066
FXUS02 KWBC 232033
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
332 PM EST FRI DEC 23 2022
VALID 12Z MON DEC 26 2022 - 12Z FRI DEC 30 2022
...A STRONG ATMOSPHERIC RIVER COULD CAUSE NOTABLE HEAVY
RAIN/FLOODING FOR THE WEST COAST ALONG WITH HEAVY MOUNTAIN SNOW IN
THE WEST NEXT WEEK...
..OVERVIEW
THE MODELS AND ENSEMBLE MEANS HAVE BEEN CONSISTENTLY SHOWING A
SIGNIFICANT UPPER LEVEL PATTERN CHANGE OVER THE COURSE OF NEXT
WEEK. THE EASTERN PACIFIC TROUGH/WESTERN U.S. RIDGE/EASTERN TROUGH
CONFIGURATION AT THE START OF THE WEEK SHOULD MOVE EASTWARD WITH
TIME, WITH A MEAN TROUGH ULTIMATELY SETTLING OVER THE ROCKIES/HIGH
PLAINS WHILE A RIDGE BUILDS OVER THE EAST COAST. VIGOROUS SYSTEMS
AHEAD OF THE PACIFIC TROUGH, AND IN PARTICULAR A STORM REACHING
THE WASHINGTON COAST OR VANCOUVER ISLAND BY TUESDAY AND ITS
TRAILING FRONT, WILL BRING A STRONG ATMOSPHERIC RIVER WITH A LONG
FETCH OF TROPICAL MOISTURE INTO THE WEST DURING THE FIRST HALF OF
NEXT WEEK. THIS EVENT WILL LIKELY PRODUCE HEAVY RAIN, POTENTIALLY
CAUSING FLOODING ESPECIALLY FOR COASTAL REGIONS OF SOUTHERN OREGON
AND CALIFORNIA, ALONG WITH HEAVY SNOW POSSIBLE IN HIGHER
ELEVATIONS OF THE WEST. ADDITIONAL ROUNDS OF PRECIPITATION ARE
LIKELY ACROSS MUCH OF THE WEST THROUGH LATE NEXT WEEK. MEANWHILE
FARTHER EAST, THE PATTERN CHANGE WILL BRING AN END TO LAKE EFFECT
SNOW THAT LINGERS INTO MONDAY, WHILE FLIPPING TEMPERATURES OVER
THE EASTERN HALF OF THE COUNTRY FROM WELL BELOW NORMAL ON MONDAY
TO ABOVE NORMAL AFTER MIDWEEK. MOISTURE SHOULD ALSO BEGIN TO FLOW
NORTHWARD THROUGH THE MISSISSIPPI VALLEY BY LATE IN THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE UPDATED FORECAST MAINTAINED THE APPROACH OF USING AN
OPERATIONAL MODEL COMPOSITE FOR ABOUT THE FIRST HALF OF THE PERIOD
FOLLOWED BY A TRANSITION TO A COMBINATION OF OPERATIONAL MODELS
AND ENSEMBLE MEANS. THIS PROVIDED GOOD CONTINUITY FOR MOST ASPECTS
OF THE FORECAST. THERE ARE SOME NOTABLE SHORTWAVE DIFFERENCES THAT
DEVELOP WITHIN THE ROCKIES/PLAINS MEAN TROUGH BY THURSDAY-FRIDAY
(LATEST GFS RUNS LEANING SLOW/AMPLIFIED, CMC ON THE FASTER SIDE),
LEADING TO SOME BOUNCING AROUND FOR MOST LIKELY POSITIONS FOR
WAVES ALONG A MEAN FRONTAL BOUNDARY, WHILE A FAIR AMOUNT OF SPREAD
ALSO ARISES FOR SPECIFICS OF SOUTHEASTERN CANADA/NEW ENGLAND FLOW
ALONG WITH ASSOCIATED SURFACE DETAILS. IT WILL LIKELY TAKE SOME
TIME TO RESOLVE THE DETAILS OVER THOSE AREAS DURING THE LATTER
HALF OF THE WEEK. IN GENERAL THE 00Z GFS COMPARED A LITTLE BETTER
TO OTHER GUIDANCE THAN THE 06Z RUN DURING MOST OF THE PERIOD, SO
THE FORMER RUN PROVIDED THE GFS COMPONENT IN THE BLEND. ON TUESDAY
A GUIDANCE AVERAGE LOOKS REASONABLE GIVEN THE ONGOING DETAIL/TRACK
DIFFERENCES (MOST OF WHICH ARE WITHIN TYPICAL SPREAD/ERRORS FOR
FOUR DAYS OUT IN TIME) FOR THE STRONG STORM REACHING AFFECTING THE
PACIFIC NORTHWEST. FOR THIS FEATURE, THE NEW 12Z RUNS HAVE WIDENED
THE DEPTH SPREAD SOMEWHAT VALID 12Z TUESDAY, WITH THE ECMWF NOW IN
THE 950'S MB VERSUS THE UKMET BEING IN THE 970'S WHILE OTHER
MODELS ARE GENERALLY IN THE 960'S.
