Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sun Apr 29 2018


Prelim Day 1 QPF Discussion
Valid Apr 29/1200 UTC thru Apr 30/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Northeast...

The closed mid-upper low will slowly pivot across the eastern
Great Lakes and Northeast Sunday-Sunday night, with the
large-scale forcing strengthening as a result of the increased
mid-layer deformation/frontogenesis. This will support widespread
mod-heavy precipitation along a well-defined comma head within a
deepening trowal zone from northern NY state into northwestern New
England. Models have trended wetter across these regions, and are
in reasonable agreement with respect to the location of heaviest
precipitation (widespread areal-average 24 hour totals between
0.50-1.25+ inches).
Meanwhile, the low thicknesses and favorable column cooling due to
the pcpn intensity will support rains changing over to snow across
the Adirondacks today. Please see the latest QPFHSD for further
details regarding the snowfall potential.


...Pacific Northwest / Central-Northern Great Basin / Northern
Rockies...

The closed mid level low across the PAC NW early Sunday will move
slowly across the northern-central Great Basin through Sunday
night, becoming an open trough in the process. Broad deep-layer Qs
vector convergence with the difluent upper flow will allow for
widespread light-moderate orographically-aided pcpn totals, with
the model consensus for the highest totals north of this closed
low where comma head precip may pivot from just north of the
U.S./Canadian borer across southern B.C. into southwest Alberta
(also along the axis of above-average PW values). To the south of
this, showery conditions will persist through the Pacific
Northwest---northern Great Basin into the Northern Rockies.


...Central to Southern Rockies into the Southern High Plains...

A broadly upper difluent flow pattern will spread downstream of
the inland moving closed low across the northwest U.S. through the
Central to Southern Rockies and into the Southern High Plains. 
This will support widely scattered showers Sunday afternoon and
evening across the central and southern High Plains along the dry
line/lee trof position.  High-res models are more emphatic about
locally moderate to heavy precip totals along the dry line/lee
trof Sunday afternoon, although confidence remains low with
placement. Moreover, areal-average totals will be mitigated
somewhat by the limited coverage.

Hurley/Oravec