503
FXUS02 KWBC 120800
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EST FRI DEC 12 2025
VALID 12Z MON DEC 15 2025 - 12Z FRI DEC 19 2025
...POTENTIALLY HAZARDOUS COLD TEMPERATURES ACROSS THE MIDWEST TO
SOUTHEAST MONDAY...
...ADDITIONAL ATMOSPHERIC RIVERS TO IMPACT THE PACIFIC NORTHWEST
FOR MUCH OF NEXT WEEK...
..OVERVIEW
INTO NEXT WEEK, THE PATTERN ALOFT WILL MAINLY BE TRANSITIONING TO
QUASI-ZONAL FLOW OVER THE LOWER 48, THOUGH WITH MULTIPLE SHORTWAVES
CAUSING POTENTIALLY IMPACTFUL WEATHER. ROUNDS OF ENERGY WILL
DIRECT ATMOSPHERIC RIVERS INTO THE PACIFIC NORTHWEST, CAUSING
ADDITIONAL CONCERNS FOR HEAVY RAIN AND FLOODING, ALONG WITH SOME
MOUNTAIN SNOW. SHORTWAVES AND FRONTAL SYSTEMS CONTINUING EAST COULD
LEAD TO AT LEAST MODEST PRECIPITATION CHANCES ACROSS THE NORTHERN
TIER AS WELL AS TO THE MIDWEST/MISSISSIPPI VALLEY TOWARDS MIDWEEK
AND TOWARD THE EASTERN U.S. THURSDAY. TEMPERATURE-WISE, COLD MEAN
NORTHWEST FLOW AND HIGH PRESSURE AT THE SURFACE WILL LEAD TO MUCH
BELOW AVERAGE TEMPERATURES ACROSS THE MIDWEST TO OHIO VALLEY TO
SOUTHEAST INTO MONDAY, BUT MOST OF THE LOWER 48 SHOULD WARM UP TO
ABOVE NORMAL AS THE UPPER-LEVEL PATTERN FLATTENS AS THE WEEK
PROGRESSES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE BEGINS THE PERIOD MONDAY IN REASONABLY GOOD
AGREEMENT WITH THE OVERALL PATTERN, CONSISTING OF EXITING TROUGHING
IN THE WESTERN ATLANTIC, COLD SURFACE HIGH PRESSURE BEHIND, AND
RIDGING ACROSS THE SOUTH-CENTRAL U.S. INTO THE GREAT BASIN, WHILE
SOUTHERN STREAM TROUGHING IS PRESENT ATOP SOUTHERN
CALIFORNIA/NORTHERN MEXICO INTO THE FOUR CORNERS REGION. THE 12/18Z
GFS RUNS WERE ON THE SLOWER SIDE IN MOVING THE SOUTHERN STREAM
TROUGH EASTWARD TUESDAY-WEDNESDAY, BUT THE 00Z GFS HAS SPED UP SOME
AND ALIGNS BETTER WITH OTHER GUIDANCE. THE WPC FORECAST USED A
MULTI-MODEL BLEND FAVORING THE 12Z ECMWF FOR THE EARLY PERIOD.
THERE ARE INCREASING DETAIL DIFFERENCES IN THE MODELS FROM MIDWEEK
AND BEYOND THAT COULD HAVE SENSIBLE WEATHER IMPACTS. FIRST, THE
12Z AND NEW 00Z CMC BOTH SEEM TO BE OUT OF PHASE WITH THE ECMWF AND
GFS RUNS (AND THEIR AI COUNTERPARTS) ACROSS THE NORTHERN TIER BY
EARLY WEDNESDAY, WITH THE CMC NOT SHOWING A SHORTWAVE IN THE GREAT
LAKES. THEN BEHIND THIS FEATURE, MODELS DO SHOW ANOTHER SHORTWAVE
MOVING ACROSS THE U.S./CANADA BORDER ALONG WITH A SURFACE LOW.
