346
FXUS02 KWBC 081900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SAT MAR 8 2025
VALID 12Z TUE MAR 11 2025 - 12Z SAT MAR 15 2025
...POTENT SYSTEM BRINGS PRECIPITATION TO THE WEST WEDNESDAY-
THURSDAY AND THE PLAINS/EAST-CENTRAL U.S. FRIDAY-SATURDAY...
..OVERVIEW
A LEADING SOUTHERN STREAM COMPACT CLOSED UPPER LOW/SHORTWAVE WILL
PROGRESS FROM OFFSHORE SOUTHERN CALIFORNIA EARLY TUESDAY AND
CONTINUE EASTWARD WITH TIME, SPREADING LIGHT TO MODERATE
PRECIPITATION OVER THE SOUTHWEST INTO MIDWEEK AND THEN THE LOWER
MISSISSIPPI VALLEY INTO SOUTHEAST WEDNESDAY-THURSDAY AS FLOW AHEAD
OF ASSOCIATED LOW PRESSURE TAPS INTO GULF MOISTURE. THIS SYSTEM
WILL WEAKEN THEREAFTER. UPSTREAM, CONFIDENCE REMAINS HIGH IN A DEEP
AND PHASED EASTERN PACIFIC UPPER TROUGH REACHING NEAR THE WEST
COAST BY AROUND EARLY THURSDAY ALONG WITH A LEADING SURFACE
LOW/FRONTAL SYSTEM AND ATMOSPHERIC RIVER. THIS SYSTEM WILL BRING
WIDESPREAD RAIN AND HIGHER ELEVATION SNOW ACROSS THE WEST IN THE
MID-LATE WEEK TIME FRAME. MOST GUIDANCE SUGGESTS THE UPPER TROUGH
WILL CLOSE OFF AN EMBEDDED UPPER LOW OVER THE PLAINS TOWARD THE END
OF THE WEEK, SUPPORTING STRONG SURFACE LOW DEVELOPMENT FROM THE
CENTRAL HIGH PLAINS INTO UPPER MIDWEST FRIDAY-SATURDAY. EXPECT
RAINFALL TO INCREASE IN COVERAGE/INTENSITY OVER AND JUST EAST OF
THE MISSISSIPPI VALLEY BY FRIDAY-SATURDAY, WHILE SNOW IS POSSIBLE
TO THE NORTHWEST OF THE SURFACE LOW TRACK. MEANWHILE AREAS OF
STRONG WINDS WILL BE POSSIBLE AND THE STORM PREDICTION CENTER IS
MONITORING SEVERE WEATHER POTENTIAL. THE PACIFIC TROUGH CROSSING
THE WEST WILL BRING BELOW NORMAL HIGHS TO THAT REGION WHILE THE
LEADING RIDGE (AND POSSIBLY A WEAKER ONE FARTHER EAST) SHOULD
PROMOTE ABOVE NORMAL TEMPERATURES OVER THE CENTRAL/EASTERN U.S.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE MAINTAINS THE RECENT THEME OF REASONABLE AGREEMENT
FOR THE LARGE SCALE PATTERN EVOLUTION BUT WITH SOME DIFFERENCES
FOR EMBEDDED DETAILS. THESE DIFFERENCES INVOLVE THE FORECAST OF THE
LEADING SOUTHERN TIER SYSTEM, MID-LATE WEEK EVOLUTION OVER THE
NORTHEAST AND VICINITY, A SYSTEM AFFECTING THE PACIFIC NORTHWEST
AROUND WEDNESDAY (AHEAD OF THE LARGE SCALE PACIFIC UPPER TROUGH),
AND THEN THE DEEP CENTRAL U.S. SYSTEM TOWARD THE END OF THE WEEK.
SOME SPREAD ALSO ARISES FOR EAST PACIFIC/WESTERN U.S. FLOW BY THE
END OF THE PERIOD NEXT SATURDAY.
