391
FXUS21 KWNC 151801
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 15 2025
SYNOPSIS: ONE OR MORE SURFACE LOW PRESSURE SYSTEMS FAVORED IN THE LEE OF THE
ROCKIES SUPPORTS INCREASED CHANCES FOR LOCALLY HEAVY PRECIPITATION FOR MUCH OF
THE SOUTH-CENTRAL AND SOUTH-EASTERN CONTIGUOUS U.S (CONUS), WITH FLOODING
POSSIBLE NEAR THE ARKLATEX REGION DURING WEEK-2. DUE TO EXCESSIVE PRECIPITATION
OBSERVED IN THE MISSISSIPPI AND OHIO RIVER VALLEYS DURING THE PAST FEW WEEKS,
ANY ABOVE-NORMAL PRECIPITATION RECEIVED MAY TRIGGER ADDITIONAL FLOODING IN THIS
PART OF THE COUNTRY.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, MIDDLE AND LOWER MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, SOUTHERN
APPALACHIANS, AND SOUTHEAST, WED-SUN, APR 23-27.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF CALIFORNIA AND THE PACIFIC NORTHWEST,
WED-SAT, APR 23-26.
FLOODING POSSIBLE FOR THE MIDDLE AND LOWER MISSISSIPPI, AND LOWER OHIO RIVERS.
FLOODING POSSIBLE FOR PARTS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR FRIDAY APRIL 18 - TUESDAY APRIL 22:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY APRIL 23 - TUESDAY APRIL 29: TOWARDS THE MIDDLE OF NEXT WEEK,
DYNAMICAL MODEL ENSEMBLE MEAN 500-HPA HEIGHT FORECASTS CONTINUE TO FAVOR FULL
LATITUDE RIDGING OVER EASTERN NORTH AMERICA, WITH NEAR TO BELOW-NORMAL MEAN
500-HPA HEIGHTS UPSTREAM OVER THE WESTERN CONUS. SINCE YESTERDAY, BOTH THE GEFS
AND ECMWF ARE BEGINNING TO DEPICT MORE OF A WESTERLY SOLUTION OF THIS LATTER
MID-LEVEL FEATURE, WITH BETTER SUPPORT FOR INCREASED HEIGHTS OVERSPREADING THE
NORTHERN AND CENTRAL PLAINS FROM THE EAST. AS A RESULT OF THIS TREND, THE
POTENTIAL FOR SHORTWAVE ENERGY EJECTING FROM THE ROCKIES REMAINS AT PLAY,
THOUGH ANY RENEWED HEAVY PRECIPITATION RISK WOULD APPEAR LIKELY TO BE CONFINED
TO THE SOUTHERN TIER OF THE CONUS, AT LEAST INITIALLY DURING THE PERIOD. LATEST
ENSEMBLES SHOW MEAN SURFACE LOW PRESSURE DEVELOPMENT LIMITED TO THE SOUTHERN
HIGH PLAINS, WITH HIGHER MEAN SURFACE PRESSURE REACHING INTO THE TENNESSEE AND
LOWER MISSISSIPPI VALLEY IN THE WAKE OF A FRONTAL SYSTEM LATE IN WEEK-1.
NOTWITHSTANDING, THIS SYNOPTIC SETUP WOULD STILL PROVIDE MOISTURE ADVECTION
FROM THE GULF AND PLENTY OF FRONTAL FORCING FOR HEAVY PRECIPITATION, WHICH IS
SUPPORTED BY THE PROBABILISTIC EXTREME TOOLS (PETS) EARLY IN WEEK-2.
BY DAYS 10 AND 11 (APR 25-26), THERE ARE BETTER INDICATIONS OF ANOMALOUS
MID-LEVEL TROUGHING TAKING SHAPE OVER THE GREAT BASIN IN THE GEFS AND ECMWF,
WITH MORE LOWER-LEVEL MOISTURE BEING ADVECTED FURTHER NORTHWARD INTO THE
CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY. ALTHOUGH THE GEFS PET IS LESS
SUPPORTIVE OF A HEAVY PRECIPITATION RISK BY THE MIDDLE OF WEEK-2, ITS
UNCALIBRATED TOTALS ARE MORE SUGGESTIVE OF THE WETNESS PERSISTING OVER THIS
PART OF THE COUNTRY. BY COMPARISON, THE ECMWF PET MAINTAINS THE WET SIGNALS
EVEN THROUGH THE END OF THE PERIOD, AND ITS UNCALIBRATED COUNTERPART IS FAIRLY
BULLISH WITH >40% CHANCES FOR 3-DAY AMOUNTS EXCEEDING AN INCH EXPANDING
NORTHWARD INTO THE MIDDLE MISSISSIPPI AND OHIO VALLEYS THROUGH THE MIDDLE OF
WEEK-2. THEREFORE, TO BEST CAPTURE THE EVOLUTION AND EXTENT OF THE HEAVY
PRECIPITATION THREAT, A BROAD SLIGHT RISK AREA OF HEAVY PRECIPITATION REMAINS
POSTED, AND NOW VALID THROUGH DAY 12 (APR 27). A KEY CHANGE IS ITS COVERAGE
BEING EXPANDED FURTHER WESTWARD WHERE THERE ARE HIGHER CHANCES FOR 3-DAY TOTALS
EXCEEDING THE 85TH PERCENTILE IN THE PETS COMPARED TO YESTERDAY. WITHIN THE
HIGHLIGHTED AREA, THUNDERSTORM ACTIVITY AND CONVECTIVE PRECIPITATION IS QUITE
POSSIBLE BASED ON DETERMINISTIC SOLUTIONS, AND ALSO COINCIDES WITH AN UPTICK IN
CLIMATOLOGY FOR SUCH CONDITIONS DURING MID TO LATE APRIL OVER PARTS OF THE
SOUTHERN PLAINS AND THE MISSISSIPPI VALLEY. EPISODES OF HIGH WINDS ARE ALSO
POSSIBLE OVER PORTIONS OF THE PLAINS, THOUGH RAW ENSEMBLES AND PETS REMAIN
UNSUPPORTIVE OF A WIND HAZARD AT THIS TIME.
