Early-season winter storm in the Northern Plains

October 12th, 2019 |

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly surface weather type plotted in red [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly surface weather type plotted in red [click to play animation | MP4]

An early-season winter storm produced very heavy snowfall and blizzard conditions across the Northern Plains — particularly in central/eastern North Dakota and southern Manitoba — during the 10 October12 October 2019 period. GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed the long duration of precipitation across that region. A text summary of snowfall totals and wind gusts is available from the WPC, NWS Bismarck and NWS Grand Forks.

On 11 October, GOES-16 “Red” Visible (0.64 µm) images with an overlay of GLM Flash Extent Density (below) revealed intermittent clusters of lightning activity over northwestern Minnesota, northeastern North Dakota and southern Manitoba — while no surface stations explicitly reported a thunderstorm, NWS Grand Forks received calls from the public about thundersnow. The texture of cloud tops in the Visible imagery also supported the presence of embedded convective elements, which likely enhanced snowfall rates as they pivoted across that area (note that this convection was occurring along the leading edge of the mid-tropospheric dry slot seen in the Water Vapor imagery above). An animation of GOES-16 Visible imagery with plots of GLM Groups and surface weather type is available here.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with an overlay of GLM Flash Extent Density [click to play animation | MP4]

One important aspect of this storm was the formation of a trough of warm air aloft or trowal (SHyMet | Martin, 1998) as the surface low began to enter its occluded phase on 11 October — contours of Equivalent Potential Temperature along the 295 K isentropic surface (below) helped to diagnose the axis of the trowal as it curved cyclonically across southwestern Ontario, southern Manitoba and then southward over North Dakota.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with 295 K equivalent potential temperature contours plotted in yellow and surface fronts plotted in red [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with 295 K Equivalent Potential Temperature contours plotted in yellow and surface fronts plotted in red [click to play animation | MP4]

A similar animation with contours of 295 K specific humidity (below) also displayed the orientation of a west-to-east cross section B-B’ (green) across northern Northern Minnesota and northern Minnesota.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with 295 K Specific Humidity contours plotted in yellow and surface fronts plotted in red [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with 295 K Specific Humidity contours plotted in yellow and surface fronts plotted in red [click to play animation | MP4]

The Line B-B’ cross section at 16 UTC (with and without contours of Equivalent Potential Temperature) is shown below. Note the deep column of upward vertical velocity (highlighted by color shading of Omega) centered over Langdon, North Dakota — the moist trowal airstream can be seen sloping isentropically upward and westward behind the 3 g/kg Specific Humidity contour, as it approached the region of upward vertical motion. Langdon received 27 inches of snowfall; the prolonged southward passage of the trowal over North Dakota likely contributed to this accumulation.

Cross section of RAP40 model fields along Line B-B' at 16 UTC [click to enlarge]

Cross section of RAP40 model fields along Line B-B’ at 16 UTC [click to enlarge]

As the storm was gradually winding down on 12 October, it exhibited a very broad middle-tropospheric signature on GOES-16 Water Vapor imagery (below).

GOES-16 Mid-level Water Vapor (6.9 µm) images, with surface frontal positions [click to play animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with surface frontal positions [click to play animation | MP4]

 

Fresh snow cover in Montana and Alberta

September 30th, 2019 |

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]

Through breaks in the cloud cover, GOES-16 (GOES-East) Day Cloud Phase Distinction Red-Green-Blue (RGB) images on 30 September 2019 (above) showed the bright green signature of fresh snow cover across northern Montana and southern Alberta in the wake of a record-setting snowfall event that occurred during the previous 2-3 days (NWS Great Falls summary). Note that the surface air temperatures over the areas of fresh snow cover only rose into the upper 20s and low 30s F, in contrast to 40s F in adjacent areas with minimal or no snow cover — in fact, many locations set daily record low maximum temperatures.


GOES-16 Mid-level Water Vapor (6.9 µm) images from 0001 UTC on 28 September to 0901 UTC on 30 September (below) covered the duration of the winter storm — the circulation of an anomalously-deep mid-tropospheric low over the Pacific Northwest was evident, in addition to a long fetch of middle/high-level moisture from the southwestern US toward Montana. Another notable feature included widespread mountain waves over Colorado beginning on 29 September, which eventually extended downwind over western Nebraska/Kansas; Colorado had a peak wind gust of 81 mph during this event (WPC storm summary).

GOES-16 Mid-level Water Vapor images, with hourly plots of precipitation type [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of precipitation type [click to play animation | MP4]

===== 01 October Update =====

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

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

With less cloud cover on 01 October, a comparison of GOES-16 Day Cloud Phase Distinction and Day Snow-Fog RGB images (above) provided a better view of the areal coverage of snow cover. Note that while the Day Cloud Phase Distinction RGB (snow=green) produces “sharper” imagery — since it uses the higher spatial resolution of the 0.64 µm Visible data — the Day Snow-Fog RGB (snow=red) does a better job at highlighting thin supercooled cloud features (shades of white) over snow cover.  The combination of fresh snow cover, light winds and minimal cloudiness allowed Cut Bank to record the coldest official temperature in the US at +1ºF (although a couple of sites unofficially dropped below 0ºF).

