277
FXUS02 KWBC 150706
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
206 AM EST SUN DEC 15 2024
VALID 12Z WED DEC 18 2024 - 12Z SUN DEC 22 2024
..OVERVIEW
THE PATTERN SHOULD BE TURNING MUCH MORE AMPLIFIED DURING THE
MEDIUM RANGE PERIOD AS MEAN TROUGHING BECOMES ESTABLISHED OVER THE
EAST, AND STRONG RIDGING BUILDS OVER THE WEST. A COUPLE OF
SHORTWAVES WILL HELP REINFORCE THE EASTERN TROUGH DURING THE
PERIOD, INCLUDING AN INITIAL ONE LATE THIS WEEK WHICH SHOULD ALLOW
A LOW PRESSURE SYSTEM TO LIFT FROM THE MID-SOUTH TO THE NORTHEAST
WITH POTENTIAL SNOW ON THE NORTH SIDE OF THE TRACK. THE NEXT
SHORTWAVE DIGGING DOWN THE WEST SIDE OF THE TROUGH SHOULD BRING
WITH IT A FRESH BLAST OF ARCTIC AIR TO THE EAST BY NEXT WEEKEND,
WHILE THE WEST TURNS PROGRESSIVELY WARMER. AN ATMOSPHERIC RIVER MAY
BRING A PERIOD OF HEAVY RAIN/MOUNTAIN SNOWS TO PARTS OF THE WEST
COAST BY NEXT WEEKEND AS WELL.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND ENSEMBLES CONTINUE TO SHOW GENERALLY GOOD
AGREEMENT ON THE OVERALL SYNOPTIC PATTERN BUT PLENTY OF UNCERTAINTY
IN THE DETAILS. MODELS ARE TRENDING CLOSER TOGETHER WITH THE
INITIAL SHORTWAVE OFF THE SOUTHEAST COAST AND MORE NORTHERLY/INLAND
WITH ASSOCIATED LOW PRESSURE OFF THE NORTHEAST COAST, BUT THERE
DOES REMAIN SOME UNCERTAINTY IN THE TIMING. THE NEXT SHORTWAVE
SHOULD MOVE THROUGH THE MIDWEST INTO THE EAST LATE WEEK INTO NEXT
WEEKEND WITH PLENTY OF UNCERTAINTY IN THE DETAILS. UPSTREAM,
RIDGING BUILDS OVER THE WEST THEN EVENTUALLY SHIFTS EASTWARD AS THE
NEXT SHORTWAVE MOVES INTO THE WEST COAST NEXT WEEKEND. GENERALLY
GOOD AGREEMENT ON THIS SETUP, BUT UNCERTAINTY IN THE TIMING AND
EVOLUTION OF ENERGY AS IT PROGRESSES INLAND.
THE WPC BLEND FOR TONIGHT LEANED MORE HEAVILY ON THE ECMWF, WITH
MINOR CONTRIBUTIONS FROM THE CMC AND UKMET EARLY PERIOD SINCE THE
GFS WAS TOO SLOW/DIFFERENT WITH THE EASTERN TROUGH. WITH INCREASING
UNCERTAINTY, USED INCREASINGLY MORE ENSEMBLE MEANS MID TO LATE
WEEK AND NEXT WEEKEND.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT SHIFTING THROUGH THE EAST MID WEEK WILL BE
ACCOMPANIED BY MODEST PRECIPITATION. MODERATE TO HEAVY RAINFALL IS
POSSIBLE ACROSS PORTIONS OF THE TENNESSEE/OHIO VALLEY INTO THE
CENTRAL APPALACHIANS BUT LOW RAINFALL RATES AND THE OVERALL
PROGRESSIVE NATURE OF THE FRONT SHOULD LIMIT ANY SORT OF EXCESSIVE
RAINFALL/FLASH FLOOD THREAT. SOME WINTRY WEATHER IS POSSIBLE ON THE
NORTHWESTERN SIDE OF THE SURFACE LOW WHICH TRACKS NEAR THE
NORTHEAST COAST, WITH HIGHEST PROBABILITIES IN THE HIGHER TERRAIN.
BEHIND THIS SYSTEM, WESTERLY FLOW ACROSS THE STILL RELATIVELY WARM
LAKES SHOULD ALLOW FOR SOME LAKE EFFECT SNOWS, REINFORCED BY THE
NEXT SHORTWAVE THROUGH THE REGION LATE WEEK/NEXT WEEKEND.
MEANWHILE, OUT WEST, CONDITIONS SHOULD DRY OUT BY THE MEDIUM RANGE
PERIOD, EXCEPT FOR SOME INCREASED PRECIPITATION ASSOCIATED WITH
WEAK SHORTWAVES INTO THE NORTHWEST. INCREASING PRECIPITATION LOOKS
LIKELY BY NEXT WEEKEND WITH THE NEXT ATMOSPHERIC RIVER INTO THE
REGION.
AFTER A WARMER DAY ON WEDNESDAY, THE EASTERN U.S. SHOULD TREND
MUCH COLDER THROUGH THE PERIOD AS AN ARCTIC HIGH PRESSURE EXPANDS
ACROSS THE MIDWEST AND EAST. BY NEXT WEEKEND, TEMPERATURES ACROSS
MUCH OF THIS REGION COULD BE 10 TO 15 DEGREES BELOW NORMAL.
MEANWHILE, FROM THE ROCKIES AND WESTWARD, TEMPERATURES SHOULD TREND
WARMER WITH TIME WITH SOME SPOTS 10-15+ DEGREES ABOVE NORMAL.
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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