604
FXUS21 KWNC 291907
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 29 2025
SYNOPSIS: THERE IS AN ELEVATED RISK FOR BELOW-NORMAL TEMPERATURES ACROSS PARTS
OF THE NORTHWESTERN CONTIGUOUS U.S. (CONUS) EARLY IN WEEK-2 UNDERNEATH
MID-LEVEL LOW PRESSURE. WHILE QUANTITATIVE PRECIPITATION AMOUNTS ALONG THE WEST
COAST ARE LOWER COMPARED TO LATE IN WEEK-1, CONTINUING ONSHORE FLOW SUPPORTS A
HEAVY SNOW RISK ACROSS THE CASCADES, KLAMATH, AND SIERRA NEVADA MOUNTAINS. SOME
SNOW OR WINTRY WEATHER CANNOT BE RULED OUT OVER LOWER ELEVATION AREAS INCLUDING
THE CITIES OF PORTLAND, OR AND SEATTLE, WA DUE TO THE ANOMALOUSLY COLD AIR MASS
PREDICTED TO BE IN PLACE. THE PROGRESSION OF THE MID-LEVEL PATTERN IS MORE
UNCERTAIN DURING THE SECOND HALF OF THE PERIOD, BUT A GENERAL TREND TOWARD A
MORE ZONAL FLOW PATTERN ACROSS THE CONUS APPEARS MORE LIKELY, WITH BROAD
MID-LEVEL LOW PRESSURE ACROSS THE WEST-CENTRAL CONUS. THIS CAN LEAD TO ONE OR
MORE SURFACE LOW PRESSURE SYSTEMS EJECTING OUT OF THE ROCKIES AND POTENTIALLY
RESULTING IN HEAVY PRECIPITATION ACROSS PARTS OF THE EAST, WITH SNOW POSSIBLE
ACROSS THE NORTHERN TIER.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE PACIFIC
NORTHWEST, THU-FRI, FEB 6-7.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE
NORTHWESTERN CONUS AND EXTENDING INTO THE NORTHERN ROCKIES AND PLAINS, THU-SUN,
FEB 6-9.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE CASCADES, KLAMATH, AND SIERRA
NEVADA MOUNTAINS, AND ALSO INCLUDING LOWER ELEVATIONS OF WASHINGTON AND OREGON,
THU-SAT, FEB 6-8.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES,
NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, AND NORTHERN GREAT LAKES, THU-SAT,
FEB 6-8.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF NEW ENGLAND, THU-SUN, FEB 6-9.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS MUCH OF THE EASTERN CONUS, THU-SUN,
FEB 6-9.
SLIGHT RISK OF HIGH WINDS ACROSS MUCH OF THE SOUTHWESTERN CONUS, THU-SAT, FEB
6-8.
DETAILED SUMMARY
FOR SATURDAY FEBRUARY 01 - WEDNESDAY FEBRUARY 05:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY FEBRUARY 06 - WEDNESDAY FEBRUARY 12: TROUGHING IS FORECAST ACROSS
THE NORTHWESTERN CONUS DURING WEEK-2 RESULTING IN BELOW-NORMAL TEMPERATURES
ALONG THE WEST COAST AND INTO PARTS OF THE NORTHERN ROCKIES AND NORTHERN
PLAINS. THE MOST ANOMALOUS COLD IS PREDICTED TO BE ACROSS THE PACIFIC
NORTHWEST, WHERE THE ECENS PROBABILISTIC EXTREMES TOOL (PET) DEPICTS
PROBABILITIES OF AT LEAST 40 PERCENT FOR MINIMUM TEMPERATURES FALLING BELOW THE
15TH CLIMATOLOGICAL PERCENTILE. THESE PROBABILITIES INCREASE TO ABOVE 60
PERCENT IN THE GEFS PET. THE UNCALIBRATED 0Z ECENS AND GEFS BOTH DEPICT
SUBFREEZING TEMPERATURES OVER COASTAL AREAS, WITH TEMPERATURES IN THE LOWER 20S
DEG F IN THE GEFS. A MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES IS
HIGHLIGHTED ACROSS COASTAL WASHINGTON AND OREGON, FEB 6-7, CORRESPONDING WITH
THE LARGEST PREDICTED NEGATIVE TEMPERATURE ANOMALIES AND WHERE COLD WEATHER
HAZARDS CRITERIA IS MOST LIKELY TO BE MET. THE 0Z ECENS IS QUICKER TO WEAKEN
THE TROUGH OVER THE NORTHWEST COMPARED TO THE GEFS, AND THEREFORE THE ECENS
DEPICTS A QUICKER WARMING TREND WITH A DIMINISHING SIGNAL FOR HAZARDOUS
TEMPERATURES IN THE CORRESPONDING PET BY THE MIDDLE OF THE PERIOD. DUE TO THE
INCREASING UNCERTAINTY, THE SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES IS
ONLY VALID THROUGH FEB 9. THE SLIGHT RISK AREA EXTENDS ACROSS THE NORTHERN
ROCKIES AND PLAINS WHERE SUBZERO TEMPERATURES ARE POSSIBLE. WHILE THESE
TEMPERATURES ARE CONSIDERABLY COLDER COMPARED TO THE COASTAL PACIFIC NORTHWEST,
IT IS LESS CERTAIN IF APPARENT TEMPERATURES WILL REACH THE VERY COLD CRITERIA
ACROSS THESE AREAS, JUSTIFYING ONLY A SLIGHT RISK.
ALONG WITH THE COLD TEMPERATURES, AN ENHANCED ONSHORE FLOW PATTERN ASSOCIATED
WITH THE TROUGHING FAVORS PERIODS OF HEAVY PRECIPITATION ACROSS THE WEST COAST.
