600
FXUS02 KWBC 281900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST WED DEC 28 2022
VALID 12Z SAT DEC 31 2022 - 12Z WED JAN 04 2023
...MULTIPLE ROUNDS OF PRECIPITATION FOR THE WEST WITH LOWER
ELEVATION HEAVY RAIN/FLOODING AND HIGHER ELEVATION/INLAND HEAVY
SNOW...
...WINTER STORM THREAT FOR THE NORTH-CENTRAL ROCKIES/PLAINS AND
UPPER MIDWEST EARLY IN 2023 AS A HEAVY RAIN/SEVERE WEATHER THREAT
REEMERGES FOR THE MID-LOWER MISSISSIPPI VALLEY/MID-SOUTH THEN
SOUTHEAST U.S....
..OVERVIEW
THE UPPER-LEVEL PATTERN OVER THE WEEKEND WILL BE CHARACTERIZED BY
AN UPPER TROUGH LIFTING FROM THE CENTRAL U.S. TO THE GREAT LAKES
REGION PRODUCING MAINLY RAIN ACROSS THE EAST, WHILE ADDITIONAL
TROUGHING WORKS INTO THE WEST. AN ATMOSPHERIC RIVER WILL LEAD TO
ADDITIONAL HEAVY RAIN AND POSSIBLE FLOODING ACROSS PARTS OF
CALIFORNIA IN PARTICULAR. THE WESTERN TROUGH IS FORECAST TO WORK
ACROSS AN UNSETTLED WEST INTO THE CENTRAL U.S. AS NEXT WEEK
PROGRESSES, WHILE AT THE SURFACE, MODELS ARE COMING INTO
REASONABLY GOOD AGREEMENT FOR A LOW TO CONSOLIDATE/DEEPEN OVER THE
CENTRAL HIGH PLAINS BY LATE SUNDAY-MONDAY AND TRACK NORTHEASTWARD
THROUGH THE MIDWEST/GREAT LAKES REGION. DEEP LAYERED MOISTURE
RETURN FROM THE GULF OF MEXICO IS LIKELY TO PRODUCE HEAVY RAINFALL
AND POSSIBLE SEVERE WEATHER ACROSS THE LOWER MISSISSIPPI VALLEY
INTO THE TENNESSEE VALLEY AND SOUTHEAST MONDAY-WEDNESDAY, WHILE ON
THE BACKSIDE OF THE LOW THERE ARE INCREASING CHANCES FOR HEAVY
SNOW/WINTRY WEATHER ACROSS THE CENTRAL ROCKIES INTO THE NORTHERN
HALF OF THE PLAINS AND THE UPPER MIDWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODEL CYCLES HAVE KEPT WITH THE PATTERN OF RELATIVELY GOOD
AGREEMENT WITH THE LARGE SCALE PATTERN DESCRIBED ABOVE. BUT THERE
ARE STILL SOME DIFFERENCES IN THE DETAILS LIKE EXACT SHORTWAVE/LOW
PRESSURE/FRONTAL PLACEMENTS THAT ARE CERTAINLY WITHIN RANGE OF
TYPICAL MEDIUM RANGE SPREAD. THESE INCLUDE SOME VARIATIONS IN THE
MAIN CENTRAL U.S. SURFACE LOW TRACK MONDAY-WEDNESDAY. WHILE THE
DIFFERENCES ARE RELATIVELY MINOR FOR THE TIME RANGE, THE EXACT
TRACK WILL MATTER IN TERMS OF PRECIPITATION TYPES FOR ANY
PARTICULAR AREA, AND THIS MAY TAKE ADDITIONAL TIME TO RESOLVE. THE
WPC FORECAST APPROACH WAS TO USE A BLEND OF THE BEST CLUSTERED 00
UTC GFS/ECMWF/UKMET DETERMINISTIC MODELS EARLY ON WITH INCREASING
PROPORTIONS OF THE 00 UTC GEFS AND EC MEANS AS THE PERIOD
PROGRESSED GIVEN THE INCREASING (BUT STILL WITHIN REASON,
ESPECIALLY CONSIDERING THE OVERALL ACTIVE/STORMY FLOW) MODEL
SPREAD.
