Eastern US winter storm

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and Near-Infrared “Snow/Ice” (1.61 µm, right) images, with plots of hourly surface reports [click to play MP4 animation]

The initial impacts of a large Eastern US winter storm were seen in a comparison of GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (above) on 03 January 2018 — areas of southeastern Georgia received freezing rain and/or 1-6 inches of snowfall. As clouds began to dissipate, the resulting snow cover appeared bright on the Visible images (since fresh snow is highly reflective at the 0.64 µm wavelength), and darker shades of gray on the Near-Infrared images (since snow and ice are strong absorbers of radiation at the 1.61 µm wavelength). Note the brief appearance of a cloud plume streaming southward from the Hatch Nuclear Power Plant.

Earlier that morning, the Florida Panhandle also received snowfall (text | map), but the lighter accumulations there were insufficient to exhibit a good satellite signature.

In a toggle between Suomi NPP VIIRS true-color and false-color Red-Green-Blue (RGB) images from RealEarth (below), the deeper snow cover in Georgia appears as darker shades of cyan.

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

===== 04 January Update =====

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0620 UTC (1:20 AM Eastern time) on 04 January (above; courtesy of William Straka, CIMSS) showed a nighttime view of the rapidly-intensifying storm when it had an estimated minimum central pressure of 972 hPa or 28.70″. Note the signature of snow cover — extending from southeastern Georgia across eastern portions of South Carolina and North Carolina — which is evident on the “visible image at night” Day/Night Band (made possible by ample illumination from the Moon, which was in the Waning Gibbous phase at 92% of Full). A full-resolution version of the Day/Night Band image is available here.

During the following daytime hours, 30-second interval Mesoscale Sector GOES-16 “Red” Visible (0.64 µm) images (below) showed the evolution of the low pressure center of circulation as it continued to rapidly intensify (surface analyses) off the US East Coast.

30-second GOES-16

30-second GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly surface weather type plotted in yellow [click to play MP4 animation]

A larger-scale view (using 5-minute CONUS sector data) of GOES-16 “Red” Visible (0.64 µm) images with hourly plots of surface weather (above) depicted the widespread precipitation associated with the storm. Similarly, plots of hourly wind gusts (below) portrayed the large wind field of the system. Some of the highest snowfall/ice accumulations and peak wind gusts are listed here and here.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly surface wind gusts plotted in yellow [click to play MP4 animation]

In the wake of the departing storm, the tropospheric column over Florida and the southeastern US was dry enough (3.7 mm or 0.15″ at Tallahassee FL and 4.0 mm or 0.16 ” at Charleston SC) to allow the GOES-16 Lower-level (7.3 µm) Water Vapor imagery (below) to detect the thermal contrast of surface land/water boundaries — portions of the coastline and a few of the larger inland lakes were evident.

"GOES-16

(7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) images [click to play animation]” class=”size-medium” /> GOES-16 Lower-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) images [click to play animation]

A full-resolution Suomi NPP VIIRS true-color RGB image at 1738 UTC (below) revealed interesting storm features such its very large cloud shield and convection near the circulation center, as well as the swath of snow cover across parts of Georgia, South Carolina and North Carolina.

Suomi NPP VIIRS true-color RGB image [click to enlarge]

Suomi NPP VIIRS true-color RGB image [click to enlarge]

A toggle between the corresponding Suomi NPP VIIRS Visible (0.64 µm) and Snow/Ice RGB images (below) helped to highlight locations which received a significant accrual of ice from freezing rain– these areas show up as a darker shade of red on the Snow/Ice RGB image (along the southeastern edge of the swath of snow cover, which is a lighter shade of red). Notable ice accumulations included 0.50″ at Brunswick and Folkston GA, 0.25″ at Georgetown and Myrtle Beach SC, and 0.25″ at Kure Beach NC.

Suomi NPP VIIRS Visible (0.64 µm) and Snow/Ice RGB images, with surface station identifiers plotted in white [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Snow/Ice RGB images, with surface station identifiers plotted in white [click to enlarge]

Finally, a 30-meter resolution Landsat-8 false-color RGB image viewed using RealEarth (below) showed the snow-covered Charleston, South Carolina area — areas with less dense trees and vegetation showed a more pronounced snow cover signature (shades of cyan). The Charleston International Airport remained closed, due to snow and ice-covered runways.

Landsat-8 false-color RGB image [click to enlarge]

Landsat-8 false-color RGB image [click to enlarge]

Additional imagery of this explosive cyclogenesis event can be found at this blog post.

A Remarkable Nor’easter

Let me provide a couple of observations that will blow your mind this morning.

At 6 AM MST, it was 31ºF on Alta's Mt. Baldy (11,066 ft.).

At the same time, it was 30ºF in Tallahassee, Florida, with ice pellets and snow.

That's right.  SNOW.  In Florida.

A remarkable weather event is unfolding as a nor'easter develops along the eastern seaboard.  It is a textbook event, of the type I watched for as a kid viewing the evening news.  The loop below shows the classic high-amplitude wave setup with a ridge over western North America and a deep trough over eastern North America.  In addition, there is a short wave trough moving through the long wave pattern.  You can see it moving from near Wyoming to the Golf coast in the loop below.  


In the loop above, you can see how the large-scale ascent associated with the upper-level trough is generating clouds and precipiation as it moves over the southeast United States.  However, that trough will also spark cyclogenesis as it rounds the long-wave trough and is able to move over warm, unstable, water-vapor-laden air over the Atlantic Ocean and along the Gulf Stream.  


The end result is a very powerful nor'easter.  The NAM forecast initialized at 0600 UTC deepens the system from a weak, inverted trough along the Florida coast with a minimum sea level pressure of about 1013 mb at 1200 UTC this morning to a 961 mb low off the coast of North Carolina by 1200 UTC 4 Jan and then 953 mb by 0000 UTC 5 Jan over the Gulf of Maine.  




The GFS isn't quite as deep (not shown), but the 0000 UTC had similar numbers to the NAM with central pressures of 961 mb and 948 mb at 1200 UTC 4 Jan and 0000 UTC 5 Jan respectively.  

Using numbers from the NAM, that is a fall in central pressure of 52 mb in 24 hours and 60 mb in 36 hours, easily meeting the criteria for what is known as explosive cyclogenesis, or rapid cyclone development.  

The structure of the NAM-forecast storm off the North Carolina coast is consistent with an intense marine cyclone.  The cold and warm/occluded fronts are oriented at right angles, forming a frontal T-bone.  The temperature gradient along the cold front weakens near the warm/occluded, a characteristic known as the frontal fracture (there is some uncertainty in the exact cold front position in this forecast and one might place it further west than I have).  The 925-mb temperature contours (black) become quite concentrated along the occluded front near the low center and its back-bent extension south of the low, where the strongest 925 mb winds are found (color fill).  This area of strong winds is referred to as the poisonous tail of the back-bent occlusion by Norwegian meteorologists.  Cold air has encircled the low center, cutting off a pocket of warm air known as a warm-core seclusion.  


The severity of ompacts along the eastern seaboard will depend strongly on storm track as a slight shift to the west or east will make a difference in the amount of precipitation, which  and severity of winds along the coast.  One need only look at the watches, warnings, and advisories map from the Boston National Weather Service Office to realize what a mess this storm could bring.  

If you are in the area, monitor official forecasts.