684
FXUS21 KWNC 091942
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 09 2023
SYNOPSIS: AREAS OF MID-LEVEL LOW PRESSURE ARE FORECAST ACROSS ALASKA AND OVER
THE SOUTHWESTERN CONTIGUOUS U.S. AT THE OUTSET OF WEEK-2, WITH THESE FEATURES
SERVING AS THE BASIS FOR THE HAZARDS OUTLOOK EARLY IN THE PERIOD. WHILE ONSHORE
FLOW IS FORECAST TO DIMINISH ACROSS THE CALIFORNIA COAST, HEAVY SNOW REMAINS
POSSIBLE ACROSS PORTIONS OF THE ROCKIES. AS THE MID-LEVEL LOW MOVES FURTHER
EASTWARD, HIGH WINDS MAY SPREAD ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, ALONG WITH POSSIBLE SURFACE LOW PRESSURE DEVELOPMENT. STRONG ONSHORE
FLOW IS FORECAST ACROSS SOUTHEAST ALASKA, AND POSSIBLY EXTENDING SOUTHWARD INTO
THE NORTHWESTERN CONUS. THIS MAY LEAD TO EPISODES OF HIGH WINDS AND HEAVY
PRECIPITATION ACROSS BOTH OF THESE AREAS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE PACIFIC NORTHWEST,
FRI-SUN, NOV 17-19.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE PACIFIC NORTHWEST, FRI-SUN, NOV
17-19.
SLIGHT RISK OF HEAVY SNOW FOR NORTHERN PORTIONS OF THE CASCADES, FRI-SUN, NOV
17-19.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF UTAH AND COLORADO,
FRI-SAT, NOV 17-18.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE INTERIOR WEST AND CENTRAL AND
SOUTHERN PLAINS, FRI-SUN, NOV 17-19.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE EASTERN CENTRAL AND
SOUTHERN PLAINS, MIDDLE AND LOWER MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, AND
THE SOUTHEAST, FRI-SUN, NOV 17-19.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF SOUTHEAST ALASKA, FRI-SUN,
NOV 17-19.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF SOUTHEAST ALASKA, FRI-SUN, NOV 17-19.
DETAILED SUMMARY
FOR SUNDAY NOVEMBER 12 - THURSDAY NOVEMBER 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY NOVEMBER 17 - THURSDAY NOVEMBER 23: THE 0Z GEFS, ECMWF, AND CANADIAN
ENSEMBLES REMAIN IN GOOD AGREEMENT REGARDING 500-HPA TROUGHING SHIFTING FROM
THE EASTERN PACIFIC TO INLAND OVER THE SOUTHWESTERN CONUS EARLY IN WEEK-2. THIS
FAVORS DECREASING CHANCES FOR HEAVY PRECIPITATION, HIGH WINDS, AND HEAVY SNOW
ACROSS CALIFORNIA, ALTHOUGH SOME LINGERING MOISTURE REMAINS POSSIBLE ON DAY-8
WITH THE CANADIAN MODEL BEING THE SLOWEST TO PROGRESS THE TROUGH INLAND. THE
ASSOCIATED HAZARDS OVER CALIFORNIA HAVE BEEN REMOVED FROM TODAY’S WEEK-2
HAZARDS OUTLOOK AS THE GREATEST POTENTIAL HAS NOW SHIFTED INTO THE WEEK-1
TIMEFRAME, AND INTERESTS SHOULD CONSULT WITH THE WEATHER PREDICTION CENTER OR
THEIR LOCAL FORECAST OFFICE FOR THE LATEST UPDATES.
AS THE TROUGH MOVES INLAND, AREAS OF HIGH ELEVATION HEAVY SNOW REMAIN POSSIBLE
ACROSS THE ROCKIES, SPECIFICALLY OVER PARTS OF UTAH AND COLORADO. THE GEFS SNOW
WATER EQUIVALENT (SWE) PROBABILISTIC EXTREMES TOOL (PET) DEPICTS THESE AREAS
HAVING AT LEAST A 20 PERCENT CHANCE SWE EXCEEDS THE 85TH CLIMATOLOGICAL
PERCENTILE AND A HALF-INCH EARLY IN THE PERIOD, SUPPORTING A SLIGHT RISK FOR
HEAVY SNOW REMAINING IN PLACE NOV 17-18. ADDITIONALLY, THE RISK OF HIGH WINDS
IS FORECAST TO REMAIN ELEVATED ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
ROCKIES AND SPREADING INTO THE GREAT PLAINS. WHILE THE SIGNALS IN THE PETS FOR
HIGH WINDS ARE MODEST, THE SYNOPTIC EVOLUTION WITH STRONG MID-LEVEL FLOW AHEAD
OF THE TROUGH SUPPORTS THE SLIGHT RISK OF HIGH WINDS FOR NOV 17-19. THIS TROUGH
MAY ALSO LEAD TO SURFACE LOW PRESSURE DEVELOPMENT IN THE LEE OF THE ROCKIES,
ALTHOUGH THE UNCALIBRATED 0Z ECMWF, GEFS, AND CANADIAN DEPICT RATHER MEAGER
PRECIPITATION AMOUNTS ASSOCIATED WITH THIS FEATURE. THE ECMWF PET IS A BIT MORE
ROBUST, INDICATING AN EXPANSIVE AREA HAVING AT LEAST A 20 PERCENT CHANCE 3-DAY
PRECIPITATION TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH
ACROSS PARTS OF THE EASTERN CENTRAL AND SOUTHERN PLAINS, MIDDLE AND LOWER
MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, AND THE SOUTHEAST WHERE A SLIGHT RISK
FOR HEAVY PRECIPITATION REMAINS POSTED NOV 17-19.