WITH COPIOUS ANTECEDENT RAINFALL AND RECURRING FLOODING CONCERNS FOR PORTIONS
OF THE LOWER OHIO, MIDDLE AND LOWER MISSISSIPPI VALLEYS, A FLOODING POSSIBLE
HAZARD REMAINS POSTED FOR THIS PART OF THE COUNTRY GIVEN THE POTENTIAL FOR NEW
AND RENEWED RISES IN RIVER LEVELS DURING WEEK-2. WHILE MAIN CHANNELS ARE
ALREADY VERY HIGH, AND THUS LIKELY WON'T RESPOND TOO MUCH TO ADDITIONAL
PRECIPITATION, TRIBUTARIES AND STREAMS WILL BE MORE SUSCEPTIBLE TO RENEWED
FLOODING OR FLASH FLOODING IF ADDITIONAL RAINFALL OCCURS. DUE TO POTENTIALLY
HEAVY PRECIPITATION FORECAST THIS WEEKEND OVER THE ARKLATEX REGION AND ADJACENT
AREAS OF KANSAS AND MISSOURI, WITH LITTLE REPRIEVE FAVORED BEFORE THE HEAVY
PRECIPITATION RISK RETURNS AND POTENTIALLY PERSISTS DURING WEEK-2, ANOTHER
FLOODING POSSIBLE HAZARD IS POSTED. FLASH FLOODING OVER THE COMPLEX TERRAIN OF
THE OZARKS AND STREAMFLOW RISES ARE ALSO POSSIBLE IN THE ARKLATEX REGION DURING
WEEK-2.
OVER THE WESTERN U.S., A SLIGHT RISK OF HIGH WINDS IS POSTED FOR APR 23-26 FOR
PARTS OF CALIFORNIA AND THE PACIFIC NORTHWEST. ALTHOUGH PETS ARE RATHER WEAK
WITH WIND POTENTIAL IN GENERAL, AN EASTWARD ADVANCING AREA OF STRONG SURFACE
HIGH PRESSURE OVER THE EASTERN PACIFIC, WITH MEAN LOW PRESSURE ESTABLISHED OVER
THE GREAT BASIN MAY INDUCE EPISODES OF ELEVATED WINDS IN THE HIGHLIGHTED
REGION. FOR ALASKA, ABOVE NORMAL PRECIPITATION AND TEMPERATURES ARE
PREDOMINATELY FAVORED OVER THE SOUTHERN MAINLAND, WITH BELOW NORMAL
TEMPERATURES OVER NORTHEASTERN ALASKA AND THE YUKON OF CANADA TIED TO AN
ANOMALOUS RIDGE CENTER OVER THE CHUKCHI SEA. THIS PATTERN IS SUGGESTIVE OF
SEASONAL RIVER ICE BREAKUP BEING DELAYED, THOUGH AS TEMPERATURES CONTINUE TO
WARM, THE EVENTUAL RIVER ICE BREAKUP MAY LEAD TO ICE JAMS AND ASSOCIATED
FLOODING IN THE COMING WEEKS. OVER THE CENTRAL PACIFIC, PERSISTENT TROUGHING IS
FAVORED UPSTREAM OF AN AMPLIFIED EAST PACIFIC RIDGE DURING WEEK-2. AN
ACCOMPANYING AREA OF SURFACE LOW PRESSURE IS FAVORED TO DEVELOP TO THE NORTH OF
THE HAWAIIAN ISLAND CHAIN, WHICH COULD BRING LOCALLY HEAVY PRECIPITATION TO THE
NORTHERN WINDWARD ISLANDS.
FORECASTER: NICK NOVELLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page