Mesoscale Precipitation Discussion 0690...Corrected
NWS Weather Prediction Center College Park MD
1200 PM EDT Mon Jul 10 2023
Corrected for Flash Flooding Likely
Areas affected...Northern NY...State of VT...Western NH...Western
MA
Concerning...Heavy rainfall...Flash flooding likely
Valid 101540Z - 102140Z
SUMMARY...A significant and dangerous flooding event is likely to
continue in parts of central New England as excessive rainfall
rates look to persist into the afternoon hours.
DISCUSSION...An upper low is beginning to form over central NY
while an 850mb low is taking shape over the Lower Hudson Valley.
Mean 850-500mb streamflow remains out of the south, and as the
upper low deepens this afternoon, winds in the in the 850-700mb
layer will become southeasterly. Latest RAP guidance shows strong
850mb theta-e advection originating from southern New England that
will then wrap around the northern flank of the 850mb low.
Unfortunately, this means that copious amounts of moisture will
still be at athe atmosphere's disposal. The aforementioned
southeasterly flow oriented orthogonally to the Green and White
Mountains will also enhance rainfall rates due to upslope flow.
Due to the large amount of cloud cover in place, CAPE values will
be hard to come by (up to 500 J/kg generally), capping most hourly
rainfall rates below 2"/hr. However, PWATs ranging between
1.5-1.75" remain at or above the 90th climatological percentile.
Sampled RAP soundings throughout the highlighted region feature
low-mid level RH values >90% and warm cloud layers up to 13,000ft
deep. So despite the lack of instability, strong vertical ascent
courtesy of divergent flow ahead of the upper low and a strong
southeasterly 850mb moisture transport supports warm rain
processes within areas of heavy showers and thunderstorms.
Soils have become overly saturated and in some cases can no longer
take in any additional rainfall. FFGs are exceptionally low, with
portions of central and southern VT, western MA, and northeast of
KALB sporting 6-hr FFGs <1.5". The latest 12Z HREF is showing
30-40% probabilities of 6-hr QPF > 100-yr ARI between 18-00Z today
in northern VT, which is both impressive and highly concerning.
Given the impacts parts of the region have already witnessed from
this event, additional significant to even catastrophic impacts
are expected. Potential impacts include but are not limited to
flooded and washed out roads, flooded homes, mudslides, and fast
moving creeks and streams.
Mullinax
ATTN...WFO...ALY...BOX...BTV...GYX...
ATTN...RFC...NERFC...NWC...
LAT...LON 45237307 45237215 45187138 44707131 43557168
42787211 42187268 42087331 42227380 42727410
43847388 44777372 45137353