476
FXUS02 KWBC 042042
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
341 PM EST WED JAN 04 2023
VALID 12Z SAT JAN 07 2023 - 12Z WED JAN 11 2023
...SIGNIFICANT HEAVY PRECIPITATION THREATS FOR CALIFORNIA TO RENEW
THIS WEEKEND AND EARLY NEXT WEEK...
..GUIDANCE/PREDICTABILITY ASSESSMENT
MUCH OF THE PREDICTABILITY CHALLENGE OVER THE MEDIUM-RANGE
FORECAST PERIOD REVOLVED AROUND THE HANDLING OF EMBEDDED
SHORTWAVES IN THE LARGER SCALE FLOW. THE PATTERN EAST TO WEST AT
THE START OF THE PERIOD CONSISTED OF GENERALLY LOW-AMPLITUDE ZONAL
FLOW IN THE SOUTHERN STREAM WITH EMBEDDED WAVES FOR THE EASTERN
AND CENTRAL CONUS, SLIGHT RIDGING OVER THE WEST, AND MEAN
TROUGHING OFF THE WEST COAST IN THE EASTERN PACIFIC. THE 00Z GEFS
AND CMCENS MEANS WERE REMARKABLY SIMILAR IN CAPTURING THE OVERALL
PATTERN WITH THE 00Z ECENS MEAN ONLY SLIGHTLY DIFFERENT. OPTED TO
BEGIN THE WPC FORECAST SUITE BLEND WITH A COMBINATION OF THE 00Z
DETERMINISTIC GUIDANCE (GFS/CMC/ECMWF) AND SOME ENSEMBLE MEAN
GUIDANCE (GEFS/ECENS/CMCENS) WHICH FOLLOWS A SIMILAR BLEND TO THE
PRIOR WPC FORECAST. THE 00Z GFS WAS CHOSEN OVER THE 06Z GIVEN MORE
SMALL SCALE DIFFERENCES COMPARED TO OTHER GUIDANCE AT 00Z. ONE OF
THE MORE NOTABLE TRENDS EARLY IN THE PERIOD WAS THE
INTENSIFICATION OF A WAVE OVER THE CENTRAL U.S. RUN-TO-RUN IN THE
DETERMINISTIC GFS AND ECMWF WHICH WILL HAVE IMPLICATIONS ON THE
EVOLUTION OF A SURFACE FRONTAL SYSTEM MOVING THROUGH THE PLAINS
INTO THE MIDWEST/SOUTH. THE 00Z CMC CONCURED WITH THE LATEST TREND
IN THE 00Z GFS AND ECMWF, WITH THE 06Z GFS REMAINING SIMILAR TO
THE 00Z RUN AFTER PREVIOUS RUN-TO-RUN DIFFERENCES. THE INITIAL
CHOSEN BLEND OF THE 00Z GFS/ECMWF AND GEFS/ECENS MEANS CONTINUED
TO REPRESENT THIS EVOLUTION WELL AND TRENDED TOWARDS A MORE
COMPACT/DEEPER WAVE THAN THE PRIOR WPC FORECAST. HOWEVER, THE
INFLUENCE OF THE 00Z CMC AND CMCENS MEAN WAS REDUCED GIVEN A MUCH
DEEPER CLOSED LOW IN THE EASTERN PACIFIC COMPARED TO THE OTHER
GUIDANCE.
DIFFERENCES AMONGST SMALLER SCALE FEATURES BECOME MORE DIFFICULT
TO RESOLVE DURING THE MIDDLE OF THE FORECAST PERIOD. THE FLOW
INITIALLY BECOMES EVEN MORE ZONAL OVERALL ACROSS THE CONUS, WITH
RUN-TO-RUN DIFFERENCES BETWEEN THE GFS AND ECMWF NOT FOLLOWING ANY
PARTICULAR TREND, LESSENING CONFIDENCE IN THE EVOLUTION OF THE
OVERALL PATTERN. RELIANCE ON THE 00Z GEFS/ECENS/CMCENS MEANS WAS
INCREASED TO CAPTURE THE SUBTLE LOW-AMPLITUDE TROUGHING OVER THE
EASTERN CONUS AND EASTERN PACIFIC AND RIDGING OVER THE
CENTRAL/WESTERN CONUS. INCONSISTENT RUN-TO-RUN DIFFERENCES IN THE
DETERMINISTIC GUIDANCE BECOME EVEN GREATER LATE IN THE PERIOD AS
THE FLOW BEGINS TO AMPLIFY WITH TROUGHING IN THE EAST, RIDGING
OVER THE CENTRAL CONUS, AND THE TROUGH OVER THE EASTERN PACIFIC
MOVING OVER THE WEST. THERE WAS ALSO A NOTABLE INCREASE IN SPREAD
AMONGST THE INDIVIDUAL ENSEMBLE MEMBERS IN THE GEFS AND ECENS
INCREASING CONCERNS OVER PREDICTABILITY. THE WPC FORECAST BLEND
FOR THE LATE PERIOD THUS CONSISTED OF AN ADDITIONAL INCREASE OF
THE 00Z GEFS/ECENS MEANS WITH SOME INFLUENCE OF THE 00Z GFS/ECMWF
GUIDANCE RETAINED TO HELP AMPLIFY THE PATTERN A BIT MORE COMPARED
TO THE MEANS. REMOVED THE 00Z CMC/CMCENS MEAN FROM THE BLEND AS
THERE WERE MORE SIGNIFICANT DIFFERENCES COMPARED TO THE OTHER
GUIDANCE, SPECIFICALLY IN THE DEVELOPMENT OF A DEEP, CLOSED LOW
OVER SOUTHEASTERN CANADA. DESPITE THE CONCERNS OVER
PREDICTABILITY, THE UPDATED WPC FORECAST DID REMAIN RELATIVELY
CONSISTENT WITH THE PRIOR FORECAST INDICATING THE LARGE-SCALE
PATTERN OVERALL IS HOPEFULLY WELL CAPTURED WITH SMALLER SCALE
DIFFERENCES TO BE SORTED OUT OVER TIME.
