Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
242 AM EDT Tue May 29 2018


Prelim Day 1 QPF Discussion
Valid May 29/1200 UTC thru May 30/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Alberto / Southeast U.S. / Ohio-Mississippi Confluence...
The Alberto track forecast was generally doing well, and not
changing in any dramatic way. The inherited QPF had this system
handled pretty well - we merely enhanced amounts just a bit near
the center as it tracks toward western Tennessee, but we also did
trend a little westward with the QPF swath there. The hi-res
models, in particular, want to deflect the more intense rainfall
west of the circulation center. This seems a little
counter-intuitive, although with southerly shear the stronger
echoes can advect north of the center and get drawn back to the W
or SW. We handled the trend by using 40 percent continuity and 20
percent each of the HREF blended mean, 00z NAM, and WRF-NMMB. The
NMMB has done well this spring, and represented a less stark
contrast to the continuity forecast.

Elsewhere there is concern that the confluent moist inflow south
of the circulation will overlap with areas in Alabama which
experienced the core rains on Monday, leading to particularly high
2-day totals which may warrant maintenance of a Moderate Risk of
excessive rainfall there. Moderate Risk will likely be included up
along the center track - pending collaboration with the Field, and
also maintained over through the upslope areas in the Carolinas.
The QPF in the higher terrain did not change much, but we did
split the precipitation over central and eastern North Carolina as
the conveyor belt is shed from the cyclone, and model QPFs trended
downward.


...Central U.S...
The MCS in northwest Oklahoma will have a hard time making
eastward progress into an area of large inhibition this morning.
Expect the next round to have more success Tuesday afternoon as
the western U.S. trough punches out into a negative tilt and acts
to cool the mid levels north of I-40. WPC expects an MCS track
somewhere across central to southeast KS and northern OK Tue
night, leaning on the GFS, ECMWF, and WRF-ARW. We spread generous
coverage of convective QPF northward along the instability axis to
Minnesota, and also within the secondary frontal zone that hangs
back over the High Plains and Dakotas. Overall the QPF in this
region leaned toward the GFS, WRF-ARW, and WRF-NMMB. The Canadian
GEM Regional also gave support.

Burke