038
FXUS02 KWBC 190701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST MON DEC 19 2022
VALID 12Z THU DEC 22 2022 - 12Z MON DEC 26 2022
***BITTERLY COLD TEMPERATURES EXPECTED OVER ALL OF THE PLAINS AND
MIDWEST STATES, AND VERY COLD WEATHER REACHES THE GULF COAST
REGION***
***SIGNIFICANT WINTER STORM OVER THE EASTERN U.S. LATE IN THE WEEK
WILL LIKELY CAUSE TRAVEL DISRUPTIONS***
..SYNOPTIC OVERVIEW
AN AMPLIFYING UPPER LEVEL PATTERN ACROSS THE CONTINENTAL U.S. WILL
RESULT IN A VERY IMPACTFUL WEEK OF SEVERE COLD AND WINTER WEATHER
ACROSS THE EASTERN TWO-THIRDS OF THE NATION. AN UPPER RIDGE AXIS
NEAR THE WEST COAST AND A POTENT BLOCKING HIGH OVER GREENLAND AND
NORTHEAST CANADA WILL PROVIDE THE MEANS FOR A LOBE OF THE POLAR
VORTEX TO BREAK OFF AND SINK SOUTHWARD ACROSS THE NORTH-CENTRAL
U.S., AND THIS WILL HERALD THE ARRIVAL OF THE COLDEST AIRMASS OF
THE SEASON BY FAR FOR MOST LOCATIONS EAST OF THE ROCKIES. THIS
POTENT UPPER TROUGH WILL THEN SPUR SURFACE CYCLOGENESIS ACROSS THE
EASTERN U.S. BY THE END OF THE WEEK WITH WIDESPREAD RAIN, SNOW,
AND STRONG WINDS, AND THIS WILL DISRUPT THOSE THAT ARE TRAVELING
LATE THIS WEEK. THE INTENSIFYING LOW THEN LIFTS NORTHWARD ACROSS
EASTERN CANADA BY SATURDAY WITH WIDESPREAD GUSTY WINDS AND LAKE
EFFECT SNOW IN ITS WAKE. A SOUTHERN STREAM SHORTWAVE WILL LIKELY
CROSS THE GULF COAST REGION AROUND SUNDAY, BUT MOST OF THE
PRECIPITATION FROM THIS IS CURRENTLY EXPECTED TO REMAIN OFFSHORE.
THE ARCTIC AIRMASS IS EXPECTED TO GRADUALLY MODERATE GOING INTO
THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS NOW COME INTO BETTER AGREEMENT ON
THE EXPECTED SYNOPTIC SCALE SET-UP FOR THE MAJOR EASTERN U.S. LOW
PRESSURE SYSTEM, AND RECENT MODEL TRENDS HAVE STABILIZED AFTER
SIGNIFICANT MODEL DIFFERENCES OVER THE PAST COUPLE OF DAYS. THE
GFS IS STILL A LITTLE SLOWER WITH THE LOW TRACK AND SLIGHTLY
FARTHER SOUTH WITH THE MAIN CLOSED LOW OVER THE OHIO VALLEY,
WHILST THE UKMET IS SLIGHTLY FASTER THAN THE CONSENSUS WITH THE
LOW LIFTING NORTH FROM UPSTATE NEW YORK TO QUEBEC. THE 00Z
ECMWF/CMC SERVE AS A GOOD MIDDLE GROUND SOLUTION AND THESE TWO
MODELS WERE WEIGHTED MOST IN THE WPC FRONTS/PRESSURES FORECAST FOR
THURSDAY AND FRIDAY, ALONG WITH SOME OF THE GFS AND THE ENSEMBLE
MEANS. THERE HAS ALSO BEEN A TREND FOR A BETTER DEFINED SOUTHERN
STREAM SHORTWAVE THAT THE GFS HAS PORTRAYED OVER THE PAST FEW
RUNS, AND NOW THE OTHER DETERMINISTIC GUIDANCE IS SHOWING SOME
SUPPORT FOR THIS AS THE TROUGH TRACKS FROM THE SOUTHWESTERN U.S.
TO THE GULF COAST REGION, WITH THE GFS REMAINING MOST AMPLIFIED
WITH THIS FEATURE. TOWARDS THE END OF THE FORECAST PERIOD, MORE
SIGNIFICANT MODEL DIFFERENCES ARE APPARENT ACROSS THE NORTHEAST
PACIFIC WITH THE NEXT STORM SYSTEM TO AFFECT THE PACIFIC
NORTHWEST, SO MORE OF A ENSEMBLE MEAN BASED APPROACH WORKS WELL
FOR SUNDAY AND INTO MONDAY.