THE INTEGRATED VAPOR TRANSPORT (IVT) TOOL DERIVED FROM THE ECENS AND GEFS
DEPICT AT LEAST A 50 PERCENT CHANCE IVT VALUES EXCEED 250 KG/M/S ALONG THE
OREGON AND CALIFORNIA COAST LATE IN WEEK-1, WITH DECREASING PROBABILITIES BY
THE START OF WEEK-2. THE BEST CHANCES FOR HEAVIEST PRECIPITATION ALONG THE WEST
COAST NOW FALLS WITHIN THE WEEK-1 TIMEFRAME ALLOWING THE RELATED HAZARD TO BE
DISCONTINUED. HOWEVER, CONTINUING ONSHORE FLOW EARLY IN WEEK-2, COMBINED WITH
THE COLD AIR MASS IN PLACE ACROSS THE PACIFIC NORTHWEST DURING THE FIRST HALF
OF THE PERIOD, SUPPORTS ENHANCED CHANCES OF HEAVY SNOW OR WINTRY WEATHER EVEN
IN LOW ELEVATION AREAS INCLUDING THE CITIES OF PORTLAND, OR AND SEATTLE, WA.
THEREFORE, A SLIGHT RISK OF HEAVY SNOW IS POSTED ACROSS THESE AREAS, AND FOR
THE HIGHER ELEVATIONS OF THE CASCADES, KLAMATH, AND SIERRA NEVADA MOUNTAINS,
FEB 6-8. THE STRONGER TROUGHING IN THE GEFS SUPPORTS A SLIGHT RISK FOR HIGH
WINDS AT THE BASE OF THE TROUGH AXIS OVER THE SOUTHWESTERN CONUS THROUGH 2/8,
AS DEPICTED IN THE CORRESPONDING PET.
ONE OR MORE AREAS OF SURFACE LOW PRESSURE ARE PREDICTED TO EJECT OUT OF THE
ROCKIES DURING WEEK-2, AIDED BY SOME ENHANCED BAROCLINICITY TIED TO INCREASING
MID-LEVEL HIGH PRESSURE OVER THE SOUTHEAST AND BROAD TROUGHING OVER THE
WEST-CENTRAL CONUS. DETERMINISTIC SOLUTIONS FROM THE GFS AND ECMWF VARY
REGARDING TRACKS AND IMPACTS, BUT A SWATH OF HEAVY SNOW CANNOT BE RULED OUT
ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES, NORTHERN PLAINS AND UPPER
MIDWEST, WHERE THE GEFS SNOW WATER EQUIVALENT (SWE) PET DEPICTS SOME AREAS WITH
AT LEAST A 20 PERCENT CHANCE SWE EXCEEDS THE 85TH CLIMATOLOGICAL PERCENTILE AND
0.5-INCHES (1-INCH ACROSS THE ROCKIES) EARLY IN WEEK-2. THEREFORE, A SLIGHT
RISK FOR HEAVY SNOW IS POSTED ACROSS MUCH OF THE NORTHERN TIER, FEB 6-8. BOTH
THE GEFS AND ECENS PETS DEPICT AT LEAST A 20 PERCENT CHANCE 3-DAY PRECIPITATION
EXCEEDS THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH ACROSS PARTS OF THE
SOUTH, ALTHOUGH THESE AREAS ARE PREDICTED TO BE IN THE WARM SECTOR WITH RAIN
THE MOST LIKELY OUTCOME. THE UNCALIBRATED 0Z ECENS DEPICTS AT LEAST A 20
PERCENT CHANCE 3-DAY PRECIPITATION EXCEEDS 1-INCH EXTENDING FARTHER NORTH INTO
THE OHIO VALLEY AND NORTHEAST AND IS GENERALLY FASTER, WITH THE GEFS STILL MORE
UNCERTAIN IN REGARDS TO TIMING AND AMPLITUDE. GIVEN THE ELEVATED POTENTIAL, A
SLIGHT RISK FOR HEAVY PRECIPITATION IS HIGHLIGHTED OVER MUCH OF THE EASTERN
U.S., FEB. 6-9. THERE IS SOME RISK OF FLOODING ACROSS PARTS OF THE MISSISSIPPI
AND OHIO VALLEYS IF THE MORE AMPLIFIED SOLUTIONS VERIFY. EASTWARD PROGRESSION
OF WINTRY WEATHER IS POSSIBLE ON THE NORTHERN SIDE OF THE SYSTEM SUPPORTING A
SLIGHT RISK OF HEAVY SNOW ACROSS NEW ENGLAND ON FEB 6-9.
RIDGING IS FORECAST OVER ALASKA DURING WEEK-2 FAVORING RELATIVELY WARMER
TEMPERATURES OVER MUCH OF THE MAINLAND AND ALEUTIANS COMPARED TO WEEK-1.
BELOW-NORMAL TEMPERATURES REMAIN FORECAST ACROSS SOUTHEAST ALASKA, BUT HAZARDS
THRESHOLDS ARE UNLIKELY TO BE REACHED. BELOW-NORMAL PRECIPITATION IS ALSO
PREDICTED OVER MUCH OF SOUTHEASTERN ALASKA, WITH RIDGING PUSHING HIGHER CHANCES
OF PRECIPITATION FURTHER TO THE NORTH ACROSS THE NORTHWESTERN MAINLAND.
ENHANCED PROBABILITIES OF HIGH WIND SPEEDS (GREATER THAN 40-MPH) ARE DEPICTED
IN THE GEFS PET OVER PARTS OF THE ALEUTIANS, BUT THERE IS NOT ENOUGH CONFIDENCE
CRITERIA WILL BE MET WARRANT A RELATED HAZARD, ESPECIALLY GIVEN THE PREDICTED
RIDGE PLACEMENT.
FORECASTER: THOMAS COLLOW
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