369
FXUS02 KWBC 011900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SAT FEB 1 2025
VALID 12Z TUE FEB 04 2025 - 12Z SAT FEB 08 2025
...ATMOSPHERIC RIVER EVENT LIKELY TO LAST INTO TUESDAY FOR
CALIFORNIA, WITH ADDITIONAL ROUNDS OF PRECIPITATION ACROSS THE
WEST THROUGH MUCH OF NEXT WEEK...
..OVERVIEW
GUIDANCE SHOWS LOW AMPLITUDE UPPER FLOW ACROSS MUCH OF THE LOWER
48 NEXT WEEK, BUT THE OVERALL PATTERN AND EMBEDDED FEATURES WILL
STILL PRODUCE AREAS OF IMPACTFUL WEATHER. A SLOW MOVING UPPER LOW
DRIFTING NEAR/OFFSHORE VANCOUVER ISLAND AND THE PACIFIC NORTHWEST
WILL SUSTAIN A STRONG ATMOSPHERIC RIVER INTO CALIFORNIA AS THE
PERIOD BEGINS TUESDAY. THE MOISTURE AXIS MAY DRIFT SOUTH FOR A
TIME BUT GUIDANCE IS STARTING TO CLUSTER TOWARD THE IDEA OF ANOTHER
SYSTEM BRINGING A REBOUND OF RAIN/SNOW AFTER MIDWEEK. PERSISTENT
MOISTURE WILL ALSO LEAD TO ADDITIONAL ROUNDS OF PRECIPITATION FOR
MUCH OF THE INTERMOUNTAIN WEST THROUGH MOST OF NEXT WEEK. THIS
INCLUDES SNOW WITH THE POTENTIAL FOR SIGNIFICANT ACCUMULATIONS,
PARTICULARLY ACROSS THE HIGHER ELEVATIONS. FARTHER EAST, MOISTURE
RETURN AND SOME DEGREE OF FRONTAL WAVE DEVELOPMENT WILL LEAD TO
INCREASING PRECIPITATION CHANCES ACROSS THE EASTERN THIRD OF THE
LOWER 48 MID TO LATE WEEK, INCLUDING POSSIBLE WINTER WEATHER FOR
THE NORTHEAST. SHORTWAVE ENERGY EJECTING FROM THE WEST NEXT
SATURDAY MAY SUPPORT A CENTRAL U.S. FRONTAL WAVE WITH EXPANDING
PRECIPITATION. THE QUASI-ZONAL FLOW PATTERN WITH SUBTROPICAL
RIDGING NEAR THE BAHAMAS/CUBA WILL PROMOTE ABOVE NORMAL
TEMPERATURES ACROSS A MAJORITY OF THE COUNTRY, THOUGH A CANADIAN
SURFACE HIGH NUDGING INTO THE NORTHWESTERN TO NORTH-CENTRAL U.S.
SHOULD LEAD TO MUCH BELOW NORMAL TEMPERATURES THERE WITH COLDEST
ANOMALIES TUESDAY-WEDNESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FROM THE LARGE SCALE PERSPECTIVE, THE ENSEMBLE MEANS HAVE BEEN
PROVIDING A FAIRLY STEADY AND AGREEABLE FORECAST OVER RECENT DAYS--
HELPING TO ANCHOR THE FORECAST WITHIN SOME PRONOUNCED SPREAD FOR
VARIOUS SIGNIFICANT FEATURES. LATEST MODEL RUNS STILL SHOW A LOT OF
SPREAD AND VARIABILITY FOR FRONTAL WAVE DEVELOPMENT FORECAST TO
REACH THE OHIO VALLEY/GREAT LAKES BY THURSDAY AND CONTINUING
RAPIDLY ONWARD THEREAFTER, BUT SEEM TO BE STARTING TO CONVERGE
SOMEWHAT FOR A POTENTIAL SYSTEM TRACKING INTO CALIFORNIA AROUND
THURSDAY OR SO, ALONG WITH MEAN TROUGHING THAT SHOULD MOVE INTO THE
WEST BY SATURDAY.
