268
FXUS02 KWBC 031900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST MON FEB 3 2025
VALID 12Z THU FEB 06 2025 - 12Z MON FEB 10 2025
...ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION FOR CALIFORNIA THURSDAY...
...WINTRY WEATHER FORECAST FOR THE NORTHEAST THURSDAY AND AGAIN
OVER THE WEEKEND...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW THE LARGE SCALE PATTERN EVOLVING TOWARD
A BROAD MEAN TROUGH FROM NORTHEASTERN CANADA THROUGH THE WESTERN
U.S. BY THE WEEKEND AND EARLY NEXT WEEK, IN RESPONSE TO A STEADILY
AMPLIFYING PACIFIC THROUGH ALASKA UPPER RIDGE. THIS EVOLUTION
FOLLOWS A PERIOD OF FLAT FLOW EXTENDING INTO LATE THIS WEEK. A
SYSTEM REACHING CALIFORNIA ON THURSDAY AND CONTINUING INLAND
THEREAFTER WILL BRING A FINAL SURGE OF RAIN AND HIGHER ELEVATION
SHOW INTO THE WEST BEFORE A DRIER TREND ACROSS THE REGION. THE
EASTERN HALF OF THE COUNTRY WILL LIKELY SEE TWO EVENTS WITH THE
FULL RANGE OF PRECIPITATION TYPES, ONE LASTING INTO THURSDAY AND
THEN ANOTHER OVER THE WEEKEND. EACH SYSTEM MAY PRODUCE SOME AREAS
OF MODERATE TO HEAVY RAIN AND/OR SNOW (POSSIBLY SEPARATED BY A
WINTRY MIX) DEPENDING ON SYSTEM DETAILS. THE SOUTHERN TIER WILL
SEE THE MOST PERSISTENT WARMTH DURING THE PERIOD, THOUGH
INDIVIDUAL SURFACE LOW/FRONTAL SYSTEMS WILL BRIEFLY PULL WELL
ABOVE NORMAL TEMPERATURES SOMEWHAT FARTHER NORTHWARD, ESPECIALLY
ON THURSDAY. THE EVOLVING UPPER PATTERN AND CANADIAN SURFACE HIGH
PRESSURE SHOULD PROMOTE BELOW NORMAL TEMPERATURES FROM THE
NORTHWEST INTO THE NORTHERN PLAINS WITH THE COLDEST ANOMALIES
CENTERED OVER MONTANA THURSDAY AND PERHAPS OVER A SIMILAR AREA
AGAIN EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
TODAY'S MODELS AND ENSEMBLES REMAIN FAIRLY AGREEABLE FOR THE
OVERALL PATTERN WITH TYPICAL SCATTER FOR INDIVIDUAL FEATURES AND
SHORTWAVE DETAILS. LATEST RUNS HAVE CONVERGED WELL ENOUGH FOR THE
INITIAL GREAT LAKES/NORTHEAST/SOUTHERN CANADA SYSTEM AND EASTERN
PACIFIC LOW PRESSURE MOVING INTO THE WEST TO FAVOR A 00Z/06Z MODEL
COMPOSITE FOR THIS FORECAST UPDATE'S STARTING POINT EARLY-MID
PERIOD. FROM LATE SATURDAY ONWARD, PLAINS THROUGH NORTHEAST LOW
PRESSURE CLUSTERS DECENTLY AMONG THE MODELS/MEANS WHILE SHORTWAVE
DETAILS DIVERGE SOMEWHAT WITHIN THE OVERALL CANADA/WESTERN U.S.
UPPER TROUGH. A TRANSITION TOWARD A MODEL/ENSEMBLE MEAN MIX
(REACHING 40 PERCENT MEAN WEIGHT BY NEXT MONDAY) REPRESENTS THE
MOST COMMON IDEAS OF GUIDANCE AT THAT TIME.
FOR THE LATE WEEK GREAT LAKES/NORTHEAST/SOUTHERN CANADA SYSTEM,
GUIDANCE HAS FAVORABLY CONVERGED TOWARD COMPROMISE IDEAS FAVORED
IN RECENT RUNS. THE GFS HAS TRENDED NORTHWARD FOR ITS WAVE AS OF
EARLY THURSDAY AND THE ECMWF CLUSTER HAS TRENDED WEAKER--AS
STEADILY FAVORED BY MACHINE LEARNING (ML) GUIDANCE, WITH CONSENSUS
THEREAFTER EMPHASIZING A DEEPENING LOW OVER SOUTHERN CANADA
BECOMING THE PRIMARY SYSTEM.
