775
FXUS02 KWBC 181900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SAT JAN 18 2025
VALID 12Z TUE JAN 21 2025 - 12Z SAT JAN 25 2025
...HAZARDOUS COLD TEMPERATURES EARLY WEEK EAST OF THE ROCKIES
SHOULD GRADUALLY MODERATE WITH TIME...
..A WINTER STORM IS LIKELY TUESDAY IN THE SOUTH
..OVERVIEW
MODELS AND ENSEMBLES CONTINUE TO SHOW A VERY AMPLIFIED MEAN
PATTERN INTO TUESDAY CONSISTING OF A DEEP UPPER TROUGH OVER MUCH OF
THE LOWER 48 AND AN EASTERN PACIFIC RIDGE. CONFIDENCE REMAINS HIGH
IN A SURGE OF ARCTIC AIR WHICH SHOULD BE IN PLACE EAST OF THE
ROCKIES DUE TO THIS TROUGH ALOFT AND COLD HIGH PRESSURE AT THE
SURFACE. THIS TROUGH SHOULD LIFT NORTH AND EAST AS THE WEEK
PROGRESSES FOR GRADUALLY MODERATING TEMPERATURES, BUT TROUGHING IS
FORECAST TO RELOAD IN THE CENTRAL U.S. FOR LATER WEEK AND GRADUALLY
MOVE EAST. SYSTEMS ON THE SOUTHERN PERIPHERY OF THIS PATTERN WILL
CAUSE PRECIPITATION FROM THE SOUTHERN PLAINS TO SOUTHEAST. A WINTER
STORM ACROSS THE SOUTHERN TIER IS STILL ON TRACK FOR TUESDAY,
WHICH COULD PRODUCE SNOW/SLEET CLOSE TO THE WESTERN/CENTRAL GULF
COAST ACROSS THE SOUTHEAST AND CAROLINAS, WITH NOTABLE FREEZING
RAIN POSSIBLE FOR THE FLORIDA PANHANDLE AND SOUTHERN GEORGIA. THERE
IS STILL UNCERTAINTY WITH THE WINTRY PRECIPITATION AMOUNTS AND
AXIS THOUGH. ROUNDS OF MAINLY PRECIPITATION ARE POSSIBLE IN THE
NORTHERN TIER THROUGH THE WEEK AND THEN UNCERTAIN TROUGHING MOVING
INTO THE NORTHWEST COULD PRODUCE LIGHT TO MODERATE PRECIPITATION
INTO LATE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE SHOWS GENERAL AGREEMENT ON THE LARGE SCALE AS THE
FORECAST PERIOD BEGINS TUESDAY, WITH A POSITIVELY TILTED TROUGH
FROM THE MIDWEST TO SOUTHWEST. THE SHORTWAVE ON THE SOUTHERN SIDE
WILL PIVOT QUICKLY EASTWARD TO PROVIDE FORCING FOR THE WINTER STORM
IN THE SOUTH WHILE THE NORTHERN SIDE OF THE TROUGH MOVES MORE
SLOWLY THROUGH THE GREAT LAKES. MEANWHILE THE PRECIPITATION TYPES
AND AMOUNTS ARE MORE VARIABLE AND WILL BE MUCH HARDER TO RESOLVE
UNTIL CLOSER TO THE EVENT. MODELS HAVE WAFFLED WITH HOW FAR INLAND
THE WINTRY PRECIPITATION WOULD REACH BUT THIS FORECAST TRENDED
TOWARD A SLIGHT INLAND EXPANSION. A MULTI-MODEL BLEND SEEMED TO
SERVE AS A GOOD STARTING POINT FOR THE WPC FORECAST.