GUIDANCE GENERALLY SHOWS THIS MID-UPPER FEATURE DEEPENING AND
BROADENING A BIT MORE INTO A NOTABLE TROUGH MOVING ACROSS THE
MIDWEST AND THEN THE EAST LATER NEXT WEEK. HOWEVER, GFS RUNS ARE
THE EXCEPTION. GFS RUNS HAVE BEEN SHOWING MORE NORTHEAST PACIFIC
ENERGY ENTERING THE NORTHWEST BY WEDNESDAY-THURSDAY, WHICH SHUNTS
THE MIDWEST TROUGH EASTWARD MORE QUICKLY (NOT TO MENTION THE
IMPACTS OF TIMING OF ANOTHER POTENTIAL AR COMING INTO THE
NORTHWEST). EVEN THE AI-GFS IS MORE AGREEABLE WITH GUIDANCE OTHER
THAN THE GFS. RECENT GFS RUNS HAVE BEEN CONSISTENT WITH EACH OTHER
BUT INTERESTINGLY, GFS RUNS FROM A DAY OR TWO AGO WERE MORE LIKE
THE CURRENT MODEL CONSENSUS. THUS FOR THE LATTER HALF OF THE
PERIOD, REDUCED THE PROPORTION OF THE DETERMINISTIC GUIDANCE,
ESPECIALLY THE GFS, IN FAVOR OF THE ENSEMBLE MEANS. THE MEANS
COMPRISED ABOUT HALF THE BLEND DAY 6 AND MORE DAY 7 AMID THE
INCREASING SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
INTO MONDAY, ANOTHER ATMOSPHERIC RIVER IS FORECAST TO TAKE AIM AT
THE PACIFIC NORTHWEST. THIS AR SHOULD BE SHORTER LIVED THAN THIS
EXTREME RECENT EVENT. HOWEVER, THERE LOOKS TO BE STRONG IVT MOVING
INTO WASHINGTON AND OREGON ESPECIALLY EARLY MONDAY. ONE LIMITING
FACTOR SHOULD BE THAT THIS SHOULD BE ORIENTED MORE SOUTHWESTERLY
RATHER THAN COMPLETELY ORTHOGONAL TO THE TERRAIN. HOWEVER,
ANTECEDENT CONDITIONS WILL BE QUITE SENSITIVE TO ADDITIONAL
RAINFALL. A SLIGHT RISK HAS BEEN ADDED TO THE DAY 4/MONDAY ERO FOR
FLOODING CONCERNS. MOIST INFLOW (THOUGH NOT AS STRONG) SHOULD
CONTINUE INTO TUESDAY. HIGHER IVT LOOKS TO GET RENEWED LATE
TUESDAY, BUT FARTHER SOUTH TOWARD NORTHERN CALIFORNIA, WHICH HAS
NOT BEEN NEAR AS WET LATELY. THUS FOR DAY 5/TUESDAY, SHOW A
MARGINAL RISK IN THE ERO AS A STARTING POINT. YET ANOTHER AR SEEMS
LIKELY TO IMPACT THE NORTHWEST BY THURSDAY.
ON MONDAY, LAKE EFFECT SNOW IS POSSIBLE IN THE COLD WESTERLY FLOW
PATTERN BEHIND THE EXITING UPPER TROUGH. THEN AS IMPULSES MOVE OUT
OF THE NORTHWEST ACROSS THE NORTHERN TIER, RAIN AND SNOW COULD
SPREAD ACROSS THE NORTHERN PLAINS AROUND TUESDAY-WEDNESDAY AND INTO
THE GREAT LAKES REGION WEDNESDAY-THURSDAY. FARTHER SOUTH, SOME
GULF MOISTURE RETURN IS POSSIBLE FOR LIGHT TO MODERATE RAIN ACROSS
EASTERN TEXAS INTO THE LOWER AND MIDDLE MISSISSIPPI VALLEY FOR
TUESDAY AND WEDNESDAY. BY THURSDAY THESE SYSTEMS ARE LIKELY TO
INTERACT AND SPREAD BROADENING PRECIPITATION CHANCES ACROSS THE
EASTERN THIRD OF THE U.S. MOST OF THIS PRECIPITATION IS LIKELY TO
BE RAIN EXCEPT IN THE GREAT LAKES TO INTERIOR NORTHEAST.
COLD HIGH PRESSURE WILL SPREAD MUCH BELOW NORMAL TEMPERATURES
ACROSS THE MIDWEST, OHIO AND TENNESSEE VALLEYS, AND ALL THE WAY TO
THE GULF COAST EARLY MONDAY, WITH TEMPERATURES 15 TO 30 DEGREES
BELOW NORMAL. A FEW RECORD LOWS ARE POSSIBLE, AND WIND CHILLS MAY
DIP AS LOW AS THE TEENS AS FAR SOUTH AS THE SOUTHEASTERN ATLANTIC
AND GULF COASTS SUNDAY NIGHT/MONDAY MORNING. HOWEVER, UPPER LEVEL
RIDGING OVER THE WEST WILL ALLOW TEMPERATURES TO REACH 15F TO 25F
ABOVE SEASONAL AVERAGES, SPREADING EAST ACROSS MUCH OF THE LOWER 48
FOR MIDWEEK AND BEYOND, CREATING A DECEMBER THAW.
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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