335
FXUS02 KWBC 121957
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM 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
GUIDANCE HAS REMAINED CONSISTENT IN SHOWING A PATTERN CHANGE NEXT
WEEK FROM A MORE AMPLIFIED FLOW WITH MEAN UPPER-TROUGHING OVER THE
CENTRAL TO EASTERN U.S. AND UPPER-RIDGING FROM THE CENTRAL TO
WESTERN U.S. TO A QUASI-ZONAL PATTERN. FOLLOWING THE DEPARTURE OF
AN UPPER-TROUGH AND SURFACE LOW PRESSURE/FRONTAL SYSTEM OFF THE
EAST COAST SUNDAY, THE FLOW FLATTENS WITH BOTH AN ACTIVE NORTHERN
AND SOUTHERN STREAM SETTING UP OVER THE CONUS FEATURING MULTIPLE
SHORTWAVE PASSAGES AND SURFACE SYSTEMS. THE ACTIVE PATTERN WILL
ALSO BRING AT LEAST A COUPLE MORE ATMOSPHERIC RIVER EVENTS TO THE
PACIFIC NORTHWEST/NORTHERN CALIFORNIA, WITH ONE CENTERED ON MONDAY
AND THEN POTENTIALLY THURSDAY-FRIDAY LATER NEXT WEEK.
THE DETERMINISTIC GUIDANCE IS GENERALLY WELL CLUSTERED TO START
THE PERIOD WITH DIFFERENCES TIED MOSTLY TO THE SMALLER- SCALE AND
HARDER TO PREDICT TIMING OF EMBEDDED SHORTWAVES. THUS, THE INITIAL
UPDATED WPC FORECAST FEATURED A BLEND OF THE ECMWF/GFS/CMC ALONG
WITH A SMALL CONTRIBUTION FROM THE ECENS MEAN TO HELP WEIGHT THE
FORECAST CLOSER TOWARDS THIS BETTER-CENTERED CONSENSUS. THE
GUIDANCE BEGINS TO DIVERGE MORE INTO THE MIDDLE OF THE PERIOD
WEDNESDAY, AS THE CMC IS FASTER WITH BRINGING A NORTHERN STREAM
UPPER-WAVE/SURFACE LOW EAST ALONG THE U.S/CANADIAN BORDER. THE
BLEND WAS ADJUSTED TO INCLUDE MORE OF THE CMC ENSEMBLE MEAN OVER
THE CMC AS THIS BETTER MATCHED THE OTHER GUIDANCE. THEN, THE GFS
BEGINS TO SIGNIFICANTLY DIVERGE, AS THE ECMWF/CMC AND ENSEMBLE
MEANS BRING THIS SYSTEM EASTWARD ACROSS THE MIDWEST AND INTO
SOUTHEASTERN CANADA FASTER, WITH THE UPPER-LEVEL PATTERN ALSO
AMPLIFYING MORE. ADDITIONALLY, A SOUTHERN STREAM SYSTEM
PROGRESSES/SHEARS OUT FASTER, WITH THE COMBINATION OF THE STRONGER
NORTHERN STREAM SYSTEM AND FASTER/WEAKER SOUTHERN STREAM SYSTEM
ALLOWING POST- FRONTAL HIGH PRESSURE TO BUILD SOUTHWARD OVER THE
MIDWEST AND INTO THE SOUTHEAST COMPARED TO THE GFS. THUS, FOR THE
LATTER PART OF THE PERIOD, THE GFS WAS NOT INCLUDED AND A GREATER
CONTRIBUTION FROM THE SIMILARLY ALIGNED ECENS AND CMC ENSEMBLE
MEANS, AND EVEN A MORE CLOSELY ALIGNED GEFS MEAN, WAS INCLUDED. THE
NBM QPF HAS REMAINED MUCH DRIER AHEAD OF THESE NORTHERN AND
SOUTHERN STREAM SYSTEMS COMPARED TO OTHER GUIDANCE, SO THE WPC
FORECAST INCLUDED INCREASED AMOUNTS SPECIFICALLY IN THE TUESDAY TO
THURSDAY TIMEFRAME. THE NBM LOOKED REASONABLE ACROSS THE PACIFIC
NORTHWEST THROUGH THE TIME PERIOD DURING THE MULTIPLE ATMOSPHERIC
RIVER EVENTS, REASONABLY ACCOUNTING FOR TIMING, STRENGTH, AND
ORIENTATION DIFFERENCES.
..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 DOES NOT LOOK COMPARATIVELY AS HIGH AS MONDAY, AND IS
ORIENTED FARTHER SOUTH TOWARD NORTHERN CALIFORNIA AS WELL, 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.
PUTNAM/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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