Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
315 AM EDT Mon Apr 30 2018


Prelim Day 1 QPF Discussion
Valid Apr 30/1200 UTC thru May 01/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1


...Northeast...

The closed mid-upper low along the New England coast early Monday
morning will make slow eastward progress during the day 1
period...passing just south of Nova Scotia by 12Z Tue.
Precipitation is expected to remain fairly well defined in the
comma head/deformation axis n-nw-w of the closed low, though will
become less organized today as drier air continues to wrap into
the mid-upper circulation. With continued consensus among the
latest models, the day 1 QPF in this region was fairly
straightforward and essentially a blend of the high-res ensembles
(including the HREF, NBM, and dynamically-downscaled 5km WPC
ensemble QPF). Highest additional QPF (12Z Mon-12Z Tue) will
average around 0.50+ inch across far northern portions of ME, with
pockets of 0.25-0.50" over the remainder of northern ME as well as
over elevated terrain in eastern NY (Adirondacks and Catskills)
and across the Green-White Mtns in VT-NH.


...Northern Rockies - Uinta Mountains - Wasatch Range...

A broad mean upper trof will persist day 1 across the western U.S.
from the Pacific Northwest through the Great Basin and into the
Rockies. A lead shortwave will be rotating through the base of
this trough across UT-WY and into the northern High Plains by 12Z
Tuesday. This feature will be responsible for moderate-heavy pcpn
from the Wasatch/Uinta Mountains into the WY ranges, while
convective clusters develop out ahead of this wave Tuesday night
across portions of the northern Plains (including north-central
NE), owing to some enhanced deep layer lift/low level
frontogenesis via the right entrance region of an upper level jet
streak. The strong deep-layer shear environment (0-6km bulk shear
values of 50+ kts) will allow for swift moving cell motions and
thus mitigate an excessive rainfall threat.


...Southern High Plains...

Broadly difluent upper flow downstream of the mean western trof
will support scattered convection during the peak heating hours
this afternoon and evening along the dry line situated across the
Southern High Plains. Once again, confidence remains low with
regard to the precip details on any precip details in this
scattered convective pattern -- as some of the high-res CAMs (ARW
and ARW2 in particular) are a bit more prolific with the QPF
totals. Given the degree of spread with the amounts and placement,
continued with the light to locally moderate areal-average totals.

Hurley