074
FXUS02 KWBC 210742
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EST WED DEC 21 2022
VALID 12Z SAT DEC 24 2022 - 12Z WED DEC 28 2022
***A MAJOR WINTER STORM EXITING INTO EASTERN CANADA WILL LIKELY
CONTINUE TO CAUSE STRONG WINDS ON SATURDAY NEAR THE GREAT LAKES,
ALONG WITH BITTERLY COLD TEMPERATURES FOR CHRISTMAS WEEKEND***
..SYNOPTIC OVERVIEW
AFTER AN EXTREMELY IMPACTFUL WINTER STORM HAMMERS THE EASTERN U.S.
DURING THE SHORT RANGE PERIOD, THINGS START TO IMPROVE GOING INTO
CHRISTMAS WEEKEND AS THE CORE OF THE LOW LIFTS NORTHWARD ACROSS
QUEBEC AND THEN HUDSON BAY. HOWEVER, IT WILL STILL BE QUITE WINDY
ACROSS THE GREAT LAKES REGION AND THE NORTHEAST ON SATURDAY WITH A
STRONG PRESSURE GRADIENT STILL IN PLACE, ALONG WITH SOME LAKE
EFFECT SNOW. THE IMPRESSIVELY COLD AIRMASS WILL BEGIN MODIFYING
AS THE SURFACE HIGH SETTLES ACROSS THE SOUTHERN TIER STATES.
LOOKING AHEAD TO EARLY NEXT WEEK, AN ALBERTA CLIPPER SYSTEM TRACKS
ACROSS THE CENTRAL/NORTHERN PLAINS, AND A SOUTHERN STREAM
DISTURBANCE TRACKS EASTWARD NEAR THE GULF COAST. MULTIPLE
SHORTWAVE PASSAGES NEAR THE PACIFIC NORTHWEST WILL KEEP THINGS
UNSETTLED FROM NORTHERN CALIFORNIA TO WASHINGTON STATE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST 00Z MODEL GUIDANCE SUITE INDICATES VERY GOOD SYNOPTIC
SCALE AGREEMENT THIS WEEKEND ON THE OVERALL UPPER LEVEL PATTERN
THAT FEATURES A WEST COAST RIDGE AND A POTENT EASTERN U.S. TROUGH,
WITH PACIFIC SHORTWAVES ROUNDING THE RIDGE AND FEEDING INTO THE
MEAN TROUGH. ATTENTION TURNS TO THE PLAINS AND THEN THE GULF
COAST REGION AS TWO DISTINCT SHORTWAVES TRACK DOWN THE EAST SIDE
OF THAT RIDGE, BUT RIGHT NOW THE GUIDANCE DOES NOT INDICATE ANY
APPRECIABLE PHASING OF THESE DISTURBANCES THROUGH MONDAY, SO THIS
WOULD LIMIT THE POTENTIAL FOR ANY COASTAL SURFACE LOW TRYING TO
DEVELOP NEAR THE SOUTHEAST U.S. BUT STILL WORTH MONITORING. BY
THE END OF THE FORECAST PERIOD ON WEDNESDAY, THE 00Z ECMWF IS MUCH
STRONGER WITH A CLOSED LOW NEAR THE GREAT LAKES, AND THE GFS
STRONGER WITH THE TROUGH EXITING THE EAST COAST, AND THERE ARE
MORE SIGNIFICANT TIMING DIFFERENCES OVER THE PACIFIC NORTHWEST, SO
MORE OF AN ENSEMBLE MEAN APPROACH WORKS WELL BY TUESDAY INTO
WEDNESDAY.
..WEATHER/HAZARD HIGHLIGHTS
THE DEPARTING WINTER STORM IS STILL LIKELY TO PRODUCE STRONG AND
POTENTIALLY DAMAGING WINDS FROM MICHIGAN TO UPSTATE NEW YORK
THROUGH THE DAY SATURDAY BEFORE GRADUALLY ABATING BY SATURDAY
NIGHT. INTENSE COLD AIR ADVECTION OVER THE WARMER LAKE WATERS IS
EXPECTED TO PRODUCE BANDS OF LAKE EFFECT/ENHANCED SNOW, SOME OF
WHICH COULD BE LOCALLY HEAVY. FRIGID WIND CHILLS WILL ALSO BE A
HARSH REALITY FROM THE MIDWEST TO THE OHIO/TENNESSEE VALLEY, AND
THEN EXTENDING EASTWARD TO THE EAST COAST WHILST NOT QUITE AS
SEVERE AS LOCATIONS WEST OF THE APPALACHIANS. THE WIDESPREAD SNOW
FROM EARLIER IN THE EVENT IS EXPECTED TO PRODUCE A WHITE CHRISTMAS
FOR MANY LOCATIONS.
WIDESPREAD ANOMALIES ON THE ORDER OF 20-30 DEGREES BELOW AVERAGE
FOR HIGHS AND 15-25 DEGREES FOR LOWS ARE EXPECTED FOR MOST
LOCATIONS IN THE CENTRAL AND EASTERN U.S. ON SATURDAY, AND THINGS
WILL IMPROVE GOING INTO MONDAY WITH HIGHS 10-20 DEGREES BELOW
AVERAGE, AND THEN RETURNING CLOSER TO AVERAGE BY THE MIDDLE OF
NEXT WEEK, AND SLIGHTLY ABOVE AVERAGE FOR THE ROCKIES AND
EXTENDING TO THE EAST COAST.
A MULTI-DAY HEAVY PRECIPITATION EVENT IS BECOMING MORE LIKELY FOR
THE WEST COAST AS A COUPLE OF POTENTIAL ATMOSPHERIC RIVER EVENTS
ADVECT COPIOUS MOISTURE INLAND FROM THE SIERRA TO THE CASCADES,
WITH THE HIGHEST TOTALS APPEARING LIKELY MONDAY NIGHT AND INTO
TUESDAY WITH SEVERAL INCHES OF RAIN AND A FEW FEET OF SNOW AT THE
HIGHEST ELEVATIONS. SHOWERS MAY ALSO INCREASE IN COVERAGE ACROSS
PARTS OF FLORIDA ON TUESDAY NEAR THE DEVELOPING COASTAL FRONTAL
BOUNDARY.
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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