385
FXUS02 KWBC 130659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST TUE DEC 13 2022
VALID 12Z FRI DEC 16 2022 - 12Z TUE DEC 20 2022
...HEAVY SNOW THREAT SHIFTING THROUGH THE INTERIOR NORTHEAST
FRIDAY INTO SATURDAY, WITH HEAVY RAIN POSSIBLE ACROSS COASTAL
LOCATIONS...
..OVERVIEW
A DEEP UPPER LEVEL LOW (THE SAME ONE RESPONSIBLE FOR A NORTHERN
PLAINS WINTER STORM EARLY THIS WEEK) WILL BE IN PLACE OVER THE
UPPER MIDWEST AT THE START OF THE PERIOD ON FRIDAY. SHORTWAVE
ENERGY ROUNDING THE BASE OF THIS TROUGH WILL LIKELY INDUCE COASTAL
LOW DEVELOPMENT BY EARLY FRIDAY NEAR THE MID-ATLANTIC, WITH HEAVY
SNOWFALL FOR PORTIONS OF THE INTERIOR NORTHEAST ONGOING AS IT
LIFTS NORTH. SOME ACCUMULATING LAKE EFFECT SNOWFALL WILL BE
POSSIBLE BEHIND THE SYSTEM AS WELL. THE INITIAL UPPER LOW MAY
WOBBLE OVER THE GREAT LAKES FOR A PERIOD OF TIME BEFORE IT WEAKENS
AND QUICKLY TRACKS EASTWARD ACROSS SOUTHEAST CANADA AS THE NEXT
SYSTEM DROPS IN FROM WESTERN CANADA. THERE IS A LOT OF UNCERTAINTY
REGARDING THE SPECIFICS AND TRACK OF THIS SYSTEM (A CLOSED LOW FOR
SOME PERIOD OF TIME) BUT IN GENERAL IT SHOULD SEND TROUGHING
THROUGH THE WESTERN AND CENTRAL U.S., PROMOTING MUCH BELOW NORMAL
TEMPERATURES ACROSS MUCH OF THE NORTHERN ROCKIES TO NORTHERN AND
CENTRAL PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE REMAINS GOOD CLUSTERING FOR BOTH THE UPPER LOW PLACEMENT
OVER THE UPPER MIDWEST AS WELL AS THE COASTAL LOW EXPECTED TO
TRACK NORTHWARD FROM THE MID-ATLANTIC COAST AS A NOR'EASTER. THERE
REMAIN SOME UNCERTAINTIES SURROUNDING INDIVIDUAL WAVES OF ENERGY
ROUNDING THE BASE OF THE TROUGH, BUT A GENERAL MODEL BLEND SEEMED
TO MITIGATE THESE SMALLER SCALE DIFFERENCES. THERE IS BETTER
AGREEMENT NOW THAN PREVIOUS RUNS FOR THIS LOW TO LINGER FOR A DAY
OR SO OVER THE UPPER GREAT LAKES BEFORE SHEERING OFF TO THE EAST
OVER SOUTHEAST CANADA OR NEW ENGLAND.
BY DAY 5/SUNDAY, THERE ARE INCREASING UNCERTAINTIES REGARDING BOTH
TRACK AND INTENSITY OF THE NEXT SYSTEM FROM WESTERN CANADA, WHICH
FOR A TIME LOOKS TO CONSOLIDATE INTO A COMPACT CLOSED LOW OVER
SOUTHWEST CANADA. THERE IS SOME AGREEMENT THAT THIS SYSTEM SHOULD
EVENTUALLY SEND TROUGHING INTO THE CENTRAL U.S. BUT THE DETAIL
DIFFERENCES AS EARLY AS DAY 5 RESULTS IN SOME MUCH GREATER LARGER
SCALE DIFFERENCES BY EARLY NEXT WEEK. THE PAST COUPLE OF RUNS OF
THE GFS HAVE BEEN A LITTLE WEAKER WITH THE SYSTEM SKIRTING THE
NORTHERN TIER WITH AN EVENTUAL CLOSED LOW CONSOLIDATING AGAIN OVER
THE UPPER GREAT LAKES BY TUESDAY. THE ECMWF LINGERS THE LOW OVER
SOUTHWEST CANADA BEFORE ENERGY SWEEPS THROUGH THE NORTHERN PLAINS.
