069
FXUS21 KWNC 301820
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 30 2024
SYNOPSIS: COLD SURFACE HIGH PRESSURE SLIDING SOUTHWARD OUT OF CANADA IS
FORECAST TO INTERACT WITH A MID-LEVEL LOW DEVELOPING IN THE SOUTHWEST, CREATING
THE POTENTIAL FOR SIGNIFICANT SNOWFALL OVER PARTS OF THE CENTRAL AND SOUTHERN
ROCKIES AND THE ADJACENT HIGH PLAINS. THE GRADIENT BETWEEN HIGH SURFACE
PRESSURES OVER THE CENTRAL AND NORTHERN ROCKIES AND LOWER PRESSURES IN THE
ADJACENT HIGH PLAINS COULD PRODUCE STRONG DOWNSLOPING WINDS NEAR THE CENTRAL
AND SOUTHERN FRONT RANGE OF THE ROCKIES. MEANWHILE, A POTENT STORM SYSTEM
POTENTIALLY MERGING WITH A TROPICAL CYCLONE MAY BRING HEAVY PRECIPITATION AND
HIGH WINDS TO THE SOUTHERN TIER OF ALASKA, WITH WINDY CONDITIONS POSSIBLY
EXTENDING WESTWARD ACROSS THE ALEUTIANS.
HAZARDS
SLIGHT RISK OF HIGH WINDS OVER AND NEAR THE FRONT RANGE OF THE NORTHERN AND
CENTRAL ROCKIES THU-SAT, NOV 7-9.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE CENTRAL AND SOUTHERN ROCKIES AND
ADJACENT HIGH PLAINS THU-FRI, NOV 7-8.
SLIGHT RISK OF HEAVY PRECIPITATION IN SOUTH-CENTRAL AND SOUTHEASTERN ALASKA,
THU-FRI, NOV 7-8.
SLIGHT RISK OF HIGH WINDS FOR SOUTHERN ALASKA, INCLUDING SOUTHWESTERN ALASKA
AND THE ALEUTIANS, THU-FRI, NOV 7-8.
DETAILED SUMMARY
FOR SATURDAY NOVEMBER 02 - WEDNESDAY NOVEMBER 06:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY NOVEMBER 07 - WEDNESDAY NOVEMBER 13: AS WEEK-2 BEGINS, A
POSITIVELY-TILTED MID-LEVEL TROUGH SHOULD BE DRAPED FROM THE NORTH-CENTRAL
CONTIGUOUS UNITED STATES (CONUS) INTO THE SOUTHERN ROCKIES WITH MID-LEVEL
RIDGING FARTHER EAST OVER THE EASTERN CONUS. EARLY IN WEEK-2, THE TROUGH IS
EXPECTED TO BE LIFTING EASTWARD AND DE-AMPLIFYING. MEANWHILE, A SECOND PIECE OF
VORTICITY IS EXPECTED TO DROP SOUTHWARD INTO THE SOUTHWESTERN CONUS WHICH
ESTABLISHES A MID-LEVEL LOW OVER THE SOUTHWEST, ALTHOUGH MOST TOOLS SHOW A
WEAKER FEATURE THAN YESTERDAY. RESULTS FROM MOST TOOLS DOWNPLAY THE CHANCES FOR
HEAVY PRECIPITATION OVER THE CENTRAL AND EASTERN CONUS RELATIVE TO YESTERDAY.
ONLY THE OPERATIONAL VERSIONS OF THE GFS AND THE CANADIAN AND THE EUROPEAN
PROBABILISTIC EXTREMES TOOL (PET) SHOW POTENTIAL FOR HEAVY PRECIPITATION TODAY,
AND IT IS LIMITED TO PORTIONS OF THE SOUTHERN PLAINS. GIVEN THE AGREEMENT
BETWEEN MOST OF THE TOOLS AND THE CONTINUING TREND TOWARD LOWER PRECIPITATION
TOTALS EARLY WEEK-2, THE SLIGHT CHANCE FOR HEAVY PRECIPITATION IN THE CENTRAL
AND EAST-CENTRAL CONUS IS REMOVED.
A HIGH SURFACE PRESSURE SYSTEM IS EXPECTED TO SLIDE SOUTHWARD OUT OF CANADA AND
SLOWLY DRIFT SOUTHWARD THROUGH THE ROCKIES DURING THE FIRST FEW DAYS OF WEEK-2.
MEANWHILE, A SURFACE TROUGH OF LOWER PRESSURE IS FORECAST FARTHER EAST. THE
GRADIENT BETWEEN THESE TWO FEATURES CREATES A SLIGHT RISK FOR HIGH WINDS OVER
CENTRAL AND NORTHERN PORTIONS OF THE EASTERN ROCKIES AND ADJACENT PLAINS, WHICH
COULD BE AMPLIFIED BY THE POTENTIAL FOR DOWNSLOPING SURFACE FLOW. THE
OPERATIONAL GFS AND CANADIAN MODELS ARE MOST BULLISH WITH THIS SET-UP, AND THE
PETS BASED ON THE CANADIAN AND EUROPEAN ENSEMBLES ALSO SHOW SOME SUPPORT, WITH
ODDS FOR WINDS ABOVE THE 85TH PERCENTILE REACHING 30 PERCENT IN THIS AREA. AS
THE HIGH PRESSURE SYSTEM CONTINUES TO SLIDE SOUTHWARD IN THE ROCKIES, AND
MID-LEVEL RIDGE IS EXPECTED TO DRIFT INTO THE CENTRAL CONUS, INCREASING SURFACE
PRESSURES AND REDUCING THE HIGH WIND THREAT BY THE MIDDLE OF WEEK-2.