MOST GUIDANCE INITIALLY SHOWS GOOD AGREEMENT ON TUESDAY, WITH A
WEAK PACIFIC FRONTAL WAVE TRACKING INTO CALIFORNIA TUESDAY-TUESDAY
NIGHT AND HELPING TO MAINTAIN ENHANCED PRECIPITATION OVER PARTS OF
THE STATE. HOWEVER SOLUTIONS RAPIDLY DIVERGE FOR THE DEVELOPING
EASTERN SYSTEM AS WELL AS OVER THE EASTERN PACIFIC/WESTERN U.S.
RECENT AND NEW 12Z GUIDANCE SHOWS SIGNIFICANT SPREAD AND WAFFLING
FOR DETAILS OF WAVE DEVELOPMENT FROM THE EAST-CENTRAL U.S. THROUGH
AND BEYOND THE NORTHEAST. UKMET RUNS CONTINUE TO BE ON THE STRONG
SIDE, WHILE ECMWF RUNS HAVE BECOME MORE ERRATIC AND THE GFS REMAINS
ON THE WEAK SIDE. CMC/CMCENS RUNS HAVE BEEN RUNNING FAST BUT THE
12Z RUN HAS NUDGED A LITTLE SLOWER. MACHINE LEARNING (ML) MODELS
HAVE CONSISTENTLY FAVORED THE WEAK SIDE OF THE SPREAD, AND SEEM TO
HAVE TRENDED TOWARD MORE POTENTIAL FOR SECONDARY WAVE DEVELOPMENT
THAT WOULD TRACK OFFSHORE NEW ENGLAND. THIS OFFERS SUPPORT FOR
INCLUDING THE GFS AS PART OF A COMPROMISE, THOUGH THE 12Z GFS
APPEARS OVERDONE WITH HOW FAR SOUTHWARD THE OFFSHORE WAVE TRACKS.
MEANWHILE, GUIDANCE HAS VARIED WIDELY FOR THE EXACT SHAPE OF FLOW
AROUND THE INITIAL UPPER LOW OFFSHORE THE PACIFIC NORTHWEST AND
VANCOUVER ISLAND, AS WELL AS FOR ANOTHER MID-LOWER LATITUDE WAVE
THAT MAY TRACK TO THE SOUTH. GUIDANCE HAD BEEN SPLIT AS FAR AS
WHETHER A WELL-DEFINED WAVE WOULD TRACK TOWARD CALIFORNIA AFTER
MIDWEEK, THOUGH LATEST ML RUNS ARE STARTING TO SHOW MORE SUPPORT
FOR AN EVOLUTION LIKE RECENT GFS RUNS IN CONTRAST TO THE SLOW/WEAK
ECMWF. NEW 12Z RUNS INCLUDING THE ECMWF SEEM TO BE CLUSTERING
BETTER TOWARD A WELL-DEFINED SYSTEM ARRIVING AROUND THURSDAY OR SO.
PREFERENCE LEANED TOWARD DEPICTING THIS SYSTEM BUT IN WEAKER
FASHION GIVEN THE UNCERTAINTY THROUGH THE 00Z/06Z CYCLES.
MOST ML MODELS MATCHED UP FAIRLY WELL WITH THE ENSEMBLE MEANS AND
AN AVERAGE OF RECENT ECMWF/GFS RUNS FOR THE OVERALL UPPER TROUGH
THAT SHOULD REACH THE WEST COAST AROUND EARLY FRIDAY AND CONTINUE
INLAND IN POSITIVELY-TILTED FASHION BY SATURDAY. UPSTREAM ENERGY
DROPPING DOWN FROM ALASKA COULD COMPLICATE THE FORECAST WITH
RESPECT TO SPECIFICS THOUGH. THE OVERALL SHAPE AND POSITION OF THE
TROUGH BY SATURDAY HAS DECENT SUPPORT FROM TELECONNECTIONS RELATIVE
TO THE UPSTREAM PACIFIC/ALASKA UPPER RIDGE. IN CONTRAST, THE 00Z
CMC TRENDED OUT OF PHASE RELATIVE TO CONSENSUS BY THE END OF THE
PERIOD.
