Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
325 AM EDT Sat May 26 2018


Prelim Day 1 QPF Discussion
Valid May 26/1200 UTC thru May 27/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Tropics / Gulf...
Sub-tropical storm Alberto is expected to become more organized
and strengthen. Most of the heavy precipitation will affect the
open waters of the Gulf, but also Cuba through Saturday night.
Some heavy rain will fall, however, over the Florida Keys and
south Florida. Alberto is embedded with what is still a weakly
baroclinic, broad scale trough, and the warm conveyor belt /
southerly flow is forecast to migrate out from the center toward
Florida by afternoon/evening. This should enhance convergence
within the very moist and moistening atmosphere that was in place
there. Using the official NHC track for Alberto as a guide, WPC
QPF favored the ECMWF, SREF, and continuity in this area. The
WRF-ARW2 was one of the more useful hi-res models. The NCEP
guidance was generally a little drier than the new 00Z ECMWF,
causing us to lower 24-hour totals a tad in the FL Keys.
Nevertheless, some tropical downpours are likely, and the
potential for focused bands and training of echoes should increase
as the system takes shape. The QPF will be revisited and may be
massaged upwards for the final 0930Z package.

...Eastern U.S...
Sea breezy activity along the Gulf Coast and then a generally
supportive mix of May sun angle and plentiful moisture should
yield large coverage of measurable rainfall today everywhere east
of a Dallas to Green Bay line. Focus for more greatly organized
thunderstorms is expected to exist with a shortwave trough over
the Ohio Valley, within a confluent flow regime with strong
moisture advection over the Mid-Atlantic states, and along a
northern stream frontal boundary in New England. WPC QPF was
derived primarily from the NAM, NAM CONUS Nest, and WRF-ARW2, as
these were more generous with the more moderately forced regimes,
especially that in the mid Atlantic.

...Western U.S...
The upper low over Nevada will move eastward into areas that quite
a bit drier in the low levels, so much of the diurnal thunderstorm
activity on Saturday will occur in the post frontal environment
back across Nevada and up through the northern Rockies. The models
also hint strongly at MCS development over eastern Montana to the
north of a developing warm front this evening. WPC QPF favored the
WRF-ARW2 and NAM CONUS Nest.

Burke