A classic winter weather pattern developed over the Pacific Ocean this week setting the stage for significant drought relief for the western U.S., along with heavy to excessive coastal rains and mountain snow measured in feet for the Sierras and Rockies.

Even though this is a “classic” winter pattern, it hasn’t been prevalent during the past few winters. The absence of this weather feature is part of the reason why much of the western U.S. is experiencing severe to extreme drought.

An Atmospheric River pattern is expected to persist into January 2023 with many areas becoming hydrologically sensitive to additional precipitation. Concerns for flooding and/or mudslides are heightened in western locations with burn scars from recent wildfires.

The persistent AR pattern is reflected in NOAA’s CPC Precipitation Outlooks:

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A sequence of GOES-16 (GOES-East) Nighttime Microphysics RGB and Day Snow-Fog RGB images (above) showed plumes of “ocean effect” clouds (including a “sound effect” cloud band, originating over Long Island Sound) that produced periods of snowfall from coastal Connecticut and Rhode Island (as well as Block Island) to Martha’s Vineyard, Nantucket Island and Cape Cod in Massachusetts during the 24 December – 25 December 2022 period — with notable snowfall accumulations occurring across Martha’s Vineyard (NWS Public Information Statement | NOHRSC). The northern edge of the sound effect cloud band only passed over coastal Connecticut and Rhode Island briefly, producing moderate snow at Groton CT (KGON) and light snow at Westerly RI (KWST). 

As mentioned in Area Forecast Discussions from NWS Boston, this configuration of a significant Long Island Sound effect snow band was rare, with most of their ocean effect snow events occurring with northerly flow. 

An extremely rare and significant snow band has been impacting
Marthas Vineyard this morning on very cold west to southwest
flow. Most of the time our ocean effect snow events are dealing
with northerly flow with a shallow inversion layer and often a
limited fetch. This results in very minor snow accumulations in
most cases. In this situation...rare arctic air invaded the
region on a 240/250 degree wind. The soundings indicate a rather
deep mixed layer up to the inversion at 4-5 thousand feet with
uniform WSW winds. Large temp differentials from the top of the
mixed layer to the SST were on the order of 22C/23C.

A comparison of GOES-16 Nighttime Microphysics RGB, Cloud Top Phase and Cloud Top Height images at 0001 UTC on 24 December (below) showed that the Long Island Sound effect cloud band’s top was composed of supercooled water droplets, with cloud top height values in the 5000-7000 feet range. As this cloud band was passing over Central Long Island Sound Buoy 44039 during the 24-25 December period, strong surface winds caused an upwelling of cooler sub-surface water which reduced sea surface temperatures about 3ºF.  

On 26 December, GOES-16 True Color RGB images from the CSPP GeoSphere site (below) revealed the whiter shades of snow cover across Martha’s Vineyard, Nantucket Island and southern portions of Cape Cod — with the lesser snow depths across Nantucket Island and Cape Cod beginning to melt more quickly compared to the deeper snow cover across Martha’s Vineyard. 

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GOES-16 (GOES-East) Day Snow-Fog RGB images (above) showed widespread horizontal convective rolls (HCRs) that were streaming southeastward across much of the north-central US — in the wake of a strong arctic cold front — on 22 December 2022. This HCR signature is often accompanied by significant blowing snow; in fact, many Interstate highways were closed on this day in portions of North Dakota, South Dakota and Iowa. Wind gusts as high as 60 mph were recorded in South Dakota.

On 23 December, GOES-16 Day Snow-Fog RGB images (below) displayed a long but narrow plume of HCRs that originated over the southern end of Lake Manitoba — which crossed the US/Canada border and streamed across far northeastern North Dakota and northwestern Minnesota. Surface visibility was reduced to 1/4 mile at some sites in Minnesota where the HCR signature was observed; wind gusts as high as 52 mph were reported across that area.

These blowing snow events occurred during a significant and widespread outbreak of arctic air across much of the Lower 48 states during the 21 December – 23 December period, as an anomalously-deep mid-tropospheric trough descended southward and southeastward from Canada — GOES-16 Air Mass RGB images (below) displayed the beige to pale orange hues that are normally associated with such arctic outbreaks (for example, in January 2019). On the morning of 22 December, two locations in western Montana reported low temperatures of –50ºF (the first occurrence of -50ºF in the Lower 48 states during the 2022-2023 winter season).

Additional details and imagery of this arctic outbreak and associated episodes of blowing snow can be found on the Satellite Liaison Blog.

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NOAA‘s GOES ABI has been monitoring the late year cold air outbreak over the contiguous US.

Infrared Imagery

During these extreme cold air outbreaks, it may seem like the infrared imagery “confuses” clouds and the cold ground, but this isn’t the case as the instrument just monitors the heat of the radiating surface, be it a cold cloud top or cold land (or warmer sea surfaces). More likely, as the case below, a certain temperature threshold is used for the color enhancement, in this case colder than -20C. More imagery, including the CONUS sectors. A still image from 13 UTC on December 23, 2022.

Land Surface Temperature

The Land Surface Temperature is one of the many derived products from the ABI. Both the Full Disk and CONUS sectors are included. Note how the cold air has come from central Canada.

Cloud Heights

Cloud heights are another derived quantity from the ABI radiances. Most algorithms are able to discern the cold ground from cold clouds.

And the corresponding legend.

H/T

Thanks to all those to help produce the GOES radiances and derived products. More information on Level 2 products.

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