046
FXUS02 KWBC 230721
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM 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
TROUGHING MOVING INTO THE WEST AS WELL AS A DEEP SURFACE LOW AND
FRONTAL SYSTEM WILL BRING A STRONG ATMOSPHERIC RIVER WITH A LONG
FETCH OF TROPICAL MOISTURE INTO THE REGION AROUND MONDAY-TUESDAY,
WITH 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, THERE COULD BE LINGERING
LAKE EFFECT SNOWS DOWNWIND OF THE GREAT LAKES PARTICULARLY MONDAY,
WHILE BELOW NORMAL TEMPERATURES GRADUALLY MODERATE CLOSER TO AND
THEN ABOVE NORMAL FOR THE CENTRAL AND EASTERN U.S. AS NEXT WEEK
PROGRESSES. GENERALLY DRY CONDITIONS ARE LIKELY UNTIL MOISTURE
INCREASES ACROSS THE MISSISSIPPI VALLEY FOR THE LATTER PART OF
NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE SHOWS REASONABLY GOOD AGREEMENT FOR A FAIRLY
PROGRESSIVE PATTERN DURING THE MEDIUM RANGE PERIOD AS SHORTWAVES
MOVE THROUGH AN EASTERN TROUGH THAT LOOKS TO EJECT EAST INTO THE
ATLANTIC ON TUESDAY WHILE IN THE WEST, TROUGHING WILL DEEPEN AND
PUSH TOWARD THE CENTRAL U.S. BY THE END OF THE PERIOD FRIDAY WITH
RIDGING BUILDING AHEAD OF IT. IN BOTH THE EAST AND WEST, MINOR
SHORTWAVE DIFFERENCES WERE GENERALLY HANDLED BY A MULTI-MODEL
BLEND OF DETERMINISTIC GUIDANCE THROUGH THE FIRST HALF OF THE
PERIOD. SOME SLIGHT INCREASES IN MODEL SPREAD OCCUR TOWARD LATER
NEXT WEEK--FOR EXAMPLE, GFS RUNS TEND TO BE SLOWER WITH THE
WESTERN TROUGH MOVING EAST DUE TO SOME STREAM SEPARATION COMPARED
TO MORE PHASED OTHER GUIDANCE--AND INCREASING PROPORTIONS OF THE
GEFS AND EC ENSEMBLE MEANS WERE USED FOR DAYS 6-7, BUT STILL WITH
A MAJORITY OF DETERMINISTIC MODELS GIVEN THE FAIRLY GOOD MODEL
CLUSTERING. THIS LED TO GOOD MODEL CONTINUITY WITH THE PREVIOUS
FORECAST AS WELL.
..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 ADDED TO WPC'S
EXPERIMENTAL DAYS 4-5 EROS 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. ROUNDS OF PRECIPITATION ARE LIKELY TO CONTINUE IN THE
WEST THROUGH MUCH OF NEXT WEEK THOUGH AT THIS POINT LOOK TO BE NOT
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 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.
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 THE EASTERN U.S.
UNDERNEATH THE STRENGTHENING UPPER RIDGE.
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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