Mesoscale Precipitation Discussion: #0451
(Issued at 1133 AM EDT Wed Jul 08 2020 )
MPD Selection
Mesoscale Precipitation Discussion 0451
NWS Weather Prediction Center College Park MD
1133 AM EDT Wed Jul 08 2020
Areas affected...Eastern PA...Northern NJ...Southern NY
Concerning...Heavy rainfall...Flash flooding possible
Valid 081533Z - 082133Z
Summary...Convection developing late this morning will be capable
of producing rain rates 1-2"/hr across eastern PA, northern NJ,
and southern NY. Localized flash flooding will be possible.
Discussion...Along a higher moisture axis characterized by PWs in
the 1.7 to 1.9" range and an instability pool (upwards of 3000
J/kg SBCAPE as of 15Z), scattered convection has developed across
portions of eastern PA and southern NY per latest GOES-E IR
imagery and radar returns. This activity is developing within weak
but persistent warm advection and likely initiating off old
outflow boundaries from earlier convection. Through 21Z, the
uncapped environment and weak mean flow should allow for continued
development of storms with pulse to loosely organized modes driven
by cell mergers and boundary interactions that will drift east.
After 17Z, the RAP suggests an increase in low level inflow to 25
kts along with increasing CAPE values to above 2000 J/kg MUCAPE.
This will support higher rain rates that could approach
1.5-2.0"/hr - the 12Z HREF probabilities for exceeding 1" are in
the 60-80 percent range and around 20-30 percent for 2"/hr.
Through 21Z, total amounts of 2-3" are possible with some isolated
amounts 3-4" possible (supported by the 6-hr probs for 3"+ around
40 percent). Antecedent conditions vary across the outlook area
with some portions having seen recent heavy rainfall and 7-day
preip departures up to 300 percent of normal. The hi-res guidance
does favor the drier areas which could limit the flash flood
potential, but the intense near-term rain rates would overcome
poor drainage, the highly urban corridor, and other low-lying ares
and may lead to flash flooding into the afternoon hours.
Taylor
ATTN...WFO...ALY...BGM...CTP...OKX...PHI...
ATTN...RFC...MARFC...NERFC...NWC...