424
FXUS02 KWBC 170659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST SAT DEC 17 2022
VALID 12Z TUE DEC 20 2022 - 12Z SAT DEC 24 2022
***BITTERLY COLD TEMPERATURES LIKELY TO SETTLE OVER THE NORTHERN
PLAINS FOR MUCH OF NEXT WEEK, SPREADING SOUTH AND EAST AFTER
WEDNESDAY***
***POTENTIAL FOR A SIGNIFICANT WINTER STORM OVER THE EASTERN U.S.
LATE IN THE WEEK***
..SYNOPTIC OVERVIEW
A SIGNIFICANT PATTERN CHANGE IS FORECAST TO EVOLVE ACROSS MUCH OF
THE CONTINENTAL U.S. FOR MIDDLE TO LATE WEEK AS A PRONOUNCED UPPER
TROUGH DIGS SOUTHWARD ACROSS THE CENTRAL PART OF THE NATION,
ACCOMPANIED BY AN IMPRESSIVE ARCTIC AIRMASS SETTLING SOUTHWARD
ACROSS THE PLAINS AND THEN ADVECTING EASTWARD, WITH WIDESPREAD
SUBZERO TEMPERATURES LIKELY FOR THE NORTH-CENTRAL STATES AS THE
COLDEST AIRMASS OF THE SEASON ARRIVES. THIS IS MAINLY IN RESPONSE
TO A BUILDING WEST COAST UPPER RIDGE (+PNA PATTERN) AND A NEGATIVE
ARCTIC OSCILLATION (-AO PATTERN) THAT ALLOWS ARCTIC AIRMASSES TO
DROP SOUTHWARD FROM CANADA. MOST GUIDANCE SUGGESTS THAT THE
AMPLIFYING TROUGH WILL SUPPORT STRONG SURFACE LOW DEVELOPMENT
BEGINNING ON THURSDAY, PRODUCING AREAS OF HEAVY RAIN AND/OR SNOW
ALONG WITH STRONG WINDS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS STILL INDICATING SOME MEANINGFUL
DIFFERENCES AS EARLY AS TUESDAY, BOTH ACROSS THE GULF COAST WITH
THE GFS/GEFS SLOWER THAN THE OTHER GUIDANCE, AND THE GFS IS ALSO A
BIT MORE AMPLIFIED ACROSS THE UPPER MIDWEST, SIMILAR TO ITS
PREVIOUS RUNS. BY WEDNESDAY, THE DIFFERENCES WITH THE GFS/GEFS
BECOME QUITE PRONOUNCED ACROSS THE GREAT LAKES REGION AND EVEN
BECOME SOMEWHAT OUT OF PHASE WITH THE NON-NCEP GUIDANCE BY
THURSDAY ACROSS THE NORTHEAST. THERE HAS ALSO BEEN A TREND FOR
THE SURGE OF ARCTIC AIR TO BE CENTERED FARTHER WEST AND INCLUDING
THE HIGH PLAINS OF COLORADO AND WYOMING WITH A TREND FOR EVEN
COLDER CONDITIONS BY MID-LATE WEEK.
THE FORECAST REMAINS CHALLENGING FOR THE SECOND HALF OF THE
FORECAST PERIOD REGARDING THE EVENTUAL DEVELOPMENT OF A
POTENTIALLY STRONG LOW PRESSURE SYSTEM ACROSS THE EASTERN U.S.
LATE IN THE WEEK. THE OVERALL TREND COMPARED TO YESTERDAY HAS
BEEN FOR THE MAIN SURFACE LOW TO TRACK CLOSER TO THE APPALACHIANS
AND LESS OF A COASTAL LOW SCENARIO THAT EARLIER SOLUTIONS WERE
PORTRAYING, AND THIS GENERALLY MEANS MORE RAIN THAN SNOW FOR THE
MAJOR CITIES ALONG THE INTERSTATE 95 CORRIDOR, AND SNOW CONFINED
TO INTERIOR PORTIONS OF THE MID-ATLANTIC AND NORTHEAST. HOWEVER,
THE GFS IS STILL MAINTAINING THE IDEA OF A STRONG LOW NEAR THE
COAST, BUT GIVEN THE DIFFERENCES NOTED, THIS IS NOT THE PREFERRED
SOLUTION AT THIS TIME. THERE HAS ALSO BEEN A SLIGHTLY SLOWER
TREND IN THE ARRIVAL OF HEAVIEST PRECIPITATION.
