Weather Prediction Center issues Mesoscale Precipitation Discussion #820 concerning HEAVY RAINFALL...FLASH FLOODING LIKELY
346
AWUS01 KWNH 061841
FFGMPD
RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-070030-
Mesoscale Precipitation Discussion 0820
NWS Weather Prediction Center College Park MD
241 PM EDT Tue Aug 06 2024
Areas affected...Mid-Atlantic States from central MD through
southern CT including the I-95 corridor
Concerning...Heavy rainfall...Flash flooding likely
Valid 061840Z - 070030Z
Summary...Showers and thunderstorms will expand across the
Mid-Atlantic states this afternoon and evening. Rainfall rates
will steadily increase to 2+"/hr, which through training could
produce 2-4" of rain with locally higher amounts above 5".
Instances of flash flooding are likely.
Discussion...The GOES-E day-cloud phase distinction RGB this
afternoon shows expanding Cu/TCu with increasing glaciation
indiciating of strengthening updrafts and thunderstorms. Within
this area, the Lightningcast probabilities have increased to more
widespread 50-70%, further indicative of the strengthening
environment, and likely the precursor to widespread thunderstorms
through the aftn. This convection is blossoming within an
extremely robust thermodynamic environment characterized by PWs
measured by GPS around 2 inches, colocated with MLCAPE that has
climbed steadily to 1500-2000 J/kg. A complicated surface pattern
is enhancing the convective risk as well, with a wave of low
pressure analyzed along a stationary front draped from PA into
southern CT, and multiple surface troughs (sea breeze boundary
north of the Chesapeake Bay, outflow boundary over Long Island)
causing enhanced convergence for ascent. Recent radar-estimated
rain rates within this fresh convection has locally already
exceeded 1.5"/hr.
The recent HRRR runs have really under-initialized the ongoing
convective coverage, and while the 17Z run is a bit better, the
ARW/ARW2 appear to be a much better indicator of the future. These
models suggest convection will become widsepread and focused along
the front, which is where convergence of the best moisture
transport vectors occurs within the gradient of highest
instability. This will be in addition to development along the
residual surface troughs, and this should result in activity
rapidly blossoming to become widespread during the next few hours.
Rainfall rates within the intense thermodynamics have a high
probability (>70%) on both the HREF and REFS to exceed 2"/hr, with
brief more intense rates to 3"/hr possible, especially where any
organization into clusters can occur through 0-6km bulk shear of
25-35 kts. Individual cells will remain progressive to the east as
propagation vectors suggest storm motions of 15-25 kts, however,
these are aligned to the mean 0-6km winds and the front,
indicating a high potential for training cells.
Additionally, there is potential for some backbuilding cells along
the surface troughs where they interact with locally higher
PWs/instability. This may be most likely near the northern
Chesapeake Bay, or in the vicinity of the Tri-State area of
NY/CT/NJ. Confidence is modest in this evolution, but mesoscale
ingredients support this, and is reflected by locally higher HREF
and REFS neighborhood probabilities for 3"/6hr and 5"/6hr reaching
70-80% (10-20%). This indicates that many areas could receive 2-4"
of rain with locally higher amounts above 5" possible.
The flash flood potential will be most significant over urban
areas, especially where any backbuilding can occur to lengthen the
duration of heavy rain. However, AHPS 7-day rainfall in much of
the region has exceeded 150% of normal which is reflected by 3-hr
FFG as low as 1.5"/3hrs in some areas. Flash flooding is possible
trough training anywhere this evening, but is most likely along
the I-95 corridor where isolated significant flash flooding is
possible.
Weiss
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ALY...BGM...BOX...CTP...LWX...OKX...PHI...
ATTN...RFC...MARFC...NERFC...NWC...
LAT...LON 41507233 41207136 40857160 40537224 40047351
39917366 39307560 39197679 39437738 39947769
40507763 40987695 41367564 41497416
Source: Weather Prediction Center issues Mesoscale Precipitation Discussion #820 concerning HEAVY RAINFALL...FLASH FLOODING LIKELY (https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=820&yr=2024)
----------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!