730
FXUS02 KWBC 050648
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 AM EST THU JAN 05 2023
VALID 12Z SUN JAN 08 2023 - 12Z THU JAN 12 2023
...SIGNIFICANT HEAVY PRECIPITATION THREATS FOR CALIFORNIA TO RENEW
AGAIN LATER WEEKEND THROUGH EARLY NEXT WEEK...
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE WEATHER PATTERN OVER MUCH OF THE CONTINENTAL U.S. REMAINS VERY
ACTIVE AND MORE COMPLICATED THAN USUAL, WITH MULTIPLE UNCERTAIN
EMBEDDED SHORTWAVES ALOFT WITHIN RELATIVELY WELL DEFINED NORTHERN
AND SOUTHERN STREAM FLOWS. HOWEVER, FORECAST SPREAD AND RUN TO RUN
CONTINUITY IN GUIDANCE HAS SLOWLY IMPROVED OVER THE PAST FEW
GUIDANCE CYCLES TO BOLSTER FORECAST CONFIDENCE AND PREDICTABILITY.
THE EASTERN PACIFIC WILL CONTINUE TO BE EXTREMELY ACTIVE WITH WITH
A SERIES OF DEEPENED LOW PRESSURE SYSTEMS FOR THE WEST COAST WITH
LEAD ATMOSPHERIC RIVER MOISTURE TO SIGNIFICANTLY AMPLIFY AMOUNTS
AND IMPACTS. THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY
DERIVED FROM A BLEND OF BEST CLUSTERED GUIDANCE FROM THE 18 UTC
GFS/GEFS MEAN, 12 UTC ECMWF/UKMET AND ECMWF ENSEMBLE MEAN, WPC
CONTINUITY AND THE 01 UTC NATIONAL BLEND OF MODELS (NBM). WPC
PREFERRED BLEND WEIGHTING SHIFTS MORE IN FAVOR OF THE COMPATIBLE
ENSEMBLE MEANS AT LONGER TIME FRAMES BY NEXT MIDWEEK IN AN EFFORT
TO BEST MITIGATE GROWING SMALLER SCALE VARIANCES CONSISTENT WITH
PREDICTABILITY. THE LATEST 00 UTC GUIDANCE SUITE GENERALLY REMAINS
IN LINE WITH THIS FORECAST STRATEGY.
..WEATHER/HAZARD HIGHLIGHTS
LEAD 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 FROM THE
VICINITY OF THE LOWER OHIO VALLEY TO THE MID-ATLANTIC COAST SUNDAY
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 WESTERN GULF COAST INTO SUNDAY AND MODESTLY TO THE SOUTHEAST
INTO EARLY NEXT WEEK. WPC QPF AND WEATHER GRIDS WERE ACCORDINGLY
ADJUSTED.
HOWEVER, THE BIG WEATHER STORY REMAINS WELL UPSTREAM OVER
CALIFORNIA. WPC EXPERIMENTAL DAY 4/5 EXCESSIVE RAINFALL OUTLOOK
(ERO) "SLIGHT" RISK AREAS HAVE BEEN ISSUED VALID SUNDAY AND MONDAY
FOR NORTHERN AND NORTH-CENTRAL CALIFORNIA RESPECTIVELY. THE THREAT
IS AMPLIFIED AS ADDITIONAL ROUNDS OF HEAVY RAINFALL WITH AMPLE
RUNOFF ISSUES ARE LIKELY TO PERSIST THROUGH EARLY NEXT WEEK IN A
DANGEROUSLY WET PATTERN WITH MULTIPLE ATMOSPHERIC RIVERS WORKING
INLAND AHEAD OF A SERIES OF DEEPENED EASTERN PACIFIC STORMS.
FORECAST RAINFALL AMOUNTS ON MONDAY IN PARTICULAR LOOK FOR
MULTIPLE INCHES OVER A BROAD AREA OF NORTHERN AND CENTRAL
CALIFORNIA. MANY AREAS ARE LIKELY TO BE SENSITIVE TO ADDITIONAL
RAINFALL GIVEN THE AMPLE RECENT AND SHORTER TERM FORECAST
RAINFALL. HIGH PROBABILITIES FOR SIERRA SNOWFALLS ARE ALSO
DEPICTED IN THE WPC WINTER WEATHER OUTLOOK (WWO) SUNDAY THROUGH
NEXT MIDWEEK. 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 TOWARD THE ROCKIES, BUT PERHAPS
ESPECIALLY BY NEXT MIDWEEK WITH A BETTER MAINTAINED SYSTEM PUSHING
INLAND ACROSS THE REGION WITH SNOW AMOUNTS TRENDING UPWARD IN THE
RECENT FORECASTS. THIS SYSTEM THEN HAS POTENTIAL TO SPAWN MODERATE
CENTRAL PLAINS CYCLOGENESIS LATE PERIOD WHOSE POTENTIAL LEAD
RETURN GULF INFLOW UP THROUGH THE MS VALLEY/VICINITY MAY OFFER AN
OPPORTUNITY FOR AN EXPANDING AREA OF LATE PERIOD RAINFALL ALONG
WITH EMERGING SNOW/ICE/FREEZING RAIN POTENTIAL ON THE NORTHERN
PERIPHERY OF THE PRECIPITATION AREA AS MOISTURE FEEDS INTO A
COOLED ANTECEDENT HIGH PRESSURE AIRMASS THAT MAY DIG IN ADVANCE
FROM CANADA INTO THE NORTH-CENTRAL THROUGH EASTERN U.S..
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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