049
FXUS02 KWBC 141841
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
141 PM EST SUN DEC 14 2025
VALID 12Z WED DEC 17 2025 - 12Z SUN DEC 21 2025
...ANOTHER SIGNIFICANT ATMOSPHERIC RIVER WILL IMPACT THE PACIFIC
NORTHWEST, PARTICULARLY INTO THURSDAY...
..OVERVIEW
IT GENERALLY REMAIN THE CASE THAT AS THE MEDIUM RANGE PERIOD
BEGINS MIDWEEK, QUASI-ZONAL FLOW WILL BE IN PLACE ACROSS THE LOWER
48 WITH QUICKLY MOVING EMBEDDED SYSTEMS, INCLUDING A COUPLE OF
SHALLOW SHORTWAVES OVER THE GREAT LAKES AND THE NORTHWEST. THE
NORTHWEST SHORTWAVE IS FORECAST TO BROADEN/DEEPEN AS IT MOVES EAST
INTO THE NORTH-CENTRAL U.S. THURSDAY AND INTO THE EAST BY FRIDAY
ACCOMPANIED BY A SURFACE LOW PRESSURE SYSTEM. UPSTREAM, STRONG
WESTERLY FLOW WILL FORCE ANOTHER ATMOSPHERIC RIVER (AR) INTO THE
NORTHWEST/NORTHERN CALIFORNIA INTO THURSDAY. ADDITIONAL FLOODING
IS POSSIBLE ESPECIALLY IN AREAS THAT HAVE SEEN EXCESSIVE RAINFALL
RECENTLY, AND HEAVY SNOW IS LIKELY IN THE HIGHER TERRAIN.
TEMPERATURE-WISE, THE FLAT FLOW WILL ALLOW FOR ABOVE AVERAGE
TEMPERATURES FOR MOST OF THE CONUS, THOUGH THE NORTHERN TIER COULD
SEE COLDER PERIODS WITH SHORTWAVES MOVING THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE QUASI-ZONAL PATTERN MIDWEEK INTO NEXT WEEKEND WITH EMBEDDED
SHORTWAVES IN FAST FLOW LEADS TO SOMEWHAT LOWER CONFIDENCE IN THE
DETAILS OF THE PATTERN THAT COULD HAVE SENSIBLE WEATHER IMPACTS,
THOUGH THE BROAD PATTERN REMAINS QUITE AGREEABLE. AS THE
AFOREMENTIONED SHORTWAVE TRACKS QUICKLY ACROSS THE NORTHERN TIER,
MOST DETERMINISTIC AND AI MODELS NOW SHOW REASONABLE CONSENSUS AND
A MULTI-MODEL BLEND SEEMS REASONABLE.
THERE IS GOOD MODEL AGREEMENT IN THE ATMOSPHERIC RIVER (AR)COMING
INTO THE PACIFIC NORTHWEST INTO THURSDAY, BUT THE EXACT
ORIENTATION WILL MAKE A DIFFERENCE IN HOW MUCH OVERLAP OF HEAVY
RAIN THERE IS WITH THE WETTEST ANTECEDENT CONDITIONS OF THE RECENT
STRONG AR. WHILE GUIDANCE CLUSTERING HAS IMPROVED, WILL CONTINUE TO
MONITOR EVEN RELATIVELY SMALL MODEL DIFFERENCES THAT COULD BE
IMPACTFUL. BEHIND THIS AR, SHALLOW TROUGHING SHOWS SOME TIMING
DIFFERENCES THAT ARE HARD TO PICK OUT WITH THE FAST OVERALL FLOW
INTO THE REGION AND PROGRESSIVELY DOWNSTREAM OVER THE LOWER 48.
