847
FXUS02 KWBC 110659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST TUE FEB 11 2025
VALID 12Z FRI FEB 14 2025 - 12Z TUE FEB 18 2025
...RAINFALL TRENDING LIGHTER FOR COASTAL CALIFORNIA BY FRIDAY WHILE
HEAVY HEAVY SNOW CONTINUES FROM THE SIERRA NEVADA INLAND...
...ANOTHER ROUND OF SNOW FROM THE MIDWEST TO NORTHEAST FRIDAY-
SUNDAY WITH HEAVY RAIN LIKELY IN THE TENNESSEE VALLEY AND NEARBY
AREAS ESPECIALLY ON SATURDAY...
..OVERVIEW
THE VERY WET AND SNOWY SYSTEM REACHING THE WEST COAST ON THURSDAY
WILL INITIALLY SPREAD RAIN AND HEAVY MOUNTAIN SNOW OVER THE WEST ON
FRIDAY. THEN EXPECT A BROAD AREA OF HEAVY RAIN TO DEVELOP FROM NEAR
THE SOUTH-CENTRAL MISSISSIPPI VALLEY THROUGH THE TENNESSEE VALLEY
INTO CENTRAL APPALACHIANS BY SATURDAY AS DEVELOPING LOW PRESSURE
TRACKS NORTHEASTWARD, WITH THE LOW CONTINUING THROUGH THE NORTHEAST
INTO THE CANADIAN MARITIMES SUNDAY-MONDAY. AREAS FROM THE UPPER
MIDWEST THROUGH THE NORTHEAST WILL SEE THE BEST POTENTIAL FOR
SIGNIFICANT WINTRY WEATHER WITH THIS SYSTEM. THE NEXT PACIFIC
SYSTEM WILL TRACK FARTHER NORTH THAN THE LEADING ONE, CONFINING
THE RAIN AND HIGHER ELEVATION SNOW MORE TO THE NORTHWEST DURING THE
WEEKEND. THIS SYSTEM SHOULD SPREAD SOME RAIN AND MOUNTAIN SNOW
SOUTHEASTWARD INTO THE CENTRAL ROCKIES BY EARLY NEXT WEEK. THE
NORTHERN-CENTRAL PLAINS WILL SEE THE MOST PRONOUNCED AND PERSISTENT
COLD ANOMALIES, WITH A MODIFIED FORM OF THIS COLD REACHING THE EAST
EARLY NEXT WEEK. INCREASING PACIFIC INFLUENCE SHOULD HELP THE WEST
TO MODERATE FROM ITS CHILLY TEMPERATURES LEADING INTO FRIDAY. THE
SOUTHEAST WILL TEND TO SEE ABOVE NORMAL TEMPERATURES DURING THE
WEEKEND, WITH SOME OF THIS WARMTH BRIEFLY EXTENDING NORTHWARD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
BROADLY SPEAKING, LATEST GUIDANCE HAS DISPLAYED BETTER THAN AVERAGE
AGREEMENT AND CONTINUITY FOR MOST ASPECTS OF THE FORECAST, BUT AS
USUAL THERE ARE SOME EMBEDDED DETAIL UNCERTAINTIES ALONG WITH ONE
SOLUTION OR ANOTHER DIFFERING FROM CONSENSUS AT TIMES. OF
PARTICULAR INTEREST IS THE EASTERN U.S. SYSTEM DURING THE WEEKEND.
