![\"GOES-17](\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/images\/2021\/01\/210123_goes17_airMassRGB_pv1.5pressure_Southern_California_anim.gif\")
<\/a>GOES-17 Air Mass RGB images, with contours of PV1.5 pressure [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>As an anomalously-deep<\/strong><\/a> 500 hPa low began to move inland over Southern California during the 23 January<\/strong><\/a> – 24 January 2021<\/strong><\/a> period, GOES-17 (GOES-West)<\/em>\u00a0 Air Mass RGB<\/strong><\/a> images\u00a0(above)<\/strong><\/em> 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<\/strong><\/a>.<\/p>\n A west-to-east oriented cross section of RAP40 model fields along Line A-A’ (below)<\/strong> <\/em>depicted the descending dynamic tropopause at 19 UTC.<\/p>\n Cross section of RAP40 model fields along line A-A’ [click to enlarge]<\/p><\/div>GOES-17 Mid-level Water Vapor (6.9 \u00b5m<\/strong><\/a>) images (below)<\/strong><\/em> 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<\/strong><\/a> and Long Beach<\/strong><\/a> around 03 UTC. Storm total precipitation<\/strong><\/a> amounts included rainfall of 1.40 inch and snowfall of 12-18 inches.<\/p>\n GOES-17 Mid-level Water Vapor (6.9 \u00b5m)<\/em> images, with plots of hourly surface weather type [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>GOES-17 Water Vapor images at 2301 UTC and 0246 UTC (below)<\/strong><\/em> revealed sporadic lightning activity (indicated by small clusters of GLM<\/strong><\/a> Groups).<\/p>\n GOES-17 Mid-level Water Vapor (6.9 \u00b5m)<\/em> image at 2301 UTC, with GLM Groups plotted in red [click to enlarge]<\/p><\/div> GOES-17 Mid-level Water Vapor (6.9 \u00b5m)<\/em> image at 0246 UTC, with GLM Groups plotted in red [click to enlarge]<\/p><\/div> ===== 24 January Update =====<\/strong><\/p>\n GOES-17 Day Snow-Fog RGB images [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>On the following day, as clouds began to clear the areal extent of resulting fresh snow cover\u00a0(darker shades of red)<\/em> was seen in GOES-17 Day Snow-Fog RGB<\/strong><\/a> images (above)<\/strong><\/em>. 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).<\/p>\n Suomi NPP VIIRS True Color RGB and False Color RGB images (below)<\/strong> <\/em>showed the snow cover (shades of cyan)<\/em> at 2036 UTC.<\/p>\n<\/a><\/a><\/a><\/a><\/a>