Mesoscale Precipitation Discussion 0809
NWS Weather Prediction Center College Park MD
345 AM EDT Sun Jul 27 2025

Areas affected...Central and Eastern NY...Southwest VT...Northwest
MA

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

Valid 270745Z - 271345Z

SUMMARY...Increasing coverage of showers and thunderstorms can be
expected over the next few hours. Heavy rainfall rates and
localized areas of cell-training may result in isolated pockets of
flash flooding through the early morning hours.

DISCUSSION...Upstream shortwave energy crossing the Lower Great
Lakes region coupled with broad warm air advection and a very
moist airmass will contribute to an increase in shower and
thunderstorm activity over the next few hours.

There is already broken coverage of relatively warm-topped
convection advancing across central NY with alignment in close
proximity to a warm front advancing east across the region. A
westerly low-level jet of 30 to 40+ kts impinging on the area
should further support a general expansion of convection off to
the east, and especially with some increase in elevated CAPE, with
MUCAPE values increasing to 500 to 1000 J/kg.

Weak right-entrance region upper jet dynamics over the region
coupled with the warm air advection/isentropic ascent regime
should foster swaths of heavy shower and thunderstorm activity
going through the early morning hours, with some localized areas
of cell-training possible where the convection becomes oriented in
bands with better alignment with the deeper layer steering flow.

The PW environment is very moist with values of 2.0 to 2.25 inches
across central NY. In fact, the 00Z/27 RAOB sounding at KBUF
depicted a PW of 2.18 inches which is a record for the date. This
deeply tropical airmass shows up very well in the latest CIRA-ALPW
data, with enhanced moisture concentrations noted well up through
the 500/300 mb layer.

The setup is conducive for highly efficient rainfall processes
that will promote locally very high rainfall rates that could
reach or briefly exceed 2 inches/hour. In fact, the latest GOES-E
IR satellite imagery and MRMS-data suggest some ongoing warm rain
processes with the current activity.

Areas of central and eastern NY should see the heaviest
concentrations of rainfall going through the early morning hours,
with perhaps some downstream areas of southwest VT and northwest
MA potentially getting into some heavy rainfall after dawn.

Some localized swaths of 3 to 4+ inch rainfall totals will be
possible, and there is at least some potential for this to drive
isolated pockets of flash flooding.

Orrison

ATTN...WFO...ALY...BGM...BOX...BTV...BUF...

ATTN...RFC...RHA...TAR...NWC...

LAT...LON   44077534 43797406 43247296 42487295 42207367
            42307465 42627546 43137631 43647646 44007606