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


Prelim Day 1 QPF Discussion
Valid May 31/1200 UTC thru Jun 01/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr



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

Ongoing MCS over the southern Plains early this morning (and
ensuing MCV) will certainly have implications on the new day 1 QPF
downstream into the lower-mid MS Valley-lower OH Valley, and TN
Valley. While still showing a a good heavy rainfall footprint, the
spread among the 00Z high-res CAM guidance (notably N-S) was less
than desirable for a day 1 period. The WPC QPF initialized with
continuity and a blend with the NBM and HREF mean, however evolved
toward a NSSL-WRF/WRF-ARW2 combination late Thu and Thu night.
Like the idea from these models of 2 main axes of higher totals,
the first one farther south (across much of Arkansas) where the
instability pool in the warm sector should be more than sufficient
(while mid level capping not an inhibition) in supporting a
developing QLCS south of the MCV. The other QPF max was noted
across the mid MS Valley, including se MO, southern IL-IN, and
western KY given the bolstered 850-700 mb moisture flux/theta-e
transport out ahead of the MCV track.


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

As the trough over the upper Midwest translates eastward this
period, and the upper ridge axis pushes off the Atlantic coast, a
northwest-southeast oriented boundary and the leading edge of a
very moist airmass extending from the Mid-Atlantic from the Great
Lakes is expected to move north this period. Guidance shows deep
moisture surging north along the central Appalachians and
Mid-Atlantic as the low level flow backs ahead of the approaching
trough. This moisture along with afternoon heating and the larger
scale forcing afforded by the approaching trough (broad-scale
upper difluence) is expected to support and increasing threat for
moderate to locally heavy amounts focused along the higher terrain
and ahead of a cold front pushing across the lower Great Lakes.
WPC QPF gave significant weighting to the HREF Mean through most
of the period.

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

As an upper level trough continues to amplify across the
Northwest, a developing upper jet streak across southern
Alberta-Manitoba along with ample (anomalous) moisture along and
east of the low-level front will support mid-heavy rainfall along
the eastern slopes of the northern Rockies and spreading into the
northern Plains. WPC QPF reflects a consensus of the hi-res models
here as well. The shear profiles support more forward (downwind)
propagation of convection than otherwise; however, given the
antecedent wet soils (relatively low FFG across much of the
region), areas that receive the heaviest rainfall may experience
isolated runoff issues in the short term.

Hurley