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WPC Met Watch

Mesoscale Precipitation Discussion: #0043
(Issued at 1137 PM EST Wed Jan 31 2024 )

MPD Selection

Graphic for MPD #0043
Mesoscale Precipitation Discussion 0043
NWS Weather Prediction Center College Park MD
1137 PM EST Wed Jan 31 2024

Areas affected...Central to Southern California...

Concerning...Heavy rainfall...Flash flooding possible

Valid 010445Z - 011500Z

SUMMARY...Warm conveyor moisture axis is starting to become more
progressive.  Yet, strong convergence along the axis and favorable
orientation to the terrain will support quick hitting moderate to
heavy rainfall with 2-4" pose flooding concerns.  Widely scattered
embedded thunderstorms along/west of the axis may allow for
isolated rates up to 1-1.5"/hr posing the highest risk for flashy
conditions through 15z. 

DISCUSSION...GOES-W WV suite denotes stronger core of upper low
well to the NW between 130-140W north of 40N; though broad
diffluent southwesterly flow and hint of southeast edge of the
trof providing some cold air advection aloft steepening lapse
rates in a subtle negative tilt to the upper-level trof.   This is
also supporting eastward propagation of the deep layer moisture
stream across the narrowing axis.  LPW shows north-south
orientation remains directed toward the Santa Cruz range but will
shifting quickly southeast along the central CA coast, eventually
rounding Cape Conception after 09-10z.  Backed sfc to low level
flow of 35-50kts quickly veers along the moisture axis to
southwest and west in a few dozens of miles supporting very strong
moisture convergence and a south to north flux into the terrain. 
Total moisture of 1.25" and these 35-50kts of flow 500-700 kg/ms
IVT generally allowing for broad .25-.33"/hr rates though
strongest orographic ascent will support localized .5-.75"/hr
rates, with values of .75" occasionally ticking up to 1"/hr as the
orientation of the ascent channel becomes nearly orthogonal across
the Transverse ranges after 09-15z.  HREF 2"/3hrs reaches 40-50%
between 12-15z with 85-95% of 3"/6-12hrs across the Transverse
range.  Given the duration, spots of flash flooding can be
considered possible.

Current 10.3um EIR loop and local RADAR loops have shown some
embedded convective elements near San Francisco Bay, Santa Cruz
Mtns into the Northern Santa Lucia Range.  These cells appear to
be along, just west of the core of deeper moisture but at the
eastern edge of steepening lapse rates with CAA aloft in the weak
negative tilting mid-level trof.  Lingering moisture should be
sufficient for some solid moisture flux into the shallow cells and
capable of 1-1.5"/hr rates.  Duration is likely going to be
limited but spots of 1-2" totals in 1-2hrs also pose possible
localized flash flooding.  Given broad ascent after the warm
conveyor moves through, spots of these cores should become more
scattered in nature but may still make landfall through early
morning/day break maintaining this small scale risk for Central
California coast/coastal ranges through 15z as well.




LAT...LON   38522146 37692100 36222022 35191933 34931846
            34751775 34101758 33561797 33651848 33931918
            33851986 33902041 34372070 35122098 35782150
            36292198 36772240 37572263 38042304 38502255
Download in GIS format:    Shapefile  | KML

Last Updated: 1137 PM EST Wed Jan 31 2024

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Page last modified: Thursday, 12-May-2022 19:44:52 GMT