A MULTI-RUN AVERAGE OF THE ECMWF/ECENS MEAN HAVE BEEN PARTICULARLY
STABLE WITH AN EARLY SUNDAY SURFACE LOW POSITION OVER THE CENTRAL
APPALACHIANS/NORTHERN MID-ATLANTIC, WITH OTHER SOLUTIONS WAFFLING
SOMEWHAT NORTH OR SOUTH DEPENDING ON EXACT DETAILS OF UPPER
DYNAMICS. THEREAFTER, MOST MODELS SHOW MUCH STRONGER DEVELOPMENT
(EVEN IF NOT QUITE TO THE DEGREE OF THE ECMWF) THAN RECENT GFS RUNS
AS THE SYSTEM CONTINUES INTO THE CANADIAN MARITIMES. THIS MAY BE
RELATED TO THE GFS BEING A LITTLE SLOWER TO PULL AN INITIAL HUDSON
BAY/SOUTHEASTERN CANADA UPPER LOW EASTWARD. MACHINE LEARNING (ML)
MODELS ARE GENERALLY NOT QUITE AS DEEP AS THE DYNAMICAL MODEL
AVERAGE WITH THIS SYSTEM SUNDAY-MONDAY BUT CAN SOMETIMES BE A
LITTLE SLOW TO REFLECT A DEEPER CONSENSUS A FEW DAYS OUT IN TIME. A
MODEL/ENSEMBLE MEAN BLEND LOOKS GOOD FOR THE NEXT UPPER TROUGH
REACHING THE WEST EARLY NEXT WEEK, WITH REASONABLE AGREEMENT FROM
THE ML MODELS. THE 18Z GFS GOT QUESTIONABLY SHARP WITH ITS
SHORTWAVE BY NEXT TUESDAY.
THE UPDATED FORECAST STARTED WITH MORE 18Z GFS/12Z ECMWF EMPHASIS
RELATIVE TO THE 12Z UKMET/CMC EARLY-MID PERIOD, REFLECTING
CONSENSUS/CONTINUITY FOR SIGNIFICANT FEATURES. THEN BY MONDAY-
TUESDAY THE BLEND INCORPORATED 30-40 PERCENT TOTAL WEIGHT OF THE
18Z GEFS/12Z ECENS MEANS WHILE SWITCHING GFS INPUT FROM THE 18Z RUN
TO 12Z RUN.
..WEATHER/HAZARDS HIGHLIGHTS
AS OF EARLY FRIDAY, UPPER TROUGHING WILL BE STARTING INTO MOVE INTO
THE WEST WHILE THE ASSOCIATED SURFACE FRONT PASSES THROUGH FAR
SOUTHERN CALIFORNIA. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
MAINTAINS A MARGINAL RISK AREA ALONG THE FAR SOUTHERN COAST, WITH
LINGERING MOISTURE ALONG THE FRONT EARLY IN THE DAY AND THE UPPER
TROUGH PROVIDING SOME POSSIBLE INSTABILITY OVER BURN SCAR AREAS
THAT WOULD BE MOST SENSITIVE TO ADDITIONAL SHOWERS.
CONTINUED PROGRESSION OF THIS SYSTEM WILL SPREAD AREAS OF RAIN AND
HEAVY MOUNTAIN SNOW FARTHER INLAND, EASTWARD TO THE ROCKIES. THE
UPPER TROUGH WILL LIKELY SUPPORT SURFACE LOW DEVELOPMENT OVER THE
EASTERN HALF OF THE COUNTRY DURING THE WEEKEND. GUIDANCE HAS BEEN
FAIRLY AGREEABLE AND CONSISTENT IN DEPICTING POTENTIAL FOR A BROAD
AXIS OF HEAVY RAINFALL FROM THE SOUTH-CENTRAL MISSISSIPPI VALLEY
NORTHEASTWARD INTO THE CENTRAL APPALACHIANS ON SATURDAY, WITH
ANOMALOUS MOISTURE REPRESENTING A COMBINATION OF PACIFIC AND GULF
ORIGINS. SOME INSTABILITY SHOULD HELP TO ENHANCE RAIN RATES OVER
AT LEAST SOUTHERN AREAS AS WELL. IN ADDITION, A LARGE PORTION OF
THIS REGION WILL HAVE ALREADY EXPERIENCED HEAVY RAINFALL IN THE
SHORTER TERM. REFLECTING THE COMBINATION OF FORECAST RAINFALL AND
LIKELY WET GROUND CONDITIONS, THE DAY 5/SATURDAY ERO STARTS OUT
WITH A BROAD SLIGHT RISK AREA FROM THE SOUTH-CENTRAL MISSISSIPPI
VALLEY INTO THE CENTRAL APPALACHIANS. A DECENT PORTION OF THIS AREA
WOULD BE CONSIDERED A "HIGHER END" SLIGHT RISK AT THIS TIME, WITH
CLOSE EVALUATION FOR POTENTIAL UPGRADE AT SOME POINT DEPENDING ON
FUTURE GUIDANCE BEHAVIOR/CLUSTERING. THE SURROUNDING MARGINAL RISK
EXTENDS INTO THE NORTHERN MID-ATLANTIC WHERE GUIDANCE DEPICTS LESS
HEAVY BUT STILL SIGNIFICANT RAINFALL IN COMBINATION WITH WHAT WILL
LIKELY BE WET GROUND FROM SHORT-TERM SNOW AND RAIN. THERE IS A
MODEST SIGNAL THAT ACTIVITY COULD ALREADY GET LOCALLY HEAVY OVER
PARTS OF THE MISSISSIPPI VALLEY LATE IN THE DAY 4 TIME FRAME BUT
AGREEMENT IS NOT GOOD ENOUGH YET FOR A RISK AREA THEN.