UPSTREAM, THE NEXT POTENT SHORTWAVE OR TWO WILL DIG INTO THE
NORTHERN ROCKIES BY WEDNESDAY AND DROP SOUTH AND EASTWARD WITH TIME
TO PRODUCE A LARGER LONGWAVE TROUGH. MODELS CONTINUE TO VARY WITH
THE DEPTH OF THIS ENERGY, AND THE DETAILS OF THE TROUGH (AND
POTENTIAL FOR A BRIEF RIDGE IN BETWEEN THIS TROUGH AND THE EASTERN
ONE) WILL BE MAIN FACTORS IN DETERMINING ANOTHER POSSIBLE ROUND OF
GULF COAST STATES PRECIPITATION THAT COULD SPREAD NORTH OVER AT
LEAST PARTS OF THE EASTERN SEABOARD. THIS REMAINS QUITE UNCERTAIN
AS MODELS CONTINUE TO VARY.
BEHIND THIS TROUGH, AN UPPER RIDGE ACROSS THE WEST COAST SHOWS
GOOD MODEL AGREEMENT THROUGH WEDNESDAY UNTIL QUICKLY INCREASING
MODEL DIFFERENCES FORM ON ITS NORTHERN SIDE IN WESTERN CANADA. THE
GFS/GEFS SUITE HAS BEEN PERSISTENT IN MAINTAINING RIDGING WELL TO
THE NORTH, WHILE THE ECMWF AND CMC AND MOST OF THEIR ENSEMBLE
MEMBERS AS WELL AS MANY OF THE AI/ML MODELS INDICATE THAT THE
NORTHERN SIDE WOULD BE SUPPRESSED BY SHORTWAVE ENERGY. THE LATTER
CLUSTER BRINGS TROUGHING INTO THE NORTHWEST BY FRIDAY DIGGING SOUTH
INTO THE GREAT BASIN BY NEXT SATURDAY, WHILE THE GFS/GEFS SHOW
SLOWER AND WEAKER TROUGHING AND BECOMES OUT OF PHASE WITH THE NON-
NCEP SOLUTIONS. THIS FORECAST LEANED AWAY FROM THE GFS/GEFS TYPE
SOLUTIONS BUT HEAVILY USED THE EC ENSEMBLE MEAN IN THE FORECAST
BLEND BY LATE PERIOD TO NOT GO TOO FAR TO THE EC/CMC OPERATIONAL
RUNS EITHER. FAVORING THIS TIMING PUSHED THE FRONT MORE QUICKLY
ACROSS THE NORTHWESTERN QUADRANT OF THE LOWER 48 FRIDAY-SATURDAY
COMPARED TO THE PREVIOUS FORECAST, BUT FUTURE ADDITIONAL CHANGES
MAY BE NEEDED GIVEN THE UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
BY TUESDAY, AN EXPANSIVE AREA OF HAZARDOUSLY COLD ARCTIC AIR WILL
BE IN PLACE BASICALLY FROM THE ROCKIES EASTWARD, WITH LOW
TEMPERATURES THAT ARE BELOW AVERAGE BY 20-30F IN THE ROCKIES TO
PLAINS TO MIDWEST. ACTUAL TEMPERATURES WILL BE IN THE -20S IN THE
NORTHERN TIER, AND THE MIDWEST COULD EVEN SEE SUBZERO HIGHS. WIND
CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS. THE
NORTHERN/CENTRAL PLAINS SHOULD RAPIDLY WARM BY TUESDAY AFTERNOON
AND REACH NEAR TO ABOVE NORMAL VALUES FOR THE LATTER HALF OF THE
WEEK. MEANWHILE THE COLDEST TEMPERATURE ANOMALIES (20-30 DEGREES
BELOW NORMAL) WILL MIGRATE INTO THE OHIO VALLEY TOWARD THE
WESTERN/CENTRAL GULF COAST MIDWEEK AND INTO THE EASTERN SEABOARD
THURSDAY, LEADING TO SOME DAILY RECORD LOW MAXES AND MINS.
TEMPERATURES ARE FORECAST TO GRADUALLY MODERATE LATE WEEK. THE WEST
ON THE OTHER HAND CAN EXPECT NEAR NORMAL TEMPERATURES GRADUALLY
WARMING TO SLIGHTLY ABOVE NORMAL, BEFORE TRENDING COLDER AGAIN BY
FRIDAY OR SATURDAY.
