738
FXUS02 KWBC 200659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST TUE DEC 20 2022
VALID 12Z FRI DEC 23 2022 - 12Z TUE DEC 27 2022
***A MAJOR WINTER STORM FROM THE MIDWEST TO THE NORTHEAST LATE IN
THE WEEK WILL LIKELY CAUSE BLIZZARD CONDITIONS AND TRAVEL
DISRUPTIONS, ALONG WITH BITTERLY COLD TEMPERATURES AND STRONG
WINDS TO CLOSE OUT THE WEEK***
..SYNOPTIC OVERVIEW
AN IMPRESSIVE DIP IN THE JET STREAM AND A HIGHLY ANOMALOUS UPPER
TROUGH/CLOSED LOW OVER THE OHIO VALLEY ON FRIDAY WILL SUSTAIN
EXPLOSIVE SURFACE CYCLOGENESIS ACROSS THE GREAT LAKES WITH CENTRAL
PRESSURES FALLING WELL BELOW 980 MB BY FRIDAY EVENING. THIS WILL
CAUSE AN INCREDIBLY STRONG COLD FRONT TO SWEEP ACROSS THE EASTERN
U.S. WITH FRIGID TEMPERATURES FROM THE PLAINS TO THE EAST COAST IN
TIME FOR CHRISTMAS WEEKEND. THE LOW LIFTS NORTHWARD ACROSS QUEBEC
ON SATURDAY WITH LAKE EFFECT SNOW CONTINUING, AND HEAVY RAINFALL
EXITS NEW ENGLAND. THE HUGE ARCTIC SURFACE HIGH THEN SETTLES
ACROSS THE SOUTH-CENTRAL U.S. AND THEN MODIFIES WITH GRADUALLY
WARMING TEMPERATURES GOING INTO CHRISTMAS DAY AND EARLY NEXT WEEK.
FARTHER WEST, MULTIPLE SHORTWAVE IMPULSES WILL PASS OVER THE
PACIFIC NORTHWEST AND RESULT IN PERIODS OF HEAVY RAIN AND HIGH
MOUNTAIN SNOW FROM WESTERN OREGON TO WESTERN WASHINGTON.
..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 WITH A
SLIGHT EASTWARD ADJUSTMENT IN THE PLACEMENT OF THE LOW (12Z ECENS
SLIGHTLY NORTHWEST OF 00Z MODEL CONSENSUS). THEREFORE, A GENERAL
MODEL COMPROMISE SUFFICES AS A STARTING POINT IN THE FORECAST
PROCESS, EVEN THOUGH SOME SMALLER MESOSCALE DIFFERENCES IN THE
GUIDANCE REMAIN. THERE ALSO REMAINS A GOOD MODEL SIGNAL FOR A
BETTER DEFINED SOUTHERN STREAM SHORTWAVE, WITH THE CMC REMAINING
MOST AMPLIFIED WITH THIS FEATURE AS IT DROPS SOUTHWARD OVER
EASTERN MEXICO. TOWARDS THE END OF THE FORECAST PERIOD, MODEL
DEPICTION HAS IMPROVED WITH AN AMPLIFYING TROUGH ACROSS THE
NORTHEAST PACIFIC EARLY NEXT WEEK WITH THE NEXT STORM SYSTEM TO
AFFECT THE PACIFIC NORTHWEST. HOWEVER, THERE IS MORE MODEL SPREAD
WITH A TROUGH BUILDING OVER THE MIDWEST BY NEXT TUESDAY, SO MORE
OF THE ENSEMBLE MEANS WERE INCORPORATED FOR DAYS 6 AND 7.
..WEATHER/HAZARD HIGHLIGHTS
THE MAIN WEATHER STORY IS THE 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 TO THE WEST WITH BLIZZARD
CONDITIONS FROM THE MIDWEST TO 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, ESPECIALLY IF THIS
RAINFALL FALLS OVER REGIONS THAT MAY STILL HAVE A SNOW PACK FROM
LAST WEEK'S STORM. THEREFORE, A SLIGHT RISK OF EXCESSIVE RAINFALL
REMAINS IN EFFECT FOR THE DAY 4 PERIOD ON FRIDAY TO ACCOUNT FOR
THIS. STRONG AND POTENTIALLY DAMAGING WINDS ARE LIKELY ACROSS
PORTIONS OF OHIO, PENNSYLVANIA, AND WESTERN NEW YORK FRIDAY AND
INTO EARLY SATURDAY AS A STING JET MIXES STRONG WINDS ALOFT TO THE
SURFACE.
THE TRULY MASSIVE EXPANSE OF FRIGID TEMPERATURES ACROSS BASICALLY
ALL OF THE CENTRAL AND EASTERN U.S. EAST OF THE ROCKIES WILL ALSO
CONTINUE TO MAKE WEATHER HEADLINES TO CLOSE OUT THE WEEK, WITH
HARD FREEZES LIKELY FOR MUCH OF THE DEEP SOUTH AND WELL INTO
TEXAS. THERE WILL BE WIDESPREAD SUBZERO READINGS FOR BOTH
OVERNIGHT LOWS AND EVEN DAYTIME HIGHS FROM THE NORTHERN ROCKIES TO
THE CENTRAL/NORTHERN PLAINS AND THE UPPER MIDWEST, ESPECIALLY ON
FRIDAY AND SATURDAY. ALTHOUGH THE FRIGID AIRMASS WILL MODIFY SOME
AS IT REACHES THE OHIO/TENNESSEE VALLEY REGION, IT WILL STILL BE
IMPRESSIVELY COLD WITH WIDESPREAD 0S AND 10S FOR HIGH
TEMPERATURES, AND SOME SUBZERO OVERNIGHT LOWS. HARD FREEZE
CONDITIONS ARE EXPECTED FOR MUCH OF THE DEEP SOUTH AND TEXAS
THURSDAY NIGHT THROUGH AT LEAST FRIDAY NIGHT, WITH LOWS WELL INTO
THE 10S AND LOW 20S, EVEN TO THE GULF COAST. COLD WEATHER WILL
ALSO REACH WELL INTO FLORIDA IN TIME FOR THE CHRISTMAS WEEKEND,
WITH LOWS FALLING INTO THE 30S AND 40S ACROSS MUCH OF THE
PENINSULA.
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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