DYNAMICAL AND MACHINE LEARNING (ML) MODELS MAINTAIN SOME SPREAD
FOR THE LEADING SOUTHERN TIER SYSTEM. BASED ON GUIDANCE FROM THE
00Z/06Z CYCLE, THE ECMWF WAS ON THE SLOW SIDE BUT COULD BE USED AS
PART OF A COMPROMISE. THE NEW 12Z ECMWF RUN ADJUSTED FASTER TO THIS
COMPROMISE, WHILE THE 12Z GFS NUDGED FASTER FROM ITS PRIOR
INTERMEDIATE SOLUTION.
MEANWHILE GUIDANCE HAS BEEN SHOWING DIFFICULTY IN RESOLVING THE
EVOLUTION OF SMALL-SCALE SHORTWAVE ENERGY OFF THE WEST COAST
WEDNESDAY-THURSDAY, AFFECTING LOW PRESSURE FORECAST TO TRACK JUST
OFF THE PACIFIC NORTHWEST COAST. ECMWF RUNS HAVE BEEN THE MOST
PERSISTENT WITH ENERGY SPINNING UP A CONCENTRATED AND DEEP UPPER
LOW WITH CORRESPONDING DEEP LOW PRESSURE. IN CONTRAST, LATEST CMC
RUNS HAVE A MORE OPEN WAVE AND THUS FASTER/WEAKER LOW PRESSURE. ML
GUIDANCE IS SPLIT (VERSUS ALL RUNS BEING WEAK YESTERDAY) BUT THE
CLUSTER THAT DEVELOPS A STRONGER LOW IS MORE IN LINE WITH THE
GFS/00Z UKMET THAT ARE AROUND 980 MB VERSUS THE DEEPER 00Z ECMWF.
THE NEW 12Z ECMWF HAS ADJUSTED TO THIS INTERMEDIATE IDEA THAT WAS
FAVORED.
AS THE UPPER TROUGH MOVES INLAND ACROSS THE WEST AND INTO THE
PLAINS, THE CONSENSUS OF DYNAMICAL MODEL/ENSEMBLE AND ML GUIDANCE
SUGGESTS THAT THE 00Z ECMWF MAY BE A LITTLE ON THE SLOW SIDE, AND
INDEED THE 12Z ECMWF HAS ADJUSTED FASTER TOWARD THE MAJORITY.
ACCORDINGLY, THE NEW ECMWF IS DEEPER AT THE SURFACE. THE ML MODEL
AVERAGE FOR CENTRAL HIGH PLAINS INTO UPPER MIDWEST LOW PRESSURE IS
GENERALLY IN THE LOWER HALF OF THE 980S MB, ADDITIONALLY MAKING THE
00Z ECMWF QUESTIONABLY WEAK. TIME WILL TELL ABOUT THE STRONGER
SIDE OF THE SPREAD. THE DEEP 00Z CMC OVER THE UPPER MIDWEST ON
SATURDAY TRENDED A FEW MB HIGHER IN THE 12Z RUN, WHILE GFS RUNS
HAVE BEEN INCONSISTENT BUT AVERAGING IN THE DEEPER HALF OF THE
SPREAD. A MODEL/ENSEMBLE BLEND WITH MANUAL ADJUSTMENT TO SUPPORT
LOW 980S DEPTH FRIDAY-SATURDAY LOOKS REASONABLE AND MAINTAINS
CONTINUITY. AS FOR THE EXPANDING RAINFALL SHIELD AHEAD OF THIS
SYSTEM, ML GUIDANCE FOR SATURDAY SHOWS THE AXIS OF HEAVIEST RAIN
MAY EXTEND FARTHER SOUTH TOWARD OR TO THE GULF COAST THAN GFS/GEFS
RUNS SUGGEST.
