Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
227 AM EDT Wed Apr 18 2018


Prelim Day 1 QPF Discussion
Valid Apr 18/1200 UTC thru Apr 19/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Northern to Central Plains across the MS Valley and Great Lakes
and into the Northeast...

A compact and well defined shortwave is crossing the Plains early
this morning. Overall a pretty dynamic system, with a strong upper
level divergence signature noted along with some elevated
instability feeding into the east side of the storm. Limited
moisture and quick storm motion will end up limiting total QPF
amounts, however the strong dynamics will overcome this to some
degree through this morning, with a swath of moderate to locally
heavy rain/snow from portions of eastern NE into far southeast SD,
and portions of IA. The system begins to lose some of its dynamics
by this afternoon as the wave opens and divergence decreases in
the upper levels. Thus generally expect to see decreasing
intensity of precipitation as things push into the Great Lakes.
Still will however see a swath of mainly light QPF spread east
with time as the wave begins to interact with a northern stream
shortwave by the end of the day 1 period.

Still some model differences noted with the exact axis of higher
QPF totals today into tonight across this region. Overall there
continues to be a slight southward shift in the expected axis, and
thus WPC trended our QPF in this direction as well. Thought going
for a model consensus approach would probably be the best option
to account for the various north/south differences in the guidance
and differences with the northern gradient. Going for a consensus
approach resulted in WPC QPF looking pretty close to the 0z HREF
mean. Trends and the overall consensus suggests the 0z GFS is
probably a bit too far north over the MS Valley.


...West...

A trough will move into the West today with a strong closed mid
level low moving into CA by tonight. Overall a pretty dynamic
system, but moisture will be limited. Thus in general only looking
at light QPF amounts across portions of OR/CA/NV. WPC QPF blended
the GFS/ECMWF and HREF mean.

Chenard