GUIDANCE COMPARISONS/PREFERENCES LED TO STARTING THE 500MB/SURFACE
FORECAST WITH HALF 00Z ECMWF AND HALF 00Z/06Z GFS FOR THE FIRST
HALF OF THE PERIOD, WITH A TRANSITION TOWARD SOME INCORPORATION OF
THE 06Z GEFS/00Z ECENS AFTER EARLY THURSDAY.
..WEATHER/HAZARDS HIGHLIGHTS
A STRONG AND LONG-LASTING ATMOSPHERIC RIVER TAKING AIM AT
CALIFORNIA WILL BE ONGOING AS THE PERIOD BEGINS TUESDAY. GUIDANCE
IS STILL INDICATING THAT SUBTLE DETAIL DIFFERENCES AT THE SURFACE
AND ALOFT, THOUGH WITH GENERAL AGREEMENT THAT ARRIVAL OF A WEAK
FRONTAL WAVE WILL SUPPORT ENHANCED PRECIPITATION, WILL AFFECT THE
PRECISE AXIS OF HEAVIEST RAINFALL OVER COASTAL/LOW ELEVATION AREAS
SOMEWHERE WITHIN NORTH-CENTRAL TO SOUTH-CENTRAL PARTS OF THE STATE.
THE OVERALL COMBINATION OF MODEL GUIDANCE, EXCESSIVE RAINFALL
FIRST-GUESS FIELDS, AND PRIOR DAYS OF HEAVY RAINFALL SEEM TO
PROVIDE ENOUGH SUPPORT TO INTRODUCE A SLIGHT RISK AREA IN THE DAY
4/TUESDAY ERO. THIS AREA EXTENDS FROM THE COAST 100-150 MILES NORTH
AND SOUTH OF SAN FRANCISCO INTO WESTWARD FACING TERRAIN OF THE
SIERRA NEVADA BELOW THE SNOW LEVEL. THE MOISTURE FEED INTO THE WEST
COAST SHOULD TREND WEAKER/SOUTHWARD INTO WEDNESDAY, LEADING TO
REDUCED RAIN AMOUNTS. THERE IS SOME POTENTIAL FOR RAIN TO LINGER
ACROSS AREAS OF SOUTHERN CALIFORNIA OVER RECENT BURN SCARS THAT
WOULD BE SENSITIVE TO MODERATE RAIN, BUT MODEL GUIDANCE VARIES. THE
DAY 5 ERO DEPICTS NO MARGINAL RISK AREAS FOR THIS REGION BECAUSE
OF THE MODEL SPREAD (WHICH INCLUDES POTENTIAL FOR LITTLE TO NO
RAINFALL), BUT WILL CONTINUE TO MONITOR. THEN LATEST GUIDANCE IS
SHOWING A BETTER SIGNAL FOR WHAT COULD BE A FAIRLY VIGOROUS SYSTEM
REACHING CALIFORNIA AROUND THURSDAY/THURSDAY NIGHT WITH ANOTHER
EPISODE OF SIGNIFICANT RAINFALL ALONG WITH THE POSSIBILITY OF SOME
GUSTY WINDS.
SNOW WILL ALSO BE LIKELY FROM HIGHER ELEVATIONS OF THE SIERRA
NEVADA ACROSS MUCH OF THE INTERMOUNTAIN WEST INTO THE NORTHERN
ROCKIES. INTO TUESDAY, EXPECT THE HEAVIEST SNOW AMOUNTS FROM THE
SIERRA NEVADA INTO THE NORTHERN ROCKIES, WHILE THE NORTHERN GREAT
BASIN ALSO RECEIVES SNOW. SOME SNOW SHOULD EXTEND INTO THE WASATCH
AND CENTRAL ROCKIES FOR MIDWEEK AND BEYOND WHILE SOME MODERATE
SNOWS PERSIST IN THE SIERRA, CASCADES, AND NORTHERN ROCKIES. THE
POSSIBLE THURSDAY SYSTEM MAY PRODUCE A BETTER DEFINED PERIOD OF
ENHANCED SNOWFALL IN THE SIERRA NEVADA. THE PATTERN WILL ALSO
PROMOTE STRONG WINDS ESPECIALLY ON MOUNTAIN RIDGES LIKE THE SIERRA
AND CENTRAL ROCKIES, BUT SOME GUSTY CONDITIONS MAY REACH LOWER
ELEVATIONS OF THE GREAT BASIN AND FOUR CORNERS TOO.