AND THE CMC IS MUCH DEEPER WITH THE LOW AND GENERALLY KEEPS IT
OVER WESTERN CANADA THROUGH THE PERIOD. THE ENSEMBLE MEANS TEND TO
FOLLOW SUIT WITH THEIR RESPECTIVE DETERMINISTIC COUNTERPARTS
FURTHER MAKING IT DIFFICULT TO DECIDE A MORE CLEAR DIRECTION.
THE FORECAST FOR TONIGHT STARTED WITH A GENERAL MODEL COMPROMISE
DAYS 3 AND 4, QUICKLY TRENDING TOWARDS THE ENSEMBLE MEANS BY LATER
IN THE PERIOD DUE TO UNCERTAINTIES OUTLINED ABOVE. THIS APPROACH
MAINTAINED FAIRLY GOOD CONSISTENCY WITH THE PREVIOUS WPC FORECAST
AS WELL (THROUGH DAY 6).
..WEATHER/HAZARD HIGHLIGHTS
THE LIKELY DEVELOPMENT OF A NOR'EASTER NEAR THE MID-ATLANTIC COAST
AND SUBSEQUENT NORTHWARD TRACK SHOULD CONTINUE A THREAT FOR WINTRY
WEATHER AND POTENTIALLY HEAVY SNOWFALL ACROSS INTERIOR PORTIONS OF
THE NORTHEAST. THERE REMAINS PLENTY OF UNCERTAINTY IN THE DETAILS
OF THIS SYSTEM, AND EVEN SMALL SHIFTS IN THIS LOW TRACK COULD
CAUSE SIGNIFICANT DIFFERENCES IN PRECIPITATION TYPES/AMOUNTS.
CLOSER TO THE COAST, RAIN COULD BE HEAVY AT TIMES OVER EASTERN NEW
ENGLAND, BUT WITH A GENERAL LACK OF INSTABILITY, IS UNLIKELY TO
CREATE ANY SIGNIFICANT HAZARDS. ELSEWHERE, LINGERING WRAP-BACK
MOISTURE ON THE BACKSIDE OF THE MAIN UPPER LOW WILL CONTINUE TO
SUPPORT SOME LIGHT SNOWFALL ACCUMULATIONS ACROSS THE UPPER MIDWEST
WITH ALSO SOME LAKE EFFECT SNOWS DOWNWIND OF THE FAVORABLE LAKES.
A SHORTWAVE INTO CALIFORNIA THIS WEEKEND MAY SPREAD PRECIPITATION
INTO THE SOUTHWEST. THIS SHORTWAVE WILL THEN TRACK ACROSS THE
SOUTHERN TIER AND COULD THEN INFLUENCE SPECIFICS OF MOISTURE THAT
MAY SPREAD ACROSS AND NORTH FROM THE GULF COAST LATE WEEKEND INTO
NEXT WEEK WITH SOME INDICATIONS FOR WIDESPREAD MODERATE TO HEAVY
RAIN. SOME PRECIPITATION MAY ALSO REACH THE NORTHWEST/NORTHERN
ROCKIES AS UPPER TROUGHING DESCENDS TOWARD THE REGION. SNOW LEVELS
COULD BE FAIRLY LOW OVER SOME AREAS.
BEHIND THE SYSTEM MOVING OFF THE EAST COAST, TEMPERATURES ACROSS
MOST OF THE CONUS SHOULD BE NEAR TO BELOW NORMAL BY FRIDAY AND
ESPECIALLY NEXT WEEKEND. THE MOST WIDESPREAD AND EXTREME COLD
ANOMALIES WILL LIKELY BE ACROSS THE WEST INTO THE NORTHERN PLAINS,
TRENDING COLDER WITH TIME. BY SUNDAY AND ESPECIALLY MONDAY AND
TUESDAY, DAYTIME TEMPERATURES ACROSS THE NORTHERN PLAINS COULD BE
AS MUCH AS 30-40 DEGREES BELOW NORMAL, EQUATING TO WIDESPREAD
SINGLE DIGIT TEMPERATURES WITH SOME BELOW ZERO READINGS ACROSS
EASTERN MONTANA AND NORTH DAKOTA. RECENT TRENDS SUGGEST PARTS OF
THE NORTHWEST COULD BE 10-25 DEGREES BELOW NORMAL BY THE START OF
NEXT WEEK.
SANTORELLI
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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