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FXUS21 KWNC 211907
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 21 2026
SYNOPSIS: TODAY'S MODEL ENSEMBLES PREDICT A MID-LEVEL LOW PRESSURE NEAR THE
WEST COAST AND A HIGHLY ANOMALOUS MID-LEVEL HIGH PRESSURE OVER THE WESTERN GULF
OF ALASKA DURING WEEK-2. IN ADDITION, A WEAK HIGH PRESSURE IS FORECAST TO
FLATTEN AND MOVE ACROSS THE GREAT LAKES AND NORTHEAST, BEFORE REAMPLIFYING
TOWARDS THE END OF THE PERIOD NEAR NOVA SCOTIA. HEAVY PRECIPITATION IS FAVORED
ACROSS MUCH OF THE WEST COAST AND LOWER FOUR CORNERS REGION IN ASSOCIATION WITH
THE WESTERN TROUGH, AND POSSIBLY AN INFLUX OF MOISTURE FROM THE EASTERN
TROPICAL PACIFIC. ENHANCED ONSHORE FLOW ACCOMPANYING THE WESTERN MID-LEVEL LOW
ALSO PROMOTES A SLIGHT RISK OF HEAVY SNOW FOR THE KLAMATH AND SIERRA NEVADA
MOUNTAIN RANGES IN CALIFORNIA, AND PORTIONS OF THE ROCKIES. SURFACE HIGH
PRESSURE APPROACHING THE NORTHEAST OR UPPER MID-ATLANTIC COAST EARLY IN THE
PERIOD AND LOW PRESSURE OFF THE CAROLINA COAST ARE FORECAST TO RESULT IN A
STRENGTHENED PRESSURE GRADIENT AND AN INCREASED RISK OF HIGH WINDS FOR THE
SOUTHEAST COASTAL PLAIN. AS THE SURFACE HIGH MOVES OUT OVER THE WESTERN
ATLANTIC DURING MID-PERIOD, SOUTHERLY RETURN FLOW IS ANTICIPATED TO BRING A
SLIGHT RISK OF HEAVY PRECIPITATION FOR EASTERN PORTIONS OF THE SOUTHERN PLAINS,
THE MIDDLE AND LOWER MISSISSIPPI VALLEY, AND WESTERN SECTIONS OF KENTUCKY AND
OHIO. A STORMY PERIOD IS FORECAST FOR WESTERN ALASKA, AS A SERIES OF STRONG
CYCLONIC SYSTEMS APPROACH THE STATE FROM THE BERING SEA AND THE BIGGEST IMPACT
OF CONCERN WOULD BE HIGH WINDS ACROSS WESTERN PORTIONS OF THE STATE.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF ARIZONA, SAT-MON, OCT
31-NOV 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF OREGON AND CALIFORNIA,
SAT-WED, OCT 31-NOV 4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE SOUTHERN CALIFORNIA COAST, SAT-MON,
OCT 31-NOV 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE LOWER FOUR CORNERS REGION, SAT-MON,
OCT 31-NOV 2.
SLIGHT RISK OF HEAVY PRECIPITATION FROM EASTERN PORTIONS OF THE SOUTHERN PLAINS
AND THE LOWER MISSISSIPPI VALLEY NORTHEASTWARD INTO THE LOWER OHIO VALLEY,
SAT-WED, OCT 31-NOV 4.
SLIGHT RISK OF HEAVY SNOW FOR THE KLAMATH AND SIERRA NEVADA MOUNTAIN RANGES,
SAT-WED, OCT 31-NOV 4.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE ROCKIES, SAT-WED, OCT 31-NOV 4.
SLIGHT RISK OF HIGH WINDS FOR THE SOUTHEAST COASTAL PLAIN AND MOST OF FLORIDA,
THU-SAT, OCT 29-31.
MODERATE RISK OF HIGH WINDS FOR PORTIONS OF SOUTHWESTERN MAINLAND ALASKA AND
THE ALASKA PENINSULA, FRI-SAT, OCT 30-31.
SLIGHT RISK OF HIGH WINDS FOR SOUTHWESTERN MAINLAND ALASKA, THE ALASKA
PENINSULA, KODIAK ISLAND, AND THE ALEUTIANS, FRI-SAT, OCT 30-31.