RECENT DAYS OF GUIDANCE HAS BEEN AT ODDS FOR THE PATTERN OVER THE
NORTHEAST AND VICINITY AROUND THURSDAY, WITH A SPLIT AMONG THE
STRONGER SHORTWAVE/SURFACE LOW PRESSURE OF THE ECMWF/ECMWF MEAN
VERSUS THE FLATTER GFS CLUSTER ALOFT WITH MORE HIGH PRESSURE. INTO
THE 00Z/06Z CYCLE TODAY, REMAINING SUPPORT FOR THE ECMWF SCENARIO
APPEARED TO BE WANING SOMEWHAT, WITH THE NEXT CLOSEST THEME COMING
FROM SOME ML MODELS THAT HAD WEAK WAVINESS OVER THE OHIO
VALLEY/MID-ATLANTIC. CONTINUITY FAVORED HOLDING ONTO AN
INTERMEDIATE SOLUTION WITH A HINT OF SURFACE WAVINESS UNTIL
CONFIDENCE IMPROVED. THE NEW 12Z ECMWF HAS TEMPERED THE SIGNAL FOR
SUCH A WAVE, SO PROBABLE ADJUSTMENTS WOULD BE TOWARD HIGHER SURFACE
PRESSURES AND LESS PRECIPITATION.
A BLEND APPROACH PROVIDES A GOOD STARTING POINT FOR THE EASTERN
PACIFIC/WEST COAST LATE WEEK, WITH THE MAJORITY OF GUIDANCE
GENERALLY FAVORING A FLAT MEAN RIDGE ALOFT OVER THE EAST PACIFIC
TOWARD THE WEST COAST.
FORECAST PREFERENCES LED TO A STARTING BLEND CONSISTING OF THE 06Z
GFS/00Z ECMWF/00Z UKMET FOR THE FIRST HALF OF THE PERIOD, FOLLOWED
BY A TRANSITION TO SOME 06Z GEFS/00Z ECENS INCLUSION ALONG WITH
SPLITTING THE GFS COMPONENT BETWEEN THE 00Z/06Z RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
ON TUESDAY, SOME MODEST LOWER ELEVATION RAIN AND HIGHER ELEVATION
SNOW IS FORECAST ACROSS SOUTHERN CALIFORNIA AND THE SOUTHWEST,
LIKELY REMAINING BELOW EXCESSIVE RAINFALL THRESHOLDS. THEN THE MAIN
ATMOSPHERIC RIVER WILL COME INTO THE WEST AHEAD OF THE DEEP
EASTERN PACIFIC/WEST TROUGH BY LATE TUESDAY OR WEDNESDAY. WEDNESDAY
SHOULD BE THE PRIMARY DAY FOR THE AR TO MOVE THROUGH CALIFORNIA,
AND A MARGINAL RISK IS IN PLACE FOR THE DAY 5 ERO ACROSS LOWER
ELEVATION AREAS. THE RELATIVELY FAST MOVEMENT OF THE AR COULD LIMIT
THE FLOODING POTENTIAL TO STAY BELOW SLIGHT RISK LEVELS, BUT WILL
CONTINUE TO MONITOR FOR ANY LOCALIZED ENHANCED AREAS THAT COULD
FLOOD, WITH PARTICULAR CONCERN FOR BURN SCARS. THERE ALSO REMAINS A
CHANCE THAT THE AR COULD COME INTO NORTHERN CALIFORNIA/FAR
SOUTHERN OREGON BEFORE 12Z WEDNESDAY (DURING THE DAY 4 ERO PERIOD),
BUT CONTINUE TO HOLD OFF ON ANY ERO RISK FOR DAY 4 GIVEN THE MODEL
SPREAD ON THE TIMING. NEW GUIDANCE FAVORS NO CHANGE TO THE DAYS
4-5 EROS AT THIS TIME. HIGHER ELEVATION SNOW COULD BE HEAVY ACROSS
THE SIERRA NEVADA WITH THE AR. MORE BROADLY, AREAS OF RAIN AND
HIGHER ELEVATION SNOW ARE FORECAST TO SPREAD ACROSS MUCH OF THE
WEST WEDNESDAY-THURSDAY. WIDESPREAD HIGH WINDS WILL ALSO BE A
CONCERN THERE. TOWARD THE END OF THE WEEK ANOTHER FRONTAL SYSTEM
MAY BRING SOME RAIN AND MOUNTAIN SNOW OF VARYING INTENSITY TO THE
PACIFIC NORTHWEST AND NORTHERN CALIFORNIA.
