020
FXUS02 KWBC 080707
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 AM 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 CENTRAL U.S. FRIDAY...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS TUESDAY, A LEADING SOUTHERN
STREAM COMPACT CLOSED UPPER LOW/SHORTWAVE WILL MAKE ITS WAY INTO
SOUTHERN CALIFORNIA AND VICINITY. THIS SHOULD PROMOTE LIGHT TO
MODERATE PRECIPITATION SPREADING INTO THE SOUTHWEST AND EVENTUALLY
THE LOWER MISSISSIPPI VALLEY TO SOUTHEAST WEDNESDAY-THURSDAY AS THE
UPPER SHORTWAVE MOVES EASTWARD, FORMS A SURFACE LOW, AND TAPS INTO
GULF MOISTURE. UPSTREAM, THERE REMAINS HIGH CONFIDENCE THAT A DEEP
AND PHASED UPPER TROUGH WILL MOVE THROUGH THE EASTERN PACIFIC
MIDWEEK INTO THE WEST LATER WEEK ALONG WITH AN ATMOSPHERIC RIVER,
WHICH WILL BRING WIDESPREAD RAIN AND HIGHER ELEVATION SNOW ACROSS
THE WEST. A STRONG SURFACE LOW IS FORECAST TO DEVELOP IN THE
CENTRAL PLAINS IN THE LEE OF THE COLORADO ROCKIES AS THIS TROUGH
PIVOTS EAST. SNOW IS POSSIBLE ON THE BACKSIDE OF THE LOW IN THE
NORTH-CENTRAL U.S. WHILE RAIN IS LIKELY IN THE MISSISSIPPI VALLEY.
EAST OF THE MAIN TROUGH, BOUTS OF UPPER RIDGING WILL ALLOW FOR
ABOVE NORMAL TEMPERATURES ACROSS THE CENTRAL AND EASTERN U.S. FOR
MUCH OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT ON THE BROAD SCALE
WHILE SMALLER SCALE FEATURES SHOW VARYING DEGREES OF SPREAD. MODELS
CONTINUE TO VARY WITH THE TIMING OF A SOUTHEAST UPPER/SURFACE LOW
PULLING AWAY AS THE PERIOD BEGINS TUESDAY, WITH THE CMC ON THE
SLOWER SIDE OF THE ENVELOPE. THE FIRST UPPER TROUGH/COMPACT CLOSED
LOW AND THE ASSOCIATED SURFACE LOW ENTERING SOUTHERN CALIFORNIA
TUESDAY SHOW PRETTY GOOD AGREEMENT ON TIMING INITIALLY, THOUGH AS
THEY TRACK QUICKLY ACROSS THE SOUTHERN TIER, ECMWF RUNS BECOME
SLOWER THAN THE REST OF THE GUIDANCE. THE 12Z ECMWF WAS STILL
WITHIN THE BALLPARK OF OTHER MODELS BUT THE NEWER 00Z ECMWF HAS
TRENDED EVEN SLOWER. FUTURE FORECASTS WILL CONTINUE TO MONITOR TO
SEE IF OTHER GUIDANCE, INCLUDING THE 00Z RUNS OF THE AI/ML MODELS,
START TO SHOW THIS TREND. THIS WILL AFFECT AN ASSOCIATED SURFACE
LOW TRACK AND TIMING AS WELL, BUT NEWER 00Z GUIDANCE SHOWS THE
SURFACE LOW QUITE WEAK OR DISSIPATED BY EARLY THURSDAY.
THEN MODELS AGREE IN PRINCIPLE THAT DEEP TROUGHING WILL MOVE
THROUGH THE EASTERN PACIFIC AND REACH THE WEST COAST BY THURSDAY.
ONE MODEL ISSUE IS THE POTENTIAL FOR A CLOSED UPPER LOW TO BE
EMBEDDED WITHIN THE TROUGH, PEAKING IN STRENGTH ON WEDNESDAY
OFFSHORE OF THE PACIFIC NORTHEAST. THE 12Z/18Z OPERATIONAL MODELS
WERE OVERALL ON BOARD WITH THIS UPPER LOW, WHICH SUPPORTED A DEEP
SURFACE LOW, BUT THE 00Z GFS AND CMC TRENDED AWAY FROM THIS DEEP
LOW WHILE THE 00Z ECMWF KEPT IT GOING. AT LEAST GUIDANCE AGREES IN
THE SHIFT OF THE TROUGH EASTWARD WITH TIME, AND SPINNING UP A
CONSOLIDATED SURFACE LOW IN THE CENTRAL PLAINS. THE 12Z CMC WAS
EAST OF CONSENSUS WITH THE SURFACE LOW BUT THE 00Z LOOKS MORE
REASONABLE. THE 12Z AND 18Z GFS SHOWED THE TROUGH BECOMING
POSITIVELY TILTED BY NEXT SATURDAY AS SOME ENERGY IS HELD BACK INTO
THE FOUR CORNERS, WHICH WAS NOT FAVORED AS IT WAS UNLIKE THE OTHER
MODELS AND THE ENSEMBLE MEANS.
THE WPC FORECAST BEGAN WITH A BLEND OF THE DETERMINISTIC GUIDANCE
FAVORING THE 12Z ECMWF AND THE 18Z GFS, AND INCREASED THE
PROPORTION OF ENSEMBLE MEANS TO HALF DAY 6 AND MORE DAY 7 AS MODEL
SPREAD INCREASED.
..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, SO 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. 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.
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 MODEL
GUIDANCE IS TRENDING LOWER WITH PRECIPITATION CHANCES, BUT THERE
COULD BE PERIODS OF LIGHT PRECIPITATION ACROSS THE GREAT LAKES TO
NORTHEAST.
AS THE PRIMARY 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. WINDS ARE ANOTHER POSSIBLE CONCERN WITH THE DEEP LOW, AND
IN THE PLAINS BEHIND THE COLD FRONT.
ABOVE AVERAGE TEMPERATURES ARE LIKELY GENERALLY FOR AREAS EAST OF
THE ROCKIES DURING THE PERIOD. TEMPERATURES OF 15-20F 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, 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 WHILE LOWS OF 5-15 DEGREES
BELOW NORMAL ARE LIKELY.
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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