Mesoscale Precipitation Discussion 0596
NWS Weather Prediction Center College Park MD
1019 PM EDT Fri Aug 03 2018

Areas affected...Ern ME...Srn NH...Srn VT...Wrn MA...SErn
NY...NWrn CT...Nrn NJ...Ern PA...N-Cent MD...

Concerning...Heavy rainfall...Flash flooding possible

Valid 040218Z - 040815Z

SUMMARY...Narrowing but increasing moisture corridor with solid
synoptic forcing to support highly efficient warm cloud rainfall
and training to produce flash flooding throughout the overnight.

DISCUSSION...GOES-16 WV suite depict a weakly enhancing baroclinic
leaf across E Lake Ontario into the increasingly confluent (mid to
upper level jet entrance) across ME into Southeast Canada,
providing solid large scale ascent and outflow for any convective
development.   This leaf indicates the best diffluence between the
70-80kt entrance but also a weak narrow jetlet across KY to
Central PA of 70kts which will support some weak low level
cyclogenesis from NY to ME...low level response should increase
moisture convergence from the Hudson Valley/Catskills along the
weak 850-700mb deformation zone/inflection.

A strong mid-level vort center on the western side of the
Sub-tropical high has also tightened the overall gradient and
narrowed the moisture plume and increased LLJ from 20 to 35kts
across E PA increasing the flux but also the mass convergence for
these cells.  As such recent response by increased convective
vigor and coverage was noted over E PA into SE NY translating
toward MA. TPWs are exceeding 2" per GPS network/BLTPW suite.  The
limiting factor is related to weakening/reduced lapse rates and
therefore a lack of instability.  Strong forcing/slantwise
instability has been sufficient to support shallow development
with limited loss to ice/phase change and warm cloud processes
(note overall lack/reduction of lightning strikes).  Rates up to
1.5-2"/hr are expected but given forward speed observations of up
to 1" in quick 15-30 minutes across saturated grounds in the
Delaware valley and lower Hudson is sufficient for producing flash
flooding. It is the upstream redevelopment for training cells that
could lead to truly excessive totals (2-3") and make flash
flooding likely overnight (espeically in MD/PA/NY/NJ).

Further Northeast into MA/VT/NH...FFG values are higher given less
wet last few weeks, but earlier rains today have made the area a
bit more susceptible and reduced the values below 2" from
Rensselear,NY to Rockingham, NH, which current trends suggest may
be best track, though some uncertainty and shift further north due
to the deformation zone/frontogenesis is expected from Montgomery,
NY to Oxford, ME counties along/just south of the 7H shear
axis...maximized moisture convergence.    

Gallina

ATTN...WFO...ALY...BGM...BOX...BTV...CTP...GYX...LWX...OKX...
PHI...

ATTN...RFC...MARFC...NERFC...

LAT...LON   45337057 44937003 43617058 42557172 42127275
            41287357 40347464 39697595 39487641 39397736
            40897655 41987570 42937501 43497431 44077357
            44567230