415
FXUS02 KWBC 021854
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EST THU JAN 2 2025
VALID 12Z SUN JAN 05 2025 - 12Z THU JAN 09 2025
...WINTER STORM TO BRING HEAVY SNOW AND HAZARDOUS ICE FROM THE
CENTRAL PLAINS TO THE MID-ATLANTIC...
..OVERVIEW
A WINTER STORM IS LIKELY ON SUNDAY FROM THE CENTRAL PLAINS TO MID-
MISSISSIPPI AND OHIO/TENNESSEE VALLEYS AND THE MID-ATLANTIC,
LASTING INTO MONDAY FOR EASTERN AREAS. HEAVY SNOW IS POSSIBLE,
ALONG WITH SIGNIFICANT SLEET AND FREEZING RAIN IN THE MID-SOUTH
PERHAPS INTO THE SOUTHERN APPALACHIANS. ON THE SOUTHERN SIDE, HEAVY
RAIN AND THUNDERSTORMS ARE LIKELY OVER PARTS OF THE LOWER
MISSISSIPPI AND TENNESSEE VALLEYS AND SOUTHEAST. THE WEATHER IS
FORECAST TO QUIET DOWN IN TERMS OF PRECIPITATION AFTER THIS SYSTEM,
ASIDE FROM SOME RELATIVELY LIGHT LAKE EFFECT SNOW AND A COUPLE OF
AREAS OF LIGHT PRECIPITATION POSSIBLE IN THE WESTERN AND CENTRAL
U.S., BUT COLDER THAN AVERAGE TEMPERATURES ARE LIKELY TO PERSIST
THROUGH THE WEEK IN MOST AREAS EAST OF THE ROCKIES.
..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 CONSISTENTLY 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). NEW 12Z
GUIDANCE TODAY HAS CONVERGED A BIT ON TIMING WITH ECMWF SLIGHTLY
SLOWER AND GFS/CMC RUNS SIMILAR OR A BIT FASTER. SUBTLE NORTH-SOUTH
VARIABILITY CONTINUES THOUGH WHICH OBVIOUSLY WOULD HAVE POSSIBLY
SIGNIFICANT IMPLICATIONS ON P-TYPE ACROSS THE BOARD FROM THE
CENTRAL PLAINS/MID-MISSISSIPPI VALLEY INTO THE MID-ATLANTIC. THESE
DETAILS THOUGH WILL TAKE UNTIL THE SHORT RANGE TO RESOLVE. OVERALL,
GUIDANCE IS TRENDING CLOSER AND CONFIDENCE IN A IMPACTFUL TO
SIGNIFICANT WINTER STORM IS INCREASING.
THEN, MODELS CONTINUE TO SUPPORT BROAD TROUGHING IN THE CENTRAL
AND EASTERN U.S., WHILE ENERGY DIVING SOUTH THROUGH THE WESTERN
PART OF THE TROUGH OVER THE WEST SHOWS MORE SPREAD, ESPECIALLY BY
THE TIME IT REACHES THE SOUTHWEST. TIMING AND EVOLUTION OF THIS
TROUGH IS STILL VERY UNCERTAIN, WITH SOME GUIDANCE (ECMWF AND CMC)
SHOWING A CUT OFF LOW, WHILE THE GFS IS MORE INTACT AND THUS FASTER
WITH THE ENERGY.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 12Z
GFS/UKMET/CMC/ECMWF EARLY IN THE PERIOD WHICH ALLOWED FOR A NICE
MIDDLE GROUND SOLUTION FOR THE CENTRAL-EASTERN SURFACE LOW AND
CONSISTENCY WITH PREVIOUS WPC FORECASTS. GRADUALLY REDUCED THE
PROPORTIONS OF THE DETERMINISTIC MODELS IN FAVOR OF THE ENSEMBLE
MEANS AS THE FORECAST PROGRESSED, REACHING 60 PERCENT ENSEMBLE
MEANS BY DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
AN UPPER TROUGH IN THE CENTRAL U.S. SUNDAY WILL PRODUCE A
CONSOLIDATING SURFACE LOW IN THE SOUTHERN PLAINS. PRECIPITATION IS
EXPECTED TO PUSH ACROSS THE EASTERN HALF OF THE U.S. WITH THIS LOW
AND GOOD DYNAMICAL SUPPORT ALOFT. COLD AIR IN PLACE WILL ENSURE
WIDESPREAD SNOW THAT COULD BE HEAVY ACROSS SOME AREAS OF THE
CENTRAL PLAINS, MID-MISSISSIPPI VALLEY, AND OHIO VALLEY PEAKING ON
SUNDAY. SNOW COULD PUSH INTO THE MID-ATLANTIC SUNDAY NIGHT AND/OR
MONDAY DEPENDING ON THE SPEED OF THE LOW TRACK. JUST TO THE SOUTH,
THERE IS A RELATIVELY BROAD AREA THAT MAY SEE MIXED PRECIPITATION
TYPES, TRANSITIONING BETWEEN MULTIPLE P-TYPES AND/OR SEEING SNOW
AND SLEET/FREEZING RAIN. POTENTIALLY SIGNIFICANT SLEET AND FREEZING
RAIN ARE POSSIBLE ACROSS THE OZARKS EAST TO THE TENNESSEE VALLEY.
