181
FXUS21 KWNC 111930
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 11 2023
SYNOPSIS: ANY IMPACTS FROM HURRICANE LEE SHOULD HAVE ENDED BY THE START OF
WEEK-2, AND RELATIVELY UNEVENTFUL WEATHER IS ANTICIPATED THE OUTLOOK PERIOD. A
WEAK MID-LEVEL RIDGE FAVORED SHOULD KEEP TEMPERATURES ABOVE NORMAL ACROSS THE
PLAINS AND MUCH OF THE NORTHERN TIER OF THE COUNTRY, HOWEVER EXCESSIVE HEAT
CONDITIONS ARE NOT ANTICIPATED. BELOW-NORMAL PRECIPITATION (IF ANY) IS
ANTICIPATED EAST OF THE RIDGE AXIS, AND ALTHOUGH HEAT MAY NOT BE EXCESSIVE, IT
SHOULD BE HOT ENOUGH TO KEEP PART OF THE SOUTHEAST AT RISK FOR RAPID-ONSET
DROUGHT. MODERATE TO HEAVY PRECIPITATION IS POSSIBLE IN THE PLAINS DOWNSTREAM
FROM THE WESTERN CONUS TROUGH, BUT EXTREME AMOUNTS LOOK UNLIKELY. PERSISTENT
SOUTHERLY FLOW FROM THE NORTH PACIFIC IS EXPECTED TO BRING WET AND BREEZY
CONDITIONS TO SOUTH-CENTRAL AND SOUTHEASTERN ALASKA, BUT AS IS THE CASE ACROSS
THE CONUS, CONDITIONS ARE NOT EXPECTED TO REACH HAZARDS THRESHOLDS.
HAZARDS
RAPID ONSET DROUGHT RISK FOR PARTS OF THE LOWER MISSISSIPPI VALLEY AND
SOUTHEAST.
DETAILED SUMMARY
FOR THURSDAY SEPTEMBER 14 - MONDAY SEPTEMBER 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY SEPTEMBER 19 - MONDAY SEPTEMBER 25: MODELS ARE IN GOOD AGREEMENT
FOR WEEK-2, SHOWING CIRCULATION FEATURES THAT MAY BRING ANOMALOUS TEMPERATURES
OR PRECIPITATION TO PARTS OF THE NATION, BUT APPEAR TO BE TOO WEAK TO DRIVE THE
EXTREME WEATHER THAT HAS PREVAILED FOR MUCH OF THE SUMMER - ESPECIALLY THE
HEAT. THE PERIOD STARTS WITH A MID-LEVEL RIDGE AXIS IN CENTRAL NORTH AMERICA
REACHING SOUTHWARD FROM A POSITIVE 500-HPA ANOMALY CENTER NEAR HUDSON BAY.
MEANWHILE, WEAK MID-LEVEL TROUGHS EXTEND ALONG OR NEAR BOTH THE EAST AND WEST
COASTS OF THE CONTINENT. DURING WEEK-2, THE POSITIVE MID-LEVEL HEIGHT ANOMALY
CENTER NEAR HUDSON BAY IS FORECAST TO WEAKEN SLIGHTLY AND DRIFT EASTWARD,
KEEPING THE MID-LEVEL FEATURES OVER THE CONUS QUASI-STATIONARY AND REDUCING THE
AMPLITUDE OF WHAT IS ALREADY A FAIRLY FLAT, MERIDIONAL FLOW REGIME. BY THE END
OF THE PERIOD, THE EUROPEAN ENSEMBLE MEAN IS SLIGHTLY MORE AMPLIFIED WITH THE
WEST-CONUS TROUGH THAN THE GEFS AND CANADIAN ENSEMBLE MEANS, BUT THE OPPOSITE
IS TRUE OVER THE EAST CONUS, WHERE THE EUROPEAN ENSEMBLE MEAN ALMOST COMPLETELY
WASHES OUT THE TROUGH WHILE THE GEFS AND CANADIAN ENSEMBLE MEANS SHOW A BETTER
REFLECTION REMAINING IN PLACE. THE BOTTOM LINE, HOWEVER, IS THAT ALL OF THESE
FEATURES ARE RELATIVELY WEAK, AND IN THOSE AREAS WITH ENHANCED CHANCES FOR
ANOMALOUS WEATHER, CONDITIONS ARE NOT EXPECTED TO BE EXTREME ENOUGH TO WARRANT
POSTING ANY HAZARDS. THE ONLY EXCEPTION IS IN THE INTERIOR SOUTHEAST, WHERE
ABNORMALLY WARM AND DRY CONDITIONS WILL OCCUR WHERE THERE IS ANTECEDENT
DRYNESS, INCREASING THE ODDS FOR RAPID ONSET DROUGHT.