DETAILED SUMMARY
FOR SATURDAY OCTOBER 24 - WEDNESDAY OCTOBER 28:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY OCTOBER 29 - WEDNESDAY NOVEMBER 04: A MID-LEVEL TROUGH NEAR THE
WEST COAST IS FORECAST TO BRING ENHANCED ONSHORE FLOW TO MUCH OF WESTERN OREGON
AND CALIFORNIA DURING WEEK-2. UNCALIBRATED ECENS GUIDANCE SHOWS THE BULK OF THE
PRECIPITATION OCCURRING DURING THE MIDDLE AND LATTER PORTIONS OF THE PERIOD,
WITH A SOUTHWARD EXTENSION ACROSS THE SOUTHERN CALIFORNIA COAST DURING
MID-PERIOD. A 20-30% CHANCE OF HEAVY PRECIPITATION IS GENERALLY FAVORED ACROSS
THIS PART OF THE CONUS, WITH A 30-40% CHANCE ALONG THE CALIFORNIA COAST, AND
THE KLAMATH AND SIERRA NEVADA MOUNTAIN RANGES. THE UNCALIBRATED GEFS IS
SLIGHTLY WEAKER COMPARED TO THE ECENS. THERE IS SUPPORT FROM THE GEFS AND ECENS
PROBABILISTIC EXTREMES TOOLS (PET), WHICH FAVOR AT LEAST A 20-30% CHANCE OF
3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1-INCH. A SLIGHT
RISK FOR PERIODS OF HEAVY PRECIPITATION IS THEREFORE POSTED FOR PARTS OF
WESTERN OREGON AND NORTHERN AND CENTRAL CALIFORNIA FROM OCT 31-NOV 4, AS WELL
AS A SLIGHT RISK OF HEAVY SNOW FOR THE KLAMATH AND SIERRA NEVADA MOUNTAIN
RANGES IN CALIFORNIA. UNCALIBRATED ECENS GUIDANCE SHOWS AMOUNTS ON THE ORDER OF
4-6 INCHES OF SNOW OR GREATER IN THE HIGHLIGHTED RISK AREA. THE SLIGHT RISK OF
HEAVY PRECIPITATION EXTENDS SOUTHWARD ACROSS THE SOUTHERN CALIFORNIA COAST FROM
OCT 31-NOV 2.
OVER THE LOWER FOUR CORNERS REGION, A SLIGHT RISK OF HEAVY PRECIPITATION IS
POSTED FROM OCT 31 - NOV 2. THIS IS ASSOCIATED WITH A COMBINATION OF SHORTWAVE
ENERGY ACCOMPANYING THE MEAN TROUGH, AND ALSO POSSIBLE TROPICAL MOISTURE FROM
THE EASTERN PACIFIC WHICH HAS BEEN VERY ACTIVE THIS SEASON. PRECIPITATION
AMOUNTS OF 0.50-0.75 INCHES ARE PREDICTED BY THE UNCALIBRATED GEFS AND ECENS
PRECIPITATION TOOLS OVER THIS REGION, WITH THE ECENS SOLUTION REMAINING A BIT
MORE ROBUST THAN THE GEFS. AN EMBEDDED MODERATE RISK (40-60% CHANCE) OF HEAVY
PRECIPITATION IS DEPICTED OVER PORTIONS OF PRIMARILY THE HIGHER TERRAIN OF
ARIZONA FOR THE SAME PERIOD. THE POTENTIAL FOR FLASH FLOODING CONTINUES TO BE
MONITORED ACROSS ARIZONA, AND IF WARRANTED A FLOOD SHAPE MAY BE INTRODUCED
TOMORROW. RAW SNOW TOTALS FROM THE UNCALIBRATED ENSEMBLE MEANS RANGE FROM 4-6
INCHES, WITH LOCALLY GREATER AMOUNTS POSSIBLE OVER PORTIONS OF THE ROCKIES. A
SLIGHT RISK OF HEAVY SNOW THEREFORE INCLUDES WESTERN WYOMING AND WESTERN
COLORADO, FROM OCT 31-NOV 4.
