Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Apr 24 2018


Prelim Day 1 QPF Discussion
Valid Apr 25/0000 UTC thru Apr 26/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Eastern U.S...

An active closed low steadily/gradually ejects from TN/KY to over
the s-central Mid-Atlantic today into Wednesday before shifting
offshore under increasing influence from nrn stream trough energy
digging into the Great Lakes. GOES-16 and blended TPW loop imagery
leads well into a model guidance composite that continues to
depict a plume of deep layered moisture with low latitude
connection feeding into the associated surface low/system with
lead thetae advection especially into terrain and coastal areas
along the warm front and inverted coastal trough. Expect
widespread enhanced rains/convection to spread from the Ohio
Valley/Appalachians and srn Mid-Atlantic northward across the nrn
Mid-Atlantic and Northeast with system progression. The linearity
of the forecast mass field evolution lends a WPC day1 qpf forecast
derivation mainly from a blend heavy on continuity but
incorporating latest model and radar rainfall/convective trends
that seem well represented from a WPC in-house bias corrected qpf,
HRRR and National Blend of Models. A Marginal Risk of excessive
rainfall remains centered over the central
Appalachians/Mid-Atlantic. 


...Central U.S...

The next in a series of fairly vigorous mid level lows will remain
well defined as it drops south to southeastward through the Plains
today to the lee of an amplifying wrn u.s. mid-upper level ridge.
Given relatively scant moisture in the wake of the lead system,
expect most precipitation will be slightly post-frontal and rooted
in strong mid level ascent from South Dakota down through Kansas,
and eventually parts of TX/OK and mid-MS Valley. There may be
quite a bit of mesoscale influence to the precipitation pattern,
given the steep lapse rates, marginal low level moisture, and
interplay between the synoptics and terrain influences. Model
guidance remains in decent overall agreement for such an
environment and WPC took a consensus/continuity approach, albeit
with modest areal coverage.

Schichtel