FARTHER WEST, AN INTERMEDIATE SOLUTION RESOLVES ONGOING MODERATE
SPREAD FOR THE SPECIFICS OF EASTERN PACIFIC LOW PRESSURE TRACKING
INTO CALIFORNIA ON THURSDAY. AS THE SYSTEM TRACKS FROM THE PLAINS
THROUGH NORTHEAST DURING THE WEEKEND, THE AVERAGE OF 00Z/06Z
GUIDANCE HAS ADJUSTED A LITTLE FASTER VERSUS THE PRIOR CYCLE BUT
THE 06Z/12Z GFS HAVE ADJUSTED SLOWER AFTER A QUESTIONABLY FAST 00Z
RUN. ML MODELS ARE SHOWING LESS SPREAD VERSUS 24 HOURS AGO AND THE
AVERAGE DEPTH IS COMPARABLE TO A DYNAMICAL MODEL/ENSEMBLE MEAN
COMPROMISE. EVEN WITH SOME DETAIL/TIMING DIFFERENCES, THE GUIDANCE
CLUSTERING OVER THE NORTHEAST AS OF SUNDAY GENERALLY APPEARS
BETTER THAN AVERAGE FOR A DAY 6 FORECAST.
FLOW BEHIND THIS SYSTEM IS AGREEABLE FROM THE LARGE SCALE
PERSPECTIVE BUT EMBEDDED SHORTWAVE DETAILS HAVE MUCH LOWER
PREDICTABILITY FOR SPECIFICS, RECOMMENDING THE FAVORED
MODEL/ENSEMBLE MEAN BLEND. TELECONNECTIONS RELATIVE TO THE
UPSTREAM PACIFIC/ALASKA UPPER RIDGE OFFER GOOD SUPPORT FOR THE
GENERAL ORIENTATION AND POSITION OF THE CANADA/WESTERN U.S. MEAN
TROUGH PLUS THE FLAT FLOW FORECAST OVER THE EAST WITH MODERATELY
ABOVE NORMAL HEIGHTS.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT ANOTHER ATMOSPHERIC RIVER TO TAKE AIM AT CALIFORNIA ON
THURSDAY, SUPPORTED BY TROUGHING ALOFT AND SURFACE LOW PRESSURE
MOVING INLAND. THIS AR EVENT SHOULD BE SHORTER-LIVED THAN THE
CURRENT AR, BUT SOME LOCALLY HEAVY RAIN AMOUNTS ARE POSSIBLE OVER
AREAS THAT WILL HAVE QUITE WET ANTECEDENT CONDITIONS BY THAT TIME.
A MARGINAL RISK STILL LOOKS GOOD FOR THE DAY 4/THURSDAY ERO, AS
FASTER MOVEMENT OF THIS AR SHOULD TEMPER RAIN AMOUNTS SOME AND
PRECLUDE AN EMBEDDED SLIGHT RISK AREA FOR NOW. THUS FAR THE
GUIDANCE DOES NOT SHOW SUFFICIENT CHANGE IN SPECIFICS TO MERIT
ADJUSTMENT OF MARGINAL RISK AREA. RISK UPGRADES MAY STILL BE
POSSIBLE AS GUIDANCE BETTER REFINES SYSTEM DETAILS IN THE SHORTER
RANGE. LIGHTER PRECIPITATION SHOULD PERSIST INTO FRIDAY OVER
CALIFORNIA BUT THEN THE PATTERN EVOLUTION WILL LIKELY SHIFT THE
BEST POTENTIAL FOR ORGANIZED (BUT FAIRLY LIGHT) ACTIVITY INTO THE
PACIFIC NORTHWEST AND FAR NORTHERN ROCKIES DURING THE WEEKEND INTO
NEXT MONDAY, WHILE CALIFORNIA FINALLY DRIES OUT.