OVERALL, OPTED TO ADD SOME MULTI-MODEL ENSEMBLE MEAN GUIDANCE INTO
THE MODEL BLEND DAYS 5-7 TO TRY TO MITIGATE TIMING DIFFERENCES
CONSISTENT WITH INDIVIDUAL FEATURE PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
THE PACIFIC NORTHWEST CAN EXPECT A RELATIVE BREAK IN THE HEAVY
PRECIPITATION ON WEDNESDAY. HOWEVER, SOME LINGERING RAIN IS
FORECAST IN THE PACIFIC NORTHWEST, AND THE NEXT AR MAY START TO
AFFECT THE REGION OVERNIGHT WEDNESDAY. THIS COULD LEAD TO ISOLATED
FLOODING CONCERNS GIVEN THE SENSITIVE ANTECEDENT CONDITIONS, SO A
LOW END MARGINAL RISK IS IN PLACE FOR THE WPC DAY 4/WEDNESDAY ERO
FOR NORTHWEST OREGON INTO WESTERN WASHINGTON. THE NEXT AR IS
FORECAST TO IMPACT THE NORTHWEST ON THURSDAY. AS DISCUSSED ABOVE,
THE EXACT ORIENTATION AND NORTH-SOUTH AXIS OF THE AR WILL MAKE A
DIFFERENCE IN THE IMPACTS, BECAUSE OF THE POTENTIAL FOR OVERLAP
WITH THE WET ANTECEDENT CONDITIONS WITH A NORTHERN AR, OR LESS
OVERLAP IF THE AR IS FARTHER SOUTH. BUT THE MAGNITUDE OF THE IVT
AND GLOBAL MODELS SHOWING 5-7+" OF QPF GIVES SUPPORT FOR A SLIGHT
RISK IN THE DAY 5/THURSDAY ERO FOR WESTERN OREGON INTO
SOUTHWESTERN WASHINGTON FOR THE FLOODING POTENTIAL. MEANWHILE,
HEAVY SNOW IS LIKELY INTO THE CASCADES AND INTO THE NORTHERN
ROCKIES WITH THE AMPLE MOISTURE COMBINING WITH SUFFICIENTLY COLD
TEMPERATURES. THE IVT PLUME IS LIKELY TO DRIFT GRADUALLY SOUTH
TOWARD NORTHERN CALIFORNIA ON FRIDAY AND THEN LESSEN SATURDAY.
AS IMPULSES MOVE OUT OF THE NORTHWEST ACROSS THE NORTHERN TIER,
RAIN AND SNOW COULD SPREAD ACROSS THE NORTHERN PLAINS INTO
WEDNESDAY AND INTO THE MIDWEST AND 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 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.
MOST PRECIPITATION SHOULD BE PULLING AWAY ON FRIDAY, BUT WITH SOME
LAKE EFFECT PRECIPITATION POSSIBLE BEHIND THE MAIN SYSTEM. LIGHT TO
MODERATE PRECIPITATION MAY GET RENEWED ACROSS THE OHIO VALLEY BY
SATURDAY, THOUGH THIS IS UNCERTAIN.
WARMER THAN AVERAGE TEMPERATURES ARE FORECAST ACROSS THE WESTERN
AND CENTRAL U.S. THROUGH MUCH OF THE PERIOD. THE HIGHEST ANOMALIES
WILL LIKELY BE ACROSS THE HIGH PLAINS MOST DAYS, AS HIGHS IN THE
60S EXPAND INTO WESTERN NEBRASKA AND SOUTH DAKOTA ON WEDNESDAY AND
AGAIN ON FRIDAY (AFTER A COLD FRONT BRINGS BRIEFLY COOLER
TEMPERATURES THURSDAY. BY SATURDAY TEMPERATURES IN MUCH OF TEXAS
COULD REACH THE UPPER 70S TO LOW 80S. THE EASTERN U.S. CAN EXPECT
MORE TRANSIENT ABOVE AVERAGE TEMPERATURES AROUND THURSDAY AND
PERHAPS AGAIN INTO NEXT WEEKEND, BUT WITH PERIODS OF NEAR NORMAL
TEMPERATURES IN BETWEEN. MEANWHILE THE NORTHERN TIER IS FORECAST TO
SEE SHOTS OF COLD AIR WITH SHORTWAVES AND COLD SURFACE HIGHS
BEHIND COLD FRONTS.
TATE/SCHICHTEL
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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