492
FXUS02 KWBC 141920
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EST TUE JAN 14 2025
VALID 12Z FRI JAN 17 2025 - 12Z TUE JAN 21 2025
...STRONG ARCTIC SURGE PUSHING INTO THE CENTRAL U.S. BY THE WEEKEND
AND GRADUALLY EXPANDING EASTWARD...
..OVERVIEW
BY THIS WEEKEND THE GUIDANCE CONTINUES TO SHOW THE MEAN PATTERN
EVOLVING INTO A VERY AMPLIFIED REGIME CONSISTING OF A DEEP TROUGH
EXTENDING FROM CANADA THROUGH THE LOWER 48 AND A RIDGE WHOSE AXIS
EXTENDS OVER THE EASTERN PACIFIC AND WELL NORTHWARD. AS THIS
OCCURS, VERY COLD AIR WILL DROP INTO THE CENTRAL U.S. WITH THE MOST
EXTREME ANOMALIES LIKELY TO BE DURING SUNDAY-MONDAY. THE TROUGH
AXIS SHOULD NUDGE FAR ENOUGH EAST BY NEXT TUESDAY TO OFFER SOME
MODERATION OVER THE NORTHERN-CENTRAL PLAINS WHILE COLDEST ANOMALIES
BECOME ALIGNED MORE OVER THE EAST AND SOUTH. WITHIN THIS HIGHLY
CONFIDENT LARGE SCALE PATTERN, EMBEDDED SHORTWAVE UNCERTAINTIES
CONTINUE TO POSE ISSUES FOR SPECIFICS OF POTENTIALLY ENHANCED
RAINFALL OVER THE SOUTH AROUND THE END OF THE WEEK INTO THE WEEKEND
AS WELL AS FOR EAST COAST INTO WESTERN ATLANTIC FRONTAL WAVINESS
THAT COULD PRODUCE LIGHTER PRECIPITATION OF VARIOUS TYPES.
MEANWHILE EXPECT AN AREA OF SNOW TO PUSH SOUTH THROUGH THE
ROCKIES/HIGH PLAINS WITH THE COLD SURGE BEFORE TAPERING OFF NEXT
WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODELS AGREE REGARDING UPPER TROUGHING OVER THE
CENTRAL/EASTERN CONUS AND AN ARCTIC HIGH COMING IN AT THE SURFACE,
SYSTEMS ON THE PERIPHERY OF THESE FEATURES ARE MORE UNCERTAIN AND
COULD HAVE SENSIBLE WEATHER IMPACTS. AT THE START OF THE PERIOD, A
LOW PRESSURE SYSTEM FORECAST TO TRACK JUST NORTH OF MINNESOTA AND
LAKE SUPERIOR AND ITS TRAILING FRONT WILL BE THE MAIN FEATURE OF
NOTE. A MULTI-MODEL BLEND SEEMED REASONABLE FOR THIS SYSTEM AS IT
PUSHES THROUGH THE EAST AND FORMS RELATIVELY WEAK (UNTIL PERHAPS
STRENGTHENING ONCE OFFSHORE) LOW PRESSURE WAVES ALONG IT.
MEANWHILE THERE ARE LIKELY TO BE MULTIPLE SHORTWAVES DIGGING SOUTH
THROUGH THE WESTERN SIDE OF THE TROUGH, CREATING SOME DIFFERENCES
IN THE UPPER PATTERN FROM THE EASTERN PACIFIC TO THE ROCKIES DURING
MUCH OF THE PERIOD. THE 00Z CMC WAS AGGRESSIVE ENOUGH WITH
SHORTWAVE ENERGY TO REORIENT THE TROUGH AXIS TO BE MORE POSITIVELY
TILTED OVER THE WEEKEND, UNLIKE CONSENSUS. THE NEWER 12Z CMC RUN
TRENDED MORE FAVORABLY TOWARD THE OTHER MODELS. DIFFERENCES WITH AN
INITIALLY EASTERN PACIFIC UPPER LOW CONTINUE TO CAUSE MODEL
DIFFERENCES DOWNSTREAM AS IT PIVOTS EASTWARD. DETERMINISTIC AND AI
MODELS AND ENSEMBLE MEMBERS VARY QUITE A BIT ON WHETHER/HOW MUCH
ENERGY IS HELD BACK INTO THE SOUTHWEST BY NEXT TUESDAY. THE GENERAL
TREND OVER THE PAST DAY SEEMS TO BE FOR MORE ENERGY TO SEPARATE
INTO THE SOUTHERN STREAM AT LEAST SOMEWHAT FROM THE MAIN TROUGH.