FARTHER EAST, RAIN IS FORECAST TO SPREAD ACROSS THE LOWER
MISSISSIPPI AND TENNESSEE VALLEYS AND SOUTHEAST WEDNESDAY-THURSDAY
AHEAD OF THE INITIAL SHORTWAVE AND A COUPLE OF FRONTAL SYSTEMS.
FARTHER NORTH THERE IS SOME MODEL SPREAD WITH SHORTWAVES AND
FRONTAL SYSTEMS THAT COULD CAUSE PRECIPITATION. GENERALLY THE
LATEST MODEL TRENDS ARE SHOWING DECREASING PRECIPITATION
POTENTIAL/AMOUNTS ACROSS THE GREAT LAKES TO NORTHEAST.
AS THE PRIMARY UPPER TROUGH MOVES INTO THE CENTRAL U.S., THERE IS
HIGH CONFIDENCE IN SURFACE LOW DEVELOPMENT/CONSOLIDATION IN THE
CENTRAL PLAINS BY FRIDAY WITH STRONG FRONTS. ON THE BACKSIDE OF THE
LOW, SNOW COULD SPREAD ACROSS THE CENTRAL HIGH PLAINS AND INTO THE
DAKOTAS ON FRIDAY AND PERHAPS INTO THE UPPER MIDWEST ON SATURDAY.
RAIN CHANCES EMERGE AHEAD OF THE COLD FRONT ACROSS THE MISSISSIPPI
VALLEY FRIDAY, AND HEAVIER RAIN IS LIKELY BY NEXT SATURDAY WITH THE
CURRENT FORECAST SHOWING IT CENTERED IN THE TENNESSEE VALLEY AND
VICINITY, POSSIBLY EXTENDING AS FAR SOUTH AS THE GULF COAST. WINDS
ARE ANOTHER POSSIBLE CONCERN WITH THE DEEP LOW, AND IN THE PLAINS
BEHIND THE COLD FRONT. CURRENTLY THE GUIDANCE SHOWS THE POTENTIAL
FOR HIGHEST WIND SPEEDS OVER THE SOUTHERN ROCKIES/HIGH PLAINS
AROUND FRIDAY. MONITOR STORM PREDICTION CENTER OUTLOOKS FOR THE
LATEST INFORMATION REGARDING POTENTIAL SEVERE WEATHER THREATS.
ABOVE AVERAGE TEMPERATURES ARE LIKELY OVER MOST AREAS EAST OF THE
ROCKIES DURING THE PERIOD. TEMPERATURES OF 15-20F OR SO ABOVE
NORMAL ARE FORECAST ACROSS THE OHIO VALLEY TO NORTHEAST ON TUESDAY,
WITH ANOMALIES OF THAT MAGNITUDE PUSHING A BIT SOUTHWARD WEDNESDAY
WITH A BACKDOOR FRONT IN THE NORTHEAST. HIGHS COULD REACH THE 60S
AND 70S. TEMPERATURES ARE FORECAST TO INCREASE IN THE NORTHERN
PLAINS TO MIDWEST AND GREAT LAKES THURSDAY AND FRIDAY (CONTINUING
INTO SATURDAY OVER THE GREAT LAKES/UPPER OHIO VALLEY), WITH
ANOMALIES REACHING 20F TO APPROACHING 30F ABOVE AVERAGE.
TEMPERATURES IN THE SOUTH-CENTRAL U.S. COULD REACH THE 80S WHILE
LOCALIZED AREAS LIKE FAR SOUTH TEXAS CAN EXPECT 90S, EVEN
APPROACHING 100F. THE PLAINS ARE LIKELY TO COOL LATE WEEK BEHIND
THE COLD FRONT. MEANWHILE, THE TROUGHING ACROSS THE WEST ALONG WITH
INCREASING CLOUDS AND PRECIPITATION WILL PROMOTE BELOW NORMAL
TEMPERATURES SPREADING ACROSS THE REGION AS THE WEEK PROGRESSES.
HIGHS ARE FORECAST TO BE GENERALLY BELOW AVERAGE BY 15-20 DEGREES
EXCEPT OVER NORTHERN AREAS, WHILE LOWS OF 5-15 DEGREES BELOW NORMAL
ARE LIKELY.
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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