ALONG THE EAST COAST, A SURFACE RIDGE AXIS OF HIGH PRESSURE IS PREDICTED TO
EXTEND FROM ABOUT THE NEW ENGLAND COAST TO THE SOUTHERN APPALACHIANS DURING THE
FIRST FEW DAYS OF WEEK-2. A SLIGHT RISK OF HIGH WINDS (20-25 MPH) IS FORECAST
FROM OCT 29-31. HOWEVER, ACCORDING TO THE 6Z DETERMINISTIC GFS RUN, THE MOST
LIKELY DAY APPEARS TO BE OCTOBER 31ST. THIS IS DUE TO A STRENGTHENING HIGH
PRESSURE SYSTEM MOVING ACROSS ONTARIO AND QUEBEC, FUNNELING COOLER AIR
SOUTHWARD ACROSS THE ATLANTIC COASTAL PLAIN AND TIGHTENING THE PRESSURE
GRADIENT.
DURING THE MIDDLE AND LATTER PORTIONS OF WEEK-2, SURFACE HIGH PRESSURE MOVING
OFF THE NORTHEAST OR UPPER MID-ATLANTIC COAST SUPPORTS AN INCREASE IN MOIST,
SOUTHERLY FLOW FROM THE WESTERN GULF NORTHWARD ACROSS EASTERN PORTIONS OF THE
SOUTHERN PLAINS, THE LOWER AND MIDDLE MISSISSIPPI VALLEY, AND WESTERN PARTS OF
KENTUCKY AND TENNESSEE. ACCORDINGLY, A SLIGHT RISK OF HEAVY PRECIPITATION IS
DELINEATED FOR THIS REGION FROM OCT 31-NOV 4. THE ECENS AND GEFS PETS ARE
SUPPORTIVE OF THIS WET SIGNAL, AS ARE THE UNCALIBRATED TOOLS, WITH A 20-40
PERCENT CHANCE OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE AND TOTALS OF ABOUT AN INCH. THE SPATIAL EXTENT OF THE SLIGHT RISK
AREA REPRESENTS A SPLITTING OF THE DIFFERENCE BETWEEN THE CALIBRATED AND
UNCALIBRATED PRECIPITATION TOOLS; THE CALIBRATED TOOLS CONCENTRATES THE HEAVY
RAIN RISK OVER THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY, WITH THE
UNCALIBRATED TOOLS EXPANDING THE SLIGHT RISK AREA WELL INTO THE OHIO VALLEY.
IN ALASKA, THE STRONG MID-LEVEL RIDGE PREDICTED OVER THE WESTERN GULF OF ALASKA
IS FORECAST TO EXTEND NORTHWARD ACROSS MUCH OF ALASKA FOR AT LEAST THE FIRST
HALF OF WEEK-2. SEVERAL DEEP LOW PRESSURE AREAS FROM THE VICINITY OF THE
KAMCHATKA PENINSULA ARE FORECAST TO MOVE EASTWARD ACROSS THE BERING SEA AND
WESTERN ALASKA. THESE CYCLONIC SYSTEMS ARE PREDICTED TO BRING HIGH WINDS (AT
LEAST 40 MPH WINDS AND GREATER THAN THE 85TH CLIMATOLOGICAL PERCENTILE) TO THE
SOUTHWESTERN COAST OF ALASKA. THE 0Z DETERMINISTIC EUROPEAN MODEL FORECASTS 10
METER WIND SPEED GUSTS OVER BRISTOL BAY IN EXCESS OF 60 MPH, THOUGH THIS IS ONE
SINGLE MODEL RUN. A SLIGHT RISK OF HIGH WINDS IS DEPICTED OVER PORTIONS OF THE
SOUTHWESTERN MAINLAND, THE ALASKA PENINSULA, KODIAK ISLAND, AND THE ALEUTIANS
FROM OCT 30-31. A MODERATE RISK OF HIGH WINDS IS DEPICTED WITHIN A SMALLER
PORTION OF THIS REGION, NAMELY THE SOUTHWESTERN COASTAL AREAS AND THE ALASKA
PENINSULA, ALSO FROM OCT 30-31.
FORECASTER: ANTHONY ARTUSA
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