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]

Derived Motion Winds in a Dust Storm

January 15th, 2021 |

GOES-16 Visible (0.64 µm) imagery and Mesoscale Sector 2 Derived Motion Winds, 1430 -1930 UTC. Winds are available every 5 minutes, imagery is also shown every 5 minutes, rather than the default 1 minute for Mesoscale Sectors (Click to animate)

The High Plains of Kansas, Colorado, Oklahoma and Texas experienced a significant dust storm (with Dust Storm Warnings issued) on 15 January 2021, (Click here for a blog post on the blowing dust with this storm on 14 January) associated with a strong jet streak and extratropical cyclone discussed here. The animation above (Here’s the same animation, but slower) shows visible imagery along with GOES-16 Mesoscale Sector Derived Motion Winds from the Visible Channel. These derived winds are available with a 5-minute cadence, and the dust was thick enough that features could be tracked. There aren’t a lot of derived winds; how well do these derived winds compare to surface winds?

METAR Observations, GOES-16 Visible (0.64 µm) imagery, and Derived Motion Winds from Visible data, 1900 UTC on 15 January 2021 (Click to enlarge)

The image above, from 1900 UTC, shows Derived Motion winds along with METAR observations. Derived Motion winds are stronger than surface winds, as expected; compare, for example, the observations at Limon CO (KLIC) with the nearby derived wind vectors. The levels of the derived motion winds are between 800-820 hPa, away from the effects of friction/surface roughness. However, they do give a nice estimate of what surface winds might be in regions without surface observations, as apparent in the animation at the top.

It can be difficult to view dust with just one ABI channel such as the visible, especially when the sun is high(ish) in the sky and there is little forward scattering. Multi-spectral RGB products, such as the GOES-16 Dust RGB, shown below in a toggle with a VIIRS True-Color image and the GOES-16 Fire RGB (there is a fire evident near KLHX, LaJunta, CO), are a valuable tool in identifying the horizontal extent of dust plumes.  Dust is highlighted in the Dust RGB by a vivid pink/magenta color.

NOAA-20 VIIRS True-Color image, GOES-16 Dust RGB and GOES-16 Fire Temperature RGB at 1956 UTC, 15 January 2021 (Click to enlarge)

Freezing fog in the Carolinas and Virginia

January 13th, 2021 |

GOES-16 Nighttme Microphysics, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product [click to play animation | MP4]

GOES-16 Nighttime Microphysics RGB, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product [click to play animation | MP4]

GOES-16 (GOES-East) Nighttime Microphysics RGB, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product (above) showed an arc of relatively thin fog across northern South Carolina, eastern North Carolina and southeastern Virginia — which was becoming thicker/deeper in time during the hours leading up to sunrise on 13 January 2021. In areas where the Cloud Thickness increased to 400 meters or more (lighter shades of cyan), freezing fog was observed at nearby METAR sites.

GOES-16 Nighttime Microphysics RGB images with plots of surface observations (below) indicated that air temperatures were near or just below freezing at most sites across the region.

GOES-16 Nighttime Microphysics RGB images, with plots of surface observations [click to play animation | MP4]

GOES-16 Nighttime Microphysics RGB images, with plots of surface observations [click to play animation | MP4]

The band of fog over eastern North Carolina and southeastern Virginia was being pushed eastward by a lower-tropospheric trough, as shown by the NAM40 model 925 hPa wind field at 12 UTC (below).

GOES-16 Nighttime Microphysics RGB image, with a plot of NAM40 model 925 hPa winds at 12 UTC [click to enlarge]

GOES-16 Nighttime Microphysics RGB image, with a plot of NAM40 model 925 hPa winds at 12 UTC [click to enlarge]

After sunrise, GOES-16 “Red” Visible (0.64 µm) images (below) showed that most of the fog quickly dissipated across southeastern Virginia and eastern North Carolina, while thicker fog persisted over much of South Carolina.

GOES-16

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

Winter storm affecting the southern Plains and Lower Mississippi Valley

January 10th, 2021 |

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

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

GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed widespread precipitation that was developing across the southern High Plains and Lower Mississippi Valley on 10 January 2021. A closed middle-tropospheric low was providing forcing for ascent as it moved eastward across the region — and its cyclonic circulation was evident in the Water Vapor imagery. Storm total snowfall accumulations were as high as 11 inches in Texas, 8 inches in New Mexico, 6.5 inches in Louisiana and 4.5 inches in Mississippi.

GOES-16 Day Cloud Phase Distinction RGB images (below) revealed pockets of banded convection, whose glaciated cloud tops appeared as shades of green to yellow.

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]

===== 11 January Update =====

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

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

On the following day, gaps in low-level cloud cover allowed the areal extent of resulting snow cover to be seen in GOES-16 Day Cloud Phase Distinction (snow = brighter shades of green) and Day Snow-Fog (snow = darker shades of red) RGB images (above).

A toggle between VIIRS True Color and False Color RGB images from Suomi NPP at 1936 UTC (below) provided another example of a RGB variant that is useful for the discrimination of low cloud vs. snow — snow cover appeared as shades of cyan in the False Color image.

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

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