579
FXUS02 KWBC 010707
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 AM EST WED JAN 1 2025
VALID 12Z SAT JAN 04 2025 - 12Z WED JAN 08 2025
...BROAD CHANCES FOR IMPACTFUL WINTRY WEATHER ACROSS THE NORTH-
CENTRAL U.S. TO MID-MISSISSIPPI AND OHIO VALLEYS TO THE EAST COAST
SATURDAY-MONDAY...
..OVERVIEW
AN UPPER TROUGH MOVING ACROSS THE INTERIOR WEST INTO THE HIGH
PLAINS OVER THE WEEKEND WILL SPIN UP A SURFACE LOW OVER THE
SOUTHERN PLAINS BY SUNDAY. THESE FEATURES WILL COMBINE WITH
MOISTURE TO PRODUCE PRECIPITATION IN MUCH OF THE CENTRAL AND
EASTERN U.S. INTO EARLY NEXT WEEK. ON THE SOUTHERN SIDE, HEAVY RAIN
AND THUNDERSTORMS ARE LIKELY OVER PARTS OF THE LOWER MISSISSIPPI
AND TENNESSEE VALLEYS. MEANWHILE COLDER THAN AVERAGE TEMPERATURES
IN PLACE FARTHER NORTH WILL LEAD TO A BROAD AREA OF POSSIBLY
IMPACTFUL SNOW ACCUMULATIONS IN THE NORTH-CENTRAL PLAINS TO MID-
MISSISSIPPI VALLEY AND OHIO VALLEY THIS WEEKEND, PERHAPS STRETCHING
INTO THE MID-ATLANTIC MONDAY. FREEZING RAIN AND SLEET ARE LIKELY
IN THE TRANSITION ZONE, WHICH COULD BE HAZARDOUS AS WELL. THEN
ADDITIONAL ENERGY DIVING INTO THE WEST NEXT WEEK SHOULD LEAD TO
BROAD UPPER TROUGHING AND NEAR TO BELOW AVERAGE TEMPERATURES FOR
MOST OF THE LOWER 48.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE PRIMARY MODEL DIAGNOSTICS CONCERN DURING THE MEDIUM RANGE
PERIOD IS WITH THE SURFACE LOW ACROSS THE CENTRAL AND EASTERN U.S.
AND ITS TRACK AND TIMING, NATURALLY RELATED TO THE UPPER TROUGH'S
TRACK AND TIMING. ECMWF RUNS, INCLUDING SOME AI/ML MODELS AND
ENSEMBLE MEMBERS, HAVE GENERALLY BEEN ON THE FASTER SIDE OF THE
GUIDANCE. GFS RUNS HAVE BEEN ON THE SLOWER SIDE, BUT WITH MORE
NORTH/SOUTH VARIABILITY (CAUSING P-TYPE DIFFERENCES). THE 12Z GFS
WAS FARTHEST SOUTH WHILE THE 18Z AND NEW 00Z HAVE BOTH BUMPED
NORTH. THE NEW 00Z GFS ALSO SLOWED DOWN COMPARED TO ITS 12/18Z RUNS
WHILE THE NEW 00Z ECMWF TRENDED EVEN FASTER. CMC RUNS HAVE BEEN IN
BETWEEN THE GFS AND EC CAMPS ON TIMING, AS WAS THE 12Z UKMET
(THOUGH THE UKMET ENDED UP FARTHER NORTH THAN CONSENSUS BY MONDAY).
GENERALLY, AN INTERMEDIATE SOLUTION IN BETWEEN THE SLOWER AND
FASTER MODELS SEEMS LIKE THE WISEST FORECAST, SO THE WPC FORECAST
WAS IN THE MIDDLE BY INCORPORATING THE CMC/UKMET AND ENSEMBLE MEANS
BLENDED WITH THE GFS/EC. THIS ALSO MATCHED THE PREVIOUS FORECAST
LOW TRACK REASONABLY WELL.
BY TUESDAY-WEDNESDAY, MODELS DIVERGE WITH WHETHER OR NOT ENERGY
DIVING SOUTH ACROSS THE WEST WILL PULL OFF INTO A CLOSED LOW
SOMEWHERE NEAR THE EASTERN PACIFIC/CALIFORNIA/MEXICO BORDER. THE
12Z CMC AND ECMWF CREATED THIS LOW WHILE GFS RUNS DID NOT, BUT THE
00Z GFS RUN HAS TENDED TOWARD HAVING A CLOSED LOW BY WEDNESDAY,
THOUGH MUCH FARTHER WEST OF CONSENSUS. THE BLEND WAS OVER HALF
ENSEMBLE MEANS BY THIS FORECAST PERIOD, WHICH WERE MORE PHASED (DID
NOT SHOW THE CLOSED LOW) AS EXPECTED, BUT WILL CONTINUE TO MONITOR
FOR FUTURE FORECASTS.
