Quantitative Precipitation Forecast
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FXUS04 KWBC 240700

Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sat Mar 24 2018

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

Day 1

...Mid MS Valley to the lower OH Valley, TN Valley, Southern
Appalachians, and lower mid Atlantic Region...

A vigorous compact shortwave and attendant southern stream upper
jet streak will slide e-se from the central Plains into the lower
OH by late Saturday night. This southern stream feature, which
impacted central/southern CA earlier this week with torrential
rains, will continue to foster a surface low from eastern KS early
Saturday morning into the eastern TN Valley by early Sunday. Ahead
of this system, a considerable amount of moisture return from the
Gulf of Mexico within the compact warm conveyor belt (wcb) --
transported via robust southwesterly low-level inflow (40-50kts at
850 mb) -- will generate 850 mb moisture flux anomalies between
3-4 standard deviations above normal per the SREF and GEFS.
Meanwhile, another upper shortwave across western Quebec will dive
south and reinforce the northern stream trough across the
northeast. This in turn will sharpen the confluence and thus
strengthen the jet at upper levels within the trough base (into
the mid-Atlantic region), providing an uptick in northern stream
forcing (upper divergence and low-level frontogenesis) within the
right-entrance region of the jet streak. The coupled dynamical
forcing from both the southern and northern streams will allow
widespread mod-heavy pcpn to blossom in a nw-se fashion north of
the surface warm front -- while the latter (ensuing strengthened
frontogenesis) helps to narrow the corridor of steepening
isentropic lift with a sharp moisture cutoff to the north. 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.



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