Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Sun Mar 25 2018


Prelim Day 1 QPF Discussion
Valid Mar 25/1200 UTC thru Mar 26/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Western CONUS...

Shortwave energy over the eastern Pacific, pivoting on the
backside of the longwave western U.S. trough, will allow the
trough to further amplify with more pronounced height falls into
southern CA and the Southwest by the end of the period (12Z Mon).
As this occurs, broad-scale, deep-layer ridging and northerly flow
behind the trough will expand across the eastern Pacific, thereby
preventing any subtropical moisture infusion into the system as it
crosses into the Great Basin. Therefore despite the broad upper
level forcing and expansive warm conveyor belt (wcb) ahead of the
trough, the lackluster moisture profiles (PW anomalies actually
negative over most areas per the SREF and GEFS) will restrict the
potential for anything more than light-moderate precipitation
across the western U.S. this period. Late in the period (toward
12Z Mon), strengthening low-mid layer westerly flow will boost PWs
to near 0.75" toward the PAC NW coast, which along with the
favorable orographic component (moist onshore flow largely
orthogonal to the terrain), will generate localized totals between
0.50-0.75" overnight across the WA Coastal ranges (Olympics) and
northern Cascades. Elsewhere, per a multi-model blend composed of
the ECMWF and high-res means including the HREF and NBM, highest
24 hour areal-average totals of 0.50-1.00" are expected over the
eastern slopes of the WY Rockies (aided by the easterly upslope
flow).

Hurley