Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Sun Apr 01 2018


Prelim Day 1 QPF Discussion
Valid Apr 02/0000 UTC thru Apr 03/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...OH Valley into the Mid Atlantic and southern New England...

A shortwave will continue tracking quickly eastward across the MS
Valley and into the Mid Atlantic tonight. WAA ahead of this
feature, coupled with a favorable upper jet structure...supports
an area of rain/snow with this wave. Note an impressive area of
omega in the snow growth zone north of the low...with negative EPV
above the frontogenetical zone. Thus appears like a good setup for
some pretty strong banding and efficient snowfall where
temperatures are cold enough. See the QPFHSD for more information
on the snowfall potential with this system. From a QPF
perspective, this supports staying on the higher side of guidance
with the magnitude from KY northeast across WV into southern PA
and into NJ and far southern New England. Locally heavy rains
exceeding 1" are possible this evening across KY...although the
lack of instability should prevent amounts from getting much
higher.

Models are in better agreement now with the axis as well, although
some differences remain. In general, the 12z NAM and HREF are a
bit further north than the global guidance. WPC went with a
consensus of the 12z HREF mean and the 12z GFS/0z ECMWF...with a
bit more weighting given to the further north HREF. Will have some
dry air in place to the north, but given the strong omega noted
above, think this should be overcome to a degree, as depicted in
the HREF. This, combined with the seemingly realistic
extrapolation of the current activity ongoing over the MS Valley
in the high res guidance...led us to trend in their direction.
Overall this keeps good continuity from our previous forecast.


...Pacific Northwest into the Northern Rockies and Northern
Plains...

A consolidated area of strong mid level energy will drop southeast
into the Pacific Northwest through tonight. As this energy
interacts with the terrain and the arctic boundary, anticipate
widespread rain/snow. From the Pacific Northwest into the Northern
Rockies models were in good agreement...and thus a multi model
blend should work well. However, differences emerge across the
Northern Plains from eastern MT into the Dakotas. The 12z NAM is
stronger/more closed off with the mid level energy...resulting in
a further north boundary and thus further north QPF axis across MT
into the Dakotas on Monday. The NAM and the 12z HREF members are
outliers depicting this further north solution. The
GFS/ECMWF/UKMET/GEM have all been very consistent depicting a
further south solution. Given this consistency and agreement, we
think the NAM represents an unlikely solution...and thus WPC
stayed closer to a non NAM and non HREF blend for this area during
the second half of the day 1 period.

Chenard