180
FXUS21 KWNC 161801
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 16 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 GREAT PLAINS,
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, SOUTHERN APPALACHIANS, AND SOUTHEAST,
THU-MON, APR 24-28.
SLIGHT RISK OF HIGH WINDS OVER THE SOUTHWESTERN CONUS, THU-MON, APR 24-28.
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 SATURDAY APRIL 19 - WEDNESDAY APRIL 23:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY APRIL 24 - WEDNESDAY APRIL 30: THE HAZARDS PERSPECTIVE LARGELY
REMAINS ON TRACK, AS THERE IS GOOD CONTINUITY IN THE DYNAMICAL MODEL ENSEMBLE
GUIDANCE FAVORING FULL LATITUDE RIDGING OVER EASTERN NORTH AMERICA, WITH A
SOMEWHAT ZONAL PATTERN UPSTREAM OVER THE WESTERN CONUS. CONSISTENT WITH MODEL
TRENDS NOTED YESTERDAY, BOTH THE GEFS AND ECMWF FEATURE BUILDING MID-LEVEL
HEIGHTS OVER PARTS OF THE GREAT PLAINS, WITH AN EXTENSION OF THE POSITIVE
HEIGHTS DEPARTURES, ALBEIT WEAK, INTO THE INTERIOR WEST INDICATED BY THE LATEST
0Z RUNS HEADING INTO WEEK-2. NOTWITHSTANDING, PROPAGATING SHORTWAVE ENERGY AND
SURFACE LOW DEVELOPMENT IN THE LEE OF THE ROCKIES STILL APPEARS TO BE AT PLAY,
THOUGH ANY RISK OF HEAVY PRECIPITATION LOOKS TO BE CONFINED WELL TO THE SOUTH
OVER THE SOUTHERN HIGH PLAINS AND LOWER MISSISSIPPI VALLEY UNDERNEATH THE
BUILDING RIDGE EXTENSION AT THE OUTSET OF THE PERIOD.
BY DAYS 9 AND 10 (APR 25-26), THE ECMWF AND CANADIAN ENSEMBLES CONTINUE TO
FAVOR A DEVELOPING TROUGH OVER THE WEST COAST, WITH THE GEFS REMAINING
COMPARATIVELY MORE MUTED WITH THIS MID-LEVEL FEATURE. AS THE ANOMALOUS
TROUGHING PROGRESSES EASTWARD WITH STRONGER RIDGING ESTABLISHED DOWNSTREAM,
THERE IS CONTINUED SUPPORT FOR ADDITIONAL SURFACE LOW FORMATION FURTHER NORTH
OVER THE CENTRAL HIGH PLAINS, LEADING TO MORE MERIDIONAL LOWER-LEVEL FLOW AND
THE TRANSPORT OF GULF MOISTURE INTO THE LOWER MISSOURI RIVER BASIN BY THE
MIDDLE OF WEEK-2. THIS EVOLUTION IS REFLECTED IN THE DAILY RAW PRECIPITATION
AND SURFACE PRESSURE TOOLS, WITH THE GEFS BEING WEAKER OVERALL IN REGARDS TO
THE MAGNITUDE AND COVERAGE OF PRECIPITATION, THEREBY TEMPERING OUTLOOK
CONFIDENCE. BUT IN CONSIDERATION OF THE ECMWF GENERALLY OUTPERFORMING THE GEFS
THIS SPRING (AND ITS ABILITY TO BETTER RESOLVE DEVELOPING SHORTWAVE
DISTURBANCES AT THESE LEADS), A SLIGHT RISK OF HEAVY RISK OF PRECIPITATION
REMAINS POSTED FOR APR 24-28 WHERE ITS PROBABILISTIC EXTREMES TOOL (PET)
DEPICTS AT LEAST 20% CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE
AND 1 INCH. THIS SLIGHT RISK AREA IS ADJUSTED TO INCLUDE MORE OF THE LOWER
MISSOURI RIVER BASIN, WITH LESSER COVERAGE OVER PARTS OF THE OHIO VALLEY BASED
ON DRYING SIGNALS IN THE UNCALIBRATED ECMWF DUE TO THE STRONGER RIDGING FAVORED
OVER THIS PART OF THE COUNTRY. WITHIN THE HIGHLIGHTED AREA, THUNDERSTORM
ACTIVITY AND CONVECTIVE PRECIPITATION IS 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 PLAINS AND THE MISSISSIPPI VALLEY.
EPISODES OF HIGH WINDS ARE ALSO POSSIBLE, THOUGH RAW ENSEMBLES AND PETS STILL
REMAIN UNSUPPORTIVE OF A WIND HAZARD MAINLY EAST OF THE ROCKIES.
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 MAINLY ALONG THE MISSISSIPPI RIVER GIVEN THE POTENTIAL
FOR NEW AND RENEWED RISES IN 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, A SECOND FLOODING POSSIBLE HAZARD REMAINS POSTED
WHERE THE UNCALIBRATED ECMWF DEPICTS >50% CHANCES FOR AN ADDITIONAL 2 INCHES OF
PRECIPITATION FALLING DURING WEEK-2. ANY LOCALLY HEAVY PRECIPITATION COULD
CAUSE FLASH FLOODING OVER THE COMPLEX TERRAIN OF THE OZARKS AS WELL AS BRING
RENEWED STREAMFLOW RISES IN THE ARKLATEX REGION.
WITH GOOD CONTINUITY IN THE MODELS FOR THE DEVELOPMENT OF NEGATIVE HEIGHT
DEPARTURES OVER THE WESTERN CONUS, A SLIGHT RISK OF HIGH WINDS REMAINS POSTED
(APR 24-28) AND IS EXPANDED WESTWARD TO INCLUDE MUCH OF THE GREAT BASIN, DESERT
SOUTHWEST, ROCKIES, AND HIGH PLAINS NEAR THE BASE OF AMPLIFYING TROUGH AXIS.
THIS EXPANSION IS ALSO SUPPORTED BY THE ECMWF PET WHICH DEPICTS A MORE
CONTIGUOUS COVERAGE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE THROUGH THE
MIDDLE OF WEEK-2.
OUTSIDE THE CONUS, ABOVE NORMAL PRECIPITATION AND TEMPERATURES ARE
PREDOMINATELY FAVORED OVER THE SOUTHERN ALASKA 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, 500-HPA TROUGHING IS
FAVORED TO DEVELOP UNDERNEATH A NORTH PACIFIC RIDGE BEFORE DEAMPLIFYING LATER
IN WEEK-2. AN ACCOMPANYING AREA OF SURFACE LOW PRESSURE IS EXPECTED TO BRING
REDUCED TRADES MAINLY NORTH OF THE HAWAIIAN ISLAND CHAIN, WHICH COULD RESULT IN
LOCALLY HEAVY PRECIPITATION TO THE NORTHERN WINDWARD ISLANDS.
FORECASTER: NICK NOVELLA
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