TRENDS WILL CONTINUE TO BE MONITORED BECAUSE THIS WILL HAVE
CONSIDERABLE EFFECTS ON FORECAST ASPECTS LIKE PRECIPITATION THAT
COULD BE WINTRY NEXT WEEK.
THE WPC FORECAST USED A BLEND OF THE 00Z ECMWF/06Z GFS/00Z CMC/00Z
UKMET IN DECREASING PROPORTIONAL ORDER EARLY IN THE PERIOD, BUT
PHASED OUT THE CMC AND UKMET IN FAVOR OF THE GEFS AND EC ENSEMBLE
MEANS, AND INCREASED THE PROPORTION OF MEANS TO HALF DAYS 6-7 WHILE
MAINTAINING SOME EC AND GFS INCLUSION.
..WEATHER/HAZARDS HIGHLIGHTS
THE FORECAST IS FAIRLY CONSISTENT WITH RESPECT TO THE NORTHWEST
SEEING A MODERATE COOLING TREND ON FRIDAY FOLLOWED BY A PRONOUNCED
SURGE OF ARCTIC AIR DROPPING SOUTH OVER THE EASTERN ROCKIES INTO
THE PLAINS BY THIS WEEKEND. EXPECT INCREASING COVERAGE OF
TEMPERATURES THAT ARE 15-35F BELOW NORMAL, WITH EXPANSION OF THE
COLD AIR BRINGING HIGHS DOWN TO 15-25F BELOW NORMAL AS FAR EAST AS
LOCATIONS BETWEEN THE MISSISSIPPI RIVER AND APPALACHIANS BY MONDAY
AND CONTINUING TOWARD THE EAST COAST BY TUESDAY. THE MOST EXTREME
ANOMALIES ARE LIKELY TO BE OVER THE CENTRAL HIGH PLAINS AND
VICINITY DURING SUNDAY-MONDAY, WHILE COLDEST TEMPERATURES ON AN
ABSOLUTE BASIS SHOULD BE OVER FAR NORTHERN AREAS WHERE SOME SUBZERO
HIGHS AND LOWS IN THE -20S ARE EXPECTED. WIND CHILLS SHOULD BE
EVEN COLDER AND MORE DANGEROUS. KEY MESSAGES ARE SET TO BEGIN FROM
WPC IN PART DUE TO THESE COLD TEMPERATURES. THE NORTHERN-CENTRAL
ROCKIES/PLAINS SHOULD BEGIN TO MODERATE ON TUESDAY WHILE COLD
WEATHER IS EXPECTED TO LINGER FARTHER SOUTH. THE WEST WILL SEE A
PERIOD OF COOL BUT NOT EXTREME TEMPERATURES FROM THE WEEKEND INTO
THE START OF NEXT WEEK, WITH NEAR NORMAL READINGS EVENTUALLY
BEGINNING TO PUSH EASTWARD FROM THE WEST COAST. AHEAD OF THE COLD
FRONT PROGRESSING SOUTH/EAST FROM THE PLAINS FRIDAY ONWARD, AN AREA
OF ABOVE NORMAL TEMPERATURES WILL PROGRESS FROM THE CENTRAL U.S.
ON FRIDAY TO THE EAST COAST BY EARLY SUNDAY. THE UPPER MIDWEST MAY
SEE LOWS THAT ARE 20F OR MORE ABOVE NORMAL EARLY FRIDAY, WITH PLUS
5-15F ANOMALIES MORE COMMON ELSEWHERE WITHIN THIS AREA OF RELATIVE
WARMTH.
BY FRIDAY NIGHT, APPROACHING SHORTWAVE ENERGY AND A COMBINATION OF
FRONTS MAY START TO GENERATE SOME ENHANCED RAINFALL OVER THE LOWER
MISSISSIPPI VALLEY AND SOUTHEAST. THE REASONABLY FAST FRONTAL
MOVEMENT AND MODERATE RAIN RATES SHOULD KEEP THE FLASH FLOODING
POTENTIAL PRETTY MINIMAL FOR THE DAY 4 ERO TIME FRAME. THIS
ACTIVITY SHOULD CONTINUE ACROSS THE SOUTHEAST DURING SATURDAY AND
SATURDAY NIGHT WITH THE SUPPORTING WAVY SURFACE FRONT LYING DOWN A
BIT TO BECOME MORE EAST-WEST ORIENTED, POSSIBLY SUPPORTING SOME
TRAINING. THUS THERE IS SOME POTENTIAL FOR LOCALLY HEAVIER RAINFALL
INTO THE DAY 5/SATURDAY ERO PERIOD IN THE SOUTHEAST AND FLORIDA
PANHANDLE. AS RAIN OCCURRED IN THAT GENERAL VICINITY YESTERDAY,
SOIL MOISTURE PERCENTILES ARE ACTUALLY SHOWING SOME ABOVE AVERAGE
ANOMALIES THERE CURRENTLY, BUT SOILS SHOULD DRY OUT BY LATE WEEK.
