Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Tue Jun 05 2018


Prelim Day 1 QPF Discussion
Valid Jun 05/1200 UTC thru Jun 06/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


...Northern Plains - Upper MS Valley...

Upper ridge axis pushes east of the northern Plains and Upper MS
Valley region Tue night. In its wake, an uptick in broad scale
upper forcing (divergence aloft) will ensue, and get a
considerable boost within the right entrance region of an upper
level jet streak traversing southern Ontario. Meanwhile, the
increasing (and veering) nocturnal LLJ will lead to rapid
low-level moisture/theta e transport ahead of a sharpening frontal
zone. Both synoptic and thermodynamic indicators give credence to
the the multi-model signal of a developing MCS overnight along the
"ring of fire", though as is typical, the model solutions are not
well clustered with respect to the details in terms of MCS track
and thus axis of heaviest rainfall. WPC did nudge the QPF axis a
little father south from the previous forecast -- essentially in
line with the blend of the WRF-ARW, ARW2, and NSSL-WRF (all of
which aligned reasonably well, while the NAM CONUS Nest, WRF-NMMB,
NBM, and global guidance were farther north. Despite the fairly
vigorous mid-level cap, based on climo like the aforementioned
high-res depiction of the heavy rainfall footprint farther south,
along and north of the surface boundary where the coupling of
robust deep-layer elevated instability and moisture transport will
be maximized north-northeast of the 700 mb +12C isotherm. Also
supporting a more southern solution of the MCS track/heaviest QPF
would be the degree of southward propagation overnight, as the
s=sw LLJ begins to exceed the speed of the mean 850-300 mb flow.
At this point, the progged shear profiles would support a
progressive MCS; however, multiple rounds of convection as noted
from the ARW/ARW2 (first one along the initial wnw-ese warm
frontal boundary) could pose a more enhanced flash flood risk
across far northeast SD and southeast ND.


...Central Gulf Coast Region...

Mid-upper shortwave trough -- bolstered early in the period the
MCV over the ARKLATEX -- will be the catalyst for additional
diurnally-enhanced convection along the surface stationary front
south toward the Gulf coast. 0-6km bulk shear values aoa 25 kts
along with robust deep-layer instability (mucapes at 2000-3000+
j/kg) will support more organized, widespread coverage during the
afternoon through mid evening ahead of the upper trough, with the
surface moisture convergence getting an added boost from the
developing Gulf breezes. Despite the relatively high 1-3 hourly
FFG (generally 2.5-3.0" in 1 hour and 3-4" in 3 hours), localized
totals of 3-5" within a few hours per the high-res CAMs would
support a marginal risk of excessive rainfall, particularly over
portions of se LA given the relatively wetter antecedent soils
(lower FFG values).

Hurley