A MID-LEVEL VORTICITY MAXIMUM IS EXPECTED OVER THE SOUTHWEST AT THE BEGINNING
OF WEEK-2 AND FORECAST TO SLOWLY PUSH EASTWARD WHILE WEAKENING, AND INTERACTION
WITH THE COLD HIGH PRESSURE SYSTEM SLIDING SOUTHWARD OUT OF CANADA CREATES THE
POTENTIAL FOR HEAVY SNOWFALL IN THE CENTRAL AND SOUTHERN ROCKIES. THE
OPERATIONAL GFS CONTINUES TO SHOW A FAIRLY STRONG MID-LEVEL VORTICITY MAXIMUM,
BUT MOST OTHER MODELS ARE WEAKER WITH THIS SYSTEM THAN YESTERDAY. AS A RESULT,
THERE IS LESS ROBUST SUPPORT FOR HEAVY SNOWFALL IN THE CENTRAL AND SOUTHERN
ROCKIES AND ADJACENT PLAINS, AND LESS CONSISTENCY REGARDING THE LOCATION AND
TIMING OF ANY SNOWFALL. STILL, ENOUGH TOOLS AT LEAST IMPLY THE POSSIBILITY OF
HEAVY SNOW TO JUSTIFY KEEPING THE SLIGHT RISK FOR HEAVY SNOW IN PLACE,
CONTINUING THROUGH DAY 9 (NOV 8). THE AREA HIGHLIGHTED IS A BIT SMALLER THAN
YESTERDAY BECAUSE GUIDANCE SHOWS LITTLE OR NO SUPPORT FOR HEAVY SNOWFALL IN
ARIZONA AS WELL AS THE EASTERN, NORTHERN, AND WESTERN FRINGES RELATIVE TO
YESTERDAY’S OUTLOOK. TODAY’S OPERATIONAL AND ENSEMBLE MEAN MODEL OUTPUT
SNOWFALL TOTALS ARE LESS CONSISTENT THAN YESTERDAY, ESPECIALLY WITH RESPECT TO
TIMING, BUT THE GENERAL CONSENSUS IS FOR LESS SNOWFALL THAN YESTERDAY, WITH
REDUCED ODDS FOR TOTALS APPROACHING ONE FOOT.
STRONG MID-LEVEL LOW PRESSURE AND AN ASSOCIATED SURFACE STORM SYSTEM ARE
EXPECTED OVER OR NEAR THE ALEUTIANS AT THE START OF WEEK-2. THIS SYSTEM COULD
BE ENHANCED AS THE MID-LEVEL LOW MERGES WITH THE REMNANTS OF TYPHOON KONG-REY
FOLLOWING EXTRATROPICAL TRANSITION. THE MODELS SHOW A WEAKER STORM SYSTEM THAN
YESTERDAY, WITH THE DEEPEST MODELS INDICATING A SURFACE PRESSURE IN THE LOW
970S, ABOUT 20 HPA HIGHER THAN YESTERDAY’S OPERATIONAL GFS. THE OPERATIONAL
EUROPEAN AND CANADIAN MODELS ARE ALSO A BIT WEAKER THAN YESTERDAY. PREDICTABLY,
THE TOOLS OVERALL SHOW LOWER ODDS FOR HIGH WINDS AND HEAVY PRECIPITATION, AND
OPERATIONAL AND ENSEMBLE MEAN PRECIPITATION OUTPUT IS LOWER THAN YESTERDAY.
STILL, THE PETS FROM THE GEFS, EUROPEAN ENSEMBLE, AND CANADIAN ENSEMBLE ALL
SHOW ODDS EXCEEDING 30 PERCENT FOR BOTH HIGH WINDS AND HEAVY RAIN DURING THE
FIRST FEW DAYS OF WEEK-2, SO BOTH THREATS ARE UNCHANGED FROM YESTERDAY.
VERY DRY CONDITIONS HAVE PREVAILED ACROSS THE SOUTHEASTERN CONUS, THE
MID-ATLANTIC REGION, AND PORTIONS OF THE NORTHEAST FOR THE PAST FEW WEEKS. IN
PHILADELPHIA, PA, OCTOBER 30 IS THE 32ND CONSECUTIVE DAY WITHOUT MEASURABLE
PRECIPITATION, BESTING THE PRIOR RECORD OF 29 DAYS ESTABLISHED IN 1874. WITH
ONE DAY LEFT IN THE MONTH, OCTOBER HAS BROUGHT NO MEASURABLE PRECIPITATION TO
TRENTON NJ, WASHINGTON DC, AND ATLANTA GA AMONG OTHER LOCATIONS, AND MOST
LOCATIONS ALONG THE EASTERN SEABOARD FROM GEORGIA THROUGH NEW JERSEY HAVE
RECORDED ONLY A FEW HUNDREDTHS OF AN INCH SINCE OCTOBER 2. SIGNS OF SURFACE
MOISTURE STRESS HAVE BEEN INCREASING, AS REFLECTED IN THE U.S. DROUGHT MONITOR,
BUT RAPID-ONSET DROUGHT IS NOT ANTICIPATED DUE TO AUTUMNAL TEMPERATURES AND
LOWER MOISTURE DEMAND COMPARED TO SUMMER.
FORECASTER: RICH TINKER
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