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FOUS30 KWBC 170722
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
322 AM EDT SAT APR 17 2021
DAY 1
VALID 12Z SAT APR 17 2021 - 12Z SUN APR 18 2021
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL-EASTERN GULF COAST AND SOUTHEAST...
THE APPROACH OF A WEAK MID/UPPER LEVEL SHORTWAVE FROM TEXAS AND A
JET STREAK OVER THE TENNESSEE VALLEY WILL PROVIDE THE NECESSARY
FORCING FOR ASCENT FOR ANOTHER ROUND RAINFALL ACROSS PORTIONS OF
THE CENTRAL-EASTERN GULF COAST AND SOUTHEAST SATURDAY-SATURDAY
NIGHT. AT THE SURFACE, LOW PRESSURE WILL TRACK ALONG A
QUASI-STATIONARY FRONT JUST OFFSHORE THE GULF COAST SATURDAY, THEN
ACROSS NORTHERN FL/SOUTHERN GA SATURDAY NIGHT. INSTABILITY NORTH
OF THESE FEATURES WILL REMAIN RATHER MARGINAL (UPWARDS OF 500
J/KG) OVER PORTIONS OF SOUTHERN LA, SOUTHERN MS, AND SOUTHERN AL.
THIS IS WITHIN AN AREA WHERE ANOMALOUSLY HIGH PRECIPITABLE WATER
VALUES AND SUFFICIENT ONSHORE FLOW SHOULD REMAIN IN PLACE (1.6 TO
1.6 INCHES; AROUND 2 STANDARD DEVIATIONS ABOVE NORMAL). FARTHER
EAST ACROSS NORTH FL, THE LOW TRACK WILL LIFT THE WARM FRONT
THROUGH MUCH OF THE AREA, ALLOWING THIS AREA TO TAP MORE ROBUST
INSTABILITY WITHIN THE WARM SECTOR (MIXED LAYER CAPES 1000-2000
J/KG) AHEAD OF FLAT UPPER SHORTWAVE AND SURFACE COLD FRONT.
THE EXPANSIVE MARGINAL RISK AREA ACCOUNTS FOR THE POTENTIAL OF
ISOLATED OR LOCALIZED FLASH FLOODING, BASED ON THE VARYING
THERMODYNAMIC AND ANTECEDENT ENVIRONMENTS ACROSS THE OUTLOOK AREA.
FARTHER WEST (ACROSS SOUTHERN LA/MS/AL), THE LACK OF SURFACE-BASED
INSTABILITY WILL LIMIT HOURLY TOTALS TO 1" OR LESS OVER MOST
AREAS. HOWEVER, THESE ARE AREAS WHERE SOILS REMAIN QUITE SATURATED
PER THE LATEST NASA SPORT ANALYSIS (0-100 CM SOIL MOISTURE
PERCENTILE 98+ PERCENT OVER EASTERN LA/SOUTHERN MS/FAR SOUTHERN
AL), WITH LITTLE RECOVERY FROM A VERY WET WEEK. SO IT WOULDN'T
TAKE AS MUCH RAINFALL TO CAUSE POTENTIAL RUNOFF ISSUES. FARTHER
EAST (FL PANHANDLE/NORTH FL/SOUTHERN GA), STRONGER DEEP-LAYER
INSTABILITY SHOULD ALLOW FOR HEAVIER SHORT-TERM RAINFALL RATES, AS
THE HIGH-RES GUIDANCE (INCLUDING THE 00Z HRRR) INDICATES SPOTTY
CLUSTERS WITH 1.5-2.0"/HR RATES LATER THIS AFTERNOON AND EVENING.
SOILS ACROSS THESE AREAS AREN'T NEARLY AS SATURATED, NEVERTHELESS
MUCH OF NORTH FL HAS OBSERVED 200-400+ PERCENT OF NORMAL RAINFALL
OVER THE PAST WEEK.
HURLEY/TAYLOR
DAY 2
THE DAY 2 OUTLOOK WILL BE UPDATED BY 0830Z.
DAY 3
THE DAY 3 OUTLOOK WILL BE UPDATED BY 0830Z.
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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