AN EXAMINATION OF THE ICON AND JMA MODELS SUPPORTS A SOLUTION
CLOSER TO THE ECMWF/CMC/ECENS FOR FRONTS AND PRESSURES, SO THE
FORECAST WAS HEDGED IN THAT DIRECTION FOR THE ENTIRE FORECAST
PERIOD, WITH MORE WEIGHTING TOWARDS THE ECENS MEAN BY FRIDAY AND
INTO SATURDAY. FOR QPF, ABOUT HALF OF THE NBM WAS USED ALONG WITH
A NEARLY EQUAL PROPORTION OF THE ECMWF/CMC/ECENS.
..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 AND THEN FARTHER
SOUTH AND EAST BY THURSDAY AND BEYOND. A COUPLE OF REINFORCING
COLD FRONTS 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, WITH SOME LOWS
APPROACHING -30 DEGREES ACROSS PORTIONS OF MONTANA AND NORTH
DAKOTA. ALTHOUGH THE FRIGID AIRMASS WILL MODIFY AS IT REACHES THE
OHIO VALLEY AND MID-SOUTH, IT WILL STILL BE QUITE COLD WITH
WIDESPREAD 0S AND 10S FOR OVERNIGHT LOWS BY THE END OF THE WEEK,
AND THIS VERY COLD WEATHER IS EXPECTED TO HAVE SOME STAYING POWER
AS THE CLIMATE PREDICTION CENTER OUTLOOK INDICATES HIGH
PROBABILITIES OF BELOW AVERAGE TEMPERATURES PERSISTING OVER MUCH
OF THE EASTERN HALF OF THE COUNTRY FOR THE DAY 6-10 PERIOD. AS
COLD AS IT WILL LIKELY BE, IT WILL BE DIFFICULT TO CHALLENGE DAILY
RECORD LOWS/COLD HIGHS DUE TO THIS EVENT OVERLAPPING WITH PORTIONS
OF THE HISTORIC 1983 AND 1989 COLD WAVES. AT THE VERY LEAST
PORTIONS OF THE EAST MAY END UP SEEING THE COLDEST TEMPERATURES
FOR ANY DECEMBER SINCE 2017.
AS FOR THE POTENTIAL STORM AFFECTING THE EASTERN U.S. LATE NEXT
WEEK, THE MOST COMMON THEME IN THE CURRENT GUIDANCE IS THAT THE
STRONG UPPER TROUGH AMPLIFICATION AND POTENTIALLY DEEP UPPER LOW
WOULD PRODUCE A VIGOROUS SURFACE SYSTEM AND A BROAD AREA OF STRONG
WINDS. BEYOND THAT, A POTENTIAL STORM TRACK ANYWHERE BETWEEN THE
GREAT LAKES AND EAST COAST MAKE IT VERY DIFFICULT TO OUTLINE WHERE
THE HEAVIEST SNOW IS MOST LIKELY. RIGHT NOW, THE CENTRAL
APPALACHIANS INTO INTERIOR NEW ENGLAND AND UPSTATE NEW YORK
CURRENTLY HAVE THE HIGHEST PROBABILITY OF SIGNIFICANT SNOWFALL.
HOWEVER, IF TRENDS CONTINUE GOING FARTHER WESTWARD, THEN THE
GREATEST SNOW THREAT COULD REACH AS FAR BACK AS THE MIDWEST/OHIO
VALLEY WITH MORE IN THE WAY OF RAIN FARTHER EAST ALONG A STRONG
COLD FRONT. CHANGES IN FUTURE FORECASTS ARE VERY LIKELY.
ELSEWHERE, A SHORTWAVE TRACKING NEAR THE GULF COAST ALONG WITH AN
ASSOCIATED FRONTAL WAVE OVER THE NORTHERN GULF OF MEXICO COULD
PRODUCE A PERIOD OF ENHANCED RAINFALL ACROSS PORTIONS OF THE
FLORIDA PENINSULA ON TUESDAY. THE NORTHWEST SHOULD SEE MULTIPLE
EPISODES OF RAIN AND HIGHER ELEVATION SNOW WITH HIGHEST TOTALS
OVER FAVORED TERRAIN. CONFIDENCE IS MODERATE AT BEST FOR
DAY-TO-DAY DETAILS REGARDING AMOUNTS AND COVERAGE GIVEN THE
DEPENDENCE ON EXACT ORIENTATION OF THE UPPER FLOW OVER THE REGION.
THE GRADUAL WARMING TREND OVER THE WEST AS UPPER RIDGING BUILDS
TOWARD THE COAST SHOULD LEAD TO SLOWLY RISING SNOW LEVELS WITH
TIME.
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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