742
FXUS02 KWBC 160659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST MON DEC 16 2024
VALID 12Z THU DEC 19 2024 - 12Z MON DEC 23 2024
..OVERVIEW
THE PATTERN SHOULD BE TURNING MORE AMPLIFIED DURING THE MEDIUM
RANGE PERIOD AS MEAN TROUGHING BECOMES ESTABLISHED OVER THE EAST,
AND STRONG RIDGING BUILDS OVER THE WEST THROUGH NEXT WEEKEND. AN
INITIAL EAST TROUGH WILL SHIFT OFF THE COAST ON THURSDAY IN FAVOR
OF A REINFORCING SHORTWAVE TO AMPLIFY EASTERN TROUGHING AGAIN BY
NEXT WEEKEND. THIS SHORTWAVE SHOULD BRING WITH IT SNOW POTENTIAL
ACROSS THE GREAT LAKES AND A FRESH BLAST OF ARCTIC AIR TO THE EAST
BY NEXT WEEKEND, WHILE THE WEST TURNS PROGRESSIVELY WARMER. AN
ATMOSPHERIC RIVER MAY BRING A PERIOD OF HEAVY RAIN/MOUNTAIN SNOWS
TO PARTS OF THE WEST COAST BY THE WEEKEND AS WELL. AS THIS
SHORTWAVE PUSHES INLAND EARLY NEXT WEEK, IT SHOULD HELP PUSH THE
EASTERN U.S. TROUGH EASTWARD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS CONTINUE TO SHOW GOOD AGREEMENT IN THE OVERALL SYNOPTIC
PATTERN ACROSS THE CONUS DURING THE MEDIUM RANGE PERIOD BUT PLENTY
OF UNCERTAINTY STILL IN THE TIMING AND DETAILS OF INDIVIDUAL
SYSTEMS. SUFFICIENT MODEL AGREEMENT THE FIRST HALF OF THE PERIOD
ALLOWED FOR A BLEND OF THE DETERMINISTIC GUIDANCE AS A STARTING
POINT FOR THE WPC FORECAST. BY DAY 5/SATURDAY, THERE IS SOME
UNCERTAINTY IN THE TIMING OF THE SHORTWAVE AND AR AS IT REACHES THE
WEST COAST. YESTERDAY'S 12Z RUN OF THE CMC WAS NOTABLY FASTER THAN
THE GFS/ECMWF AND ENSEMBLE MEANS, BUT THE NEW 00Z RUN TONIGHT
(AVAILABLE AFTER FORECAST GENERATION TIME) WAS SLOWER AND MORE IN
LINE WITH THE CONSENSUS. SUNDAY INTO MONDAY, THERE ARE QUESTIONS ON
AMPLITUDE OF THIS FEATURE AS IT PROGRESSES ACROSS THE WEST, AS
WELL AS THE DETAILS ON ANOTHER WEAKER SHORTWAVE UPSTREAM INTO THE
NORTHWEST AT THAT TIME. IN THE EAST, MODELS CONTINUE TO RESOLVE HOW
QUICKLY THE AMPLIFIED TROUGH WILL EXIT THE EAST COAST EARLY NEXT
WEEK. FOR DAY 5 AND BEYOND, THE WPC BLEND INCORPORATED MORE OF THE
ENSEMBLE MEANS TO ACCOUNT FOR THE INCREASING UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
THE SHORTWAVE INTO THE GREAT LAKES REGION COULD BRING SOME LIGHT
TO MODERATE ACCUMULATING SNOW ACROSS PARTS OF THE UPPER MIDWEST TO
GREAT LAKES ON THURSDAY, WITH LAKE EFFECT SNOW LINGERING INTO NEXT
WEEKEND IN THE FAVORABLE LOCATIONS DOWNWIND OF LAKES MICHIGAN,
ERIE, AND ONTARIO. THIS SHORTWAVE WILL EVENTUALLY AMPLIFY TROUGHING
ACROSS THE EASTERN THIRD OF THE COUNTRY USHERING IN AN ARCTIC
AIRMASS SUPPORTING DAYTIME HIGHS BY NEXT WEEKEND AS MUCH AS 15 TO
20 DEGREES BELOW NORMAL FOR ESPECIALLY PARTS OF THE NORTHEAST.
OUT WEST, CONDITIONS SHOULD BEGIN DRY LATER THIS WEEK EXCEPT FOR
SOME INCREASED PRECIPITATION ASSOCIATED WITH WEAK SHORTWAVES INTO
THE NORTHWEST. INCREASING PRECIPITATION LOOKS LIKELY BY NEXT
WEEKEND WITH THE NEXT ATMOSPHERIC RIVER INTO THE REGION WITH HEAVY
RAIN/MOUNTAIN SNOWS POSSIBLE ACROSS COASTAL RANGES OF THE NORTHWEST
INTO NORTHERN CALIFORNIA. TEMPERATURES ACROSS THE WEST SHOULD
GENERALLY STAY ABOVE AVERAGE THROUGH THE PERIOD UNDERNEATH OF
RIDGING.
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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