Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Mon Jun 04 2018


Prelim Day 1 QPF Discussion
Valid Jun 04/1200 UTC thru Jun 05/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr



...Northeast...

The elongated, negatively tilted trough nudging into southern
Ontario and the eastern Great Lakes early this morning will become
reinforced by an upper jet streak/additional shortwave energy
entering the trough's base. The result will be a transformation
toward a more positively tilted longwave trough as the low deepens
through the mid-upper levels over southern Ontario-Quebec later
Mon-Mon night. Favorable exit region forcing east of the trough
(upper level divergence and strengthening lower tropospheric s-se
flow and positive moisture/theta-e transport) will favor
additional mod-heavy rainfall along the New England coast, along
the apex of 1.5"+ PWs ahead of the surface occluded front. The
consensus of the 00Z guidance depicted a a decided eastward shift
in the heaviest rainfall during the day 1 period (12Z Mon-12Z
Tue), i.e. mainly offshore Downeast ME while clipping eastern
MA/Cape Cod. While relatively efficient considering the deep
subtropical moisture plume (relatively high wet bulb zero levels
and 500-300 mb layer PW values near 0.25"), the absence of even
elevated instability will be a significant limitation to the short
term rainfall rates, at least with respect to the excessive
rainfall/flash flood potential given the antecedent soil
conditions/current FFG values. As a result, the Marginal risk for
excessive rainfall that was noted in yesterday's day 2 ERO has
been removed.


...Southern Plains...

A compact area of strengthened WAA and deepening elevated
instability early in the period across the southern Plains,
bolstered by the MCV ejecting east of the High Plains, has
fostered an initial round of convection early, as the decaying MCS
will bring moderate areal-average rainfall totals to central and
north-central TX later this morning. Following round 1, lingering
MCV energy and outflow boundaries along with the stationary
synoptic front will favor additional convective development this
afternoon-evening -- especially toward the mid-upper TX coast
where robust deep-layer instability (model mixed layer CAPES
2500-3500+ j/kg) will be present. The model spread however is
quite high with respect to the convection evolution (and QPF)
later this afternoon and evening, though the solutions do begin to
align somewhat more favorably late Mon evening and overnight
(especially after 06Z) as increasing low level southwesterly flow
(30-40 kts at 850 mb) supports another compact MCS from
south-central OK, across the Red River and into North TX and
western portions of the ARKLATEX. PW values are progged to spike
aoa 1.75" Monday night along the path of this MCS, with the models
(especially high-res CAMs) likely simulating the mesoscale
environment to some degree. In terms of the QPF, given the
disparity among the operational model runs (global and high-res),
WPC once again leaned toward the means, particularly the HREF and
NBM high-res means. Individual CAMs such as the WRF-ARW, ARW2.
NMMB, NSSL-WRF, and NAM CONUS-Nest all show spotty areas of 24
hour rainfall totals of 3-5+ inches, the bulk of which would
arrive late Monday night via the next MCS. Despite the relatively
high FFG initially, the prospects of at least some reduction from
rains early Mon, along with the potential for fairly prodigious
short-term rainfall rates Mon night-early Tue with the MCS, would
continue to warrant a Marginal risk area in the new day 1 ERO
(similar to the day 2 outlook from Sun).

Hurley