180
FXUS02 KWBC 020659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST FRI FEB 02 2024
VALID 12Z MON FEB 05 2024 - 12Z FRI FEB 09 2024
...ATMOSPHERIC RIVER INCREASINGLY LIKELY TO IMPACT CALIFORNIA WITH
HEAVY TO POSSIBLY SIGNIFICANT RAIN AND FLASH FLOODING THROUGH
MONDAY WITH MOISTURE ALSO SPREADING INLAND ACROSS THE WEST...
..OVERVIEW
THE GUIDANCE CONTINUES TO SHOW AN ACTIVE WEATHER PATTERN ACROSS
THE WEST AS A LARGE SCALE POSITIVELY TILTED MEAN TROUGH CONTINUES
TO PROMOTE A STRONG SOUTHWESTERLY FLOW OF MOISTURE INTO THE WEST
THROUGH ABOUT MIDWEEK. OVER A MULTI-DAY TIME FRAME. INCREASING
CONFIDENCE FOR POSSIBLY SIGNIFICANT RAIN/MOUNTAIN SNOW LIKELY TO
FOCUS OVER PARTS OF CALIFORNIA INTO MONDAY. WITH TIME SOME OF THIS
MOISTURE SHOULD EXTEND INTO PARTS OF THE INTERMOUNTAIN WEST AND
ROCKIES AS THE UPPER TROUGH DRIFTS EASTWARD AND BROADENS.
MEANWHILE AN UPPER LOW/STRONG SURFACE SYSTEM SHOULD TRACK ACROSS
FLORIDA ON MONDAY THOUGH MOST OF THE HEAVIEST RAINFALL WILL BE OFF
THE COAST BY THEN. ADDITIONALLY, A STRONG UPPER RIDGE ACROSS THE
CENTRAL U.S. WILL SUPPORT WELL ABOVE NORMAL TEMPERATURES OVER MUCH
OF THIS REGION, DRIFTING SLOWLY EASTWARD THROUGH THE LATTER PART
OF THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST RUNS OF GUIDANCE MAINTAIN A HIGH CONFIDENCE FOR AN
ACTIVE WET PERIOD FOR THE WEST COAST/PARTS OF THE SOUTHWEST WITH A
GRADUAL EASTWARD DRIFT WITH TIME AND EVENTUAL BROADENING LATER IN
THE PERIOD. PLENTY OF UNCERTAINTY STILL IN THE DETAILS OF
INDIVIDUAL UPPER FEATURES/ENERGY DROPPING INTO THE WESTERN PART OF
THE TROUGH, ESPECIALLY LATER IN THE WEEK. THE GFS WAS MORE
AMPLIFIED WITH THIS LATE WEEK, WANTING A CLOSED LOW OVER THE
SOUTHWEST DAYS 6-7. ALSO SOME TIMING UNCERTAINTY ON A SHORTWAVE
EJECTING FROM THE TROUGH, WITH A MODESTLY STRONG SURFACE LOW
TRACKING FROM THE CENTRAL PLAINS INTO THE MIDWEST
WEDNESDAY-FRIDAY. OTHERWISE, THERE IS OVERALL GOOD AGREEMENT WITH
THE AMPLIFIED RIDGE SHIFTING SLOWLY EASTWARD WITH TIME, AS WELL AS
BETTER AGREEMENT THAT THE UPPER LOW OVER THE SOUTHEAST SHOULD
MERGE WITH ANOTHER LOW TO THE NORTH AND MOVE MORE OFF THE COAST
THAN PREVIOUS MODEL RUNS MAY HAVE SHOWN.
THE WPC BLEND FOR TONIGHT FAVORED THE ECMWF WITH OTHER
DETERMINISTIC GUIDANCE FOR THE FIRST HALF OF THE PERIOD. BY DAY 5
AND BEYOND, USED A COMBINATION OF THE GFS/ECMWF WITH THE ENSEMBLE
MEANS TO HELP SMOOTH OUT THE LATE PERIOD DETAIL DIFFERENCES.