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.
WPC IS ISSUING KEY MESSAGES FOR THIS WINTER STORM. MEANWHILE
FARTHER SOUTH IN THE WARM SECTOR, SEVERE WEATHER AND HEAVY RAIN
THAT COULD CAUSE ISOLATED FLOODING ARE POSSIBLE ACROSS THE LOWER
MISSISSIPPI VALLEY TO SOUTHERN TENNESSEE VALLEY AND SOUTHEAST. A
MARGINAL RISK STILL SEEMS PRUDENT FOR THE DAY 4/SUNDAY ERO DUE TO
HIGH RAIN RATES, BUT FAST MOVEMENT OF THE STORMS SHOULD TEMPER
FLOODING POTENTIAL.
LAKE EFFECT SNOW MAY CONTINUE INTO SUNDAY, AND THEN BECOME
REJUVENATED WITH COLD AND BRISK FLOW BEHIND THE MAIN LOW PRESSURE
SYSTEM. MOST AREAS ARE FORECAST TO SEE RELATIVELY LIGHT SNOW
ACCUMULATIONS. LIGHT TO MODEST PRECIPITATION INCLUDING HIGHER
ELEVATION SNOW IS EXPECTED ACROSS THE NORTHWEST ON SUNDAY, AND
LIGHT AMOUNTS MAY BE POSSIBLE THROUGH THE WEEK IN THE ROCKIES, AND
EVENTUALLY THE NORTHERN PLAINS WITH A WEAK SURFACE LOW. FARTHER
SOUTH, THERE ARE SOME UNCERTAIN CHANCES FOR PRECIPITATION IN THE
SOUTHWEST TO SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY. WITH THE
COLD AIR IN PLACE FROM TEXAS EASTWARD, SOME AREAS COULD SEE WINTRY
PRECIPITATION, SO THIS POTENTIAL WILL CONTINUE TO BE MONITORED.
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 EVEN HIGH TEMPERATURES 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 MUCH
OF NEXT WEEK, ESPECIALLY IF AREAS ARE SNOW COVERED AND HOLD
TEMPERATURES DOWN. MEANWHILE, INITIAL UPPER RIDGING IN THE WESTERN
U.S. WILL ALLOW FOR SLIGHTLY ABOVE NORMAL TEMPERATURES IN THE
INTERMOUNTAIN WEST, AND 10-20 DEGREES ABOVE NORMAL ANOMALIES IN THE
SOUTH-CENTRAL U.S. SUNDAY WILL COOL TO BELOW NORMAL BEHIND A COLD
FRONT BY MONDAY. THE UPPER PATTERN IN THE WEST IS UNCERTAIN BY
MIDWEEK NEXT WEEK, CAUSING TEMPERATURES TO BE IN QUESTION, BUT
THERE MAY BE A TREND TOWARD WARMING FOR PARTS OF THE WEST.
SANTORELLI/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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