Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Tue May 15 2018


Prelim Day 1 QPF Discussion
Valid May 15/1200 UTC thru May 16/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Northeast/Mid-Atlantic/Central Appalachians/Ohio Valley...

A mid-level shortwave associated with ongoing convection across
the Great Lakes is expected to become embedded within the base of
a broad upper trough centered over the Great Lakes/Northeast and
move progressively across the Northeast.  This is expected to spur
a convective complex that is forecast to move across northern
Pennsylvania and southern New York into New England during the
late morning and afternoon hours.  This may produce some locally
heavy totals, but given the anticipated progressive nature of 
this system, widespread heavy amounts along the leading edge of
this system are not expected.  However, the tail end the
convection is expected to hang up across southern Pennsylvania,
northern Maryland into New Jersey as it merges with a
quasi-stationary boundary extending across the region.  Convection
will continue to train across the region into the evening hours as
a deepening moisture pool coinciding with the boundary interacts
with energy emanating from the south and west.  Meanwhile,
additional convection development initiating near a weak wave over
the Ohio valley Tue afternoon/evening is expected to move east --
resulting in an axis of moderate to heavy accumulations extending
from the northern Mid Atlantic coast back into the Ohio valley. 
WPC QPF utilized the HREF mean as starting point across most areas.

...Southeast to the southern Appalachians...

A closed low will continue to drift north over the northeast Gulf
of Mexico this period.  Southerly winds east of the center will
continue to channel deep moisture along the Florida peninsula into
southern Georgia, supporting the potential for moderate to heavy
rains across the region.  Upslope flow and pooling moisture along
an inverted trough extending to the north is expected to extend
the threat for moderate to heavy rains further to the north into
the southern Appalachians.  Here also, the HREF Mean was used as
starting point for QPF.

...Southern Plains to the lower Mississippi valley...

Several areas of thunderstorms are expected to develop as the
atmosphere becomes moderately to strongly unstable later today. 
Models are showing the typical spread with respect to the finer
details, but there is some consensus that a MCV may support some
organized heavier amounts as it moves from eastern Oklahoma into
Arkansas during the afternoon. 

Meanwhile, additional storms are expected to develop along the
Texas dryline and within an upslope flow regime further to the
north over high plains and into the foothills of northeast New
Mexico and eastern Colorado.  Slightly anomalous moisture,
supported by weak southerly flow will support the potential for
locally heavy amounts with these storms.

Pereira