..WEATHER/HAZARD HIGHLIGHTS
ONE OF THE MAIN THINGS THAT WILL MAKE WEATHER HEADLINES NEXT WEEK
WILL CONTINUE TO BE THE MASSIVE EXPANSE OF FRIGID TEMPERATURES
ACROSS BASICALLY ALL OF THE CENTRAL AND EASTERN U.S. EAST OF THE
ROCKIES THROUGH THE END OF THE WEEK, WITH HARD FREEZES LIKELY FOR
MUCH OF THE DEEP SOUTH AND WELL INTO TEXAS. AN EXTREMELY STRONG
ARCTIC FRONT WILL USHER IN THE COLDEST AIR OF THE SEASON BY A
CONSIDERABLE MARGIN WITH THE EXPECTATION OF WIDESPREAD SUBZERO
READINGS FOR OVERNIGHT LOWS FROM THE NORTHERN ROCKIES TO THE
CENTRAL/NORTHERN PLAINS AND THE UPPER MIDWEST, REACHING AS FAR
SOUTH AS NORTHERN OKLAHOMA AND SOUTHERN MISSOURI. THERE WILL
LIKELY EVEN BE SUBZERO HIGH TEMPERATURES FROM CENTRAL
NEBRASKA/CENTRAL IOWA AND POINTS NORTHWARD ON THURSDAY AND FRIDAY.
ALTHOUGH THE FRIGID AIRMASS WILL MODIFY SOME AS IT REACHES THE
OHIO/TENNESSEE VALLEY REGION, IT WILL STILL BE IMPRESSIVELY COLD
WITH WIDESPREAD 0S FOR OVERNIGHT LOWS BY THE END OF THE WEEK AND
INTO EARLY SATURDAY, AND EVEN SOME SUBZERO READINGS ACROSS
PORTIONS OF INDIANA AND ILLINOIS. HARD FREEZE CONDITIONS ARE
BECOMING INCREASINGLY LIKELY FOR MUCH OF THE DEEP SOUTH AND TEXAS
THURSDAY NIGHT THROUGH AT LEAST FRIDAY NIGHT, WITH LOWS WELL INTO
THE TEENS AND LOW 20S, EVEN TO THE GULF COAST. COLD WEATHER WILL
ALSO REACH WELL INTO FLORIDA IN TIME FOR CHRISTMAS WEEKEND, WITH
LOWS FALLING INTO THE 30S AND 40S.
THE OTHER WEATHER STORY THAT WILL BE QUITE IMPACTFUL WILL BE
EXPECTED DEVELOPMENT OF AN INTENSE LOW PRESSURE SYSTEM THAT
DEVELOPS OVER THE OHIO VALLEY AND RAPIDLY INTENSIFIES AS IT LIFTS
NORTHWARD ACROSS THE GREAT LAKES AND THEN EASTERN ONTARIO/QUEBEC
BY EARLY SATURDAY. THE EXPECTED INLAND TRACK OF THE MAIN LOW WILL
RESULT IN PERIODS OF MODERATE TO HEAVY RAIN FROM THE MID-ATLANTIC
TO NEW ENGLAND LATE THURSDAY INTO FRIDAY, AND MODERATE TO HEAVY
SNOW FROM THE CENTRAL/NORTHERN APPALACHIANS AND POINTS WEST ACROSS
THE NORTHERN OHIO VALLEY AND GREAT LAKES. THERE IS EVEN THE
POTENTIAL FOR SOME MINOR FLOODING ACROSS PORTIONS OF CENTRAL AND
EASTERN NEW ENGLAND AS 2-3 INCHES OF RAINFALL IS BECOMING MORE
LIKELY WITH STRONG MOISTURE ADVECTION FROM THE ATLANTIC AHEAD OF
THE MAIN COLD FRONT. THEREFORE, A SLIGHT RISK OF EXCESSIVE
RAINFALL IS NOW IN EFFECT FOR THE DAY 5 PERIOD ON FRIDAY TO
ACCOUNT FOR THIS. STRONG WINDS WILL LIKELY BE AN ISSUE AS WELL
OWING TO THE STRONG PRESSURE GRADIENT THAT DEVELOPS.
ELSEWHERE, THE PACIFIC NORTHWEST SHOULD SEE MULTIPLE EPISODES OF
RAIN AND HIGHER ELEVATION SNOW AS PERSISTENT ONSHORE FLOW ADVECTS
MOISTURE INLAND, WITH THE HIGHEST TOTALS OVER THE WASHINGTON
CASCADES AND THE OLYMPICS, ESPECIALLY ON SUNDAY AND INTO MONDAY.
SOME OF THIS MOISTURE WILL LIKELY MAKE IT TO THE NORTHERN ROCKIES
IN THE FORM OF MODERATE TO LOCALLY HEAVY SNOW, ESPECIALLY NEAR THE
IDAHO/MONTANA BORDER. DRY WEATHER IS EXPECTED TO CONTINUE ACROSS
THE SOUTHWESTERN U.S. WITH THE UPPER RIDGE IN PLACE.
HAMRICK
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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