..WEATHER/HAZARDS HIGHLIGHTS
MODEST PRECIPITATION INCLUDING HIGHER ELEVATION SNOW IS FORECAST
ACROSS THE NORTHWEST SATURDAY AS AN UPPER TROUGH PROVIDES SUPPORT.
SOME SNOW WILL LIKELY STRETCH INTO THE NORTHERN PLAINS. AS THE
SURFACE LOW CONSOLIDATES INTO SUNDAY, PRECIPITATION IS EXPECTED TO
PUSH ACROSS THE EASTERN HALF OF THE U.S. WITH GOOD DYNAMICAL
SUPPORT. RAIN ACROSS THE SOUTHERN TIER (LOWER MISSISSIPPI VALLEY TO
TENNESSEE VALLEY AND SOUTHEAST) MAY BE HEAVY AND STRONG
THUNDERSTORMS ARE POSSIBLE AS WELL. HAVE A MARGINAL RISK DELINEATED
ON DAY 5/SUNDAY IN THE ERO AS A STARTING POINT. COLD AIR IN PLACE
WILL ENSURE SNOW ACROSS SOME AREAS FARTHER NORTH. PROBABILITIES FOR
"PLOWABLE" SNOW/SLEET CONTINUE TO INCREASE FOR PARTS OF THE MID-
MISSISSIPPI VALLEY INTO THE OHIO VALLEY PEAKING ON SUNDAY. THEN
THERE IS A RELATIVELY BROAD AREA THAT MAY SEE MIXED PRECIPITATION
TYPES, TRANSITIONING BETWEEN MULTIPLE P-TYPES AND/OR SEEING SNOW
AND SLEET, MOST LIKELY OVER PARTS OF THE CENTRAL PLAINS INTO MIDDLE
MISSISSIPPI VALLEY TO THE TENNESSEE AND/OR LOWER OHIO VALLEY. BY
MONDAY SOME SNOW AND ICE PROBABILITIES LOOK TO COME ACROSS THE
APPALACHIANS INTO THE MID-ATLANTIC AND SOUTHERN PARTS OF THE
NORTHEAST, BUT WITH LOW CONFIDENCE IN THE AMOUNTS. THE EXACT
SURFACE LOW TRACK, WHICH IS STILL UNCERTAIN, WILL PLAY A
SIGNIFICANT ROLE IN PRECIPITATION AMOUNTS, TYPES, AND TIMING. SO
KEEP AN EYE ON FUTURE FORECASTS AS DETAILS ARE LIKELY TO CHANGE.
ELSEWHERE, LAKE EFFECT SNOW IS LIKELY TO CONTINUE SATURDAY IN COLD
BRISK FLOW AHEAD OF THE MAIN SYSTEM, TAPERING OFF ON SUNDAY, BUT
CHANCES MAY GET RENEWED BY TUESDAY AND BEYOND AFTER THE LOW EXITS.
THE NORTHWEST COULD SEE ADDITIONAL ROUNDS OF LIGHT TO MODERATE
PRECIPITATION SUNDAY. SOME LIGHT PRECIPITATION COULD OCCUR IN THE
INTERMOUNTAIN WEST AND ROCKIES INTO NEXT WEEK, WITH SOME UNCERTAIN
CHANCES FOR PRECIPITATION INTO THE SOUTHERN PLAINS AND GULF COAST
AS WELL.
COLDER THAN NORMAL TEMPERATURES ARE LIKELY ACROSS THE CENTRAL AND
EASTERN U.S. UNDERNEATH ROUNDS OF UPPER TROUGHING AND WITH COLD
SURFACE HIGH PRESSURE SYSTEMS. NOTABLE COLD IS POSSIBLE IN THE
NORTHERN TIER, WITH TEMPERATURES AT TIMES NOT REACHING OR BARELY
REACHING 0F AND LOWS BETWEEN -10F AND -20F IN SOME AREAS. THIS
SHOULD NOT BE RECORD BREAKING, BUT THE COLD COULD STILL BE
HAZARDOUS AS WIND CHILL VALUES MAY DIP BELOW -20F TO -30F.
TEMPERATURE ANOMALIES OF 10-20 DEGREES ARE ALSO LIKELY ACROSS PARTS
OF THE NORTHERN/CENTRAL PLAINS TO MIDDLE MISSISSIPPI AND OHIO
VALLEYS TO APPALACHIANS INTO NEXT WEEK, ESPECIALLY IF AREAS ARE
SNOW COVERED AND HOLD TEMPERATURES DOWN. MEANWHILE, INITIAL UPPER
RIDGING IN THE WESTERN U.S. WILL ALLOW FOR ABOVE NORMAL
TEMPERATURES IN THE INTERMOUNTAIN WEST TO SOUTHERN PLAINS OVER THE
WEEKEND. HIGHS IN THE 80S ARE LIKELY IN SOUTH TEXAS AHEAD OF A COLD
FRONT. TEMPERATURES ARE FORECAST TO COOL TO NEAR NORMAL IN THE
SOUTHWEST AND BELOW NORMAL IN THE SOUTHERN PLAINS INTO THE
WORKWEEK.
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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