271
FXUS02 KWBC 261854
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 PM EST FRI JAN 26 2024
VALID 12Z MON JAN 29 2024 - 12Z FRI FEB 2 2024
19Z UPDATE: THE 12Z MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT
WITH THE AMPLIFYING TROUGH FROM THE GREAT LAKES TO THE EAST COAST
FOR THE MIDDLE OF NEXT WEEK, ALTHOUGH THE GFS REMAINS A SLIGHTLY
SLOWER SOLUTION. IT APPEARS THAT ENSUING COASTAL LOW CYCLOGENESIS
SHOULD BE FAR ENOUGH AWAY FROM THE COAST TO KEEP PRECIPITATION
AMOUNTS LIGHT AS THE FORECAST STANDS RIGHT NOW. THERE IS BETTER
THAN AVERAGE MODEL AGREEMENT WITH THE LARGE SCALE TROUGH SETTING
UP ALONG THE WEST COAST BY MID-LATE WEEK, WITH THE GREATEST MODEL
DIFFERENCES RESIDING ACROSS SOUTHEAST CANADA WITH TIMING
DIFFERENCES IN NORTHERN STREAM FLOW. BY FRIDAY, THE GFS IS
STRONGER WITH A SHORTWAVE/UPPER LOW OVER THE GREAT LAKES REGION,
BUT IT IS COMPATIBLE WITH THE MODEL CONSENSUS ELSEWHERE. A
MULTI-DETERMINISTIC MODEL BLEND SUFFICED AS A STARTING POINT IN
THE FORECAST PROCESS FOR THE MONDAY-WEDNESDAY TIME PERIOD, AND
THEN GRADUALLY INCREASING PERCENTAGE OF THE ENSEMBLE MEANS FOR
LATER IN THE WEEK TO IRON OUT THE DIFFERENCES ACROSS THE EASTERN
U.S. AND SOUTHEAST CANADA. THE PREVIOUS FORECAST DISCUSSION IS
APPENDED BELOW FOR REFERENCE. /HAMRICK
--------------------
..OVERVIEW
MOST GUIDANCE AGREES ON A LARGE SCALE UPPER PATTERN FEATURING AN
AMPLIFIED PACIFIC TROUGH ARRIVING INTO THE WEST LATE IN THE WEEK,
A DOWNSTREAM RIDGE DRIFTING FROM THE INTERMOUNTAIN WEST INTO THE
PLAINS/MISSISSIPPI VALLEY, AND AN EAST COAST MEAN TROUGH THAT
SHOULD TREND MORE SHALLOW BY THE END OF THE WEEK. STRONG AND
MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC TROUGH WILL SUPPORT AN
ATMOSPHERIC RIVER EVENT WHOSE FOCUS SHOULD PROGRESS SOUTHWARD
ALONG THE WEST COAST OVER THE COURSE OF THE WEEK, WITH SOME
MOISTURE LIKELY EXTENDING FARTHER INLAND OVER THE WEST AFTER
WEDNESDAY. THE FORECAST PATTERN WILL PRODUCE DRIER CONDITIONS
FARTHER EAST, WITH THE PRIMARY AREAS OF PRECIPITATION BEING THE
POTENTIAL FOR LINGERING SNOW OVER SOUTHERN NEW ENGLAND ON MONDAY
WITH A DEPARTING STORM SYSTEM AND MOSTLY LIGHT RAIN/SNOW WITH A
TRAILING SYSTEM CROSSING THE EAST EARLY-MID WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVER THE WEST, THE PATTERN SEEMS TO EXHIBIT BETTER THAN AVERAGE
PREDICTABILITY AS AN OVERWHELMING MAJORITY OF DYNAMICAL
MODELS/ENSEMBLE MEANS AND 12Z ECMWF-INITIALIZED MACHINE LEARNING
MODELS BRING THE AMPLIFIED PACIFIC UPPER TROUGH TO OR JUST INLAND
FROM THE WEST COAST AS OF EARLY NEXT FRIDAY. GFS RUNS HAVE
EXHIBITED SOME VARIABILITY AT THAT FRIDAY VALID TIME, WITH THE 12Z
RUN STRAYING A BIT FAST BUT THE 18Z AND NEW 00Z RUNS SLOWER THAN
CONSENSUS. AS FOR OTHER EMBEDDED DETAILS, THE GFS EVENTUALLY
STRAYS NORTHWARD WITH THE FAIRLY DEEP LOW PRESSURE OFFSHORE THE
PACIFIC NORTHWEST, WITH THE MAJORITY OF GUIDANCE HOLDING ONTO A
DEFINED SURFACE LOW (ALBEIT WEAKENING) THAT DRIFTS TOWARD THE
COAST LATE IN THE WEEK. THERE ARE ALSO DIFFERENCES IN EXACTLY HOW
QUICKLY LEADING HEIGHT FALLS REACH THE WEST COAST, WITH A GUIDANCE
AVERAGE PROVIDING A REASONABLE STARTING POINT IN LIGHT OF NO CLEAR
CLUSTERING AT THIS TIME.
