787
FXUS02 KWBC 290658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EST THU DEC 29 2022
VALID 12Z SUN JAN 01 2023 - 12Z THU JAN 05 2023
...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...
...MULTIPLE ROUNDS OF PRECIPITATION FOR THE WEST WITH LOWER
ELEVATION HEAVY RAIN/FLOODING AND HIGHER ELEVATION/INLAND HEAVY
SNOW...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD AND THE NEW YEAR BEGIN ON SUNDAY, ONE
UPPER-LEVEL TROUGH WILL BE LIFTING OUT OF THE GREAT
LAKES/NORTHEAST WHILE ANOTHER AMPLIFIES IN THE WEST. THE LATTER
TROUGH WILL PRODUCE PRECIPITATION ACROSS THE INTERMOUNTAIN WEST
BEFORE EJECTING INTO THE CENTRAL U.S., WHILE IN RESPONSE A SURFACE
LOW CONSOLIDATES AND DEEPENS ACROSS THE CENTRAL HIGH PLAINS BY
LATE SUNDAY-MONDAY AND THEN TRACKS NORTHEASTWARD THROUGH THE
MIDWEST/GREAT LAKES REGION. ON THE BACKSIDE OF THE LOW HEAVY
SNOW/WINTRY WEATHER IS FORECAST ACROSS THE CENTRAL ROCKIES INTO
THE NORTHERN HALF OF THE PLAINS AND THE UPPER MIDWEST, WHILE
FARTHER SOUTH 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. MEANWHILE THE WEST SHOULD SEE
ADDITIONAL ROUNDS OF MODERATE TO HEAVY PRECIPITATION NEXT WEEK,
WITH AMOUNTS TRENDING UPWARD BY MIDWEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW RELATIVELY GOOD AGREEMENT WITH
THE LARGE SCALE PATTERN, NAMELY WITH THE TROUGH COMING INTO THE
WEST SUNDAY THAT SHIFTS INTO THE CENTRAL U.S. AS THE WEEK
PROGRESSES WHILE UPPER RIDGING TRACKS AHEAD OF IT, AND WITH THE
DEVELOPING SURFACE LOW. THERE ARE STILL SOME DIFFERENCES IN THE
DETAILS LIKE THE EXACT LOW PRESSURE TRACK AND FRONTAL PLACEMENTS
THAT, THOUGH WITHIN RANGE OF TYPICAL MEDIUM RANGE SPREAD, HAVE
IMPLICATIONS LIKE THE PRECIPITATION TYPES FOR ANY PARTICULAR AREA,
WHICH WILL TAKE ADDITIONAL TIME TO RESOLVE. THE 12Z ECWMF AND MANY
OF THE EC ENSEMBLE MEMBERS INDICATED A FARTHER SOUTHEAST TRACK OF
THE SURFACE LOW COMPARED TO THE GFS/CMC SUITES. THE 00Z
DETERMINISTIC ECMWF APPEARS SIMILAR TO ITS PREVIOUS RUN. THIS
RESULTS IN A SWATH OF HEAVY SNOW ACROSS NEBRASKA RATHER THAN FROM
WESTERN NEBRASKA INTO THE DAKOTAS, FOR EXAMPLE. THE WPC FORECAST
FOR THE LOW TRACK AND ASSOCIATED PRECIPITATION AND WINTER WEATHER
PROBABILITIES ATTEMPTED TO KEEP A MIDDLE GROUND SOLUTION NOT AS
FAR SOUTH AS THE EC, BUT PERHAPS SOME GFS RUNS HAVE BEEN TOO FAR
NORTH. THE DETERMINISTIC CMC RUNS MAY BE A GOOD PROXY FOR AN IN
BETWEEN SOLUTION. THERE ARE ALSO SOME DIFFERENCES WITH ENERGY
DIVING INTO THE WESTERN SIDE OF THE TROUGH AROUND TUESDAY--THE 12Z
CMC APPEARED WEAKEST BUT IS STRONGER IN THE MOST RECENT 00Z RUN.
SOME ROUNDS OF UPSTREAM ENERGY IN THE PACIFIC REACHING THE WEST
SHOW SOME VARIATIONS IN TIMING AND STRENGTH AS WELL. THUS THE WPC
FORECAST UTILIZED A BLEND OF THE DETERMINISTIC 12/18Z MODEL
GUIDANCE EARLY IN THE PERIOD, 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
THE NORTHEASTERN U.S. COULD SEE SOME MAINLY RAIN SHOWERS (WITH
PERHAPS SOME MINOR SNOW ACCUMULATIONS IN HIGHER ELEVATIONS) EARLY
SUNDAY WITH AN EXITING LOW PRESSURE SYSTEM. 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 COULD
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.
THE WEST COAST STATES CAN EXPECT A BRIEF BREAK FROM THE HEAVY
PRECIPITATION ON SUNDAY AS THE TROUGH AXIS SHIFTS EAST/FARTHER
INLAND. BUT ADDITIONAL ROUNDS OF PRECIPITATION ARE FORECAST TO
ARISE AS THE WEEK PROGRESSES. THERE IS CONSIDERABLE UNCERTAINTY
WITH THE TIMING OF ADDITIONAL HEAVY PRECIPITATION EVENTS AT THIS
POINT, BUT GENERALLY AMOUNTS LOOK TO TREND UPWARD BY
TUESDAY-THURSDAY AS A STRONGER FRONTAL SYSTEM APPROACHES. MANY
AREAS ARE LIKELY TO BE SENSITIVE TO ADDITIONAL RAINFALL BY THAT
TIME GIVEN THE AMPLE RECENT RAINFALL AND ADDITIONAL RAIN DURING
THE SHORT RANGE PERIOD.
MILDER THAN AVERAGE TEMPERATURES FOR WINTER WILL BE WIDESPREAD
ACROSS THE EASTERN HALF OF THE COUNTRY FOR EARLY NEXT WEEK. LOWS
OF AROUND 15-30F ABOVE AVERAGE AND HIGHS AROUND 10-20F ABOVE
AVERAGE WILL BE COMMON, EVEN REACHING 20-30F ANOMALIES IN THE OHIO
VALLEY/GREAT LAKES TUESDAY AND THE NORTHEAST ON WEDNESDAY. DAILY
RECORDS FOR WARM LOWS COULD BE WIDESPREAD FOR PARTS OF THE CENTRAL
AND EASTERN U.S., WHILE DAILY RECORD HIGHS ARE POSSIBLE AS WELL
ESPECIALLY IN THE OHIO VALLEY. 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
SUNDAY MORNING BEFORE 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, TRACKING INTO THE EAST-CENTRAL U.S.
BY THURSDAY.
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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