Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
226 PM EDT Fri Mar 23 2018


Prelim Day 1 QPF Discussion
Valid Mar 24/0000 UTC thru Mar 25/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Upper Midwest/middle Mississippi Valley to lower Ohio
Valley/Tennessee Valley and Southeast...

A vigorous short wave trough will emerge from the West into the
Upper Midwest this evening into Sat. This southern stream feature,
which impacted central/southern CA earlier this week with
torrential rains, will help induce a surface low across KS, as a
northern Polar boundary drapes over the circulation. A
considerable amount of moisture return from the Gulf of Mexico
with broad large scale warm advection regime will allow precip to
flourish from the mid MS Valley to the OH Valley. The guidance
captures this scenario, as the upper disturbance tracking south
and east or downstream within the upper-level confluent flow. This
will result in a weakening storm system over time with a very
sharp edge or cutoff to the precip shield, while a surface ridge
builds over the nern quad of the country. WPC favored a four way
blend of the 12z gfs, 00z/23 ecmwf, 12z nam nest and 12z href mean
for a streak of 1-2 areal avg qpf amounts with locally higher
values. The heaviest qpf appears likely to set up from IA through
south/central IL into southern IN and a large portion of KY. The
southern extent of the qpf will be moderate to heavy rain, while
potential heavy snow impacts the northern extent. For more on the
extent of the frozen precip and heavy snowfall, please refer to
the latest qpfhsd.

...Western U.S...

A very active and wet regime will persist across the West on Sat.
A large 500mb closed low and deep upper trough offshore of the Pac
NW will sweep into the region. The main mid to upper circulation
will dig south and east toward southern OR/northern CA, while the
main thermal zone pushes into the inter-mountain West. Overall the
onshore flow will remain intact but maybe elevated in one
location. A dynamic upper jet/jet streak will focus strong Pac
moisture transport into swrn OR and northern CA for possible 1-2
inch areal avg qpf amounts, especially from the coast to terrain.
Overall WPC followed a blend of the gfs and ecmwf with the hi-res
suite for qpf amounts.

Musher