181
FXUS21 KWNC 092007
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 09 2024
SYNOPSIS: FOLLOWING A RESPITE FROM THE STORMINESS ADVERSELY AFFECTING THE
WESTERN CONTIGUOUS U.S. (CONUS) THIS WEEK, STRONG MID-LEVEL LOW PRESSURE IS
FORECAST TO RETURN, LEADING TO ELEVATED RISKS OF HEAVY PRECIPITATION, HIGH
ELEVATION HEAVY SNOWFALL, AND HIGH WINDS ACROSS MANY PARTS OF THE WEST COAST
AND INTERIOR WEST DURING WEEK-2. MID-LEVEL LOW PRESSURE PREDICTED DOWNSTREAM
FAVORS INCREASED CHANCES FOR HEAVY PRECIPITATION ACROSS THE SOUTH-CENTRAL AND
SOUTHEASTERN CONUS, WITH THE POTENTIAL FOR ACCUMULATING HEAVY SNOW OVER THE
HIGHER ELEVATIONS OF THE APPALACHIANS.
HAZARDS
HIGH RISK OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA, SAT-TUE, FEB 17-20.
MODERATE RISK OF HEAVY PRECIPITATION FOR CALIFORNIA, SOUTHERN NEVADA, AND PARTS
OF ARIZONA, SAT-WED, FEB 17-21.
SLIGHT RISK OF HEAVY PRECIPITATION FOR CALIFORNIA, AND PARTS OF THE PACIFIC
NORTHWEST, NEVADA, AND THE DESERT SOUTHWEST, SAT-THU, FEB 17-23.
HIGH RISK OF HIGH ELEVATION HEAVY SNOW FOR THE SIERRA NEVADA RANGE OF
CALIFORNIA, SAT-TUE, FEB 17-20.
MODERATE RISK OF HIGH ELEVATION HEAVY SNOW FOR THE SIERRA NEVADA RANGE OF
CALIFORNIA, SAT-WED, FEB 17-21.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF CALIFORNIA, AND PARTS OF
OREGON, SAT-FRI, FEB 17-23.
MODERATE RISK OF HIGH ELEVATION HEAVY SNOW FOR THE MOGOLLON RIM OF THE DESERT
SOUTHWEST, SAT-TUE, FEB 17-20.
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE HIGHER ELEVATIONS OF THE GREAT BASIN
AND FOUR CORNERS, AND THE ROCKIES, SAT-WED, FEB 17-21.
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES AND NORTHERN HIGH
PLAINS, SAT-SUN, FEB, 17-19.
MODERATE RISK OF HIGH WINDS FOR CALIFORNIA AND PARTS OF NEVADA, SAT-WED, FEB
17-21.
SLIGHT RISK OF HIGH WINDS OVER MUCH OF THE WEST COAST EAST TO THE ROCKIES,
SAT-FRI, FEB 17-23.
MODERATE RISK OF HEAVY PRECIPITATION OVER PARTS OF THE SOUTHEAST AND THE
FLORIDA PENINSULA, SAT-MON, FEB 17-19.
SLIGHT RISK OF HEAVY PRECIPITATION OVER THE SOUTHERN PLAINS, LOWER MISSISSIPPI
VALLEY, SOUTHEAST, AND LOWER MID-ATLANTIC, SAT-WED, FEB 17-21.
SLIGHT RISK OF HEAVY SNOW OVER THE SOUTHERN AND CENTRAL APPALACHIANS, MON-WED,
FEB 19-21.
SLIGHT RISK OF HIGH WINDS OVER THE GREAT LAKES, OHIO VALLEY, APPALACHIANS,
MID-ATLANTIC, AND NORTHEAST, SAT-MON, FEB 17-19.
FLOODING POSSIBLE OVER MUCH OF CALIFORNIA, FROM THE SIERRA FOOTHILLS TO THE
COAST.
FLOODING POSSIBLE OVER PARTS OF EASTERN TEXAS.
