831
FXUS02 KWBC 251859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST MON DEC 25 2023
VALID 12Z THU DEC 28 2023 - 12Z MON JAN 01 2024
...LOCALLY HEAVY PRECIPITATION POSSIBLE FOR NORTHERN CALIFORNIA
LATE WEEK...
..OVERVIEW
IT GENERALLY REMAINS THE CASE THAT UPPER RIDGING OVER WESTERN
CANADA, AS WELL AS THE WESTERN U.S. THROUGH AT LEAST SATURDAY,
WILL SUPPORT A MEAN TROUGH OVER THE EASTERN U.S. DURING THE
PERIOD. WITHIN THE EASTERN TROUGH A LEADING UPPER LOW SHOULD
TRACK OUT OF THE LOWER OHIO VALLEY WITH CONTINUED UNCERTAINTY OVER
HOW NORTHERN STREAM FLOW MAY INTERACT. ANOTHER SHORTWAVE/SURFACE
FRONT MAY DROP INTO THE MEAN TROUGH SATURDAY ONWARD. MEANWHILE
WEAKENING SHORTWAVE ENERGY WILL QUICKLY BRUSH THE NORTHWEST EARLY
THURSDAY AND THEN A SHARPENING/NEGATIVELY TILTING TROUGH WILL
LIKELY REACH THE WEST COAST BY FRIDAY NIGHT/EARLY SATURDAY,
BRINGING A BRIEF EPISODE OF ENHANCED PRECIPITATION TO THE CENTRAL
WEST COAST. AFTER EARLY SATURDAY THE DETAILS BECOME VERY UNCLEAR
FOR WHAT WILL HAPPEN TO THIS SHORTWAVE ENERGY AS WELL AS FOR
POTENTIAL UPSTREAM ENERGY. EXPECT CHILLY TEMPERATURES FOR MOST OF
THE PERIOD OVER THE SOUTH AND NEAR TO ABOVE NORMAL READINGS OVER
MOST OTHER AREAS OF THE LOWER 48.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS CONTINUE TO TREND INTO BETTER AGREEMENT WITH THE MID-LARGER
SCALE SYSTEM AND PATTERN EVOLUTION FOR THURSDAY AND FRIDAY, ALBEIT
WITH LINGERING SMALLER SCALE DIFFERENCES THAT SEEM BEST MITIGATED
BY A COMPOSITE BLEND OF THE 06 UTC GFS AND 00 UTC
ECMWF/UKMET/CANADIAN THAT SEEMS QUITE COMPATIBLE WITH THE 13 UTC
NBM, ENSEMBLE MEANS AS WELL AS WPC PRODUCT CONTINUITY, BOLSTERING
FORECAST CONFIDENCE. CYCLE TO CYCLE MODEL CONTINUITY ISSUES AND
FORECAST SPREAD INCREASE OVER THE EXTENDED NEW YEAR'S HOLIDAY
WEEKEND INTO 2024, LOWERING FORECAST CONFIDENCE. THIS REMAINS THE
CASE WITH THE LATEST 12 UTC MODEL CYCLE. ACCORDINGLY, A BLEND OF
THE MORE REASONABLY COMPATIBLE AND CYCLE CONSISTENT GEFS/ECMWF
ENSEMBLE MEANS SEEMS TO PROVIDE A BETTER FORECAST BASIS SOME
MANUAL ADJUSTMENTS WERE APPLIED TO MAINTAIN SOME SURFACE SYSTEM
DETAIL CONSISTENT WITH SUPPORT AND GUIDANCE SIGNAL. WPC MEDIUM
RANGE SURFACE PRESSURE/FRONTAL PROGS WERE SIMPLIFIED TO BLEND BEST
WITH THE SPLIT FLOW PATTERN OVER THE NATION AND PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
A LEADING DEPARTING WAVE SHOULD BRING SOME PRECIPITATION TO THE
NORTHEAST ON THURSDAY, WITH SNOW OVER FAR NORTHERN NEW ENGLAND AND
RAIN TO THE SOUTH. THE UPPER LOW TRACKING OUT OF THE LOWER OHIO
VALLEY SHOULD SUPPORT AN AREA OF RAIN/SNOW ALONG ITS PATH LATE
THIS WEEK, WITH BEST POTENTIAL FOR HIGHEST SNOW ACCUMULATIONS OVER
FAVORED TERRAIN IN THE APPALACHIANS, BUT POCKETED COLD AIR AND
DEFORMATION TO THE NORTH OF CLOSED LOW PASSAGE MAY SUPPORT
ADDITIONAL SPILLOVER/AREAL COVERAGE AS PER THE LATEST WPC DAY
4/WWO CENTERED ON FRIDAY. INTERIOR NORTHEAST LOCATIONS COULD SEE
ANOTHER EPISODE OF SNOW DEPENDING ON DETAILS OF EASTERN CANADA
TROUGH ENERGY BY THE WEEKEND, WHILE SOME MOSTLY LIGHT
PRECIPITATION MAY BE POSSIBLE WITH A WAVE/FRONT OVER THE
CENTRAL/EASTERN U.S. FROM SATURDAY ONWARD. RAINFALL COULD BE
SOMEWHAT HEAVIER IN THE EVENT OF A LESS PROBABLE SLOWER UPPER
TROUGH IN THAT TIME FRAME.
