Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Fri May 11 2018


Prelim Day 1 QPF Discussion
Valid May 11/1200 UTC thru May 12/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Upper Mississippi Valley/Great Lakes/Northeast...

Broad warm advection ahead of an amplifying trough in the West
will continue to support moderate to locally heavy rains to the
north of a wavy slow-moving boundary extending across the mid
Mississippi and Ohio valleys.  Heaviest amounts are expected to
occur in association with a shortwave trough moving from the upper
Mississippi valley across the southern Great Lakes region late Fri
into early Sat.  Limited instability north of the boundary is
expected to hamper rainfall rates.   However, given the wet
antecedent soil conditions, rainfall totals may pose runoff
concerns across portions of the region from southern Wisconsin and
lower Michigan to western New York and northern Pennsylvania. 
Overall, WPC QPF is similar to the previous forecast -- leaning
closer to the more southerly camp of solutions, similar to the
HREF Mean. 

...Great Basin/Northern Rockies/High Plains...

The previously noted trough in the West will continue to amplify
this period, with a closed low dropping south from the Northwest
into the Great Basin.  Some of the heaviest amounts of the period
are expected to center across Wyoming -- where anomalous moisture
and sufficient instability, supported by low level easterly
inflow, is expected to interact with larger scale forcing along
the left-exit region of the upper jet.  Heavy snows are expected
for portions of the Big Horns and western Wyoming ranges, with
moderate to locally heavy rainfall totals across the lower
elevations.  Further south, some moderate to locally heavy
accumulations (including heavy snows in the Uintas) are possible
along a low-mid level frontal boundary dropping south into the
region.  Overall, guidance was in good agreement, with WPC QPF
reflecting a blend of the HREF Mean with the GFS and 12Z ECMWF.

Pereira