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FXUS21 KWNC 051804
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 05 2024
SYNOPSIS: LATE NEXT WEEK, A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO BRING
ENHANCED PRECIPITATION AMOUNTS AND EPISODES OF HIGH WINDS OVER THE EASTERN
CONTIGUOUS U.S. (CONUS). THE HEAVY PRECIPITATION THREAT IS FAVORED TO TIME OFF
BEFORE THE START OF WEEK-2, HOWEVER STRENGTHENING PRESSURE GRADIENTS IN THE
WAKE OF THE SYSTEM SUPPORT AN INCREASED RISK OF HIGH WINDS FOR MUCH OF THE
NORTHEASTERN CONUS. LATER IN WEEK-2, DEVELOPING MID-LEVEL LOW PRESSURE OVER THE
EASTERN PACIFIC AND AN ASSOCIATED INCREASE IN ONSHORE FLOW LOOKS TO BRING
ABOVE-NORMAL PRECIPITATION OVER PARTS OF THE WEST COAST, THOUGH THE RISK OF
HEAVY PRECIPITATION REMAINS LOW AT THIS TIME.
HAZARDS
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE CENTRAL APPALACHIANS,
MID-ATLANTIC, OHIO VALLEY, GREAT LAKES, AND NORTHEAST, SAT, APR 13.
DETAILED SUMMARY
FOR MONDAY APRIL 08 - FRIDAY APRIL 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY APRIL 13 - FRIDAY APRIL 19: FOLLOWING THE PASSAGE OF A SHORTWAVE
TROUGH LIFTING OUT OVER THE NORTHEASTERN CONUS TO BRING POTENTIALLY HEAVY
PRECIPITATION OVER PARTS OF THE EASTERN U.S. LATE NEXT WEEK, THERE CONTINUES TO
BE GOOD AGREEMENT IN THE DYNAMICAL MODELS FAVORING THE DEVELOPMENT OF POSITIVE
500-HPA HEIGHT DEPARTURES OVERSPREADING MUCH OF THE CENTRAL AND EASTERN CONUS.
WITH ANOMALOUS MID-LEVEL RIDGING ALSO PREDOMINANTLY FEATURED UPSTREAM ACROSS
THE WEST THROUGH THE MIDDLE OF WEEK-2, THE OVERALL MEAN HEIGHT PATTERN LOOKS TO
KEEP HAZARD POTENTIAL AT BAY, AND PROMOTE UNSEASONABLY WARM (AND RATHER
PLEASANT) SPRINGTIME TEMPERATURES FOR MUCH OF THE LOWER 48. THE HEIGHT PATTERN
IS ALSO EXPECTED TO PROMOTE INCREASINGLY DRIER CONDITIONS FOR MUCH OF THE
COUNTRY, THOUGH THE TWO POSSIBLE EXCEPTIONS FOR DISTURBED WEATHER ARE OVER THE
SOUTHERN TIER AND THE WEST COAST WHERE NEAR TO ABOVE-NORMAL PRECIPITATION IS
FAVORED IN THE MODEL GUIDANCE DURING THE PERIOD.
TIED TO THE AFOREMENTIONED TROUGHING LATE NEXT WEEK, MODELS ARE IN GOOD
AGREEMENT IN REGARDS TO THE STRENGTH AND POSITION OF THE ACCOMPANYING MEAN
SURFACE LOW PRESSURE SYSTEM OVER THE CANADIAN MARITIMES. THE HIGHEST
PRECIPITATION AMOUNTS REMAIN FAVORED TO OCCUR WELL OFFSHORE, HOWEVER THE
POTENTIAL EXISTS FOR STRENGTHENING PRESSURE GRADIENTS OVER THE NORTHEASTERN
CONUS WITH SURFACE HIGH PRESSURE BUILDING BEHIND THE SYSTEM. A SLIGHT RISK OF
HIGH WIND REMAINS ISSUED FOR DAY 8 (APR 13) BASED ON CONTINUED SUPPORT IN THE
ECMWF PROBABILISTIC EXTREMES TOOL (PET) INDICATING INCREASED CHANCES (20-30%)
FOR WIND SPEEDS EXCEEDING THE 85TH PERCENTILE IN THE HIGHLIGHTED REGION.
