408
FOUS30 KWBC 301700
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 PM EDT SUN MAR 30 2025
DAY 1
VALID 1655Z SUN MAR 30 2025 - 12Z MON MAR 31 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS AND CENTRAL GULF
COAST...
..CENTRAL GULF COAST THROUGH THE OHIO VALLEY
A PAIR OF SHORTWAVE TROUGHS EMERGE FROM THE INTERMOUNTAIN WEST
INTO THE CENTRAL U.S. TODAY, EVENTUALLY PARTIALLY PHASING WITH AN
ASSOCIATED LONGWAVE TROUGH BY LATER TONIGHT. THIS COMPLEX
INTERACTION IS EXPECTED TO RESULT IN A BROAD AREA OF ORGANIZED
CONVECTIVE ACTIVITY ACROSS MUCH OF THE EASTERN HALF OF THE CONUS,
INCLUDING PORTIONS OF THE MS, TN, AND OH VALLEYS.
DESPITE THE CONTINUED COMPLEXITY OF THE SYNOPTIC AND MESOSCALE
DETAILS, MODELS REMAIN IN FAIRLY GOOD AGREEMENT IN INDICATING
CONVECTION BREAKING OUT ACROSS THE BROAD WARM SECTOR TODAY,
INITIALLY MOSTLY DISCRETE (AND SUPPORTIVE OF SPLITTING SUPERCELLS
AND MULTICELL CLUSTERS) AND EVOLVING INTO A QLCS/LEWP AHEAD OF THE
ASSOCIATED COLD FRONT BY THIS EVENING. BROAD INFLOW FROM THE GULF
WILL RESULT IN PRECIPITABLE WATER VALUES OF 1.25-1.75" (AT OR ABOVE
THE 90TH PERCENTILE, PER CFSR CLIMATOLOGY) AND SB CAPE OF 2000-4000
J/KG, AS DEEP LAYER (0-6 KM) SHEAR INCREASES TO 40-60 KTS. HOURLY
RAINFALL OF UP TO 3"/HR ARE POSSIBLE IN THIS ENVIRONMENT,
INITIALLY HIGHLY LOCALIZED IN ASSOCIATION WITH ESTABLISHED
SUPERCELLS, THEN MORE NUMEROUS TO WIDESPREAD WITH THE PASSAGE OF
THE QLCS/LEWP. LOCALIZED TOTALS OF 2-4" ARE GENERALLY EXPECTED
WITHIN THE SLIGHT FOR THE WHOLE OF THE EVENT (WITH THE MAJORITY
FALLING IN A 3-6 HOUR PERIOD IN ASSOCIATION WITH THE QLCS PASSAGE),
WITH TOTALS NEAR THE UPPER-END OF THE RANGE (~4") BEING POSSIBLE
WHERE STORMS TRAIN AND/OR WHERE TWO OR MORE MESOCYCLONES ALIGN.
WHILE THERE WERE SOME CHANGES PER THE NEW GUIDANCE, IN GENERAL,
CONTINUITY WAS MAINTAINED.
ONGOING ORGANIZED CONVECTION IN THE GENERAL VICINITY OF MOBILE THUS
FAR HASN'T BEEN DISRUPTED BY DIURNAL CONVECTION IN ITS VICINITY,
WHICH THREATENS MERGERS AS DISORGANIZED CONVECTION MOVES MORE
NORTHWARD WHILE ORGANIZED CONVECTION MOVES MORE EASTWARD. COLD
CLOUD TOPS CONTINUE TO SHOW EXPANSION WITH THE CONVECTIVE AREA. INTRODUCED
A SLIGHT RISK ON THIS SPECIAL ISSUANCE FROM SOUTHERN MS ACROSS
SOUTHERN AL INTO THE FL PANHANDLE. HOURLY RAIN TOTALS TO 3" WITH
ADDITIONAL LOCAL AMOUNTS TO 6" REMAIN POSSIBLE FOR AS LONG AS THIS
CONVECTIVE MASS CAN PERSIST.
..FLORIDA PENINSULA/SOUTHEASTERNMOST GEORGIA
A FRONTAL BOUNDARY AT 850 HPA SLOWLY LIFTS THROUGH THE STATE,
BRINGING PRECIPITABLE WATER VALUES TO 1.5-1.75". ML CAPE SHOULD
MAXIMIZE IN THE 2000-3000 J/KG, PARTICULARLY IN THE SOUTHERN
FLORIDA PENINSULA. THERE APPEARS TO BE ENOUGH EFFECTIVE BULK SHEAR
FOR SOME DEGREE OF THUNDERSTORM ORGANIZATION AS WELL. THE MODEL
GUIDANCE --- MOSTLY MESOSCALE -- INDICATES THE POTENTIAL FOR LOCAL
AMOUNTS IN THE 5-6" RANGE. THE MARGINAL RISK WAS MAINTAINED WITH
MINIMAL CHANGE.
