Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
251 AM EDT Sun May 13 2018


Prelim Day 1 QPF Discussion
Valid May 13/1200 UTC thru May 14/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Midwest to Mid Atlantic...

A series of shortwaves embedded within the base of a broad mid to
upper level trough will continue to interact with a pool of
relatively deep moisture and instability coinciding with a
quasi-stationary boundary -- supporting additional rounds of
convection, with the potential for moderate to heavy rainfall.  
Overnight guidance suggests two areas with a greater potential for
organized heavier amounts -- the upper Ohio valley to the northern
Mid-Atlantic region and the mid Mississippi valley to the southern
Great Lakes region. 

The shortwave associated with ongoing convection across the
southern Great Lakes region is forecast to continue east, spurring
convection north of the boundary from the upper Ohio valley to the
the northern Mid-Atlantic coast. Guidance shows PWs increasing to
over 1.5 inches during the afternoon/evening hours, which along
with daytime heating and the favorable forcing aloft may produce
some moderate to heavy amounts across the region.  Across the
upper Ohio valley to the Mid-Atlantic, WPC QPF gave strong
weighting to the HREF Mean throughout the period. 

Back to the west, another round of moderate to heavy amounts is
possible from the mid Mississippi valley into the southern Great
Lakes region Sun night to Mon morning as a shortwave rounds the
crest of an upstream ridge and moisture deepens along the nose of
a strengthening low level jet (30-40 kts).  Guidance begins to
show significant latitudinal spread with respect to the axis of
heavier amounts late in the period.  The general trend of the
overnight guidance has been toward a more northerly solution
across eastern Iowa into southern Wisconsin and northern Illinois.
This is reflected in the WPC QPF. However, did not go as far north
as some of the solutions, including the NAM, which appear to be
developing heavier amounts too far north into more stable air.

Pereira