Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Mon May 14 2018


Prelim Day 1 QPF Discussion
Valid May 14/1200 UTC thru May 15/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...


...Mid Mississippi valley/Great Lakes/Ohio Valley/Mid-Atlantic...

Low amplitude shortwaves embedded within progressive mid-upper
level flow will continue to produce rounds of convection,
producing locally heavy amounts, as they interact with a
relatively deep moisture and instability pool coinciding with a
quasi-stationary boundary stretching from the Mid-Atlantic back
into the central Plains.

The overnight guidance has backed away on the intensity shown by
previous runs, but still show some potential for ongoing
convection to further develop and produce moderate to heavy rains
as it moves southeast from the upper Great Lakes region into the
upper Ohio valley this morning.  Hi-res guidance shows a better
signal for heavy amounts further downstream as the associated
shortwave moves from the upper Ohio valley into the Mid-Atlantic
region this afternoon-evening.  Deepening moisture afforded by
increasing southerly flow, along with daytime heating, may support
heavy amounts from the eastern foothills of central Virginia to
the coastal plains as it interacts with the approaching shortwave.
 Overall, the 00Z hi-res guidance is in generally good agreement
across this region, with the HREF mean showing hi probabilities of
6-hr amounts of 2-inches for the period ending 00Z Tue.

Meanwhile, additional storms are likely to develop during the
afternoon and evening hours from the mid Mississippi valley to the
southern Great Lakes region as the low level jet intensifies and
moisture deepens.  While there is a fair amount of spread with
regards to the finer details, there is fairly good signal for
heavy amounts developing in the vicinity of the lower Missouri
into the mid Mississippi valley Mon afternoon-evening as weak
surface wave, fostered by an approaching shortwave from the west,
may generate an area of enhanced low level convergence and ascent
across the region.  To account to the typical uncertainty, WPC QPF
relied on the HREF Mean as starting point across this region
through much of the period.  Further to the north, an amplifying
shortwave trough across the upper Midwest into the Great Lakes may
help develop storms further to the north, generating another round
of storms from Iowa into the southern Great Lakes Mon night.  Here
also, there was a good deal of spread in the guidance, so once
again significant weighting was given the to HREF Mean.

...Southern and Central Plains...

Frontal convergence and dryline mixing along with a string of
shortwaves embedded within southwesterly flow aloft should support
developing convection, with heavy amounts possible, as they
interact with a relatively deep moisture pool associated with the
low level jet.  There is a fair amount of spread with respect to
the details here as well, although the hi-res guidance does
cluster fairly well showing two areas of focus for heavier amounts
during the afternoon and evening hours-- northwest Texas and
central Oklahoma.

...Central Rockies and High Plains...

Moist upslope flow along with increasing instability is expected
to support another round of developing convection later today. 
These storms could produce some locally heavy rainfall amounts as
they develop and spread east from the southeast Wyoming and
Colorado foothills into the plains.

...Florida...

A closed low is expected to continue to develop and drift north
through the northeast Gulf this period.  Deep southerly flow east
of the center will continue to support anomalous moisture values
across much of the state.  There remains a fairly good model
signal for heavy amounts centering mainly along the Atlantic coast
this period -- supported by convergent surface to low level
onshore flow.  By late in the period, may also start to see
organized heavy amounts further north along the Gulf coast as
well, as the low circulation approaches the Panhandle Tue morning.

Pereira