THE MID-LEVEL RIDGE AXIS IN THE CENTRAL CONUS FAVORS ABOVE-NORMAL TEMPERATURES
ACROSS MUCH OF THE NORTHERN TIER OF THE CONUS, THE GREAT PLAINS, THE LOWER
MISSISSIPPI VALLEY, AND SOME ADJACENT AREAS. THIS WILL MAINTAIN ABOVE-NORMAL
TEMPERATURES ACROSS THESE REGIONS, AND DAILY HIGH TEMPERATURES IN THE 90’S ARE
POSSIBLE ACROSS THE PLAINS TO NEAR THE CANADIAN BORDER EARLY WEEK-2, AND ACROSS
THE SOUTH-CENTRAL CONUS THROUGHOUT THE PERIOD. THIS COULD ACCELERATE DEVELOPING
DRYNESS IN PART OF THE SOUTHEAST, BUT TEMPERATURES SHOULD BE LOWER THAN DURING
THE PERIODS OF DANGEROUS AND RELENTLESS EXCESSIVE HEAT OBSERVED FOR MUCH OF THE
SUMMER. THIS PRECLUDES POSTING ANY EXCESSIVE HEAT THREATS, BUT CONDITIONS COULD
FORCE RAPID SURFACE MOISTURE LOSS THAT INCREASES THE CHANCES FOR RAPID-ONSET
DROUGHT JUST EAST OF THE CURRENT AREAS OF EXTREME TO EXCESSIVE DROUGHT
EXTENDING FROM CENTRAL TEXAS EASTWARD THROUGH SOUTHERN MISSISSIPPI.
THE MID-LEVEL TROUGHS ALONG OR NEAR BOTH THE EASTERN AND WESTERN CONUS COASTS
SHOULD KEEP TEMPERATURES WITHIN TYPICAL RANGES FOR THIS TIME OF YEAR. IN
CYCLONICALLY-CURVED MID-LEVEL FLOW EAST OF THE WEAK WESTERN CONUS TROUGH, HEAVY
PRECIPITATION IS POSSIBLE IN PARTS OF THE SOUTH-CENTRAL AND SOUTHWESTERN
PLAINS. MUCH OF THIS REGION IS CURRENTLY ENTRENCHED IN SOME DEGREE OF DROUGHT,
AND SINCE PRECIPITATION RATES ARE NOT EXPECTED TO BE EXCESSIVE, INCREASED
RAINFALL IN THE REGION MAY DO MORE GOOD THAN HARM.
FARTHER NORTH, AS WEEK-2 GETS UNDERWAY, GUIDANCE GENERALLY AGREES THAT A
MID-LEVEL TROUGH WITH ANOMALOUSLY LOW 500-HPA HEIGHTS WILL BE ESTABLISHED OVER
OR NEAR THE BERING STRAIT, JUST NORTH OF A FLAT MID-LEVEL RIDGE WITH
ANOMALOUSLY HIGH 500-HPA HEIGHTS IN THE CENTRAL NORTH PACIFIC OCEAN. THESE
FEATURES WILL FUEL AN ANOMALOUSLY STRONG MID-LEVEL JET OVER THE NORTHERN NORTH
PACIFIC THAT BECOMES CYCLONICALLY CURVED AND DIFFLUENT FARTHER EAST OVER
SOUTH-CENTRAL AND SOUTHEASTERN ALASKA. THIS WILL ENHANCE THE IMPACT OF A
PERSISTENT SURFACE FLOW OF MOIST PACIFIC AIR INTO THE STATE, TRIGGERING
ABOVE-NORMAL PRECIPITATION AND STRONG MARITIME WINDS NEAR THE COAST. A FEW
INCHES OF PRECIPITATION MAY FALL DURING THE 7-DAY PERIOD, BUT AS IN AREAS
FARTHER SOUTH, THE RELATIVELY LOW STRENGTH OF THE MID-LEVEL AND SURFACE
FEATURES DO NOT WARRANT POSTING ANY HAZARDS IN ALASKA AT THIS TIME.
FORECASTER: RICH TINKER
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page