936
FXUS02 KWBC 131857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 PM EST MON JAN 13 2025
VALID 12Z THU JAN 16 2025 - 12Z MON JAN 20 2025
...STRONG ARCTIC SURGE PUSHING INTO THE CENTRAL U.S. BY THE WEEKEND
AND GRADUALLY EXPANDING EASTWARD...
..OVERVIEW
IT GENERALLY REMAINS THE CASE THAT THE MODELS AND ENSEMBLES STILL
SHOW THE MEAN PATTERN EVOLVING TOWARD A VERY AMPLIFIED REGIME
CONSISTING OF A RIDGE EXTENDING FROM THE EASTERN PACIFIC WELL
NORTHWARD AND A HUDSON BAY INTO NORTHERN MEXICO MEAN TROUGH BY THE
WEEKEND. AS A RESULT EXPECT VERY COLD AIR TO DROP INTO THE CENTRAL
U.S. THEN, WITH BELOW NORMAL TEMPERATURES EXPANDING INTO THE
EASTERN HALF OF THE COUNTRY BY NEXT SUNDAY- MONDAY. ALTHOUGH THE
LARGE SCALE PATTERN HAS WELL ABOVE AVERAGE
CONFIDENCE/PREDICTABILITY, THERE ARE EMBEDDED SHORTWAVE DETAILS
THAT GUIDANCE HAS BEEN SHOWING SIGNIFICANT DIFFICULTY IN RESOLVING.
AS A RESULT CONFIDENCE IS BELOW AVERAGE FOR ANY ASSOCIATED SURFACE
WAVES THAT COULD HAVE A SIGNIFICANT INFLUENCE ON SENSIBLE WEATHER
OVER THE EAST (WITH RAIN SOUTH AND POTENTIAL WINTRY WEATHER FARTHER
NORTH) FROM THE WEEKEND INTO EARLY NEXT WEEK. THERE ARE ALSO
UNCERTAINTIES WITH A LEADING SHORTWAVE CROSSING THE SOUTHEASTERN
QUADRANT OF THE LOWER 48 AROUND THURSDAY AND A LOWER LATITUDE
PACIFIC UPPER LOW WHOSE ENERGY SHOULD OPEN UP AND EJECT ACROSS THE
LOWER 48.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FOR EARLY IN THE PERIOD ON THURSDAY, THERE ARE STILL NOTABLE
DIFFERENCES WITH A SHORTWAVE FORECAST TO CROSS THE SOUTHEASTERN
QUADRANT OF THE COUNTRY. IN PARTICULAR, THE 00Z GFS IS A DEEP AND
SLOW EXTREME RELATIVE TO OTHER NEW GUIDANCE AND THIS RESULTS IN THE
MODEL RUN SPREADING MUCH MORE RAINFALL ACROSS FLORIDA. WHILE THE
MAJORITY OF GUIDANCE IS SIGNALING A WEAKER/FASTER SHORTWAVE WITH A
CORRESPONDING DRIER FORECAST OVER FLORIDA, THERE HAVE BEEN PREVIOUS
RANDOM SOLUTIONS WITH A GFS-LIKE SCENARIO. PREFERENCES SIDE WITH
THE MAJORITY SCENARIO BUT WITH THE UNDERSTANDING THAT A LOW-
PROBABILITY RISK STILL EXISTS FOR THE ALTERNATIVE. THE 06/12 UTC
GFS HAS TRENDED FROM THE OUTLIER 00 UTC GFS RUN TOWARD CONCENSUS.
GUIDANCE HAS RECENTLY NUDGED A LITTLE STRONGER WITH THE SYSTEM
FORECAST TO TRACK NEAR NORTHERN MINNESOTA/LAKE SUPERIOR AROUND
FRIDAY AND CONTINUE INTO EASTERN CANADA THEREAFTER. AMPLIFYING
DYNAMICS WILL PUSH THE TRAILING COLD FRONT SOUTH AND EAST, WITH
NOTABLE SPREAD/CONTINUITY CHANGES FOR SHORTWAVE ENERGY FORECAST TO
DROP THROUGH THE WEST. RECENT ECMWF/GFS HAVE BEEN SOMEWHAT MORE
PROGRESSIVE THAN CMC/CMCENS RUNS IN SHOWING THAT SHOW THE GREATEST
AMPLITUDE/SHARPNESS OF WESTERN ENERGY. EARLY ON SOME OF THESE
DIFFERENCES INFLUENCE THE DETAILS OF SHEARING PACIFIC UPPER LOW
ENERGY (WITH SOME INFLUENCE ON SURFACE WAVINESS/SOUTHERN TIER
RAINFALL FARTHER EAST). 12 UTC MODELS GENERALLY MAINTAIN THESE
STILL PLUASIBLE GUIDANCE CAMPS WITHOUT CLEAR RESOLVE.