ROTH/CHURCHILL
DAY 2
VALID 12Z MON MAR 31 2025 - 12Z TUE APR 01 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST & NORTHEAST...
..SOUTHEAST
THE AFOREMENTIONED PAIR OF SHORTWAVE TROUGHS ARE PROGGED TO FULLY
SEPARATE, AS THE NORTHERN STREAM SHORTWAVE CONTINUES TO PHASE WITH
THE PARENT LONGWAVE TROUGH INTO THE MID-ATLANTIC AND NORTHEAST,
WHILE THE SOUTHERN SHORTWAVE LIKELY HANGS BACK INTO THE MID-SOUTH
AND LOWER MS VALLEY. THE BEST MOISTURE AND INSTABILITY LIES OVER
PORTIONS OF THE SOUTHEAST (WHERE FORCING FROM THE SECONDARY
SHORTWAVE SHOULD STILL BE SUFFICIENT FOR ORGANIZED CONVECTIVE
ACTIVITY). THE MARGINAL RISK WAS GENERALLY MAINTAINED FOR THIS
PORTION OF THE SOUTHEAST (INCLUDING MUCH OF AL/GA WITH SURROUNDING
PORTIONS OF EAST TN, SOUTHERN MS AND THE FL PANHANDLE). LOCALIZED
TOTALS OF UP TO 2-3" ARE GENERALLY EXPECTED (PER GEFS AND ECENS
EXCEEDANCE PROBABILITIES), THOUGH THE INCLUSION OF THE FULL CAM
SUITE LATER TODAY WILL PROBABLY PUSH HIGHER-END TOTALS TO 3-4"
(STILL MOSTLY SUPPORTIVE OF ONLY A MARGINAL RISK, GIVEN ASSOCIATED
3-6 HOUR FFGS OF 2.5-4.0".
..NORTHEAST
THUNDERSTORMS WITH HEAVY RAINFALL ARE EXPECTED DURING THE AFTERNOON
AND EVENING HOURS AHEAD OF A NORTHERN STREAM SHORTWAVE AS MU CAPE
PEAKS AROUND 1000 J/KG AND PRECIPITABLE WATER VALUES PEAK IN THE
1.25-1.5" RANGE. SUFFICIENT INFLOW AND EFFECTIVE BULK SHEAR IS
AVAILABLE FOR ORGANIZED CONVECTION FOR MUCH OF THE PERIOD, WITH
ACTIVITY EXPECTED TO BE IN DECLINE PAST TUESDAY 06Z. HOURLY RAIN
TOTALS UP TO 2" ARE POSSIBLE WHERE CONVECTION TRAINS, WHICH COULD
CHALLENGE THE FLASH FLOOD GUIDANCE ACROSS URBAN PORTIONS OF THE
MID-ATLANTIC STATES. THE INHERITED MARGINAL RISK WAS MAINTAINED.
CHURCHILL/ROTH
DAY 3
VALID 12Z TUE APR 01 2025 - 12Z WED APR 02 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHEAST NEBRASKA, SOUTHWEST IOWA, NORTHEAST KANSAS, AND
NORTHWEST MISSOURI...
A BLOCKING PATTERN BEGINS TO EMERGE BY DAY 3, AS THE AFOREMENTIONED
SHORTWAVES LIFT NORTHEASTWARD INTO CANADA WITH LARGE-SCALE RIDGING
QUICKLY BUILDS ACROSS THE EASTERN CONUS FROM THE NORTH ATLANTIC.
MEANWHILE, LARGE-SCALE TROUGHING BECOMES AMPLIFIED OUT WEST, WITH A
POTENT UPPER-LOW EXPECTED TO DEVELOP OVER THE NORTHERN ROCKIES AND
PLAINS (TRANSLATING ACROSS THE ROCKIES FROM THE PACIFIC NORTHWEST).
WHILE GLOBAL MODEL SUITES ARE IN OVERALL GOOD AGREEMENT WITH THE
EVOLUTION OF THE SYNOPTIC SCALE, THE GFS/GEFS IS ODDLY AN OUTLIER
LACKING SUBSTANTIAL CONVECTION WITH THE ASSOCIATED SURFACE LOW
(WHICH IS DEPICTED AS A SUB 990 MB LOW FROM THE 00Z GFS, ECMWF, AND
CMC). MOST DETERMINISTIC SOLUTIONS DEPICT LOCALIZED TOTALS OF 2-3"
(INCLUDING THE DOWNSCALED ECMWF, THE UKMET, AND THE CMC-REG) WITH
REMARKABLY GOOD SPATIAL AGREEMENT FOR THIS RANGE, SO THE INHERITED
MARGINAL RISK WAS MAINTAINED.
CHURCHILL
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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