177
FXUS02 KWBC 181904
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 PM EST SUN DEC 18 2022
VALID 12Z WED DEC 21 2022 - 12Z SUN DEC 25 2022
***BITTERLY COLD TEMPERATURES LIKELY TO SETTLE OVER THE NORTHERN
PLAINS, SPREADING SOUTH AND EAST THROUGH THE END OF THE WEEK***
***POTENTIAL FOR A SIGNIFICANT WINTER STORM OVER THE EASTERN U.S.
LATE IN THE WEEK***
..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. A BUILDING RIDGE
AXIS NEAR THE WEST 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, AND WILL LIKELY CAUSE SOME
CHALLENGES FOR TRAVELERS. THE INTENSIFYING LOW THEN LIFTS
NORTHWARD ACROSS EASTERN CANADA BY SATURDAY WITH WIDESPREAD GUSTY
WINDS AND LAKE EFFECT SNOW IN ITS WAKE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z GUIDANCE CONTINUES TO COME INTO CLOSER ALIGNMENT WITH
RESPECT TO THE SYNOPTIC PATTERN OVER THE LOWER 48. THE LAST FEW
RUNS OF THE GFS/GEFS HAVE ESPECIALLY COME INTO BETTER AGREEMENT
WITH THE EC/CMC/UKMET GUIDANCE SUITE. SOME DIFFERENCES IN THE
ORIENTATION OF THE UPPER TROUGH EXIST ON DAYS 3 AND 4 OVER THE
GREAT LAKES/SOUTHERN CANADA, BUT SEEM TO RESOLVE THEMSELVES AFTER
DAY 5. THE 00Z EC/CMC SIGNALED A CLOSED UPPER LOW OVER THE OHIO
VALLEY ON DAY 6 WHILE THE 06Z GFS AND 00Z UKMET KEPT THE TROUGH
OPEN. PLACEMENT AND TILT OF TROUGH REMAINED REASONABLY SIMILAR
THROUGHOUT THE PERIOD. THE MEDIUM RANGE MODEL BLEND CONSISTED OF
THE 00Z EC/UK/CMC/WPC AND 06Z GFS THROUGH DAY 4. THE 06Z GEFS WAS
INTRODUCED ON DAY 5 TO MODERATE THE STRENGTHENING UPPER LOW OVER
THE MIDWEST. THE 00Z CMCE/ECE WERE INTRODUCED ON DAY 6 AND
CONTINUED THROUGH DAY 7. THERE'S STILL SOME ENSEMBLE MEMBER SPREAD
IN THE ECE/GEFS/CMCE WITH RESPECT TO TIMING OF THE UPPER TROUGH
OVER THE PLAINS ON DAY 4, BUT THERE HAS BEEN IMPROVEMENT ON THAT
SINCE YESTERDAY.
..WEATHER/HAZARD HIGHLIGHTS
THE MAIN WEATHER STORY THAT WILL MAKE WEATHER HEADLINES NEXT WEEK
WILL BE THE MASSIVE EXPANSE OF FRIGID TEMPERATURES FROM THE
NORTHERN ROCKIES/NORTHERN PLAINS TO THE MIDWEST THROUGH THE MIDDLE
OF THE WEEK, AND THEN REACHING THE GULF COAST AND MUCH OF THE
EASTERN U.S. BY FRIDAY AND INTO THE WEEKEND. 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. MANY OF THE DAILY
RECORDS DURING THIS TIME WERE SET DURING THE HISTORIC ARCTIC BLAST
OF 1983, SO THIS WILL TEND TO LIMIT THE EXTENT OF NEW RECORDS
BEING SET.
ATTENTION ALSO TURNS TO THE EXPECTED DEVELOPMENT OF A STRONG LOW
PRESSURE SYSTEM THAT EVOLVES FROM THE MERGER OF A FRONTAL LOW OVER
THE OHIO VALLEY/GREAT LAKES AND A COASTAL LOW NEAR THE
MID-ATLANTIC AND SOUTHERN NEW ENGLAND. THE EXPECTED INLAND TRACK
OF THE MAIN LOW OVER UPSTATE NEW YORK WILL TEND TO KEEP THE
MAJORITY OF THE PRECIPITATION AS RAIN ACROSS THE EAST COAST AND
THE INTERSTATE 95 CORRIDOR 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. 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. 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/KEBEDE
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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