles compare with a forecast profile? The GFS 6-h forecast profile, taken from the tropicaltidbits website, shows that NUCAPS is viewing a somewhat dryer airmass than is present within the model. NUCAPS profiles give information about moisture that might be missing (or mis-timed) in numerical model output. The horizontal extent of the dry air in NUCAPS is large, as shown in the gridded NUCAPS 850-500 mb layer relative humidity analysis shown at bottom.

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Added, 22 February 2022, 2:22 PM: NUCAPS provided another view of the thermodynamics over southern Wisconsin after noon, as shown below. Thick clouds over eastern Wisconsin prevented the retrieval from converging to a solution there (hence the red points), but three green points near/over eastern Dane County provided useful information. The sounding on the Dane County/Jefferson County border at 43^o N, 89^o W (shown here) continued to show warm air aloft that would allow for continued freezing rain/drizzle.

What did the gridded NUCAPS Temperature field at 850 mb look like? As shown below, it continues to show a warm tongue into southern Wisconsin; however, caution in interpreting this field is warranted. Many of the points that were used to create the field were from ‘yellow’ retrievals (i.e., microwave retrievals that might be unable to resolve a low-level inversion) and ‘red’ retrievals. Thus the gridded field might not represent the true values there.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Day Cloud Phase Distinction RGB images (above) displayed a narrow band of glaciated (brighter shades of green) clouds that produced snow squalls as it moved rapidly eastward across Pennsylvania on 19 February 2022. Due to the fast motion of the snow squall band, resultant snowfall amounts were generally 1 inch or less at most locations — but the visibility often quickly dropped to near zero due to intense snowfall rates and gusty winds. For example, as the snow squall moved through State College just after 16 UTC, the surface visibility went from 10 miles to less than 1/4 mile and then back to 10 miles within 30 minutes (below).

Here’s a timelapse of the snow squall as it passed through State College, shot from our office window #PAwx pic.twitter.com/cJfpjXTCxm

— NWS State College (@NWSStateCollege) February 19, 2022

In far eastern Pennsylvania, snow squalls caused a 50-vehicle pileup on Interstate 81, closing the section between the McAdoo and Hazelton exits for about 6 hours (media report) — the accident occurred as the snow squall band was moving through that area around 18 UTC, as seen in a closer view of GOES-16 Day Cloud Phase Distinction RGB images (below) .

In a before/after toggle between GOES-16 Day Cloud Phase Distinction RGB images at 1724 UTC and 1900 UTC below), the dark blue signature of bare ground in the Hazelton area prior to the arrival of the snow squall was replaced by a darker green signature of snow-covered ground.

As was seen with the snow squall passage at State College, a brief but rapid drop in surface visibility occurred at Hazelton (below) as the squall passed through around 18 UTC.

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The animation above, of the Day Cloud Phase Distinction RGB, shows bands of snow showers/squalls rotating cyclonically through northern Minnesota and northwestern Wisconsin, to the south of a strong cyclone over northern Minnesota and northwestern Ontario (link to map from 1800 UTC on 18 February). The tops of these clouds are fairly low — in the RGB they have a periwinkle color in contrast to the orange/red color of the higher cirrus to the south. The RGB also allows for good contrast between the clouds and the clear snow-covered grounds (with greenish tones) to the west.

A potency of the upper air system supporting the surface cyclone is highlighted in the Ozone Anomaly fields from gridded NUCAPS data, shown below. Anomalies of 120-140 dobson Units are present.

The National Weather Service in Duluth MN issued a series of Snow Squall Warnings; the first one, valid until 1945 UTC, is shown below (taken from this tweet); sequential tweeted Warnings are here (valid until 2015 UTC), here (valid until 2100 UTC), here (valid until 2145 UTC) and here (valid until 2215 UTC). (Note, WFO ARX — in Lacrosse, WI, is issuing Snow Squall warnings for this system as well!)

Three radars for this event are shown below: 1907, 1937 and 2007 UTC.

VIIRS imagery (available from the CIMSS LDM feed) over the Duluth Area afforded a high-resolution view of this event. The toggles below show True and False Color imagery at 1838 UTC (from Suomi NPP) and at 1929 UTC (from NOAA-20) At 1838 UTC, the clouds producing the snow — between Moose Lake and Floodwood — do not stand out. They are much more noticeable in the 1929 UTC image, southeast of Duluth and northwest of Solon Springs.

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What was the effect on visibility? That is shown in the animation below with a 10-minute time step. Note how Duluth goes from southwesterly winds with light snow and 5- to 10- mile visibility to strong northwest winds (gusts to 45 knots) and reduced visibilities as the squall moves through.

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As this front moved through southern Wisconsin, it generated lightning, as shown in the animation below (from this website).

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