486
FXUS02 KWBC 280705
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 AM EST WED DEC 28 2022
VALID 12Z SAT DEC 31 2022 - 12Z WED JAN 04 2023
...MULTIPLE ROUNDS OF PRECIPITATION ARE LIKELY IN THE WEST WITH
LOWER ELEVATION HEAVY RAIN/FLOODING AND HIGHER ELEVATION HEAVY
SNOW...
...A LOW PRESSURE SYSTEM COULD SPREAD WINTER WEATHER FROM THE
CENTRAL ROCKIES/HIGH PLAINS AND THE MIDWEST WHILE A HEAVY RAIN
THREAT REEMERGES OVER THE LOWER MISSISSIPPI VALLEY IN EARLY 2023...
..OVERVIEW
OVER THE WEEKEND, THE UPPER-LEVEL PATTERN 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 ANOTHER TROUGH
DIGS INTO THE WEST. ANOTHER ATMOSPHERIC RIVER TAKING AIM AT THE
WEST JUST AHEAD OF THE LATTER TROUGH WILL LEAD TO ADDITIONAL HEAVY
RAIN AND POSSIBLE FLOODING ACROSS PARTS OF CALIFORNIA IN
PARTICULAR. THE WESTERN TROUGH IS FORECAST TO MOVE INTO THE
CENTRAL U.S. AS THE WEEK PROGRESSES, WHILE AT THE SURFACE, MODELS
ARE COMING INTO REASONABLY GOOD AGREEMENT FOR A LOW TO CONSOLIDATE
IN THE CENTRAL HIGH PLAINS BY LATE SUNDAY-MONDAY AND TRACK
NORTHEASTWARD THROUGH THE MIDWEST/GREAT LAKES REGION. MOISTURE
RETURN FROM THE GULF OF MEXICO IS LIKELY TO PRODUCE HEAVY RAINFALL
ACROSS THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND
SOUTHEAST MONDAY-TUESDAY, WHILE ON THE BACKSIDE OF THE LOW THERE
ARE INCREASING CHANCES FOR SNOW/WINTRY WEATHER ACROSS THE CENTRAL
ROCKIES INTO THE NORTHERN HALF OF THE PLAINS AND THE UPPER MIDWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT 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 12/18Z
DETERMINISTIC MODELS EARLY ON WITH INCREASING PROPORTIONS OF THE
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 ANOTHER ROUND OF PRECIPITATION IS FORECAST
ONCE AGAIN BY MONDAY-TUESDAY.
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
THE NORTHERN HALF OF THE HIGH PLAINS AND INTO THE UPPER MIDWEST.
MEANWHILE FARTHER SOUTH, THE COLD FRONT ASSOCIATED WITH THIS LOW
COULD PROVIDE A FOCUS FOR ANOTHER BOUT OF HEAVY RAIN ACROSS PARTS
OF THE MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND SOUTHEAST
BY MONDAY-TUESDAY.
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, 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.
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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