In a toggle between GOES-16 Day Cloud Phase Distinction RGB and Topography images (below), note the darker blue gaps in snow cover in Montana and Alberta – with easterly/northeasterly winds during the snow event (Cut Bank | Havre | Great Falls), those areas experienced downslope flow which warmed the boundary layer air and minimized snow accumulation.

GOES-16 Day Cloud Phase Distinction RGB and Topography images [click to enlarge]

GOES-16 Day Cloud Phase Distinction RGB and Topography images [click to enlarge]

Snowfall across northern Alaska

September 18th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog RGB and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog Red-Green-Blue (RGB) and and Day Cloud Phase Distinction RGB images (above) showed portions of the Brooks Range and eastern North Slope of Alaska that had significant snow cover on 18 September 2019. Some areas received 4-6 inches of snowfall during the previous day (a Winter Storm Warning had been issued, forecasting accumulations in the 4-8 inch range).

Snow cover appeared brighter white in the Visible images, and darker shades of gray in the Snow/Ice images; in the RGB images, snow was darker shades of red in the Day Snow-Fog, vs brighter shades of green in the Day Cloud Phase Distinction. Note that the Day Cloud Phase Distinction RGB provided sharper images than the Day Snow-Fog RGB (below), since the former makes use of higher spatial resolution 0.64 µm data for its Green component.

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

Although much of the Bettles (PABT) area was masked by cloudiness on 18 September, that site received moderate to heavy snow for a few hours on 17 September (below), and reported a snow depth of 4 inches at 17 UTC (9 am local time).

Time series of surface data from Bettles, Alaska on 17 September [click to enlarge]

Time series of surface observation data from Bettles, Alaska on 17 September [click to enlarge]


Record May snowfall in Duluth, Minnesota

May 9th, 2019 |


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

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the cloudiness associated with a midlatitude cyclone (surface analyses) that moved across the Upper Midwest on 08 May09 May 2019.  The system produced accumulating snowfall from extreme eastern South Dakota to central/northeastern Minnesota, northwestern Wisconsin and Upper Michigan — storm total accumulations were as high as 10.6 inches at Duluth, Minnesota (observations), 10.4 inches at Poplar, Wisconsin, 5.0 inches at Atlantic Mine, Michigan and 3.0 inches at Astoria, South Dakota (NOHRSC maps of snowfall/snowdepth). Note that the NW-SE oriented band of snowfall straddling the South Dakota/Minnesota border may have been enhanced by upslope flow as northeasterly surface winds encountered rising terrain of the Coteau des Prairies.

GOES-16 Mid-level Water Vapor (6.9 µm) images (below) showed the formation of a SW-NE oriented deformation zone across Minnesota — forcing for ascent was further aided by a stretched lobe of 500 hPa vorticity and 310 K potential vorticity that moved northeastward across the region during this period, along with a favorably-coupled 250 hPa jet streak configuration. Cloud features within the deformation zone across eastern South Dakota into southern/central Minnesota had an appearance resembling convective elements/bands in both the Visible and Water Vapor imagery.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to play animation | MP4]

Although lightning was not widespread — and thunder was not explicitly reported in any first-order station observations — there were isolated small clusters of GOES-16 GLM Groups detected, first over northeastern, then central and finally over southwestern Minnesota between 2256 and 0036 UTC (below), indicating the presence of thundersnow.

GOES-16 “Red” Visible (0.64 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to enlarge]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to enlarge]




Through occasional breaks in the clouds later in the day on 09 May, GOES-16 Day Cloud Phase Distinction Red-Green-Blue (RGB) images (below) revealed the stationary signature of fresh snow cover (darker green) across central to northeastern Minnesota and far northwestern Wisconsin (glaciating cloud tops also appear as shades of green).

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

===== 10 May Update =====

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

GOES-16 Visible images (above) showed two swaths of snow cover remaining across northeastern Minnesota (where reported snow depths were 1-2 inches) and northwestern Wisconsin (where reported snow depths were 4-5 inches) on the morning of 10 May.

Comparisons of GOES-16 Land Surface Temperature (LST) and Visible images at 1401 UTC and 1501 UTC (below) indicated that LST values were as much as 10ºF colder within the areas of snow cover (brighter shades of cyan) compared to adjacent bare ground.

GOES-16 Land Surface Temperature and “Red” Visible (0.64 µm) images at 1401 UTC [click to enlarge]

GOES-16 Land Surface Temperature and “Red” Visible (0.64 µm) images at 1501 UTC [click to enlarge]