854
FXUS21 KWNC 041803
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 04 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). WHILE A HEAVY PRECIPITATION THREAT IS FAVORED TO
DIMINISH BY THE START OF WEEK-2, STRENGTHENING PRESSURE GRADIENTS IN THE WAKE
OF THE SYSTEM SUSTAINS THE RISK OF HIGH WINDS FOR MUCH OF THE NORTHEASTERN
CONUS. THE RETURN OF ENHANCED ONSHORE FLOW IS POSSIBLE OVER PARTS OF THE
WESTERN CONUS TIED TO AN AREA OF DEVELOPING MID-LEVEL LOW PRESSURE OVER THE
EASTERN PACIFIC BY MID-APRIL, HOWEVER, SUBSTANTIAL MODEL DISAGREEMENT PRECLUDES
ANY CORRESPONDING HAZARDS IN THE OUTLOOK.
HAZARDS
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE CENTRAL APPALACHIANS,
MID-ATLANTIC, OHIO VALLEY, GREAT LAKES, AND NORTHEAST, FRI-SAT, APR 12-13.
DETAILED SUMMARY
FOR SUNDAY APRIL 07 - THURSDAY APRIL 11:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY APRIL 12 - THURSDAY APRIL 18: LATE NEXT WEEK, DYNAMICAL MODELS
CONTINUE TO FEATURE SHORTWAVE 500-HPA TROUGHING LIFTING OUT OVER THE
NORTHEASTERN CONUS, WITH ANOMALOUSLY POSITIVE MID-LEVEL HEIGHTS OVERSPREADING
MUCH OF THE CENTRAL AND WESTERN CONUS UPSTREAM INTO THE WEEKEND. LATER IN
WEEK-2, A KEY DIFFERENCE BETWEEN THE ENSEMBLE GUIDANCE CONCERNS THE EVOLUTION
OF THE ANOMALOUS RIDGING FAVORED UPSTREAM. THE 0Z ECMWF FAVORS A STRONGER RIDGE
EXTENDING INTO THE NORTHEASTERN PACIFIC, WHEREAS THE 0Z GEFS IS MORE ZONALLY
NARROW WITH THIS MID-LEVEL MEAN FEATURE, WHILE ALSO FAVORING MORE TROUGHING
OVER THE EASTERN PACIFIC. THESE DIFFERENCES OVER WESTERN NORTH AMERICA
SIGNIFICANTLY REDUCE OUTLOOK CERTAINTY, AND ABSENT ANY SUBSTANTIAL TROUGHING OR
CYCLONIC FEATURES IN THE MEAN 500-HPA HEIGHT OR SURFACE FIELDS, THERE APPEARS
TO BE LITTLE IN THE WAY OF HAZARD POTENTIAL, WITH UNSEASONABLY WARM AND DRIER
THAN NORMAL CONDITIONS FOR MUCH OF THE CONUS DURING THE OUTLOOK PERIOD.
TIED TO THE AFOREMENTIONED TROUGHING OVER THE NORTHEASTERN CONUS, THERE IS FAIR
AGREEMENT BETWEEN THE GEFS AND ECMWF ENSEMBLES DEPICTING THE MEAN SURFACE LOW
POSITIONED OVER EASTERN CANADA BY THE OUTSET OF WEEK-2. THE UNCALIBRATED GEFS
AND ECMWF GENERALLY SHOW THE HIGHEST MEAN PRECIPITATION AMOUNTS OFFSHORE, AND
GIVEN THE OVERALL WEAKER PRESENTATION OF HEAVY PRECIPITATION SIGNALS IN THE
PROBABILISTIC EXTREME TOOLS (PETS), A SLIGHT RISK OF HEAVY PRECIPITATION IS
REMOVED IN THE UPDATED OUTLOOK. HOWEVER, A SLIGHT RISK OF HIGH WINDS REMAINS
ISSUED (APR 12-13), AND STILL INCLUDES PARTS OF THE GREAT LAKES AND EASTERN
SEABOARD WHERE GUIDANCE CONTINUES TO FAVOR POTENTIALLY STRONG PRESSURE
GRADIENTS WITH SUPPORT FROM THE ECMWF PET DEPICTING 20-30% FOR WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE.
IN THE NEAR-TERM, A FAIRLY POTENT LOW PRESSURE SYSTEM IS TRACKING OVER THE
NORTHEAST AND IS LIKELY TO BRING MIXED PRECIPITATION AND HEAVY SNOWFALL
ACCUMULATIONS (LOCALLY UPWARDS OF 1 FOOT) OVER NEW ENGLAND WITHIN THE NEXT DAY
OR SO. IN THE WAKE OF THIS SYSTEM, BUILDING MID-LEVEL HEIGHTS AND SOUTHERLY
FLOW ARE FAVORED, WHERE THE RETURN OF UNSEASONABLY WARMER THAN NORMAL
TEMPERATURES AND INCREASED PRECIPITATION AMOUNTS DURING WEEK-1 MAY ACCELERATE
SNOWMELT. THE INCREASED RUNOFF MAY BRING FLOODING ALONG SMALL STREAMS,
PARTICULARLY FOR AREAS WHERE THE HIGHEST SNOWFALL IS RECEIVED. NO ASSOCIATED
HAZARDS ARE POSTED AT THIS TIME, BUT THIS FLOODING POTENTIAL WILL BE MONITORED
IN UPCOMING OUTLOOKS.
AS ANOMALOUS MID-LEVEL RIDGING IS FAVORED TO OVERSPREAD THE CENTRAL AND EASTERN
CONUS THROUGH THE MIDDLE OF WEEK-2, THE GEFS FAVORS MID-LEVEL TROUGHING
SHIFTING EASTWARD FROM THE EASTERN PACIFIC, WITH INCREASED ONSHORE FLOW OVER
THE WEST COAST. THE PATTERN EVOLUTION IS AT ODDS WITH ECMWF, WHICH MAINTAINS
FAIRLY AMPLIFIED RIDGING AND A COMPARABLY DRIER PATTERN ACROSS MUCH OF WESTERN
NORTH AMERICA BY MID-APRIL. EVEN WITH INCREASED PRECIPITATION SIGNALS EVIDENT
IN THE RAW AND CALIBRATED GEFS PET, THESE AMOUNTS ARE NOT EXPECTED TO REACH
HAZARD THRESHOLDS, AND NO PRECIPITATION RELATED HAZARDS ARE ISSUED.
NO HAZARDS ARE ISSUED OVER ALASKA. NEAR TO BELOW NORMAL TEMPERATURES AND 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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