OVERALL, THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS WPC
FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A MODERATE TO STRONG ATMOSPHERIC RIVER WILL BE ONGOING AS THE
PERIOD BEGINS MONDAY WITH WELL ABOVE NORMAL MOISTURE SUPPORTING
SIGNIFICANT TO EXTREME RAINFALL ACROSS PARTS OF SOUTHERN
CALIFORNIA. GUIDANCE INDICATES MULTI-DAY TOTALS (DAY 3 INTO DAY 4)
POSSIBLY NEAR A FOOT FOR SOUTHERN FACING TERRAIN NEAR THE
TRANSVERSE RANGES. ESPECIALLY CONSIDERING ANOTHER AR IN THE SHORT
RANGE PERIOD WORKING TO PRE-CONDITION SOILS, A MODERATE RISK
REMAINS IN EFFECT FOR THIS REGION ON THE DAY 4/MONDAY EXCESSIVE
RAINFALL OUTLOOK WITH ONLY MINOR MODIFICATIONS NEEDED TO THE
PREVIOUS ISSUANCE. THE SLOW MOVEMENT OF THE SUPPORTING UPPER
TROUGH MAY PRODUCE A CONTINUED SOUTHWESTERLY FLOW OF MOISTURE INTO
THE REGION THROUGH AT LEAST TUESDAY ALTHOUGH THE LEADING EDGE OF
THE MOISTURE SHOULD PUSH INTO THE SOUTHWEST/GREAT BASIN. THE DAY
5/TUESDAY ERO SHOWS A BROAD MARGINAL RISK AREA FROM SOUTHERN
CALIFORNIA INTO THE SOUTHWEST, WITH SMALLER SLIGHT RISKS
HIGHLIGHTED FOR THE LA-SAN DIEGO CORRIDOR AS WELL AS ACROSS PARTS
OF WEST-CENTRAL ARIZONA. HEAVY SNOW IN THE HIGHER TERRAIN ACROSS
MUCH OF THE WEST IS EXPECTED IN THIS PATTERN, WITH POSSIBLY
SIGNIFICANT MULTI-DAY TOTALS FOR PARTS OF THE SIERRA NEVADA.
AS LEADING ENERGY FROM THE WESTERN TROUGH LIFTS EJECTS INTO THE
PLAINS, THIS SHOULD HELP SPIN UP A MODERATELY DEEP SURFACE CYCLONE
THAT TRACKS NORTHEASTWARD WITH TIME INTO THE UPPER MIDWEST LATE
WEEK. THE ASSOCIATED COLD FRONT SHOULD HELP PULL MOISTURE
NORTHWARD TO FUEL PRECIPITATION, THOUGH WITH STILL PLENTY OF
UNCERTAINTY IN THE EXACT AMOUNTS. IN THE SOUTHEAST, THE HEAVIEST
PRECIPITATION SHOULD BE MOVING OFF THE COAST BY MONDAY AS A STRONG
SURFACE LOW MOVES ACROSS FLORIDA, BUT SOME MOISTURE MAY WRAP BACK
IN ACROSS THE SOUTHEAST TO FUEL SOME LINGERING SHOWERS AND
THUNDERSTORMS.
THE UPPER RIDGE FROM THE SOUTHERN PLAINS THROUGH GREAT LAKES WILL
SUPPORT A BROAD AREA OF UNSEASONABLY WARM TEMPERATURES OVER THE
CENTRAL U.S. AND MIDWEST THROUGH THE PERIOD. CONTINUE TO EXPECT
THE GREATEST ANOMALIES TO BE OVER/NEAR THE UPPER MIDWEST WHERE
MORNING LOWS MAY BE AS WARM AS 25-35F ABOVE NORMAL AND EXCEED
DAILY RECORDS FOR MULTIPLE DAYS, WHILE DAYTIME HIGHS SHOULD BE A
LITTLE LESS EXTREME, UP TO 15-25F OR SO ABOVE NORMAL. IN CONTRAST,
THE SOUTHWEST U.S./CALIFORNIA SHOULD SEE COOL DAYTIME HIGHS
THROUGH THE PERIOD WITH A FEW LOCATIONS UP TO ABOUT 10F BELOW
NORMAL ON ONE OR MORE DAYS. CLOUDS/PRECIPITATION OVER THE WEST
SHOULD KEEP MORNING LOWS NEAR TO ABOVE NORMAL. FLORIDA SHOULD SEE
A COUPLE COOL DAYS WITH HIGHS 5-10F BELOW NORMAL BY
TUESDAY-WEDNESDAY AFTER PASSAGE OF THE SOUTHEAST SYSTEM.
TEMPERATURES ACROSS THE EAST SHOULD TREND WARMER AS THE WEEK
PROGRESSES WITH THE UPPER RIDGE BUILDING IN. DAYTIME HIGHS BY NEXT
FRIDAY COULD BE APPROACHING 10-20 DEGREES ABOVE NORMAL FOR SOME
LOCATIONS.
SANTORELLI
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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