OVERALL THERE IS A LOT MORE SPREAD AND VARIABILITY WITH DETAILS
OVER THE EAST. RECENT GFS RUNS HAVE BEEN ON THE SLOW SIDE OF THE
SPREAD FOR THE AMPLIFYING SHORTWAVE CROSSING THE REGION. THIS IS
STILL THE CASE WHEN ADDING IN THE NEW 00Z RUNS BUT SLOWER TRENDS
IN THE UKMET/ECMWF MAKE THE GFS LOOK A LITTLE LESS EXTREME AND
THUS THE FULL GUIDANCE AVERAGE IS NOW A LITTLE SLOWER WITH THE
ASSOCIATED SURFACE REFLECTION THAN WHAT WAS SUPPORTED BY THE
NON-GFS MAJORITY AMONG THE 12Z/18Z DYNAMICAL MODELS/ENSEMBLE MEANS
AND MACHINE LEARNING MODELS. EASTERN CANADA INTO NEW ENGLAND FLOW
BY MID-LATE WEEK HAS ALSO BEEN AN ISSUE, WITH THE 12Z ECMWF
SHOWING A PARTICULARLY DEEP AND SLOW UPPER LOW IN CONTRAST TO
REMAINING SOLUTIONS THAT DEPICT EITHER A MORE MODEST TROUGH OR
FASTER PROGRESSION (AS REFLECTED IN THE NEW 00Z ECMWF). ANOTHER
SHORTWAVE MAY DROP INTO THE EAST COAST MEAN TROUGH BY FRIDAY, WITH
LATEST GFS RUNS BEING ON THE SLOW SIDE. THE GEFS/ECENS MEANS
PROVIDE THE BEST STARTING POINT LATE IN THE PERIOD GIVEN THE
SPREAD AND RUN-TO-RUN INCONSISTENCY IN THE GUIDANCE.
FOR THE UPDATED FORECAST BASED ON 12Z/18Z GUIDANCE, AN OPERATIONAL
MODEL COMPOSITE PROVIDED A REASONABLE STARTING POINT EARLY IN THE
PERIOD. DECREASINGLY FAVORABLE COMPARISONS FOR THE GFS OVER THE
EAST FROM MIDWEEK ONWARD AND TO SOME DEGREE OVER THE WEST BY
FRIDAY, AS WELL AS LOW CONFIDENCE IN THE 12Z ECMWF OVER THE EAST
AFTER MIDWEEK, LED TO PHASING OUT THE GFS AND QUICKLY INCREASING
TOTAL 18Z GEFS/12Z ECENS WEIGHT TO 70 PERCENT BY DAYS 6-7
THURSDAY-FRIDAY. MINORITY LINGERING INPUT FROM 12Z CMC/ECMWF
PROVIDED A LITTLE OPERATIONAL DETAIL OVER THE WEST WITHOUT
ADVERSELY IMPACTING THE PATTERN OVER THE EAST.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER TROUGH APPROACHING THE WEST COAST MONDAY-WEDNESDAY AND
THEN ARRIVING INTO THE WEST BY LATE WEEK WILL PROMOTE A STRONG
SOUTHERLY FLOW OF ENHANCED MOISTURE AND LIKELY BRING A PERIOD OF
SIGNIFICANT RAINFALL AND HIGH ELEVATION SNOW TO THE WEST COAST
STATES, EVENTUALLY REACHING FARTHER INLAND WITH TIME. DURING THE
PERIOD COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS (EARLY
MONDAY THROUGH TUESDAY NIGHT), THE MARGINAL RISK AREA THAT WAS
OVER THE OLYMPIC PENINSULA IN WESTERN WASHINGTON ON DAY 4 HAS BEEN
