760
FXUS02 KWBC 310714
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
213 AM EST SAT DEC 31 2022
VALID 12Z TUE JAN 03 2023 - 12Z SAT JAN 07 2023
...WINTER STORM THREAT FOR THE UPPER MIDWEST TO LINGER TUESDAY AS
A HEAVY RAIN/SEVERE WEATHER THREAT WORKS ACROSS THE SOUTHEAST
THROUGH MIDWEEK...
...MORE ROUNDS OF MODERATE TO HEAVY PRECIPITATION FOR THE WEST
WITH FOCUS ACROSS CALIFORNIA NEXT WEEK...
..OVERVIEW
A DEEPENED LOW PRESSURE SYSTEM FORECAST TO DEVELOP INTO EARLY NEXT
WEEK OVER THE CENTRAL U.S. WILL LIKELY SUPPORT A LINGERING HEAVY
SNOW THREAT FOR THE UPPER MIDWEST TUESDAY, WHILE HEAVY RAIN, FLASH
FLOODING, AND SEVERE WEATHER APPEAR LIKELY ACROSS THE SOUTH INTO
TUESDAY/WEDNESDAY. MEANWHILE THE WEST SHOULD SEE ADDITIONAL ROUNDS
OF MODERATE TO HEAVY PRECIPITATION NEXT WEEK, WITH HIGHEST AMOUNTS
MAINLY ACROSS CALIFORNIA NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR LARGER SCALE
PATTERN EVOLUTION NEXT WEEK. HOWEVER THERE REMAINS AMPLE
UNCERTAINTY REGARDING THE PROGRESSION OF SHORTWAVES/TROUGHING INTO
THE WEST COAST WITH A SERIES OF PACIFIC STORM SYSTEMS THAT WILL
KEEP PRECIPITATION CHANCES HIGH ACROSS THE WEST. MODEL RUN TO RUN
CONSISTENCY IS SUBPAR WITH LOW DEVELOPMENTS OFF THE WEST COAST
THROUGH MEDIUM RANGE TIME SCALES, ESPECIALLY IN RECENT RUNS OF THE
ECMWF. RUN TO RUN OUTPUT IS UNCOMMONLY NOT WELL ALIGNED WITH ECMWF
ENSEMBLES. BEST LOW CLUSTERING IN THE GEFS/NAEFS/ECMWF ENSEMBLES
AND THE OTHER MODELS HAS BEEN SLOWER THAN THE ECMWF TO WORK SYSTEM
ENERGY AND LEAD ATMOSPHERIC RIVER PLUME INLAND NEXT WEEK, BUT ALL
GUIDANCE DOES EVENTUALLY SHOW THAT MULTI-DAY THREAT. THE
GFS/UKMET/CANADIAN HOLD SYSTEMS OFFSHORE LONGER THAN THE ECMWF,
BUT THEY HAVE ALSO BEEN SHOWING LESS THAN STELLAR RUN TO RUN
CONTINUITY. ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS
PRIMARILY DERIVED FROM A BLEND OF THE GEFS/NAEFS/ECMWF ENSEMBLE
MEANS THROUGH THIS FORECAST PERIOD AND MANUAL ADJUSTMENTS WERE
APPLIED TO THE SMOOTHED BLEND TO OFFSHORE LOW CENTERS TO ENSURE
REASONABLE DEPTH CONSIDERING FAVORABLE UPPER SUPPORT.
..WEATHER/HAZARD HIGHLIGHTS
A DEEPENED LOW STORM TRACK ACROSS THE NORTH-CENTRAL U.S. WILL
SHIFT AN AXIS OF COMMAHEAD SNOWS ACROSS THE UPPER MIDWEST TUESDAY,
ALONG WITH INCREASINGLY WINDY CONDITIONS AND AN ICY TRANSITIONAL
ZONE. GUIDANCE IS CONVERGING ON A MORE COMMON SOLUTION WITH THIS
FEATURE BY THEN, BOLSTERING FORECAST CONFIDENCE. INFLOW EAST OF
THE LOW AND LINGERING COLD AIR MAY ALSO SUPPORT SOME SNOW/ICE
DOWNSTREAM ACROSS THE UPPER GREAT LAKES AND 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 SPREAD WIDESPREAD HEAVY RAIN, ALONG
WITH A THREAT OF SEVERE WEATHER AS PER SPC, ACROSS PARTS OF THE
SOUTH INTO TUESDAY/WEDNESDAY. FLASH FLOODING IS ALSO POSSIBLE AS
COVERED BY WPC'S EXPERIMENTAL DAY 4/5 "SLIGHT RISK" EXCESSIVE
RAINFALL OUTLOOKS (EROS). THEREAFTER, A TRAILING FRONTAL LOW
PRESSURE SYSTEM COULD DEVELOP AND THEN LIFT OVER THE EAST TO
SPREAD SOME MODERATE TO HEAVY RAIN UP THE MID-ATLANTIC STATES TO
COASTAL NEW ENGLAND.
ADDITIONAL ROUNDS OF PRECIPITATION ARE ALSO EXPECTED TO CONTINUE
ALONG THE WEST COAST AS THE WEEK PROGRESSES, BUT PRIMARILY WITH A
FOCUS ON CALIFORNIA. THERE IS QUITE A BIT OF UNCERTAINTY WITH THE
TIMING OF ADDITIONAL HEAVY PRECIPITATION EVENTS AT THIS POINT
GIVEN THE VARIED SHORTWAVE PROGRESSIONS AND SURFACE SYSTEM FOCUS,
BUT AMOUNTS LOOK TO TREND UPWARD BY WEDNESDAY-THURSDAY ACROSS
CALIFORNIA AS A STRONGER FRONTAL SYSTEM APPROACHES FROM THE
PACIFIC WITH ANOTHER POTENTIAL ATMOSPHERIC RIVER EVENT GIVEN THE
SIGNAL FOR A STRONG FETCH OF MOISTURE WITH THE SYSTEM. MANY AREAS
ARE LIKELY TO BE SENSITIVE TO ADDITIONAL RAINFALL BY THEN GIVEN
THE AMPLE RECENT RAINFALL AND ADDITIONAL RAIN DURING THE SHORT
RANGE PERIOD. THERE IS ALSO A MULTI-DAY THREAT FOR HEAVY SNOW THAT
WILL FOCUS OVER THE SIERRA, BUT ALSO TO A LESSER EXTENT SPREAD
NORTHWARD THROUGH THE CASCADES AND WITH SOME GUSTO INLAND ACROSS
THE INTERMOUNTAIN WEST TOWARD THE ROCKIES OVER TIME WITH SYSTEM
TRANSLATIION.
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. AS THE LARGE-SCALE UPPER TROUGH MOVES THROUGH
THE WESTERN U.S. INTO THE PLAINS, NEAR TO BELOW AVERAGE
TEMPERATURES ARE EXPECTED TO WORK THEIR WAY FROM WEST TO EAST
ACROSS THESE AREAS.
SCHICHTEL
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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