MEANWHILE FARTHER EAST, MOISTURE WILL LIKELY RETURN LATE TUESDAY
AND ESPECIALLY WEDNESDAY-THURSDAY IN THE EAST-CENTRAL U.S. AS A
DEVELOPING FRONTAL WAVE SHOULD REACH THE OHIO VALLEY/GREAT LAKES BY
EARLY THURSDAY. AN EXPANDING AREA OF PRECIPITATION WILL DEVELOP,
PARTICULARLY ACROSS OR SOMEWHAT NORTH OR SOUTH OF THE OHIO VALLEY.
THERE CONTINUES TO BE SOME THREAT FOR FLOODING SOMEWHERE WITHIN THE
OHIO VALLEY/CENTRAL OR SOUTH-CENTRAL APPALACHIANS AS INSTABILITY
COULD REACH SUFFICIENTLY FAR NORTH AND DEPENDING ON SURFACE WAVE
STRENGTH (ESPECIALLY ON THE WEAKER SIDE OF THE SPREAD) THERE COULD
BE STRONG WESTERLY FLOW AT LOW LEVELS JUST ABOVE THE SURFACE TO
PROMOTE SOME TRAINING AND TERRAIN ENHANCEMENT. HOWEVER THE WIDE
SPREAD FOR SURFACE DETAILS AND QPF PLACEMENT FAVOR HOLDING OFF WITH
ANY DAY 5/WEDNESDAY ERO RISK AREAS. THE NORTHEAST AND NORTHERN
MID-ATLANTIC HAVE POTENTIAL FOR WINTRY WEATHER ON WEDNESDAY-
THURSDAY WHERE COLD AIR HANGS ON. A TRANSITION ZONE OF SLEET AND/OR
FREEZING RAIN MAY EXIST BETWEEN THE SNOW OVER FAR NORTHERN AREAS
AND THE RAIN TO THE SOUTH. ENERGY EJECTING FROM THE WEST NEXT
SATURDAY MAY PROMOTE DEVELOPMENT OF ANOTHER WAVE OVER THE CENTRAL
U.S. WITH ASSOCIATED NORTHERN TIER SNOW AND AN EXPANDING AREA OF
RAIN OVER THE EAST-CENTRAL U.S.
COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR NORTHWESTERN AND
NORTH-CENTRAL PARTS OF THE LOWER 48 NEXT WEEK. MONTANA TO THE
DAKOTAS WILL BE PARTICULARLY COLD, WITH ANOMALIES OF 20-35 DEGREES
BELOW NORMAL AND HIGHS BARELY REACHING 0F IN SOME LOCATIONS INTO
TUESDAY-WEDNESDAY. THESE AREAS WILL LIKELY REMAIN BELOW AVERAGE BUT
WITH SOME MODERATION LATER NEXT WEEK. MEANWHILE, OTHER AREAS FROM
THE FOUR CORNERS STATES THROUGH THE EAST SHOULD SEE ABOVE TO WELL
ABOVE NORMAL TEMPERATURES DURING THE PERIOD. SOME AREAS WILL LIKELY
SEE ONE OR MORE DAYS OF MIN/MAX TEMPERATURES REACHING 20 OR MORE
DEGREES ABOVE NORMAL AND SOME DAILY RECORDS ARE LIKELY TO BE SET
NEXT WEEK. CURRENT FORECASTS SUGGEST THAT DAILY RECORDS MAY BE MOST
NUMEROUS AROUND NEXT WEDNESDAY-THURSDAY. SOME SLIGHT COOLING IS
POSSIBLE INTO FRIDAY-SATURDAY BUT TEMPERATURES SHOULD REMAIN WELL
ABOVE AVERAGE ACROSS THE SOUTHERN TIER.
RAUSCH/TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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