DROPPED, WITH THE LATEST OVERALL QPF MODEL SIGNAL OF LESS THAN 1
INCH AND HOURLY RAINFALL RATES LIKELY TO BE UNDER A QUARTER INCH,
BUT THE MARGINAL RISK REMAINS HERE FOR THE DAY 5 PERIOD AS
MOISTURE FLUX INCREASES. MEANWHILE, THE SEPARATE MARGINAL RISK
AREA ALONG COASTAL AREAS OF SOUTHERN OREGON/NORTHERN CALIFORNIA ON
DAY 5 REMAINS IN PLACE, AND THIS REFLECTS THE CONSENSUS TIMING FOR
THE ARRIVAL OF MODERATE TO LOCALLY HEAVY RAINFALL WITH THE
ATMOSPHERIC EVENT EXPECTED ON WEDNESDAY. AGAIN WITH SOME
UNCERTAINTY ON EXACT TIMING, HEAVIEST TOTALS CURRENTLY APPEAR TO
BE MOST LIKELY OVER NORTHERN-CENTRAL CALIFORNIA ON WEDNESDAY AND
THEN SHIFTING INTO CENTRAL-SOUTHERN CALIFORNIA BY THURSDAY. ALSO
BY THURSDAY EXPECT ORGANIZED PRECIPITATION TO EXTEND INTO THE
INTERMOUNTAIN WEST/SOUTHWEST. THE SOUTHERN ROCKIES/PLAINS COULD
SEE SOME PRECIPITATION BY FRIDAY.
THE SYSTEM TRACKING AWAY FROM THE EAST COAST ON MONDAY MAY PRODUCE
SOME LINGERING SNOW OVER SOUTHERN NEW ENGLAND ALONG WITH BRISK TO
STRONG WINDS OVER THE WESTERN ATLANTIC. A SYSTEM PASSING THROUGH
THE EAST EARLY-MID WEEK MAY SPREAD AN AREA OF MOSTLY LIGHT
PRECIPITATION (SNOW NORTH, RAIN SOUTH) ACROSS THE REGION.
THE NORTHERN-CENTRAL PLAINS WILL SEE ANOMALOUSLY WARM TEMPERATURES
THROUGH THE PERIOD, WITH NORTHERN AREAS TENDING TO SEE THE BEST
CHANCE FOR MULTIPLE DAYS OF MIN/MAX TEMPERATURES AT LEAST 20F
ABOVE NORMAL. SOME MORNING LOWS COULD BE UP TO 25-30F ABOVE
NORMAL AND A FEW DAILY RECORDS WILL BE POSSIBLE. THE WEST WILL BE
WARM AS WELL EARLY IN THE WEEK WITH SOMEWHAT LESS EXTREME
ANOMALIES (GENERALLY UP TO PLUS 10-20F), BUT THAT MAY STILL BE
ENOUGH TO PRODUCE SOME DAILY RECORDS. THE UPPER TROUGH MOVING IN
SHOULD BRING A COOLING TREND FOR THE LATTER HALF OF THE WEEK WITH
HIGHS OVER CALIFORNIA AND AN EXPANDING PORTION OF THE SOUTHWESTERN
U.S. TRENDING BELOW NORMAL THURSDAY-FRIDAY. BELOW NORMAL READINGS
OVER THE EAST WILL TEND TO BE CONFINED TO FLORIDA EARLY IN THE
WEEK. THE REMAINDER OF THE EAST WILL LIKELY SEE MORNING LOWS THAT
ARE WARMER THAN AVERAGE AND DAYTIME HIGHS NEAR TO SLIGHTLY ABOVE
NORMAL, WITH A COUPLE FRONTAL PASSAGES PROVIDING SOME DAY-TO-DAY
VARIABILITY.
RAUSCH
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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