A SHORTWAVE MOVING THROUGH THE SOUTHERN TIER TUESDAY-WEDNESDAY
WILL PROVIDE SUPPORT FOR PRECIPITATION ACROSS THE SOUTH AS MOISTURE
OVERRUNS FRONTS IN THE GULF OF MEXICO. GIVEN THE COLD AIRMASS IN
PLACE, THE MAJORITY OF THE PRECIPITATION WILL BE WINTRY, PERHAPS
ALL THE WAY TO THE GULF COAST. SOUTHERN TIER SNOW POTENTIAL
CONTINUES TO INCREASE AS SHOWN BY THE WINTER WEATHER PROBABILITIES
FOR 0.25 INCH LIQUID IN THE FORM OF SNOW/SLEET, WITH A TREND IN
THIS FORECAST TO OVERSPREAD AREAS FARTHER INLAND. ADDITIONALLY,
FREEZING RAIN/ICE REMAINS A CONCERN GIVEN THE POSSIBILITY OF A WARM
NOSE ATOP ARCTIC COLD AIR, WHICH IS MOST LIKELY IN NORTHERN
FLORIDA INTO SOUTHERN GEORGIA AND COASTAL SOUTH CAROLINA. WPC KEY
MESSAGES ARE ONGOING FOR THIS SOUTH WINTER STORM. JUST TO THE SOUTH
OF THE WINTER CONCERNS, MODERATE TO HEAVY RAIN IS POSSIBLE ACROSS
CENTRAL FLORIDA ON TUESDAY. A MARGINAL RISK MAY BE NEEDED IN FUTURE
CYCLES FOR TUESDAY'S ERO, BUT AT THIS POINT, THERE IS STILL
UNCERTAINTY ON QPF TOTALS/AXIS, INSTABILITY, AND RAIN RATES.
FARTHER NORTH, THE PATTERN WILL BE FAVORABLE FOR LAKE EFFECT SNOW
ACROSS/DOWNWIND OF THE GREAT LAKES INTO TUESDAY, WITH THE HIGHEST
AMOUNTS OFF OF LAKE ONTARIO, BEFORE GRADUALLY TAPERING OFF MIDWEEK
AND BEYOND. SNOW SHOWERS ARE POSSIBLE INTO THE NORTHERN PLAINS
TUESDAY-WEDNESDAY WHICH COULD PERHAPS SPREAD ACROSS PARTS OF THE
MIDWEST LATER WEEK. DEPENDING ON PATTERN EVOLUTION, BY MID-LATE
NEXT WEEK, PRECIPITATION MAY INCREASE ACROSS THE SOUTH AGAIN
INCLUDING SOME WINTER WEATHER, PERHAPS SPREADING NORTH ACROSS THE
EASTERN SEABOARD. BUT MODELS HAVE SHOWN CONSIDERABLE VARIATIONS
WITH THIS POTENTIAL AND WILL STILL NEED TO BE MONITORED.
THE MEAN UPPER RIDGE OVER THE WEST COAST THROUGH MIDWEEK WILL KEEP
CONDITIONS DRY. UNFORTUNATELY A PATTERN FAVORABLE FOR STRONGER
OFFSHORE WINDS IS POSSIBLE ACROSS SOUTHERN CALIFORNIA AND VICINITY
INTO TUESDAY, WHICH WILL INCREASE FIRE WEATHER CONCERNS. CONTINUE
TO MONITOR STORM PREDICTION CENTER FIRE WEATHER FORECASTS FOR
FURTHER INFORMATION ON THIS CRITICAL RISK. LATER IN THE WEEK, UPPER
TROUGHING IS LIKELY TO MOVE THROUGH THE NORTHWEST (ALBEIT WITH
TIMING DIFFERENCES) AND PRODUCE LIGHT TO MODERATE PRECIPITATION.
TATE/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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