DETAILED SUMMARY
FOR MONDAY FEBRUARY 12 - FRIDAY FEBRUARY 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY FEBRUARY 17 - FRIDAY FEBRUARY 23: HEADING INTO NEXT WEEKEND, THERE
IS GOOD AGREEMENT IN THE DYNAMICAL MODELS FEATURING ANOMALOUS MID-LEVEL
TROUGHING SHIFTING EASTWARD FROM THE EASTERN PACIFIC TO RENEW THE RISK OF
HAZARDOUS WEATHER CONDITIONS OVER THE WESTERN CONUS FOLLOWING A MORE TRANQUIL
PATTERN DURING WEEK-1. THIS HAS BEEN THE PRIMARY HAZARDS FOCUS THIS WEEK, AS
THE RETURN OF THE HEAVY PRECIPITATION THREAT APPEARS TO BE TRACKING WELL BASED
ON THE GEFS AND ECMWF MID-LEVEL HEIGHT, PRECIPITATION, AND INTEGRATED VAPOR
TRANSPORT (IVT) ENSEMBLE FORECASTS. AN AMPLIFIED SHORTWAVE IS SEEN BREAKING OFF
FROM THE MEAN TROUGHING PATTERN IN EASTERN PACIFIC BY THE OUTSET OF THE PERIOD,
WHERE THERE ARE HIGHER CHANCES IN IVT TOOLS FOR ATMOSPHERIC RIVER (AR) ACTIVITY
RELATIVE TO YESTERDAY. A SECONDARY IVT PULSE REMAINS EVIDENT LATER IN PERIOD
(DAYS 10-12), AND THERE IS BETTER AGREEMENT BETWEEN THE MODELS IN REGARDS TO
THE TIMING OF THE IVT SIGNALS AND THE CORRESPONDING PRECIPITATION INCREASES
OVER THE WEST COAST DURING WEEK-2.
BASED ON GOOD CONTINUITY IN THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS
(PETS) DEPICTING A LARGE SWATH OF ELEVATED CHANCES (40-70%) FOR 3-DAY
PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH THROUGH THE
MIDDLE OF PERIOD, A MODERATE RISK OF HEAVY PRECIPITATION REMAINS ISSUED FOR FEB
17-21 OVER CALIFORNIA AND INTO THE DESERT SOUTHWEST. EMBEDDED WITHIN THIS
MODERATE RISK AREA, A HIGH RISK OF HEAVY PRECIPITATION REMAINS POSTED FOR FEB
17-20, WHERE THE UNCALIBRATED ECMWF SHOWS AT LEAST A 60% (40%) CHANCE FOR 3-DAY
AMOUNTS EXCEEDING ONE (2) INCH(ES) EARLY IN THE PERIOD OVER CALIFORNIA. THE
PERSISTENCE OF ANOMALOUS MID-LEVEL MEAN TROUGHING FAVORED OVER THE WESTERN
CONUS THROUGHOUT WEEK-2 SUPPORTS A BROAD SLIGHT RISK AREA OF HEAVY
PRECIPITATION FOR FEB 17-23, AS ANOTHER STORM IMPACTING THE WEST COAST IS
POSSIBLE DURING THE BACKEND OF WEEK-2 BASED ON IVT TOOLS. ABOVE-NORMAL
PRECIPITATION FAVORED THROUGHOUT WEEK-2 ALSO SUPPORTS THE ADDITION OF A
POSSIBLE FLOODING OVER CALIFORNIA FROM THE SIERRA FOOTHILLS TO THE COASTLINE.
STREAMS AND RIVER LEVELS ARE EXPECTED TO SUBSIDE SOMEWHAT DURING A DRY PERIOD
DURING WEEK-1, HOWEVER THE HEAVY PRECIPITATION RISK DURING WEEK-2 MAY LEAD TO
SHARP STREAM RESPONSES, LOCALIZED FLOODING, AND MELTING SNOW FROM BUILD-UP IN
THE LOWER ELEVATIONS IN THE STATE. WHILE NO FLOODING HAZARDS ARE DESIGNATED IN
THE DESERT SOUTHWEST, LOCALIZED FLOODING IS POSSIBLE OVER PARTS OF ARIZONA
SHOULD ANY STORMINESS PRODUCE HIGH PRECIPITATION RATES.