..WEATHER/HAZARD HIGHLIGHTS
ANOTHER PERSISTENT ATMOSPHERIC RIVER WILL SPAN FROM FRIDAY (NOW IN
THE SHORT RANGE PERIOD) INTO SATURDAY, TAKING AIM AT CALIFORNIA
WITH HEAVY PRECIPITATION. HEAVY RAIN COULD CAUSE ADDITIONAL
FLOODING ALONG COASTAL AREAS AS WELL AS THE FOOTHILLS OF THE
SIERRA NEVADA, SO A SLIGHT RISK REMAINS IN PLACE IN THE
EXPERIMENTAL DAY 4 EXCESSIVE RAINFALL OUTLOOK. THESE AREAS ARE
LIKELY TO BE HYDROLOGICALLY SENSITIVE BY THAT TIME DUE TO THE
ONGOING STRONG AR AND THE RAINFALL ON DAY 3, AND BURN SCARS
PRESENT ESPECIALLY IN SOUTHERN CALIFORNIA COULD BE PARTICULARLY
VULNERABLE TO FLOODING. ADDITIONALLY, SIGNIFICANT SNOW AMOUNTS ARE
LIKELY IN HIGHER ELEVATIONS OF THE WEST INTO THE WEEKEND, SHIFTING
EAST WITH TIME. MODEL GUIDANCE STILL ADVERTISES A BRIEF BREAK IN
THE PRECIPITATION ALONG THE WEST COAST FOR SUNDAY AS THE TROUGH
AXIS SHIFTS EAST, BUT A LESS CERTAIN ANOTHER ROUND OF HEAVY
PRECIPITATION MAY DEVELOP AGAIN BY BY TUESDAY/WEDNESDAY.
THE EASTERN U.S. IS LIKELY TO END THE YEAR 2022 WITH RAINFALL AS
MOISTURE STREAMS IN AHEAD OF THE INITIAL CENTRAL U.S. UPPER
TROUGH. MOST PRECIPITATION SHOULD STAY RAIN BUT WITH SOME CHANCE
OF MINOR SNOW ACCUMULATIONS FOR THE HIGHER ELEVATIONS OF THE
INTERIOR NORTHEAST. THEN, AS THE NEXT UPPER TROUGH EMERGES AND
SURFACE LOW PRESSURE CONSOLIDATES ACROSS THE CENTRAL HIGH PLAINS
AFTER PRODUCING POSSIBLY HEAVY SNOW ACROSS THE CENTRAL ROCKIES,
SNOW COULD SPREAD INTO LOWER ELEVATIONS AS WELL, PARTICULARLY FOR
AN INCREASINGLY STORMY/WINDY NORTHERN HALF OF THE HIGH PLAINS AND
INTO THE UPPER MIDWEST WHERE THERE WILL ALSO BE A ICY TRANSITION
ZONE. LEAD FLOW AROUND THE LOW AND LINGERING COLD AIR MAY ALSO
SUPPORT SOME SNOW/ICE DOWNSTREAM FROM THE NORTHERN GREAT LAKES TO
NORTHERN NEW ENGLAND. MEANWHILE FARTHER SOUTH, THE FRONTAL SYSTEM
ASSOCIATED WITH THIS LOW AND FAVORABLE GULF MOISTURE/INSTABILITY
AND RIGHT ENTRANCE REGION UPPER JET LIFT SHOULD PROVIDE A FOCUS
FOR ANOTHER EPISODE OF WIDESPREAD HEAVY RAIN, ALONG WITH A THREAT
OF SEVERE WEATHER AS PER SPC, ACROSS PARTS OF THE MISSISSIPPI
VALLEY INTO THE TENNESSEE VALLEY AND SOUTHEAST BY MONDAY-WEDNESDAY.
MILDER THAN AVERAGE TEMPERATURES FOR WINTER WILL BE WIDESPREAD
ACROSS THE EASTERN HALF OF THE COUNTRY FOR THE WEEKEND INTO EARLY
NEXT WEEK. LOWS OF AROUND 15-30F ABOVE AVERAGE AND HIGHS AROUND
10-20F ABOVE AVERAGE, LOCALLY HIGHER IN THE OHIO VALLEY BY
MONDAY-TUESDAY, WILL BE COMMON. DAILY RECORDS FOR WARM LOWS COULD
BE WIDESPREAD AS THE WARMEST AIR REACHES THE EAST, ESPECIALLY BY
MIDWEEK, WHILE A FEW ISOLATED DAILY RECORD HIGHS CANNOT BE RULED
OUT. MEANWHILE IN THE WEST, THE OVERALL WET/SNOWY PATTERN WILL
TEND TO KEEP DAYTIME TEMPERATURES AROUND 5-10F BELOW NORMAL. LOWS
SHOULD GENERALLY BE A BIT ABOVE AVERAGE UNTIL EARLY NEXT WEEK AS
THE SECOND LARGE-SCALE UPPER TROUGH MOVES THROUGH, BRINGING LOWS
WITHIN A FEW DEGREES OF NORMAL. THIS TROUGH AND THE ASSOCIATED
COLD FRONT WILL BRING THE PLAINS CLOSER TO AVERAGE BY
TUESDAY-WEDNESDAY AS WELL.
SCHICHTEL/TATE
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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