798
FXUS02 KWBC 051915
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 PM EST MON JAN 5 2026
VALID 12Z THU JAN 08 2026 - 12Z MON JAN 12 2026
..OVERVIEW
QUASI-ZONAL FLOW OVER THE CONUS TO START THE MEDIUM RANGE PERIOD
WILL BECOME INCREASINGLY AMPLIFIED THURSDAY INTO THE WEEKEND. THIS
OCCURS AS A TROUGH DIGS AND DEEPENS OVER THE WESTERN/CENTRAL U.S.
BEFORE SLOWLY TRANSLATING EASTWARD ACROSS THE EASTERN U.S. THE
AMPLIFIED PATTERN WILL ALLOW FOR AN INCREASE IN PRECIPITATION
COVERAGE ALONG WITH WELL ABOVE NORMAL TEMPERATURES ACROSS MUCH OF
THE CENTRAL AND EASTERN U.S.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL GUIDANCE SHOWS REASONABLY GOOD AGREEMENT WITH
RESPECT TO THE LARGE SCALE PATTERN OVER THE COURSE OF THE MEDIUM
RANGE PERIOD, WITH EXPECTED DIFFERENCES IN SMALLER SCALE TEMPORAL
AND SPATIAL DETAILS INCREASING WITH TIME. THE PATTERN CONTINUES TO
SUPPORT SIGNIFICANT AMPLIFICATION ACROSS THE CONTINENTAL U.S., WITH
A DEEPENING TROUGH ACROSS THE CENTRAL AND EASTERN U.S. FLANKED BY
ANOMALOUS RIDGING BOTH UPSTREAM AND DOWNSTREAM. HOW THIS TROUGH AND
ITS ASSOCIATED SURFACE LOW PRESSURE EVOLVES WILL DEPEND ON THE
DEGREE OF PHASING OF MULTIPLE SHORTWAVES EMBEDDED WITHIN THE PARENT
TROUGH. GIVEN THE UPSTREAM AND DOWNSTREAM RIDGING, WHICH TENDS TO
BE UNDER-MODELED, CONTINUE TO FAVOR MORE PHASING AND A SLOWER
OVERALL EVOLUTION. THIS IS PRIMARILY SUPPORTED BY THE MACHINE
LEARNING GUIDANCE LIKE THE EC-AIFS AND THE AIGFS, WITH DYNAMICAL
SUPPORT (LESS SO) FROM THE EC, CMC, AND ICON. THE GFS IS ON THE
FASTER SIDE OF THE GUIDANCE ENVELOPE, BUT ISN'T THAT FAR OFF TO BE
COMPLETELY DETRIMENTAL TO THE FORECAST.
AS A RESULT, THE WPC FORECAST UTILIZED THE DETERMINISTIC EC, CMC,
AND GFS TO START, THEN GRADUALLY INCREASED WEIGHTING FROM THE EC
AND GEFS ENSEMBLE MEANS FOR DAYS 5-7. THIS PRODUCED A GOOD
COMPROMISE BETWEEN CAPTURING THE LARGER SCALE PATTERN WHILE
MAINTAINING SOME OF THE FINER DETAILS AND CONTINUITY.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION ACROSS THE WEST WILL BE ONGOING AS THE PERIOD
STARTS, BUT SHOULD WIND DOWN FRIDAY. SOME HEAVY SNOW IS POSSIBLE IN
THE HIGHER TERRAIN.
