Stratus clouds affecting surface temperatures in Alaska

December 17th, 2019 |

GOES-17 Nighttime Microphysics RGB and

GOES-17 Nighttime Microphysics RGB and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

A comparison of GOES-17 (GOES-West) Nighttime Microphysics RGB and “Clean” Infrared Window (10.35 µm) images (above) showed the formation and motion of patchy stratus clouds (RGB shades of yellow) over Interior Alaska on 17 December 2019.  Note how the clouds are difficult to detect and track on the 10.35 µm images, since the temperatures of cold land surfaces and stratus cloud tops were similar. Since these high latitudes receive little to no sufficient solar illumination to allow useful visible imagery during the winter season, the RGB product can be a helpful tool for monitoring the evolution of such low clouds.

Plots of surface data from Bettles (PABT) and Fort Yukon (PFYU) (below) showed that the stratus cloud deck — with bases in the 6,000-10,000 feet range — had an impact on surface air temperature trends, with warming occurring as radiational cooling was slowed and/or reversed as the clouds moved overhead. Temperatures continued to rise at Bettles as the cloud coverage remained broken to overcast, while the temperature briefly dropped again at Fort Yukon as the cloud coverage thinned to scattered.

Plot of surface data from Bettles, Alaska [click to enlarge]

Plot of surface data from Bettles, Alaska (PABT) [click to enlarge]

Plot of surface data from Fort Yukon, Alaska [click to enlarge]

Plot of surface data from Fort Yukon, Alaska (PFYU) [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]


VIIRS imagery and NUCAPS profiles near the North Pole

August 22nd, 2019 |

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A sequence of 4 consecutive Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.4 µm) images (above) showed a small swirl of clouds associated with a weak area of low pressure near the North Pole — north of Greenland (surface analyses) — on 22 August 2019.

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

There were Suomi NPP NUCAPS soundings available in the vicinity of the surface low (above) — profiles from the 4 squared green dot locations (green dots indicate successful sounding retrievals from both the CrIS and ATMS instruments) which were closest to both the surface low and the North Pole (below) revealed characteristically-low arctic tropopause heights of around 7-8 km, and surface temperatures dropping to below freezing at the 2 most northerly points of 88.28º and 88.57º N latitude. Note: the Suomi NPP (SNPP) CrIS anomaly that began on 24 March 2019 was resolved via a switch to the redundant Side-2 electronics on 24 June — so CrIS data once again became available for incorporation into SNPP NUCAPS soundings beginning on 01 August. Training material for NUCAPS in AWIPS is available here.

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

According to GCOM-W1 AMSR2 data (source), this weak surface low was over a portion of the Arctic Ocean where sea ice concentration was still high (below).

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]

Thunderstorm over the Arctic Ocean

August 11th, 2019 |

NOAK49 PAFG 110400 CCA
PNSAFG
AKZ222-111600-

Public Information Statement…CORRECTED
National Weather Service Fairbanks AK
800 PM AKDT Sat Aug 10 2019

…Lightning Detected within 300 Miles of North Pole Today…

A number of lightning strikes were recorded between 4pm and 6pm
today within 300 miles of the North Pole. The lightning strikes
occurred near 85 degrees north, 120 degrees east, which is about
700 miles north of the Lena River Delta of Siberia. This lightning
was detected by the GLD lightning detection network which is used
by the National Weather Service. This is one of the furthest
north lightning strikes in Alaska Forecaster memory.

$$

JB

As noted by the NWS Fairbanks forecast office, lightning was detected with a thunderstorm located over the Arctic Ocean north of Siberia between 6-8 pm AKDT on 10 August (or 00-02 UTC on 11 August 2019). A sequence of AVHRR Visible (0.63 µm) and Infrared Window (10.8 µm) images from NOAA-15 (at 2315 UTC), NOAA-19 (at 0100 UTC) and NOAA-15 (at 0232 UTC) (below) showed the eastward motion of this thunderstorm, which had developed in advance of a 500 hPa lobe of vorticity — the coldest cloud-top infrared brightness temperature associated with this feature was -49.9ºC (yellow enhancement) at 0100 UTC.

NOAA-19 AVHRR Visible (0.63 µm) and Infrared Window (10.8 µm) images [click to enlarge]

AVHRR Visible (0.63 µm) and Infrared Window (10.8 µm) images from NOAA-15 (at 2315 UTC), NOAA-19 (at 0100 UTC) and NOAA-15 (at 0232 UTC) [click to enlarge]