Mesoscale Precipitation Discussion 0597
NWS Weather Prediction Center College Park MD
342 AM EDT Sat Aug 04 2018

Areas affected...Northeastern NY...VT...Northern NH...Central
ME...

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

Valid 040741Z - 041330Z

SUMMARY...Persistent moderate rainfall with embedded convective
elements to produce 2-3" totals over 3-6hrs leading to flooding
with possible flashy conditions at times in complex terrain.

DISCUSSION...Strong dynamic forcing and increasing moisture flux
on a ribbon of deep moisture will maintain isentropic ascent for
the next few hours.  GOES-16 WV suite depict baroclinic leaf with
increasing transverse banding indicating solid upper level
diffluence and divergence across northeast NY into VT/NH at this
time.  Upstream strong shortwave over W NY is advancing eastward
supporting DPVA and low level frontogenetic forcing along the 7H
boundary from the southern Adirondack Mtns through the
Greens/Whites into the ME Blue Mtn Ranges across to Penobscot
county, ME.  Along and south of the boundary, CIRA Layered PWAT
show increasing but narrow ribbon of moisture currently supporting
about 1.75" Total PWATs available for isentropic ascent.   Twenty
to thirty knot 85-7H flow is backed ever so slightly to provide
sufficient convergence and ascent.  While lapse rates are in the
5-5.5C/km range, there is some available slantwise instability
from the southeast to allow for some isolated convective elements
within the line.  Generally, up to .5"/hr rain rates are supported
by the amount of flux/forcing but up to 1"-1.25"/hr are supported
by CXX/GYX radars which given the deep tropical moisture
availability seem reasonable.  Given complex terrain to aid
additional ascent but also lead to high runoff flow, flash
flooding is possible through the next few hours with these
convective elements. 

With time, as the main shortwave advances east, the orientation of
the mean flow will shift from W-E to more SSW-NNE with the pivot
of rotation near MWN to Oxford county, ME...increasing the risk
here only exacerbated by the 2-3" already estimated per RADAR. 
The increased angle of 850mb flow to the boundary as well as the
White mountain range are likely to contribute to increased rates
after 12z as well, adding to the longer term/inundation flooding
with time. 

Gallina

ATTN...WFO...ALY...BTV...CAR...GYX...

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

LAT...LON   46166866 46116783 45586778 44726884 43727139
            42767324 42897449 44057349 45017156 45497056
            45966976