Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Thu May 31 2018


Prelim Day 1 QPF Discussion
Valid Jun 01/0000 UTC thru Jun 02/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr



...Lower-Mid Mississippi Valley into the lower Ohio and Tennessee
Valleys...

Ongoing convection across the lower Ohio valley will continue to
move east toward the central Appalachians as a shortwave
associated with overnight convection over the central Plains
continues to translate east across the region.  There remains a
good model signal for additional development further west back
across the mid Mississippi valley this afternoon as trailing
energy moves out of the central Plains.  As energy aloft interacts
with anomalous moisture, these storms will have the potential to
produce heavy amounts.  The GFS show PWs remaining at or above 1.5
inches (1-2 standard deviations above normal) ahead of frontal
boundary extending southwest from the Great Lakes back into the
central Plains.  These storms are expected to push east from the
mid Mississippi into the lower Ohio valley.   However the hi-res
guidance shows a good signal for storms to develop and drop south
along a trailing outflow boundary which is forecast to move into
northern and central Arkansas overnight.  Low level southwesterly
inflow into the western flank of this boundary may support a
period of back-building training convection, resulting in locally
heavy totals across this region.  WPC QPF reflects a blend of the
HREF Mean with recent runs of the HRRR for the afternoon and even
periods, with significant weighting given to the HREF Mean through
the remainder of the period.

...Lower Great Lakes / Upper Ohio Valley / Central Appalachians /
Mid Atlantic...

A warm front extending from the Great Lakes through the
Mid-Atlantic states will push north this period with backing flow
supporting a surge of deeper moisture along the Mid Atlantic
seaboard this afternoon/evening.  This will support shower and
thunderstorms moving north with a continued threat for additional
moderate to heavy amounts extending to the south across the
region.  Given the anomalous moisture, there remains the threat
for locally heavy amounts with these storms.

...Northern Intermountain West / Northern Rockies and Plains...

A well-defined shortwave trough will continue to translate east,
assuming a negative tilt as it pivots across the Intermountain
West into the Rockies late Thu into early Fri.  Favorable upper
jet forcing along with low level convergence/frontogenesis is
expected to support widespread light to moderate amounts from the
northern Intermountain West into the northern Rockies and High
Plains this evening and overnight.  Then as the system pivots
further east, guidance shows an amplifying southerly low level jet
supporting increasing PWs of 1.5 inch or more across the central
Dakotas tomorrow afternoon-evening.  This along with approaching
upper trough is expected to spur the threat for developing showers
and thunderstorms with heavy rains across portions of the Dakotas
and Nebraska.  WPC QPF gave significant weight to the HREF Mean
through the period.

Pereira