AS THE SHORTWAVE AND THE LARGER SCALE TROUGH OVER THE WEST PHASE
INTO THURSDAY, THE COMBINED TROUGH SHOULD TAP INTO GULF MOISTURE,
ALLOWING FOR WIDESPREAD PRECIPITATION FROM THE MISSISSIPPI VALLEY
INTO THE OHIO VALLEY. A FAVORABLE UPPER JET, MOISTURE ANOMALIES
OVER THE 90TH PERCENTILE FOR THIS TIME OF THE YEAR, AND SOME
INSTABILITY REACHING AS FAR NORTH AS THE OHIO VALLEY WILL SUPPORT
CONVECTION IN THIS REGION. MODEL 24-HOURLY QPFS SHOW 1-3 INCHES OF
RAIN, WITH LOCALLY HIGHER AMOUNTS, SUPPORTING A MARGINAL RISK FOR
THE THURSDAY/DAY 4 ERO. RAIN RATES WILL NEED TO OVERCOME THE
ANTECEDENT DRY CONDITIONS, WHICH MAY LIMIT THE OVERALL RISK, AT
LEAST INITIALLY. THE SYSTEM WILL TRACK INTO THE TENNESSEE
VALLEY/MID-ATLANTIC/OHIO VALLEY ON FRIDAY, AND ANOTHER MARGINAL
RISK IS MAINTAINED ACROSS THE TENNESSEE VALLEY WHERE MODEL QPFS ARE
HIGHEST RIGHT NOW AND WHERE THE FRONT MAY BE SLIGHTLY SLOWER TO
PROGRESS THROUGH. BRIEFLY CONSIDERED AN UPGRADE TO A SLIGHT RISK,
BUT ULTIMATELY DECIDED TO KEEP THE MARGINAL FOR NOW AND WAIT FOR
ADDITIONAL MODEL CYCLES. PRECIPITATION MOVES INTO THE EAST BY
SATURDAY, LIKELY CLEARING MOST OF THE COAST IN TIME FOR SUNDAY WITH
PARTS OF THE CAROLINAS AND THE SOUTHEAST AS POSSIBLE EXCEPTIONS.
ASIDE FROM THOSE COASTAL AREAS, ALONG WITH LAKE EFFECT AND UPSLOPE
SNOW SHOWERS ACROSS THE GREAT LAKES, THE REST OF THE COUNTRY LOOKS
MAINLY DRY ON SUNDAY. SIMILAR STORY AGAIN ON MONDAY WITH MOSTLY DRY
WEATHER OVERALL ASIDE FROM A WEAK SYSTEM CLIPPING THE UPPER
MIDWEST AND ENHANCING THE LAKE EFFECT SNOW ACROSS PARTS OF THE
GREAT LAKES.
ON THE COLD SIDE OF THIS SYSTEM, THERE IS THE POTENTIAL FOR
ACCUMULATING SNOW FROM THE NORTHERN/CENTRAL PLAINS TO THE UPPER
MIDWEST AND NORTHERN GREAT LAKES MAINLY FRIDAY INTO SATURDAY.
DETAILS WILL NEED TO BE SORTED OUT IN THE COMING DAYS, BUT THE
SIGNAL FOR A SWATH OF AT LEAST A FEW INCHES AND THE POTENTIAL FOR
6"+ WILL NEED TO BE CAREFULLY EVALUATED WITH FUTURE MODEL CYCLES.
TEMPERATURES ARE LIKELY TO BE WELL ABOVE AVERAGE ACROSS THE
ENTIRETY OF THE COUNTRY EAST OF THE ROCKIES BY MIDWEEK. TEMPERATURE
ANOMALIES OF 15 TO 25 DEGREES ABOVE AVERAGE WILL BE WIDESPREAD
FROM THE CENTRAL U.S. TO THE EAST THURSDAY AND FRIDAY. DAILY
RECORDS FOR WARM LOWS AND HIGHS COULD BE SET ACROSS THE SOUTHERN
TIER. MEANWHILE THE WEST/SOUTHWEST SHOULD BE CLOSER TO NORMAL OR
SLIGHTLY BELOW AS THE PATTERN TURNS MORE AMPLIFIED AND TROUGHING
DEVELOPS. TEMPERATURES ARE LIKELY TO MODERATE BACK TO NORMAL INTO
THE PLAINS AND MISSISSIPPI VALLEY BY SATURDAY AND THE EAST NEXT
SUNDAY BEHIND A POTENT COLD FRONT JUST AHEAD OF THE UPPER TROUGH. A
BUILDING RIDGE BEHIND THIS MAY BRING ABOVE NORMAL TEMPERATURES
BACK INTO THE NORTH-CENTRAL U.S. BY NEXT MONDAY.
MILLER/SANTORELLI
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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