Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
332 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.

...Florida...

Low level southeasterly inflow east of developing closed low over
the northeastern Gulf will support deepening moisture across much
of southern into central Florida.  By early Monday, PWs are
expected to increase to near or above 2 inches (2 to 3 standard
deviations above normal) across much of the region.  This
moisture, coupled with low level frictional convergence and
divergent flow aloft may result in the onset of some very heavy
rainfall totals, especially from the Keys northward along the
Atlantic coast.  WPC QPF continued to follow a multi-model blend
across this area.

...Southern Plains...

Overnight hi-res guidance, as well as the GFS, show a good signal
for moderate to locally heavy amounts from the eastern Texas
Panhandle into western Oklahoma where convection is expected to
develop later today.  GFS shows PWs increasing to around 1.5
inches as the low level jet amplifies late this afternoon and
evening.  WPC QPF gave significant weighting the HREF Mean and GFS
across this area.

...Great Basin to the central High Plains...

Overnight guidance shows a deep closed low over the western U.S.
beginning to gradually fill as it remains centered over the Great
Basin this period.  Close to the low, favorable mid-level lapse
rates, in addition to diurnal heating, is expected to support
additional showers and storms, with the potential for some
moderate to locally heavy amounts across the region.  Meanwhile
further to the east, moist low level upslope flow coupled with
ejecting vort energy from the base of the Great Basin closed low
will foster clusters of showers and thunderstorms from the
southeastern Wyoming and northeastern Colorado foothills into the
High Plains.  WPC QPF largely followed a blend of the HREF Mean
and GFS across this region.

Pereira