519
FXUS02 KWBC 160700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST FRI DEC 16 2022
VALID 12Z MON DEC 19 2022 - 12Z FRI DEC 23 2022
...BITTERLY COLD TEMPERATURES LIKELY TO SETTLE OVER THE NORTHERN
PLAINS FROM SUNDAY ONWARD...
..SYNOPTIC OVERVIEW
A SIGNIFICANT PATTERN CHANGE IS EXPECTED TO EVOLVED ACROSS MUCH OF
THE CONTINENTAL U.S. NEXT WEEK AS A PRONOUNCED UPPER TROUGH BUILDS
IN ACROSS THE EASTERN HALF 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. 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. THINGS GET INTERESTING TOWARDS THE
END OF THE WEEK AS A POTENTIAL EAST COAST STORM DEVELOPS, AND THE
DETAILS OF THIS WILL BE DEPENDENT UPON THE PHASING OF BOTH
SOUTHERN AND NORTHERN STREAM SHORTWAVE ENERGY, AND WHEN THIS TAKES
PLACE. IF THE LOW DEVELOPS CLOSE ENOUGH TO THE COAST, IMPACTFUL
RAIN AND SNOW COULD MATERIALIZE FROM THE MID-ATLANTIC TO NEW
ENGLAND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS A GOOD OVERALL DEPICTION OF THE
WEATHER PATTERN ON MONDAY, WITH THE MAIN DIFFERENCES OBSERVED WITH
THE TIMING OF THE UPPER TROUGH/CLOSED LOW ACROSS SOUTHWESTERN
CANADA AND ITS ARRIVAL OVER THE FAR NORTHERN PLAINS. BY TUESDAY,
THE SOUTHERN STREAM TROUGH OVER TEXAS IS MORE AMPLIFIED WITH THE
GFS AND SLIGHTLY FASTER WITH THE ECMWF, AND THE GFS REMAINS
SLIGHTLY MORE AMPLIFIED GOING THROUGH WEDNESDAY. GOING INTO
WEDNESDAY NIGHT, THE SECOND LOBE FROM A PORTION OF THE POLAR
VORTEX STARTS DROPPING SOUTH ACROSS THE UPPER MIDWEST, AND THE
AXIS OF THE TROUGH IS FARTHER EAST WITH THE CMC AND ECMWF, WHEREAS
THE GFS IS SHARPER AND SLOWER. THIS WILL HAVE IMPLICATIONS ON THE
EVENTUAL DEVELOPMENT OF THE COASTAL LOW NEAR THE EAST COAST, WITH
THE GFS HAVING A MORE OFFSHORE TRACK.
THE WPC FRONTS/PRESSURES WAS PRIMARILY BASED ON A 40% ECMWF/20%
GFS/20% CMC/20% ECENS BLEND FOR MONDAY AND TUESDAY, AND THEN THE
PROPORTION OF THE ECENS AND GEFS MEANS WERE INCREASED GOING
THROUGH THE REMAINDER OF THE WEEK TO ACCOUNT FOR THE INCREASING
MODEL UNCERTAINTY. FUTURE FORECAST UPDATES WILL PROVIDE
ADDITIONAL CLARITY ON THE EVENTUAL EAST COAST STORM EVOLUTION AND
POTENTIAL IMPACTS.
..WEATHER/HAZARD HIGHLIGHTS
FAVORABLE WESTERLY FLOW ON THE BACKSIDE OF THE MAIN UPPER LOW WILL
CONTINUE TO SUPPORT SOME LAKE EFFECT SNOWS OVER DOWNWIND AREAS FOR
MULTIPLE DAYS IN THE WAKE OF THE DEPARTING NOR'EASTER OVER
SOUTHEAST CANADA. A SHORTWAVE TRACKING ACROSS THE SOUTHERN TIER
ALONG WITH AN ASSOCIATED FRONTAL WAVE OVER THE GULF OF MEXICO
COULD PRODUCE A PERIOD OF ENHANCED RAINFALL NEAR THE GULF COAST
AND INTO FLORIDA DURING MONDAY-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 BUT THERE IS A
GENERAL SIGNAL THAT TOTALS SHOULD INCREASE TOWARD
WEDNESDAY-THURSDAY. ALSO AROUND THAT TIME, UPPER TROUGH
AMPLIFICATION OVER THE PLAINS-MISSISSIPPI VALLEY AND ASSOCIATED
LOW PRESSURE/FRONTAL SYSTEM COULD BRING ANOTHER THREAT OF SNOW TO
PARTS OF THE PLAINS AND UPPER MIDWEST INTO GREAT LAKES, WITH RAIN
FARTHER SOUTH. LOWER LATITUDE WAVINESS LATE IN THE PERIOD,
POSSIBLY EVOLVING NEAR THE SOUTHEAST COAST BY THURSDAY, COULD ALSO
BRING SOME MOISTURE TO PARTS OF THE SOUTH AND EAST. CONFIDENCE IN
ANY SPECIFICS IS LOW AT THIS TIME, GIVEN THE VARIABILITY THAT
GUIDANCE HAS HAD FOR PATTERN DETAILS OVER RECENT DAYS.
THE MOST WIDESPREAD AND EXTREME COLD ANOMALIES WILL LIKELY BE
ACROSS THE NORTHERN PLAINS FROM SUNDAY ONWARD, WITH DAYTIME
TEMPERATURES AS COLD AS 30-40 DEGREES BELOW NORMAL (LOCALLY EVEN
COLDER ACROSS PARTS OF MONTANA), EQUATING TO WIDESPREAD AND
BITTERLY COLD SINGLE DIGIT TEMPERATURES WITH SOME BELOW ZERO
READINGS ACROSS EASTERN MONTANA AND NORTH DAKOTA. MORNING LOWS
COULD FALL TO AT LEAST 10-20 DEGREES BELOW ZERO (LOCALLY COLDER IN
SPOTS). SURROUNDING AREAS SHOULD SEE LESS EXTREME ANOMALIES OF
10-20F BELOW NORMAL. AFTER MIDWEEK EXPECT THE COLD AIR TO SURGE
FARTHER SOUTH AND EAST, BRINGING HIGHS DOWN TO 10-25F BELOW NORMAL
OVER THE SOUTHERN HALF OF THE PLAINS AND AN INCREASING PORTION OF
THE MISSISSIPPI VALLEY BY NEXT THURSDAY. THE EAST WILL BE CHILLY
TO FINISH THE WEEKEND AND MODERATE FOR A TIME, BEFORE STARTING TO
TREND COLDER AGAIN MID-LATE WEEK. THE WEST WILL TEND TO SEE
READINGS 5-15F BELOW NORMAL THROUGH SUNDAY AND THEN
CENTRAL/SOUTHERN AREAS SHOULD SEE A WARMING TREND. MODERATELY
ABOVE NORMAL READINGS WILL LIKELY BECOME MORE COMMON OVER THE
SOUTHERN TWO-THIRDS OF THE WEST BY WEDNESDAY-THURSDAY AS AN UPPER
RIDGE BUILDS TOWARD THE WEST COAST.
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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