790
FXUS02 KWBC 191941
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 PM 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, WITH ANORMALLY COLD WEATHER REACHING THE GULF
COAST REGION AS WELL...
...SIGNIFICANT WINTER STORM FROM THE MIDWEST TO THE NORTHEAST 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 BRING ARCTIC AIR AND 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.
TEMPERATURES FROM THE CENTRAL TO EASTERN U.S. SHOULD GRADUALLY
MODERATE FROM WEST TO EAST THIS WEEKEND AND BEYOND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW MUCH BETTER AGREEMENT ON THE
EXPECTED SYNOPTIC SCALE SET-UP FOR THE MAJOR EASTERN U.S. LOW
PRESSURE SYSTEM. THE 00Z AND 06Z RUNS OF THE GFS CONTINUED TO SHOW
A SLOWER AND SLIGHTLY FARTHER SOUTH TRACK WITH THE MAIN UPPER LOW
COMPARED TO THE ECMWF, CMC, AND UKMET, BUT THE NEW 12Z GFS RUN
(AVAILABLE AFTER FORECASTER GENERATION TIME) CAME MUCH MORE IN
LINE WITH THE CONSENSUS. THERE ALSO REMAIN SOME TRACK/PLACEMENT
DIFFERENCES ON THE UPPER AND SURFACE LOWS AS THEY TRACK NORTHWARD
INTO CANADA. SOME TIMING/AMPLITUDE DIFFERENCES, BUT THE GUIDANCE
ALSO SEEMS TO HAVE A BETTER HANDLE ON A SHORTWAVE TRACKING FROM
THE SOUTHWEST TO THE GULF COAST AS WELL THIS WEEKEND. FOR BOTH, A
GENERAL MODEL COMPROMISE SEEMED TO WORK WELL AS A STARTING POINT
FOR THE UPDATED WPC FORECAST. ANOTHER SHORTWAVE RIDING THE TOP OF
THE WESTERN U.S. RIDGE SHOWED PLENTY OF UNCERTAINTY AROUND
SUNDAY-MONDAY REGARDING AMPLIFICATION OVER THE CENTRAL U.S..
AGAIN, THE MAIN OUTLIER HERE WAS A MUCH WEAKER 06Z GFS, BUT THE
12Z LOOKS BETTER. A BLEND OF THE ECMWF, CMC, WITH THE ENSEMBLE
MEANS WORKED WELL FOR THIS SYSTEM. OVERALL, NEEDED CHANGES TO THE
PREVIOUS WPC FORECAST WERE MINIMAL.
..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 SINGLE DIGIT TEMPERATURES FOR OVERNIGHT LOWS
THROUGH THE WEEKEND. 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 THE 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 TO THE WEST FROM THE MIDWEST TO THE NORTHERN OHIO VALLEY AND
GREAT LAKES, AND THE CENTRAL/NORTHERN APPALACHIANS. 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 WEEKS STORM.
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.
SANTORELLI/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page