..WEATHER/HAZARD HIGHLIGHTS
A SERIES OF NORTHEASTERN PACIFIC SYSTEMS SHOULD BRING A MULTI-DAY
PERIOD OF PRECIPITATION TO MUCH OF THE WEST. A STRONG TO EXTREME
ATMOSPHERIC RIVER WITH A MOISTURE FETCH ALL THE WAY FROM THE
WESTERN PACIFIC IS LIKELY TO AFFECT THE WEST AND PEAK
MONDAY-TUESDAY TO PRODUCE CONSIDERABLY HIGH RAINFALL RATES AND
AMOUNTS PARTICULARLY ALONG THE OREGON AND CALIFORNIA COASTS.
SLIGHT RISKS OF EXCESSIVE RAINFALL HAVE BEEN MAINTAINED IN WPC'S
EXPERIMENTAL DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS DUE TO FLOODING
CONCERNS WITH THIS RAIN. FARTHER INLAND IN HIGHER ELEVATIONS, THIS
COULD ALSO LEAD TO HEAVY SNOW IN THE CASCADES/SIERRA NEVADA INTO
THE ROCKIES. HIGH WINDS ARE ALSO POSSIBLE ACROSS PORTIONS OF THE
WEST COAST AND GREAT BASIN--ESPECIALLY WITH THE STRONG STORM
TRACKING INTO OR NEAR THE PACIFIC NORTHWEST TUESDAY. ROUNDS OF
PRECIPITATION ARE LIKELY TO CONTINUE IN THE WEST THROUGH THE REST
OF NEXT WEEK WITH ONE OR MORE ADDITIONAL FRONTAL SYSTEMS, BUT THIS
ACTIVITY SHOULD NOT BE AS INTENSE AS EARLY IN THE WEEK.
ELSEWHERE, LINGERING LAKE EFFECT SNOW IS A POSSIBILITY THROUGH
MONDAY AND POSSIBLY TUESDAY IN OVERALL WESTERLY FLOW, WHILE A
QUICK CLIPPER COULD CAUSE LIGHT SNOW ACROSS PARTS OF THE MIDDLE
MISSISSIPPI VALLEY/OHIO VALLEY ON MONDAY. CONDITIONS SHOULD REMAIN
GENERALLY DRY ACROSS THE CENTRAL AND EASTERN U.S. OTHER THAN THAT,
UNTIL THE LATTER HALF OF THE WEEK WHEN MOISTURE INFLOW FROM THE
GULF OF MEXICO RETURNS TO THE MISSISSIPPI VALLEY AHEAD OF A COLD
FRONT AND UPPER TROUGH. WITHIN THIS EXPANDING MOISTURE SHIELD,
RAINFALL COULD BECOME LOCALLY MODERATE TO HEAVY BY FRIDAY.
TEMPERATURES ACROSS THE EASTERN HALF OF THE LOWER 48 WILL STAY
10-20F BELOW AVERAGE ON MONDAY BUT GRADUALLY MODERATE TOWARD
NORMAL BY AROUND MIDWEEK. ABOVE NORMAL TEMPERATURES BY 15-25F FOR
LOWS AND 10-20F IN TERMS OF HIGHS OVER THE WEST MONDAY-TUESDAY
SHOULD MIGRATE INTO THE CENTRAL AND EVENTUALLY MOST OF THE EASTERN
U.S. AS THE UPPER RIDGE REACHES THE EAST COAST.
RAUSCH/TATE
HAZARDS:
- HEAVY PRECIPITATION ACROSS PORTIONS OF NORTHERN CALIFORNIA AND
THE PACIFIC NORTHWEST, MON-FRI, DEC 26-DEC 30.
- HEAVY PRECIPITATION ACROSS PORTIONS OF CENTRAL CALIFORNIA,
TUE-FRI, DEC 27-DEC 30.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE
TENNESSEE VALLEY, THE SOUTHEAST, AND THE SOUTHERN PLAINS, DEC
29-DEC 30.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES AND GREAT
BASIN, TUE, DEC 27.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST.
- HIGH WINDS ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES
AND ADJACENT HIGH PLAINS, TUE, DEC 27.
- HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS, WED, DEC
28.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE PLAINS,
MIDWEST, SOUTHEAST, APPALACHIANS, AND MID-ATLANTIC, MON-TUE, DEC
26-DEC 27.
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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