WPC Met Watch |
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Mesoscale Precipitation Discussion: #0512 (2018) |
(Issued at 407 PM EDT SUN JUL 22 2018
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MPD Selection |
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MESOSCALE PRECIPITATION DISCUSSION 0512
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EDT SUN JUL 22 2018
AREAS AFFECTED...NORTHERN FLORIDA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 222006Z - 230206Z
SUMMARY...FLASH FLOODING THREAT INCREASING ACROSS PORTIONS OF
NORTHERN FLORIDA.
DISCUSSION...A NORTHWEST TO SOUTHEAST ORIENTED LINE OF CONVECTION
IS PRODUCING HEAVY RAINFALL OVER PORTIONS OF NORTHERN FL. AROUND
5000 J/KG OF MLCAPE IS SITUATED ALONG THE NORTHWEST FL COAST
FEEDING INTO THIS ACTIVITY. 850 MB WESTERLY FLOW IS PARALLEL AND
NEARLY EQUAL TO THE MEAN WINDS ACROSS THE AREA...SUPPORTIVE OF
BACKBUILDING TO THE WEST INTO THE INSTABILITY POOL. PWAT VALUES AT
OR ABOVE 2.25" ARE COMMON AS WELL...PLENTY HIGH ENOUGH FOR RATES
SUPPORTIVE OF FLOODING.
HAVE RECENTLY SEEN AN OUTFLOW BOUNDARY DROP SOUTH OUT OF THE
CONVECTION...BUT THIS BOUNDARY IS ONLY SLOWLY MOVING SOUTH AND IS
ACTING AS AN ADDITIONAL FOCUS FOR TRAINING CELLS TO ITS NORTH.
NOTE A VIGOROUS SHORTWAVE UPSTREAM APPROACHING THE AL/GA BORDER.
STORMS HAVE DEVELOPED AHEAD OF THIS FEATURE AND ARE JUST NOW
MOVING INTO THE WESTERN FL PANHANDLE. AS THIS SHORTWAVE CONTINUES
TO DROP SOUTHEAST AND OVERRUNS THE ONGOING CONVECTIVE ACTIVITY AND
OUTFLOW BOUNDARY...SEE NO REASON WHY CONVECTION WILL NOT CONTINUE
TO EXPAND IN COVERAGE. WHILE THIS FEATURE SHOULD HELP PUSH THE
EFFECTIVE OUTFLOW BOUNDARY SOUTHWARD WITH TIME...THERE WILL STILL
LIKELY BE A SEVERAL HOUR PERIOD FAVORABLE FOR TRAINING CONVECTION
ALONG AND JUST NORTH OF THE OUTFLOW. THIS SCENARIO IS DEPICTED
WELL BY THE 12Z HREF MEMBERS AND RECENT HRRR RUNS.
ANTICIPATE WE WILL SEE A SWATH OF RAINFALL EXCEEDING
5"...RESULTING IN AT LEAST SOME FLASH FLOOD POTENTIAL INTO THE
EVENING HOURS. BASED ON RECENT RADAR TRENDS...WOULD THINK THE 18Z
HRRR IS PROBABLY TOO FAR NORTH...ALTHOUGH ITS OVERALL DEPICTION
SEEMS REASONABLE. THUS PREFER SOMETHING LIKE A SOUTHWARD SHIFTED
HRRR AND THE 12Z NSSL WRF. THE OUTFLOW IS MOST PROGRESSIVE ALONG
THE EAST COAST OF FL. THUS THE HIGHEST FLASH FLOOD POTENTIAL IS
LIKELY ACROSS THE WEST COAST OF FL INTO NORTH CENTRAL FL...WHERE
THE OUTFLOW PROGRESSION IS BEING SLOWED BY THE STRONGER WESTERLY
INFLOW OF HIGHLY UNSTABLE AIR.
CHENARD
ATTN...WFO...JAX...MLB...TAE...TBW...
ATTN...RFC...SERFC...
LAT...LON 30118343 30118302 29938237 29498201 29248173
28648124 28298114 28048135 28238206 28328231
28518269 28738304 29128327 29658349 29758364
29858368
Last Updated: 407 PM EDT SUN JUL 22 2018
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