Woznicki Forecast #8 SoCal

Southern California (LA Area)

Current Analysis & Today-Tonight:

Analysis of the current weather for the Los Angeles area starts with looking at the surface observations available at UCAR's RAP Surface Obs page. Winds at the surface are out of the south-southwest at 10-20 knots area-wide, and the temperatures are only in the mid to upper 50s ahead of the shortwave trough. Rain associated with the shortwave trough and cold front is just beginning to enter the Los Angeles area, as is evident from the base reflectivity radar images from the Santa Ana Mountains Radar site and the SPC Mesoanalysis page. The Area Forecast Discussion from the LA NWS office is also useful.


1743 UTC SurfaceObs

SPC Mesoanalysis Radar

Continuing on the SPC Mesoanalysis page, the trough at the surface is tilted back towards the Pacific Ocean as higher levels in the atmosphere are analyzed. Mixing ratio values are high, and this equates to abundant moisture for this system to tap into. Some small values of frontogenesis can be observed near the front at 850 mb, and this will help the precipitation continue to develop. Some slight positive vorticity advection is also inferred as the trough at 500 mb moves closer and closer to the LA area today and tonight. Precipitation during the day today could be heavy at times on the windward side of the mountains. High Resolution Rapid Refresh (HRRR) model output precipitation forecasts indicate rainfall totals that could reach 1.5-2 inches in some areas - enhanced by orographic lifting near the mountains. Lower rainfall totals near the coast, and some fairly significant mountain snowfall totals could be observed with this system today through the nighttime hours. SPC Observed Soundings for 12 UTC this morning indicated some small values of CAPE, but this may still provide enough instability for some embedded thunderstorms within this line of showers. Some small hail may be possible with these storms, and some dangerous lightning. Highs look to only reach the low 60s today, perhaps with some higher values where the visible satellite is showing some clearing (just west of San Diego as indicated from satellite images taken from the UCAR RAP page.

HRRR Forecasted Total Rainfall

Vandenberg, CA 12 UTC Sounding

Short Term - Tomorrow 4/14 through Monday 4/16:

The rainfall from this low-pressure trough looks to exit the area ahead of a strong ridge west of the area by the early morning hours tomorrow. However, NAM Analysis does leave the 500 mb trough over the area for at least the first half of the day tomorrow, and some lingering precipitation may still be around (especially those areas where orographic lifting will be an influence. However, the ridge will quickly move into the area Saturday night and into Sunday - bringing with it much drier weather and temperatures at or above normal. Saturday looks to be a little cooler just on the backside of the precipitation, but warm air advection is prevalent on the east side of the high pressure center in the Pacific (warm valley air advected into our area) - from NAM Convective page. Winds will also begin to die down as the surface high moves closer to the area.

Long Range - Tuesday 4/17 through Thursday 4/19:

Not much change in the long range from the beginning part of the week. Temperatures continue to warm into the upper 70s as the ridge dominates the region. Sunny skies, light winds, and overall nice conditions will dominate.

18 UTC Monday 1000-500 Thickness with Precip

Other Source used: Penn State E-Wall

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Verification:

Friday Afternoon - Saturday Afternoon:

Most of the rainfall for the LA metro area began between 14 and 15 UTC on Friday, and continued in waves with the low pressure trough passage until nearly 02 UTC on Saturday. Rainfall totals in downtown LA reached 1/2 inch, but areas to the west and southwest received close to 2 inches with help from orographic lifting. Max temps only reached the upper 50s for the LA metro area on Friday, and the lower 60s on Saturday. A few record lows were also reached in the area, specifically Bob Hope Airport hit a low on Saturday morning of 39. A few severe wind reports were recorded between 22 and 23 UTC on Friday, as some tree and structural damage occurred. No hail was observed with the storms, but there was enough CAPE for some good thunder and lightning. METARs from the area around 22 UTC on Friday indicated some lightning in the area. Orographic rain seemed to end around 14 UTC on Saturday, and both the NAM and GFS showed this very well (the 12 Z runs on Saturday and Sunday). Some snow was reported in higher elevations (at the Big Bear Airport) Saturday evening/night.

Storm Reports Indicating Hail on 4/13

Total Radar Estimated Rainfall through 4/14

23 UTC Radar Reflectivity Showing Orographic Influence

Saturday Night, Sunday, and Monday:

The models did a pretty good job of clearing out the precip and clouds after the passage of the low, and temperatures were able to quickly warm up after Saturday night. Highs were close to 70 on Sunday, and Monday saw temps in the upper 70s with the ridge building in.

1000-500 mb Thicknesses for 18 UTC on Monday (looks very good compared with the map from last week above).