GIVEN THE LARGE ENHANCEMENT OF TROPOSPHERIC MOISTURE IN THE WEST, AND SUPPORT
FROM THE SNOW WATER EQUIVALENT (SWE) PET AND RAW SNOW TOOLS, A CORRESPONDING
HIGH, MODERATE, AND SLIGHT RISK AREA FOR HEAVY SNOW IS POSTED OVER THE HIGHER
ELEVATIONS OF CALIFORNIA FOR FEB 17-20, FEB 17-21, AND FEB 17-23, RESPECTIVELY.
WITH ANOMALOUS MOISTURE BEING ADVECTED EASTWARD INTO THE INTERIOR WEST, A
MODERATE RISK OF HIGH ELEVATION SNOW (FEB 17-20) REMAINS POSTED OVER THE
MOGOLLON RIM IN ARIZONA, WITH A BROADER SLIGHT RISK AREA OF HEAVY SNOW (FEB
17-21) EXTENDING ACROSS MANY HIGH ELEVATIONS AREAS OF THE FOUR CORNERS REGION.
THE GEFS SWE PET INDICATES THE HIGHEST CHANCES FOR HEAVY SNOW THROUGH THE
MIDDLE OF THE PERIOD, BEFORE THIS RISK GRADUALLY EASES TOWARDS THE END OF
WEEK-2. INCREASED CHANCES FOR HEAVY SNOW ARE ALSO POSSIBLE FURTHER NORTH OVER
THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS WHICH IS REFLECTED IN THE GEFS
SWE PET EARLY IN WEEK-2. THIS IS LIKELY TIED TO AN AREA OF SURFACE HIGH
PRESSURE DESCENDING FROM CANADA TO BRING ANOMALOUSLY COLD TEMPERATURES AND
UPSLOPE FLOW OVER THE REGION. A SLIGHT RISK OF HEAVY SNOW REMAINS POSTED OVER
MUCH OF MONTANA, AND NEIGHBORING PARTS OF WYOMING AND THE DAKOTAS FOR FEB
17-19. THE COMBINATION OF AMPLIFIED TROUGHING APPROACHING THE WEST COAST AND
STRONGER SIGNALS DEPICTED THE IVT TOOLS FOR AR ACTIVITY, WARRANTS THE
CONTINUATION OF A MODERATE RISK OF HIGH WINDS ACROSS MUCH OF THE WEST COAST FOR
FEB 17-21. A BROADER SLIGHT RISK AREA OF HIGH WINDS REMAINS POSTED AND COVERS
MUCH OF THE WESTERN CONUS FOR THE ENTIRETY OF WEEK-2 (FEB 17-23) DUE TO THE
AFOREMENTIONED UPSLOPE FLOW AND STRENGTHENING PRESSURE GRADIENTS FAVORED IN THE
ENSEMBLES.