..WEATHER/HAZARD HIGHLIGHTS
THE WPC EXPERIMENTAL DAY 4/5 EXCESSIVE RAINFALL OUTLOOKS (EROS)
RENEWS SATURDAY AND SUNDAY "SLIGHT" RISK AREAS CENTERED OVER
NORTHERN CALIFORNIA. THE THREAT FOR ADDITIONAL ROUNDS OF HEAVY
RAINFALL WITH AMPLE RUNOFF ISSUES THAT MAY EXPAND SOUTHWARD ARE
LIKELY TO PERSIST THROUGH EARLY NEXT WEEK IN A DANGEROUSLY WET
PATTERN WITH MULTIPLE ATMOSPHERIC RIVERS WORKING INLAND AHEAD OF A
SERIES OF UNCERTAIN/DEEPENED EASTERN PACIFIC STORMS. FORECAST
RAINFALL AMOUNTS ON MONDAY IN PARTICULAR LOOK TO EXCEED SEVERAL
INCHES OVER A BROAD AREA OF NORTHERN AND CENTRAL CALIFORNIA. MANY
AREAS, ESPECIALLY BURN SCARS, ARE LIKELY TO BE SENSITIVE TO
ADDITIONAL RAINFALL GIVEN THE AMPLE RECENT AND FORECAST RAINFALL.
HIGH PROBABILITIES FOR SIERRA SNOWFALLS ARE ALSO DEPICTED IN THE
WPC WINTER WEATHER OUTLOOK (WWO) SATURDAY-NEXT WEDNESDAY. PERIODS
OF STRONG, GUSTY WINDS WILL LIKELY ACCOMPANY EACH SYSTEM ACROSS
NORTHERN AND CENTRAL CALIFORNIA AND THE ADJACENT GREAT BASIN.
GUIDANCE ALSO SHOWS SOME FAVORABLE FLOW INTO THE NORTHWEST FOR
ESPECIALLY SOUTHWARD FACING TERRAIN. THERE IS ALSO THE POTENTIAL
FOR MORE MODEST SHORTWAVE/TERRAIN ENHANCED SNOW TO WORK INTO THE
GREAT BASIN, PERHAPS ESPECIALLY EARLY-MID NEXT WEEK WITH A BETTER
MAINTAINED SYSTEM PUSHING INLAND ACROSS THE REGION WITH SNOW
AMOUNTS TRENDING UPWARD IN THE LATEST FORECAST.
MEANWHILE, UPPER-LEVEL TROUGHING MOVING THROUGH THE WEST IS
FORECAST TO REACH THE PLAINS AND HELP DEVELOP A MODEST SURFACE
FRONTAL WAVE TO SUBSEQUENTLY TRACK WITH SOME UNCERTAINTY EASTWARD
ACROSS THE MID-MISSISSIPPI VALLEY TO THE MID-ATLANTIC SATURDAY
INTO MONDAY. COMPARED TO THE MODELS, THE NBM STILL SEEMS TO BE
MISSING SOME MODEST PRECIPITATION POTENTIAL THAT MAY PRODUCE SOME
LIGHT WINTRY WEATHER FOR PARTS OF THE OHIO VALLEY THROUGH THE
APPALACHIANS AS WELL AS A TRAILING AREA OF RAINFALL DOWN TROUGH
THE SOUTH-CENTRAL U.S. THIS WEEKEND AND MODESTLY TO THE SOUTHEAST
INTO EARLY NEXT WEEK. WPC QPF AND WEATHER GRIDS WERE ACCORDINGLY
ADJUSTED. GUIDANCE HAS TRENDED HEAVIER WITH ACTIVITY ACROSS
EASTERN TX AND THE LOWER MS VALLEY WHERE SOME DOWNPOURS MAY LEAD
TO LOCAL RUNOFF ISSUES. BOTH HIGH AND LOW TEMPERATURES ACROSS THE
COUNTRY WILL GENERALLY REMAIN ABOVE AVERAGE OUTSIDE OF THE MORE
DREARY WEATHER ON THE WEST COAST. HIGHS ACROSS PORTIONS OF THE
CENTRAL/SOUTHERN PLAINS, MIDWEST, AND SOUTH WILL BE RUNNING 10-15
DEGREES ABOVE AVERAGE.
PUTNAM/SCHICHTEL
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA, THE PACIFIC NORTHWEST,
AND THE SOUTHWEST, SAT-TUE, JAN
7-JAN 10.
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, WED, JAN 11.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE
SOUTHERN PLAINS, AND THE
TENNESSEE VALLEY, SAT-SUN, JAN 7-JAN 8.
- HEAVY SNOW ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL GREAT
BASIN, THE PACIFIC NORTHWEST, AND THE
SOUTHWEST, SAT-TUE, JAN 7-JAN 10.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE OHIO VALLEY.
- HIGH WINDS ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, SAT-WED, JAN 7-JAN 11.
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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