316
FXUS02 KWBC 021900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST FRI FEB 02 2024
VALID 12Z MON FEB 05 2024 - 12Z FRI FEB 09 2024
...ATMOSPHERIC RIVER LIKELY TO IMPACT CALIFORNIA WITH 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
OVER A MULTI-DAY TIME FRAME THROUGH ABOUT MIDWEEK. SIGNIFICANT
RAIN AND MOUNTAIN SNOW ARE 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
WHILE MODEL GUIDANCE IS REASONABLY AGREEABLE ON THE OVERALL
PATTERN, THERE ARE SOME IMPORTANT DETAIL DIFFERENCES THAT HAVE
SENSIBLE WEATHER IMPACTS. AS THE PERIOD BEGINS 12Z MONDAY THERE
ARE ALREADY SOME MODEL DIFFERENCES WITH THE SURFACE LOW AND
ASSOCIATED COLD FRONT WITH THE AR AHEAD OF IT. GFS RUNS HAD BEEN
ON THE STRONGER SIDE OF THE GUIDANCE ENVELOPE WITH THE SURFACE LOW
BUT THE 12Z GUIDANCE FROM OTHER MODEL SUITES ARE COMING IN
STRONGER THAN THEIR PREVIOUS RUNS. THERE HAS ALSO BEEN A BIT OF A
FASTER TREND WITH THE AR TO COME INTO SOUTHERN CALIFORNIA.
REGARDLESS OF THE EXACT STRENGTH AND TIMING VARIATIONS, THERE IS
STILL HIGH CONFIDENCE IN A SIGNIFICANT PRECIPITATION EVENT
UNFOLDING EARLY NEXT WEEK FOR CALIFORNIA WITH SOME NOTABLE
PRECIPITATION INLAND. THEN MODELS AGREE THAT THE UPPER TROUGH AXIS
WILL SHIFT ACROSS THE WEST AND TOWARD THE CENTRAL U.S. THROUGHOUT
THE WEEK. SHORTWAVES WITHIN THE TROUGH ARE MUCH MORE VARIABLE,
ESPECIALLY BY MIDWEEK AND BEYOND, WITH POTENTIAL FOR ENERGY TO DIG
ON THE WESTERN SIDE AND DISCREPANCIES IN HOW THAT MAY COMBINE WITH
ENERGY ALREADY IN PLACE. GFS RUNS THROUGH 00Z HAD BEEN CLOSING OFF
A LOW IN THE SOUTHWEST WITH THE DIGGING ENERGY AND APPEARED TO BE
OUTLIERS, AND THE 06Z AND NOW 12Z GFS HAVE BACKED AWAY. OTHER
MODELS VARY CONSIDERABLY BUT WITHOUT DEFINITE OUTLIERS. AN
EMERGING SURFACE LOW IN THE PLAINS TO MIDWEST SHOWS TYPICAL LEVELS
OF SPREAD WEDNESDAY-FRIDAY, THOUGH ECMWF RUNS MAY BE A NORTHERN
OUTLIER. FARTHER EAST, THE UPPER AND SURFACE LOWS ATOP FLORIDA AND
THE VICINITY ON MONDAY SEEM REASONABLY WELL HANDLED, WITH RIDGING
GRADUALLY MOVING INTO THE EAST BY THE LATTER HALF OF THE WEEK.
GIVEN THESE CONSIDERATIONS, THE WPC FORECAST USED A DETERMINISTIC
MODEL BLEND FAVORING THE ECMWF EARLY IN THE FORECAST PERIOD,
INTRODUCING THE GEFS AND EC ENSEMBLE MEANS INTO THE BLEND BY DAY 5
AND RAISING THEIR PROPORTION TO JUST OVER HALF BY DAY 7. OVERALL,
THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST,
THOUGH WITH A SLIGHTLY FASTER TREND OF QPF/ERO INTO SOUTHERN
CALIFORNIA PER THE LATEST GUIDANCE.
..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 THE EARLY STAGE OF THE
AR THIS WEEKEND WILL PRE-CONDITION SOILS, A MODERATE RISK REMAINS
IN EFFECT ON THE DAY 4/MONDAY EXCESSIVE RAINFALL OUTLOOK. WITH THE
SOUTHEASTWARD MOVEMENT OF THE AR, THE RISK AREAS EXPAND FARTHER
INTO SOUTHERN CALIFORNIA COMPARED TO THE SHORT RANGE/SUNDAY
OUTLOOK, BUT CERTAINLY WITH SOME OVERLAP BETWEEN DAYS 3 AND 4.
MODEL TRENDS HAVE BEEN SLIGHTLY FASTER TO BRING HEAVY RAIN INTO
THE SAN DIEGO AREA BY MONDAY AND THUS EXPANDED THE MODERATE RISK
FARTHER SOUTH THERE. THE SLOW MOVEMENT OF THE SUPPORTING UPPER
TROUGH SHOULD 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. LACK OF INSTABILITY UNTIL AFTER THE
TROUGH/FRONT COME THROUGH AND LIMIT MOISTURE MAY BE A LIMITING
FACTOR FOR FLASH FLOODING FOR THE ARIZONA AREA THOUGH. HEAVY SNOW
IN THE HIGHER TERRAIN ACROSS MUCH OF THE WEST IS EXPECTED IN THIS
PATTERN, WITH POSSIBLY SIGNIFICANT MULTI-DAY TOTALS OF MULTIPLE
FEET OF SNOW 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, WITH POSSIBLE SNOW IN THE
NORTH-CENTRAL U.S., THOUGH WITH STILL PLENTY OF UNCERTAINTY IN THE
EXACT AMOUNTS AND PLACEMENT. 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 UNTIL LATER NEXT
WEEK. FLORIDA SHOULD SEE A COUPLE COOL DAYS WITH HIGHS 5-10F BELOW
NORMAL BY MONDAY-TUESDAY 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.
TATE/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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