SNOW WILL ALSO BE LIKELY FROM HIGHER ELEVATIONS OF THE CASCADES
AND SIERRA NEVADA ACROSS MUCH OF THE INTERMOUNTAIN WEST INTO THE
NORTHERN/CENTRAL ROCKIES THURSDAY INTO FRIDAY. THE HEAVIEST SNOW
AMOUNTS ARE LIKELY IN HIGHER ELEVATIONS, BUT THE NORTHERN GREAT
BASIN MAY SEE SNOW AS WELL. 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, PRECIPITATION IS LIKELY IN ASSOCIATION
WITH A LOW PRESSURE SYSTEM LOCATED OVER THE GREAT LAKES BY EARLY
THURSDAY. RAIN IS FORECAST ACROSS THE TENNESSEE VALLEY TO
SOUTHERN/CENTRAL APPALACHIANS, BUT RAIN TOTALS ARE FORECAST TO
DECREASE BY THURSDAY (COMPARED TO WEDNESDAY) AND LIKELY STAY BELOW
THRESHOLDS FOR ANY EXCESSIVE RAINFALL AREA ON DAY 4. WILL CONTINUE
TO MONITOR THOUGH AS INSTABILITY MAY STILL BE IN PLACE FOR SOME
LOCALLY HEAVY RAIN RATES, AS SUGGESTED BY THE HEAVIER SIDE OF THE
MODEL QPF ENVELOPE. FARTHER NORTH, COLD AIR IN PLACE WILL BRING
THE POTENTIAL FOR WINTRY WEATHER TO THE NORTHEAST. PROBABILITIES
FOR PLOWABLE SNOW/SLEET ARE INCREASING ACROSS THE ADIRONDACKS INTO
NORTHERN NEW ENGLAND, WHILE SOUTH OF THE GREATEST SNOW AMOUNTS, A
TRANSITION ZONE OF SLEET AND/OR FREEZING RAIN IS LIKELY PERHAPS
AROUND THE NORTHERN MID-ATLANTIC TO SOUTHERN NEW YORK/NEW ENGLAND.
BY FRIDAY-SATURDAY THE NORTHERN TIER WILL LIKELY SEE SOME LIGHT TO
MODERATE SNOW AS WESTERN U.S. LOW PRESSURE EMERGES INTO THE
PLAINS. PRECIPITATION WILL SPREAD INTO THE EAST ONCE AGAIN AS THIS
SYSTEM SHOULD REACH THE NORTHEAST BY SUNDAY. THE CURRENT FORECAST
HAS THE GREATEST PROBABILITIES FOR IMPACTFUL SNOW ACROSS MUCH OF
PENNSYLVANIA AND NEW YORK INTO NEW ENGLAND DURING THE WEEKEND. ONCE
AGAIN RAIN IS LIKELY FARTHER SOUTH ACROSS THE OHIO AND TENNESSEE
VALLEYS INTO THE CENTRAL APPALACHIANS, AND A BAND OF WINTRY MIX
MAY SEPARATE THE TWO PRIMARY PRECIPITATION TYPES.
COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR NORTHWESTERN AND
NORTH-CENTRAL PARTS OF THE LOWER 48 THROUGH THE PERIOD. THE COLD
WILL BE ESPECIALLY PRONOUNCED ACROSS MONTANA AND NORTH DAKOTA,
WITH SINGLE DIGIT HIGHS INTO THURSDAY. THESE AREAS WILL LIKELY
REMAIN BELOW AVERAGE BUT WITH SOME MODERATION FRIDAY INTO THE
WEEKEND, BUT ANOTHER SURGE OF COLD AIR IS LIKELY BY NEXT MONDAY.
MEANWHILE, AREAS FROM THE FOUR CORNERS STATES THROUGH THE EAST
SHOULD SEE ABOVE TO WELL ABOVE NORMAL TEMPERATURES FOR MOST OF THE
PERIOD. SOME AREAS WILL LIKELY SEE ONE OR MORE DAYS OF MIN/MAX
TEMPERATURES REACHING 20 OR MORE DEGREES ABOVE NORMAL (PERHAPS EVEN
A NARROW BAND OF PLUS 30F OR GREATER ANOMALIES FOR MORNING LOWS
AROUND THE MID-SOUTH). THESE ANOMALIES COULD SET DAILY RECORDS
ESPECIALLY ON THURSDAY. EXACT TEMPERATURES/ANOMALIES VARY SOMEWHAT
AT ANY PARTICULAR PLACE FRIDAY-SATURDAY, BUT BY SUNDAY-MONDAY THERE
SHOULD BE A MORE PRONOUNCED COOLING TREND ACROSS THE FOUR CORNERS
AND SOUTH-CENTRAL U.S. TO THE MID-ATLANTIC BEHIND A STRONG COLD
FRONT. THE TREND TOWARD GREATER COVERAGE OF BELOW NORMAL
TEMPERATURES OVER THE WESTERN AND CENTRAL U.S. BY EARLY NEXT WEEK
IS CONSISTENT WITH THE FORECAST LARGE SCALE PATTERN.
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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