THEN, SHORTWAVE DIFFERENCES HAVE A MORE SIGNIFICANT INFLUENCE ON
POTENTIAL SURFACE DEVELOPMENT TOWARD NEXT SUNDAY-MONDAY. LATEST
ECMWF RUNS AND SOME MACHINE LEARNING (ML) MODELS SHOW POTENTIAL FOR
SOME COMBINATION OF SHORTWAVE ENERGY TO SUPPORT A MID-ATLANTIC
WAVE THAT TRACKS JUST OFFSHORE NEW ENGLAND AND INTO OR SOUTH OF
THE CANADIAN MARITIMES. YESTERDAY'S 18Z GFS FIT INTO THIS CLUSTER
AS WELL, BUT YESTERDAY'S 12Z AND NEW 00Z RUNS SHOW A MORE INLAND
SURFACE LOW TRACK THAT SEEMS TO HAVE MINIMAL SUPPORT FROM OTHER
GUIDANCE. THE NEWER 12 UTC GFS NOW DEVELOPS A ORGANIZED LOW, BUT
JUST OFFSHORE. CMC/ICON RUNS SHOW A FLATTER EVOLUTION DUE TO
HOLDING THE SHARPEST UPPER TROUGHING FARTHER WEST. FINALLY, THERE
IS A FAIR AMOUNT OF SPREAD AMONG DYNAMICAL/ML MODELS FOR THE
STRENGTH AND LOCATION OF HIGH PRESSURE OVER THE CENTRAL U.S. BY
NEXT MONDAY, WITH NO DOMINANT CLUSTERING EVIDENT AT THIS TIME.
ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY
DERIVED FROM A BROAD COMPOSITE MODEL AND ENSMEBLE MEAN BLEND
THROUGH MEDIUM RANGE TIME SCALES. THIS REMAINS BROADLY ALIGNED
WITH WPC PRODUCT CONTINUITY AND THE NATIONAL BLEND OF MODELS.
..WEATHER/HAZARDS HIGHLIGHTS
AFTER A CHILLY START TO THURSDAY OVER PARTS OF THE EAST, EXPECT
TEMPERATURES TO MODERATE FROM LATE WEEK INTO THE WEEKEND AS ABOVE
NORMAL TEMPERATURES OVER THE PLAINS/MISSISSIPPI VALLEY ON
THURSDAY-FRIDAY (LOWS UP TO 15-25F ABOVE NORMAL OVER THE UPPER
MIDWEST) THEN REACH THE EAST WITH LESS PRONOUNCED ANOMALIES AHEAD
OF A COLD FRONT. BEHIND THE FRONT, EXPECT THE NORTHWEST TO SEE A
COOLING TREND ON FRIDAY, BUT THEN DURING THE WEEKEND THE EASTERN
ROCKIES INTO THE PLAINS WILL SEE A PRONOUNCED SURGE OF ARCTIC AIR.
EXPECT INCREASING COVERAGE OF TEMPERATURES THAT ARE 15-35F BELOW
NORMAL, WITH EXPANSION OF THE COLD AIR BRINGING HIGHS DOWN TO
10-20F BELOW NORMAL OVER THE EAST BY NEXT MONDAY. THE MOST EXTREME
ANOMALIES ARE LIKELY TO BE OVER THE CENTRAL HIGH PLAINS AND
VICINITY, WHILE COLDEST TEMPERATURES ON AN ABSOLUTE BASIS SHOULD BE
OVER FAR NORTHERN AREAS WHERE SOME SUBZERO HIGHS ARE POSSIBLE.
MUCH OF THE LOWER 48 SHOULD BE FAIRLY DRY ON THURSDAY. THE BEST
ORGANIZED ACTIVITY SHOULD BE ACROSS PARTS OF THE GREAT LAKES INTO
THE CENTRAL APPALACHIANS WITH PERIODS OF SNOW FROM A COMBINATION OF
LAKE EFFECT AND A WEAKENING FRONTAL SYSTEM PASSING THROUGH THE
REGION. BY FRIDAY OR FRIDAY NIGHT, APPROACHING SHORTWAVE ENERGY AND
A COMBINATION OF FRONTS MAY START TO GENERATE SOME ENHANCED
RAINFALL ACROSS THE SOUTHERN TIER. HOWEVER DIFFERENCES IN SHORTWAVE
DETAILS LEAD TO A FAIR AMOUNT OF SPREAD FOR LOCATION AND MAGNITUDE
OF AMOUNTS. THEREFORE THE DAY 5 EXCESSIVE RAINFALL OUTLOOK DOES NOT
REFLECT ANY RISK AREAS AT THIS TIME. POTENTIAL EXISTS FOR MUCH OF
THE EAST TO SEE AT LEAST SOME PRECIPITATION IN THE SATURDAY INTO
SUNDAY OR MONDAY PERIOD, BUT GUIDANCE DIFFERENCES FOR POTENTIAL
SURFACE DEVELOPMENT KEEP CONFIDENCE LOW FOR DETAILS OF
PRECIPITATION COVERAGE AND AMOUNTS. BEST POTENTIAL FOR WINTRY
WEATHER WILL BE FROM THE MID-ATLANTIC NORTHWARD, WITH RAIN FARTHER
SOUTH AND A POSSIBLE TRANSITION ZONE IN-BETWEEN. FARTHER WEST,
EXPECT SNOW TO MOVE SOUTHWARD ACROSS THE ROCKIES/HIGH PLAINS LATE
THIS WEEK INTO THE WEEKEND AS PART OF THE ARCTIC SURGE, WITH
UPSLOPE FLOW HELPING TO ENHANCED ACCUMULATIONS OVER SOME AREAS.
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 (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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