Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Fri Jun 01 2018


Prelim Day 1 QPF Discussion
Valid Jun 01/1200 UTC thru Jun 02/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


...Central-Northern Plains...

A well-defined shortwave trough will continue to translate east,
assuming a negative tilt as it pivots across the northern Rockies
and into the central-northern Plains. Favorable upper level
forcing (robust upper difluence and resultant deep-layer Qs vector
forcing) will result in highly-anomalous 850-700 mb moisture flux
into the central and especially northern Plains on Friday. PW
values (1.5+ inches) will be equally as impressive, averaging
about 2-2.5 standard deviations above normal. By afternoon,
700-500 mb lapse rates between 8-8.5 c/km will foster vigorous
deep-layer instability (MUCAPES 2000-3000+ j/kg). The 00Z
guidance, especially the high-res CAMs, continue to show a signal
for heavy (potentially excessive) rainfall across ND (especially
central ND) late this afternoon into the evening as the southerly
low-level inflow increases to 50+ kts. The high-res simulated
reflectivity in fact shows the convection growing upscale (QLCS)
while the eastward progression begins to slow down a bit during
the evening (corresponding to the strengthening LLJ), which owing
to the strength of the upwind propagation, would lead to a greater
potential for cell training. As a result, WPC will maintain a
Slight risk in the day 1 ERO, which is supported by the 00Z HREF
probabilities of 3 hourly QPF exceeding FFG (50-70+ percent across
western-central ND between 21-03Z).

Farther south -- the guidance also depicts a heavy rainfall
footprint across portions of the central Plains into the lower MO
Valley -- especially from eastern NE-northeast KS into northwest
MO. This area of convection is expected to be triggered by the
compact upper jet streak/associated vort lobe that will traverse
the 4 Corners area this morning and lift into the central high
Plains this evening. In this region, also expect rather robust
deep-layer instability (again largely due to the steep mid-level
lapse rates) as over this area MUCAPEs would be more likely to
exceed 3000 j/kg per the models. The models show the southerly LLJ
in this region not as strong compared to the northern Plains,
while also denoting considerably more deep layer shear (both
directional and speed shear). As a result expect more
forward/downwind propagation than otherwise as the convection
grows upscale during the peak late-day heating -- however given
the strength of the thermodynamic parameters (instability and
anomalous deep-layer moisture), the risk for 1-3 hour QPF>FFG
exceedance will continue to warrant a Slight risk in the day 1 ERO.

Hurley