Mesoscale Precipitation Discussion: #0323 (Issued at 214 PM EDT Mon May 22 2023 )

 

Mesoscale Precipitation Discussion 0323
NWS Weather Prediction Center College Park MD
214 PM EDT Mon May 22 2023

Areas affected...Central Florida Peninsula...

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

Valid 221815Z - 230000Z

SUMMARY...Colliding outflow boundaries from sea-breeze
thunderstorms, to result in rapid slab up/downdraft with potential
for 3+"/hr and possible rapid inundation flooding.

DISCUSSION...Above average moisture and proximity to stronger than
normal mid to upper level flow favorable to maintain updraft
strength resides across northern FL into the northern Peninsula. 
As such stronger than normal sea breeze convergence is starting to
occur with new cells developing along both coasts.  Very strong
updrafts (see MCD 836 from SPC) with 1500-2000 MLCAPE and ample
low level moisture (near 2" total PWat) should allow for efficient
rainfall production.  Though there is some modest mid-level dry
air to allow for some cold pool generation.  Weak steering flow
may allow for localized 2-3" totals in short-period but it is the
outflow dominance with the sea breeze convection that should aid
secondary development along the outflow boundaries.

Propagation inward across the peninsula will enhance and
strengthen moisture flux convergence into the next round and
eventually will lead to those larger outflow boundary collisions.
As a result a much larger/broader updrafts or slab ascent will
result in very high moisture loading to those updrafts.  Given 2"
total PWat and convergence values, 2.5-3.5"/hr rates are quiet 
possible, though much may fall in sub-hourly duration.  Localized
2-5" totals across the north-central peninsula in proximity to the
urban corridor resulting in localized rapid inundation flooding
conditions mainly between 21-00z.  Hi-Res CAMs support this
evolution unzipping from north-central toward Lake Okeechobee with
time as HREF probabilities range between 10 to 30% for 3"/hr and
as high as 80% for 3"/3hr from Marion to Polk county by 00z.  Thus
adding confidence in the above normal potential today versus
average sea-breeze convective days and making flooding considered
possible this afternoon across the central Peninsula.

Gallina