OVER THE LOWER LATITUDES OF NORTH AMERICA, ENSEMBLES REMAIN CONSISTENT FAVORING
A SHORTWAVE DISTURBANCE PROPAGATING OVER MEXICO AND INTO THE SOUTHERN PLAINS
EARLY IN WEEK-2. THIS LOOKS TO INDUCE AN AREA OF DEEPENING LOW PRESSURE OVER
THE GULF OF MEXICO, BRINGING INCREASED, AND POSSIBLY HEAVY PRECIPITATION
AMOUNTS OVER PARTS OF THE GULF STATES. SINCE YESTERDAY, BOTH THE GEFS AND ECWMF
PETS HAVE BACKED OFF ON THE HEAVY PRECIPITATION POTENTIAL OVER SOUTHEASTERN
TEXAS, AS THE RISK APPEARS TO BE TIMING OFF OVER THE SOUTHERN PLAINS WITH THE
HIGHEST AMOUNTS CONCENTRATED FURTHER EAST. ENHANCED WET SIGNALS IN THE
CALIBRATED PRECIPITATION GUIDANCE HAVE ALSO INCREASED OVER THE EASTERN GULF
WITH THE LOW TRACKING EASTWARD, AS BOTH THE GEFS AND ECMWF SHOW 30-50% CHANCES
OF 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH. AS A RESULT, THE
MODERATE RISK FOR HEAVY PRECIPITATION OVER SOUTHEASTERN TEXAS IS REMOVED FROM
THE OUTLOOK, HOWEVER A MODERATE RISK IS ADDED TO PARTS OF THE SOUTHEAST AND THE
FLORIDA PENINSULA FOR FEB 17-19. THE SLIGHT RISK REMAINS ISSUED OVER THE GULF
STATES AND EXTENDING INTO THE SOUTHEAST AND LOWER MID-ATLANTIC WHERE PETS SHOW
AT LEAST A 20% CHANCE FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1
INCH FOR FEB 17-21. DESPITE THE DRIER OUTLOOK OVER THE SOUTHERN PLAINS, PARTS
OF EASTERN TEXAS HAVE REGISTERED VERY LARGE PRECIPITATION SURPLUSES DURING THE
PAST 30 DAYS WITH SEVERAL LOCATIONS EXPERIENCING ELEVATED RIVER LEVELS. DUE TO
INCREASED PRECIPITATION FAVORED DURING THE NEXT TWO WEEKS, A FLOODING POSSIBLE
SHAPE REMAINS POSTED FOR EASTERN TEXAS.
THERE IS STILL A GOOD AMOUNT OF UNCERTAINTY ASSOCIATED WITH THE EVENTUAL TRACK
OF THE SURFACE LOW AS IT CROSSES INTO THE ATLANTIC. THE ECMWF FAVORS A MORE
SUPPRESSED STORM TRACK, WHEREAS THE GEFS SHOWS A STRONGER MEAN LOW OFFSHORE OF
THE CAROLINAS WITH HIGHER PRECIP AMOUNTS OVER THE EASTERN SEABOARD DURING THE
MIDDLE OF WEEK-2. WITH ANOMALOUS COLD AIR IN PLACE OVER THE SOUTHEAST DURING
THIS TIME, THERE IS SOME POTENTIAL FOR ACCUMULATING AND POSSIBLE HEAVY SNOW ON
THE BACKSIDE OF THE LOW OVER THE SOUTHERN AND CENTRAL APPALACHIANS, THUS A
SLIGHT RISK OF HEAVY SNOW REMAINS ISSUED FOR FEB 19-21. OVER THE NORTHEASTERN
CONUS, A SLIGHT RISK OF HIGH WINDS REMAINS ISSUED FOR FEB 17-19 GIVEN
PERSISTENT TROUGHING AND SURFACE LOW PRESSURE FORECAST OVER THE CANADIAN
MARITIMES.
NO HAZARDS ARE POSTED FOR ALASKA. THE GEFS 500-HPA HEIGHT FORECASTS CONTINUE TO
FAVOR AN EXPANDING AREA OF ANOMALOUS RIDGING OVER THE BERING STRAIT, WHERE THE
RESULTANT NORTHWESTERLY FLOW WOULD HELP BRING COLDER TEMPERATURES FOLLOWING AN
ANOMALOUSLY WARM 6-10 DAY PERIOD. THIS IS REFLECTED IN THE GEFS PET GUIDANCE
SHOWING INCREASED CHANCES FOR MINIMUM TEMPERATURES FALLING BELOW THE 15TH
PERCENTILE TOWARDS THE MIDDLE OF THE PERIOD, BUT THERE IS MUCH LESS SUPPORT FOR
THIS IN THE ECMWF PET.
FORECASTER: NICK NOVELLA
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