Heavy rainfall and snowfall in Southern California

January 23rd, 2021 |

GOES-17 Air Mass RGB images, with contours of PV1.5 pressure [click to play animation | MP4]

GOES-17 Air Mass RGB images, with contours of PV1.5 pressure [click to play animation | MP4]

As an anomalously-deep 500 hPa low began to move inland over Southern California during the 23 January24 January 2021 period, GOES-17 (GOES-West)  Air Mass RGB images (above) showed a compact Potential Vorticity (PV) anomaly approaching the coast — and the RAP40 model indicated that the “dynamic tropopause” (defined here as the pressure of the PV1.5 surface) was descending to the 675 hPa pressure level at 18 UTC.

A west-to-east oriented cross section of RAP40 model fields along Line A-A’ (below) depicted the descending dynamic tropopause at 19 UTC.

Cross section of RAP40 model fields along line A-A' [click to enlarge]

Cross section of RAP40 model fields along line A-A’ [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images (below) showed the increasing reports of rain and snow that resulted as the PV Anomaly moved inland and provided additional forcing for ascent. Near the coast, thunderstorms were reported at Fulton and Long Beach around 03 UTC. Storm total precipitation amounts included rainfall of 1.40 inch and snowfall of 12-18 inches.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of hourly surface weather type [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of hourly surface weather type [click to play animation | MP4]

GOES-17 Water Vapor images at 2301 UTC and 0246 UTC (below) revealed sporadic lightning activity (indicated by small clusters of GLM Groups).

GOES-17 Mid-level Water Vapor (6.9 µm) image at 2301 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 2301 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 0246 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 0246 UTC, with GLM Groups plotted in red [click to enlarge]

===== 24 January Update =====

GOES-17 Day Snow-Fog RGB images [click t play animation | MP4]

GOES-17 Day Snow-Fog RGB images [click to play animation | MP4]

On the following day, as clouds began to clear the areal extent of resulting fresh snow cover (darker shades of red) was seen in GOES-17 Day Snow-Fog RGB images (above). Even parts of the high desert — north and east of the mountain ranges — received some snowfall (for example, 2-3 inches were reported at Hesperia).

Suomi NPP VIIRS True Color RGB and False Color RGB images (below) showed the snow cover (shades of cyan) at 2036 UTC.

Suomi NPP VIIRS True Color RGB and False Color RGB images [click to enlarge]

Suomi NPP VIIRS True Color RGB and False Color RGB images [click to enlarge]

Strong winds, gravity waves and turbulence across Northern California

January 19th, 2021 |

GOES-17 Mid-level Water Vapor (6.9 µm) images, with Pilot Reports of turbulence [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with Pilot Reports of turbulence [click to play animation | MP4]

GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm) images which included Pilot Reports (PIREPS) of turbulence (above) revealed a diverse variety of gravity waves across much of Northern California on 19 January 2021. Three types of waves were prevalent: (1) quasi-stationary mountain waves caused by strong northeasterly flow interacting with topography of the Sierra Nevada and Coastal Ranges, (2) long, narrow corridors of fast-moving waves flowing offshore, and (3) west-to-east oriented arcs of waves drifting slowly northward (against the ambient flow). With such disparate wave structures and the intersections of their wave fronts, the prospects for atmospheric turbulence were elevated — in fact, there were a few pilot reports of moderate to severe turbulence, at both low and high altitudes.

GOES-17 Mid-level Water Vapor images with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC (below) showed the strong northeasterly flow in the middle troposphere, with speeds as high as 100-110 knots.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC [click to enlarge]

Cold air advection in the Bering Sea

January 5th, 2021 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) displayed cloud streets across the Bering Sea — cloud features that frequently occur in areas with a strong flow of cold air over warmer water. This northerly flow of cold air across the Bering Sea was due to a strong pressure gradient between high pressure over Siberia and broad low pressure centered over the Gulf of Alaska (surface analyses).

In a GOES-17 Visible image with plots of ASCAT scatterometer surface winds from Metop-A (below), ASCAT sampled winds with speeds as high as 33 knots (although the instrument did not adequately sample the western portion of the Bering Sea, where the strongest winds likely existed).

GOES-17 "Red" Visible (0.64 µm) image, with plots of Metop-A ASCAT winds [click to enlarge]

GOES-17 “Red” Visible (0.64 µm) image, with plots of ASCAT winds from Metop-A [click to enlarge]

A sequence of Suomi NPP VIIRS Day/Night Band (0.7 µm) images (below) provided higher-resolution views of the cold air advection cloud streets.

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

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

A toggle between Suomi NPP VIIRS Day/Night Band (DNB) and GOES-17 Visible images around 2320 UTC (below) highlighted the advantage of  VIIRS DNB imagery at high latitudes, particularly during low-light periods of the winter season.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and GOES-17

Suomi NPP VIIRS Day/Night Band (0.7 µm) and GOES-17 “Red” Visible (0.64 µm) images [click to enlarge]

Tornadoes in Northern California

January 4th, 2021 |

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.35 µm, right) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.35 µm, right) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed thunderstorms moving eastward across Northern California on 04 January 2021, which produced 2 tornadoes (SPC Storm Reports) in the Sacramento Valley south and southeast of Red Bluff (KRBL). Vertical wind shear was evident in the Visible imagery, with low clouds moving northwestward and mid/upper-level clouds moving eastward.

A toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2148 UTC (below) showed the storm that produced a tornado in Corning approximately 8 minutes earlier. The coldest cloud-top infrared brightness temperatures were around -38ºC (darker shades of yellow).

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

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

MIMIC Total Precipitable Water images during the 02-04 January time period (below) showed a long ribbon of moisture (a necessary ingredient for convection) impinging upon Northern California — and a mid-tropospheric trough (500 hPa analysis) along with a cold front that was moving inland (surface analyses) provided forcing for ascent to further enhance convective development.

MIMIC Total Precipitable Water images [click to play animation | MP4]

MIMIC Total Precipitable Water images [click to play animation | MP4]