103
FXUS02 KWBC 150700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 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.
WITHIN AN INITIAL GENERALLY MILD PATTERN ACROSS THE LOWER 48,
WARMEST ANOMALIES SHOULD EXTEND FROM THE SOUTHWEST/ROCKIES INTO TO
THE EAST ON TUESDAY. EXPECT A DECENT AREA OF HIGHS 10-15 DEGREES
ABOVE NORMAL AND ANOMALIES UP TO PLUS 15-25 DEGREES IN PLACES FOR
MORNING LOWS. AFTER WEDNESDAY, TEMPERATURES SHOULD TREND BACK TO
NORMAL ACROSS THE CENTRAL- EASTERN U.S. WITH A WARMING TREND OUT
WEST. AS TROUGHING GETS ESTABLISHED ACROSS THE EAST LATE WEEK, AN
ARCTIC HIGH WILL SPREAD BELOW NORMAL TEMPERATURES FROM THE NORTHERN
PLAINS/UPPER MIDWEST INTO MUCH OF THE EAST BY NEXT WEEKEND.
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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