OVER THE WEST, A LATE WEEK PACIFIC SHORTWAVE/WEAKENING FRONTAL
SYSTEM WILL PROVIDE THE BEST FOCUS FOR MEANINGFUL PRECIPITATION
ALONG THE CENTRAL WEST COAST. THE DAY 5/FRIDAY EXCESSIVE RAINFALL
OUTLOOK PROPOSES A MARGINAL RISK AREA COVERING PORTIONS OF
NORTHERN CALIFORNIA AND FAR SOUTHWEST CORNER OF OREGON. MODEL
QPFS VARY OVER THIS REGION BUT THERE IS AN INDICATION OF SOME
INSTABILITY REACHING THE CALIFORNIA COAST AND THE SYSTEM'S
ORIENTATION COULD ALLOW FOR SOME TRAINING BANDS OF ENHANCED
RAINFALL. ANOTHER EVENT A COUPLE DAYS EARLIER SHOULD LEAD TO DAMP
ANTECEDENT CONDITIONS AS WELL. SOME ACTIVITY MAY LINGER INTO
SATURDAY, WHILE SNOW IS POSSIBLE AT HIGH ELEVATIONS. CONFIDENCE
REMAINS LOW REGARDING COVERAGE OF ANY LIGHTER PRECIPITATION THAT
COULD EXTEND FARTHER INTO THE WEST. THE PACIFIC NORTHWEST SHOULD
ALSO SEE SOME PRECIPITATION FROM THIS EVENT BUT WITH LOWER TOTALS
THAN FORECAST ALONG THE CENTRAL WEST COAST.
THE FORECAST PATTERN WILL FAVOR MULTIPLE DAYS OF CHILLY WEATHER
ACROSS THE SOUTH, WITH TEMPERATURES 5-15F BELOW NORMAL. FLORIDA
SHOULD SEE THE BEST POTENTIAL FOR DOUBLE-DIGIT ANOMALIES. THE
SOUTHEAST SHOULD BEGIN TO MODERATE BY SUNDAY-MONDAY BUT WITH
FLORIDA LIKELY STAYING BELOW NORMAL THROUGH THAT TIME. ON THE
OTHER HAND, PARTS OF THE FAR NORTHERN PLAINS AND UPPER MIDWEST
WILL BE CONSISTENTLY ABOVE NORMAL BY 10F OR MORE. MORNING LOWS
FROM THE UPPER MIDWEST INTO NORTHEAST MAY BE AT LEAST 20F ABOVE
NORMAL ON THURSDAY, WHICH COULD LEAD TO SOME DAILY RECORDS FOR
WARM LOWS IN THE NORTHEAST IF THEY HOLD FOR THE CALENDAR DAY.
MUCH OF THE WEST WILL SEE MODERATELY ABOVE NORMAL READINGS DURING
THE PERIOD BUT WITH A SLIGHT COOLING TREND IF UPPER RIDGING
WEAKENS A LITTLE AS CURRENTLY FORECAST.
RAUSCH/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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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