791
FOUS30 KWBC 290052
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 PM EDT FRI MAR 28 2025
DAY 1
VALID 01Z SAT MAR 29 2025 - 12Z SAT MAR 29 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER TEXAS COAST THROUGH SOUTHWEST LOUISIANA...
01Z UPDATE: MAINTAINED THE SLIGHT RISK FOR THE DAY 1 ERO UPDATE FOR
PORTIONS OF THE UPPER TEXAS COAST REGION AND AREAS INLAND ACROSS
SOUTHEAST TEXAS/SOUTHWEST LOUISIANA WHILE TRIMMING THE SLIGHT AND
MARGINAL RISK AREAS FARTHER SOUTH. TRENDS IN SATELLITE AND RADAR
IMAGERY SHOWED A VORT MAX LIFTING NORTHEASTWARD WHICH WAS HELPING
TO SUPPORT THE AREA OF RAIN APPROACHING THE TEXAS/LOUISIANA BORDER.
THE 28/18Z HREF NEIGHBORHOOD PROBABILITIES STILL FOCUSED ON
SOUTHWEST LOUISIANA INTO THE OVERNIGHT HOURS FOR 1- AND 2-INCH
PER HOUR RATES WITH 25 PCT CHANCES OF 3 INCH PER HOUR TOTALS IN THE
29/00Z - 29/12Z PERIOD. TOWARDS THE COASTAL AREAS...THE
PROBABILITIES INCREASE TO MORE THAN INLAND AND MORE THAN 40
PERCENT ALONG THE LOUISIANA COAST. IN ADDITION...LATEST RADAR AND
SATELLITE IMAGERY WAS BEGINNING TO SHOW THAT ADDITIONAL CONVECTION
WAS PERCOLATING JUST OFF THE UPPER TEXAS COAST...SIMILAR TO WHAT
THE HRRR STARTED SUGGESTING EARLIER IN THE DAY.
CONSEQUENTLY...MAINTAINED THE SLIGHT RISK AREA A BIT FARTHER SOUTH
AND WEST THAN THE HREF WAS SHOWING. AN ISOLATED...BUT
PERSISTENT...CELL OVER KENEDY COUNTY SUCH THAT WE MAINTAINED THE
MARGINAL RISK THAT FAR SOUTH FOR THE TIME BEING.
BANN
DAY 2
VALID 12Z SAT MAR 29 2025 - 12Z SUN MAR 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL GULF COAST...
A CONTINUATION OF THE DECREASING FLASH FLOOD RISK IS EXPECTED FROM
DAY 1 INTO DAY 2, AS ENSEMBLE GUIDANCE INDICATES THE POTENTIAL FOR
LOCALIZED TOTALS OF 1-3" (MOSTLY CONCENTRATED NEAR THE GULF COAST
WHERE FFGS ARE RATHER HIGH). THE LIMITED INHERITED MARGINAL RISK
AREA WAS MAINTAINED FOR THIS UPDATE, AS FORCING AND INSTABILITY
CONTINUE TO LOOK RATHER MINIMAL (AND MOST DETERMINISTIC GUIDANCE AT
THIS POINT INDICATES LOCALIZED TOTALS OF LESS THAN 1" FOR THE MOST
PART, INCLUDING THE NEW WPC FORECAST, BUT DECIDED TO MAINTAIN THE
MARGINAL. ANY LOCALIZED FLASH FLOOD THREAT SHOULD MOSTLY BE
CONFINED CLOSER TO THE GULF COAST (AND LIMITED TO MORE SENSITIVE
URBAN AREAS).
CHURCHILL/TAYLOR
DAY 3
VALID 12Z SUN MAR 30 2025 - 12Z MON MAR 31 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS...
20Z UPDATE:
A BROAD AREA OF CONVECTION IS EXPECTED SUNDAY INTO SUNDAY NIGHT
WITH A PAIR OF SHORTWAVES MOVING INTO THE CENTRAL U.S. DURING THE
PERIOD. THE FORCING FOR ASCENT AND ASSOCIATED MOISTURE TRANSPORT
SUGGESTS SEVERAL AREAS OF HEAVIER PRECIPITATION FROM THE LOWER MS
VALLEY NORTHWARD INTO THE OHIO VALLEY. THE OVERLAP OF THE BEST
INSTABILITY AND FORCING RIGHT NOW POINTS TOWARD PORTIONS OF THE TN
VALLEY INTO THE MID SOUTH REGION AND THIS COINCIDES WHERE THE
ENSEMBLES SHOW THE GREATEST POTENTIAL FOR SOME HIGHER RAINFALL
TOTALS (2-4"). ULTIMATELY, A SLIGHT RISK MAY BE NEEDED IN FUTURE
UPDATES IF CONFIDENCE INCREASES BUT FOR NOW, CONFIDENCE IN EXACT
PLACEMENT IS LOW AS WELL AS THE FORWARD PROGRESSION OF CONVECTION
THAT MAY BE JUST FAST ENOUGH TO LIMIT DURATION OF HEAVY RAINFALL AT
ANY LOCATION FOR TOO LONG. PREVIOUS DISCUSSION FOLLOWS...
A MUCH BROADER INHERITED MARGINAL RISK AREA (RELATIVE TO DAY 2) HAS
BEEN LARGELY MAINTAINED (AND EXPANDED A BIT), AS MULTIPLE SHORTWAVE
TROUGHS EMERGING FROM THE INTERMOUNTAIN WEST AND PHASE WITH THE
POLAR JET AND AN ASSOCIATED LONGWAVE TROUGH. THIS COMPLEX
INTERACTION IS EXPECTED TO RESULT IN A BROAD AREA OF CONVECTION
ACROSS MUCH OF THE EASTERN CONUS, INCLUDING PORTIONS OF THE MS, TN,
AND OH VALLEYS. DESPITE THE COMPLEXITY OF THE SYNOPTIC AND
MESOSCALE DETAILS, GLOBAL MODELS ARE IN FAIRLY GOOD AGREEMENT IN
INDICATING A CONVECTION BREAKING OUT ACROSS A BROAD WARM SECTOR
(CHARACTERIZED BY PWATS OF 1.5-2.0", SB CAPE OF 1000-2000 J/KG, AND
EFFECTIVE BULK SHEAR OF 40-60 KTS). MOST DETERMINISTIC SOLUTIONS
DEPICT 1-3" LOCALIZED TOTALS (WITH 2-3" AMOUNTS MOST COMMONLY
LOCATED FARTHER SOUTH ACROSS THE LOWER MS VALLEY AND MID-SOUTH,
WHERE BETTER INSTABILITY AND MOISTURE TEND TO BE LOCATED) WITH BOTH
THE GEFS AND ECENS INDICATING 2" EXCEEDANCE POTENTIAL (WITH THE
GEFS FAVORING PORTIONS OF THE MID-SOUTH FROM NORTH MS INTO WEST AND
MIDDLE TN, WHILE THE ECENS FAVORS LOCATIONS FARTHER SOUTHWEST INTO
THE MS DELTA). THESE TYPES OF PROBABILITIES FROM THE ENSEMBLE
GUIDANCE SUGGEST THAT CAMS MAY WELL DEPICT 2-4" LOCALIZED TOTALS,
AND A TARGETED SLIGHT RISK INTRODUCTION MAY BE NECESSARY IN
SUBSEQUENT OUTLOOKS (ONCE BETTER ENSEMBLE AGREEMENT AND/OR A
STRENGTHENING TREND IS MORE EVIDENT IN THE GLOBAL GUIDANCE).
CHURCHILL/TAYLOR
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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