Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Thu Mar 22 2018


Prelim Day 1 QPF Discussion
Valid Mar 22/1200 UTC thru Mar 23/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Western U.S...


On Day 1, the models target California for the heaviest
precipitation with several inches of liquid equivalent
precipitation in the coastal ranges of southern CA and along the
spine of the CA Sierra Nevada range. One distinct area is within
the plume of deepest moisture streaming onshore into southern CA
into the southern CA Sierra Nevada ranges. The integrated water
vapor imagery is well above normal and the slow movement of the
max precipitable water values in the streaming streaming onshore
in the counties north of Los Angeles combines with 850 mb
convergence and 300 mb divergence to produce areas of heavy rain,
with ascent aided by windward terrain. The continuation o9f the
high moisture and water vapor transport into interior southern Ca
leads to maxima along the foothills and mountains of interior CA
with heavy Sierra Nevada snows, with several feet likely over the
next day and a half.

A second area covers northern CA to the OR border as the northeast
Pacific upper low and trough drift towards
the coast...with a jet max streaming onshore and inland into the
ranges of ID and adjacent western MT.
The upper jet moving into NV Thu afternoon supports upper
divergence maxima streaming northeast from the CA Sierra across NV
into UT with a maxima near the northern Wasatch/Uintas of UT,
driving precipitation in windward terrain.

QPF was derived from a combination of the latest high resolution
guidance -- particularly the HREF means and the 04Z NBM. See the
winter weather forecast amounts and snow probabilities for heavy
snow potential in the mountains of CA.

Hurley/Petersen