MEANWHILE, AREAS FROM THE MIDWEST INTO THE NORTHEAST WILL SEE THE
BEST POTENTIAL FOR SIGNIFICANT SNOW FRIDAY-SUNDAY. A TRANSITION
ZONE OF WINTRY MIX MAY SEPARATE THE RAIN/SNOW AREAS. THERE IS STILL
SOME UNCERTAINTY IN THE PRECISE STRENGTH OF THE SURFACE LOW,
AFFECTING THE EXTENT OF VARIOUS PRECIPITATION TYPES. THERE MAY BE
A PERIOD OF GUSTY WINDS OVER PARTS OF THE EAST BEHIND THIS SYSTEM.
A NORTHEASTERN PACIFIC SYSTEM WILL LIKELY SPREAD RAIN AND HIGHER
ELEVATION SNOW INTO THE PACIFIC NORTHWEST ON SATURDAY. THERE IS
SOME UNCERTAINTY OVER INITIAL INTENSITY, THOUGH OVERALL EXPECT
MODERATE TOTALS. SUNDAY'S PRECIPITATION WILL LIKELY BE SOMEWHAT
HEAVIER WHILE MOISTURE BEGINS TO SPREAD FARTHER EASTWARD INTO THE
NORTHERN ROCKIES. RAIN AND HIGHER ELEVATION SNOW WILL PROGRESS
EAST/SOUTHEAST THROUGH THE ROCKIES EARLY NEXT WEEK WHILE TAPERING
OFF OVER THE PACIFIC NORTHWEST. THE EASTERN PERIPHERY OF ANOTHER
SYSTEM COULD BEGIN TO INFLUENCE THE REGION BY NEXT TUESDAY BUT WITH
LOW CONFIDENCE IN DETAILS AT THIS TIME.
THE NORTHERN AND CENTRAL PLAINS WILL BE MOST PERSISTENTLY BELOW
NORMAL FOR TEMPERATURES DURING THE PERIOD. COLDEST ANOMALIES UP TO
25-30F BELOW NORMAL FOR HIGHS ARE POSSIBLE OVER THE NORTHERN HIGH
PLAINS ON FRIDAY AND EXPANDING SOUTHWARD DURING THE WEEKEND.
DEPARTURE OF THE WEEKEND STORM IN THE EAST AND THE TRAILING UPPER
TROUGH WILL BRING BELOW NORMAL READINGS EASTWARD EARLY NEXT WEEK,
WITH HIGHS AT LEAST 10-20F BELOW NORMAL OVER THE GREAT LAKES/OHIO
VALLEY INTO THE NORTHEAST. AHEAD OF THIS STORM, EXPECT A BRIEF
SURGE OF WARMER AIR OVER THE EAST SATURDAY INTO SUNDAY. SOME HIGHS
OVER THE FLORIDA PENINSULA COULD CHALLENGE DAILY RECORDS,
ESPECIALLY ON SATURDAY. THE NORTHWEST MAY STAY A LITTLE BELOW
NORMAL FOR MOST OF THE PERIOD, BUT THE REMAINDER OF THE WEST
SHOULD TREND TOWARD NORMAL BY SUNDAY AND REACH MODESTLY ABOVE
NORMAL NEXT MONDAY. A COLD FRONT WILL LIKELY CONFINE THE WARMTH TO
FAR SOUTHERN AREAS BY TUESDAY (AND EXTENDING INTO SOUTHERN TEXAS).
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 (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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