Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Wed Mar 28 2018


Prelim Day 1 QPF Discussion
Valid Mar 28/1200 UTC thru Mar 29/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Central and Eastern U.S...

The northern stream jet streak and associated upper vort lobe will
continue to dive se down the upper ridge and into the western
periphery of the southern stream trough. This will result in a
more progressive tough and surface front by Thursday, in-turn
reducing the excessive rainfall threat. Until then however, a well
established, slow moving warm conveyor belt (wbc) is continuing to
fuel the "Atmospheric River" of deep-layer moisture into the
southern Plains northeast across the MS Valley and Ohio Valley, as
noted from the ESRL AR detection tool. The continued subtropical
connection aloft (from south of Baja) along with the strong
low-mid layer moisture transport/flux off the western GOMEX are
maintaining anomalous PW values into these regions -- about
2.5-3.0 standard deviations above normal per the SREF and GEFS. 

Convection should be undergoing a weakening trend later this
morning as it outruns the better forcing/instability, as depicted
by the high-res CAMs, although some locally heavy rains should
continue from portions of east TX into northern LA, southern AR,
and western TN. By late morning into the afternoon, we should see
convection regenerate across east TX into western LA. This
convection will have strong support synoptically as the
southwestern U.S. shortwave finally begins to eject east. Some
uncertainty whether this convection forms along the morning
outflow closer to the TX Gulf Coast or farther northwest along the
actual cold front, or whether both boundaries eventually become
active. Given these uncertainties we preferred to stay close to a
consensus of the high res ARW/ARW2, which seemed to offer a good
middle ground solution. Either way some heavy totals will be
possible from east TX into LA...with some solutions suggesting a
period when convection could train. Thus we will likely see an
increasing flash flood risk again Wednesday afternoon in this
area...with future model trends hopefully giving more insight as
to whether the highest threat ends up closer to the coast or a bit
inland.

Hurley/Chenard