CONTINUED TO HOLD OFF ON INTRODUCING ANY ERO AREAS AS THERE IS
UNCERTAINTY IN WHETHER THE FORECAST RAIN AMOUNTS WOULD CAUSE
FLOODING ISSUES, BUT THERE IS LIKELY A NONZERO THREAT ESPECIALLY IF
TRAINING OR REPEATING SHOWERS AND STORMS WITH HEAVY RATES OCCUR.
SOME RAINFALL MAY PERSIST OVER PARTS OF THE SOUTHEAST, ESPECIALLY
NORTHERN FLORIDA, BEYOND SATURDAY.
MUCH LIGHTER PRECIPITATION OF VARYING TYPES WILL BE POSSIBLE
FARTHER NORTH OVER THE EAST DURING THE WEEKEND AND POSSIBLY INTO
EARLY NEXT WEEK. THERE ARE STILL SIGNIFICANT DIFFERENCES FOR
POTENTIAL FRONTAL WAVE DEVELOPMENT, KEEPING CONFIDENCE LOW FOR
DETAILS OF PRECIPITATION COVERAGE AND AMOUNTS. HOWEVER WHAT SIGNALS
EXIST SUGGEST THAT ANY WAVES SHOULD BE FAIRLY WEAK WITH RELATIVELY
LIGHT PRECIPITATION (WHICH COULD BE OF THE WINTRY VARIETY FROM THE
MID-ATLANTIC/APPALACHIANS NORTHWARD). PROBABILITIES OF 0.25 INCH
LIQUID IN THE FORM OF SNOW REFLECT THIS, WITH LOW COVERAGE OF 10
PERCENT OR GREATER VALUES, THOUGH HIGHER ELEVATIONS LIKE THE
ADIRONDACKS HAVE HIGHER PROBABILITIES. SOME LOCALLY HEAVIER SNOW
WILL BE POSSIBLE TO THE LEE OF THE GREAT LAKES FROM THE WEEKEND
INTO EARLY NEXT WEEK, AS WELL AS ACROSS THE APPALACHIANS WITH
UPSLOPE FLOW.
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 ENHANCE ACCUMULATIONS
OVER SOME AREAS. SNOW SQUALLS ARE OF CONCERN FRIDAY WITH THE COLD
FRONTAL PASSAGE. INTO MONDAY OR TUESDAY OF NEXT WEEK, IT IS
UNCERTAIN HOW MUCH PRECIPITATION EMERGES OVER THE SOUTHERN TIER
FROM TEXAS EASTWARD ON THE PERIPHERY OF THE UPPER TROUGH AND
SURFACE HIGH PRESSURE. HOWEVER, THE SOUTHERN EXTENT OF THE COLD AIR
AT THE SURFACE MEANS THAT IF THERE IS PRECIPITATION IT WOULD
MAINLY BE IN THE FORM OF WINTRY PRECIP, PERHAPS ALL THE WAY TO THE
GULF COAST, AND FREEZING RAIN/ICE IS AN INCREASING CONCERN FOR
PARTS OF THE SOUTH GIVEN THE POSSIBILITY OF A WARM NOSE ATOP ARCTIC
COLD AIR.
UNCERTAINTIES IN THE SETUP ALOFT OVER THE SOUTHWEST INTO NEXT WEEK
MAKE THE PATTERN AT THE SURFACE SOMEWHAT UNCERTAIN AS WELL.
HOWEVER, THERE IS A GENERAL TREND FOR WEAKER WINDS OVER SOUTHERN
CALIFORNIA FRIDAY INTO THE WEEKEND, BUT OFFSHORE FLOW MAY
STRENGTHEN AGAIN BY MONDAY AS 850MB WINDS INCREASE (DRAMATICALLY IN
SOME MODELS). KEEP AN EYE ON SPC FIRE WEATHER FORECASTS FOR
FURTHER INFORMATION.
TATE/RAUSCH
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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