WITHIN THE HIGHLIGHTED REGION, IT IS WORTH NOTING THAT A MAJOR SPRINGTIME
SNOWSTORM JUST BROUGHT UPWARDS OF A FOOT OF SNOW OVER MANY PARTS OF NEW
ENGLAND, WITH ADDITIONAL SNOWFALL FORECAST IN THE REGION WITHIN THE NEXT DAY OR
SO. IN THE WAKE OF THIS SYSTEM, BUILDING MID-LEVEL HEIGHTS AND SOUTHERLY FLOW
ARE FAVORED, AND THE UNSEASONABLY WARM SPRING TEMPERATURES AND PERIODS OF
RAINFALL DURING WEEK-1 COULD ACCELERATE SNOWMELT. NO CORRESPONDING FLOODING
HAZARD IS ISSUED GIVEN NEAR TO BELOW NORMAL PRECIPITATION FAVORED DURING
WEEK-2, THOUGH ANY ADDITIONAL RAINFALL MAY EXACERBATE RUNOFF MAY BRING FLOODING
ALONG SMALL STREAMS, PARTICULARLY FOR AREAS WHERE THE HIGHEST SNOWFALL AMOUNTS
WERE RECENTLY RECEIVED.
DURING THE FIRST SEVERAL DAYS OF WEEK-2, ENSEMBLES DEPICT A WEAKNESS IN THE
HEIGHT FIELD OVER NORTHERN MEXICO UNDERNEATH MUCH OF THE ANOMALOUS RIDGING
CONCENTRATED TO THE NORTH. COMPARED TO THE GEFS AND CANADIAN, THE ECMWF
ENSEMBLE IS MORE PRONOUNCED WITH THIS FEATURE, DEPICTING MORE CYCLONIC FLOW AND
HIGHER PRECIPITATION AMOUNTS OVER PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY ON DAYS 9 TO 11 (APR 14-16). LIKEWISE, AN INCREASED
POTENTIAL FOR HEAVY PRECIPITATION IS SHOWN IN THE ECMWF PET, WITH 20-30%
CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH DURING THE
MIDDLE OF THE PERIOD. HOWEVER, BOTH THE RAW AND CALIBRATED GUIDANCE FROM THE
GEFS AND CANADIAN ARE MORE UNSUPPORTIVE OF THIS RISK, AND GIVEN THE LACK OF A
DISTINGUISHABLE MEAN SURFACE LOW ANALYZED IN THE DAILY SURFACE PRESSURE FIELDS,
AND MORE ZONAL SURFACE FLOW FROM THE GULF OF MEXICO, NO CORRESPONDING
PRECIPITATION HAZARD IS POSTED.
FROM THE MIDDLE OF APRIL AND ONWARD, MUCH OF THE ANOMALOUS RIDGING OVER THE
INTERIOR WEST AND GREAT PLAINS IS GENERALLY FAVORED TO SHIFT EASTWARD WITH
TIME, ALLOWING FOR MORE TROUGHING TO DEVELOP OVER THE EASTERN PACIFIC AND
EVENTUALLY ENCROACH THE WEST COAST. THE ASSOCIATED INCREASE IN ONSHORE FLOW IS
REFLECTED IN THE RAW PRECIPITATION TOOLS AS WELL AS THE GEFS AND ECWMF PETS
WITH INCREASING CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE OVER
PARTS OF THE PACIFIC NORTHWEST AND THE NORTHERN HALF OF CALIFORNIA. DESPITE
GOOD MODEL AGREEMENT EVEN AT THIS LEAD, NO CORRESPONDING PRECIPITATION HAZARDS
ARE ISSUED AS ACTUAL DAILY AMOUNTS ARE UNLIKELY TO REACH HAZARD CRITERIA.
NO HAZARDS ARE ISSUED OVER ALASKA. NEAR TO ABOVE NORMAL PRECIPITATION IS
FAVORED ACROSS THE SOUTHERN MAINLAND AND SOUTHEAST, AND THIS IS NOT ANTICIPATED
TO ADVERSELY AFFECT THE UPCOMING RIVER BREAK-UP SEASON.
FORECASTER: NICK NOVELLA
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