A SEPARATE SYSTEM IS FORECAST TO BRING ENHANCED PRECIPITATION TO PORTIONS OF
THE GULF COAST DURING WEEK-1, AND THE ECMWF AND CANADIAN ENSEMBLES DEPICT SOME
OF THIS MOISTURE MOVING ACROSS FLORIDA AND NEAR THE U.S. EAST COAST AT THE
START OF WEEK-2. SEVERAL GEFS ENSEMBLE MEMBERS ALSO CONTINUE TO DEPICT A
TROPICAL CYCLONE (TC) TRACKING FROM THE CARIBBEAN TOWARD THE BAHAMAS AND
WESTERN ATLANTIC EARLY IN WEEK-2, WITH SOME INDIVIDUAL MEMBERS BRINGING THE
SYSTEM CLOSER TO FLORIDA. THE ECMWF CONTINUES TO FAVOR SLOWER TC DEVELOPMENT
ACROSS THE WESTERN CARIBBEAN. THE NATIONAL HURRICANE CENTER DOES NOT EXPECT TC
DEVELOPMENT IN THE NEXT 7-DAYS PER THE LATEST UPDATE (1PM EST 11/9). THEREFORE,
NO RELATED HAZARDS ARE POSTED ALONG THE EASTERN SEABOARD DUE TO THE HIGH
UNCERTAINTY IN THE OVERALL PATTERN EVOLUTION, BUT MODELS WILL CONTINUE TO BE
MONITORED.
RIDGING AND ASSOCIATED SURFACE HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE
EASTERN PACIFIC IN THE WAKE OF THE DEPARTING TROUGH. AT THE SAME TIME, STRONG
TROUGHING IS PREDICTED ACROSS ALASKA, WITH SURFACE LOW PRESSURE FORECAST ACROSS
THE GULF OF ALASKA AT THE START OF WEEK-2. THIS SET-UP FAVORS A TIGHT PRESSURE
GRADIENT AND SUBSEQUENT ENHANCED ONSHORE FLOW PATTERN ACROSS SOUTHEASTERN
ALASKA AND EXTENDING INTO THE NORTHWESTERN CONUS. SLIGHT RISKS OF HEAVY
PRECIPITATION AND HIGH WINDS ARE POSTED ACROSS SOUTHEAST ALASKA AND THE PACIFIC
NORTHWEST NOV 17-19, WITH A CORRESPONDING SLIGHT RISK FOR HEAVY SNOW ACROSS THE
NORTHERN CASCADES. ACROSS SOUTHEAST ALASKA, THE GEFS AND ECMWF PETS DEPICT AT
LEAST A 20 PERCENT CHANCE 3-DAY PRECIPITATION TOTALS (WIND SPEEDS) EXCEED THE
85TH CLIMATOLOGICAL PERCENTILE AND 2-INCHES (40-MPH) OVER PARTS OF THE REGION.
FURTHER SOUTH ACROSS THE NORTHWEST CONUS, THE SIGNAL IS NOT AS ROBUST IN THE
PETS BASED ON PERCENTILES, ALTHOUGH ELEVATED PROBABILITIES (AT LEAST 20
PERCENT) OF 3-DAY PRECIPITATION TOTALS EXCEEDING 1.5-INCHES ARE DEPICTED.
ADDITIONALLY, THE INTEGRATED VAPOR TRANSPORT TOOL (IVT) BASED ON THE 0Z ECMWF
ENSEMBLE DEPICTS AT LEAST A 40 PERCENT CHANCE IVT VALUES EXCEED 250 KG/M/S
EARLY IN THE PERIOD SUPPORTING THE EXTENSION OF THE HAZARDS INTO THE PACIFIC
NORTHWEST.
FORECASTER: THOMAS COLLOW
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