031
FXUS02 KWBC 291852
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
151 PM EST MON JAN 29 2024
VALID 12Z THU FEB 01 2024 - 12Z MON FEB 05 2024
...ATMOSPHERIC RIVER TO SPREAD HEAVY PRECIPITATION ACROSS MUCH OF
THE WEST THIS WEEK, THEN REACHES THE GULF COAST BY THE WEEKEND...
...ANOTHER STRONG WEATHER SYSTEM INCREASINGLY LIKELY TO IMPACT
CALIFORNIA LATE THIS WEEKEND INTO EARLY NEXT WEEK...
..OVERVIEW
THE UPPER LEVEL PATTERN IS EXPECTED TO BECOME INCREASINGLY BLOCKY
THROUGH THIS WEEK AS A PACIFIC UPPER TROUGH BECOMES ELONGATED
ALONG THE WEST COAST BY MID WEEK, SLOWING DOWN AND TAKING ON A
NEUTRAL TO NEGATIVE TILT. THIS SYSTEM WILL BRING A PERIOD OF
ACTIVE WEATHER AND HEAVY PRECIPITATION TO THE WEST, EVENTUALLY
REACHING THE GULF COAST BY LATE WEEK INTO THIS WEEKEND. MEANWHILE,
DOWNSTREAM RIDGING WILL BECOME MORE PRONOUNCED OVER THE NORTHERN
PLAINS, ALLOWING TROUGHING TO DEVELOP OVER THE NORTHEAST
REINFORCED BY A FEW EMBEDDED SHORTWAVE TROUGHS. THE RESULTING
OMEGA BLOCK WILL DOMINATE THE PERIOD INTO THIS WEEKEND. BY LATE IN
THE WEEKEND INTO EARLY NEXT WEEK, AN ACTIVE SOUTHERN STREAM SYSTEM
WILL BEGIN TO APPROACH CALIFORNIA THOUGH FORECAST UNCERTAINTY IN
THE TIMING AND MAGNITUDE OF THAT POTENTIAL SYSTEM IS LOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MODEL BLEND PREFERENCES FOR THIS FORECAST CYCLE INCLUDED
MAINLY THE DETERMINISTIC GFS AND ECMWF TO START FOLLOWED BY A
HIGHER WEIGHT/INCLUSION OF THE GEFS AND ECENS MEANS BY DAY 6-7.
WHILE THERE REMAINS A FAIR AMOUNT OF MODEL UNCERTAINTY, THE MAIN
MODEL OUTLIER WAS THE CMC/CMCENS AND THEREFORE WASN'T INCLUDED AT
ALL IN THE FORECAST BLEND PREFERENCES. GUIDANCE CONTINUES TO BE
WELL BEHAVED WITH THE SYSTEM COMING INTO THE WEST THROUGH
FRIDAY-SATURDAY, BUT WITH LATITUDE AND TIMING SPREAD PERSISTING
FOR THE UPPER LOW THAT BREAKS OFF ACROSS THE SOUTHERN TIER FROM
THE WEEKEND INTO MONDAY. OVERALL TRENDS TO BE A BIT FASTER WITH
THE SYSTEM REACHING THE PLAINS, AND A NUDGE TO THE NORTH ACROSS
THE PLAINS TO SOUTHEAST COMPARED TO EARLIER CYCLES. LATEST TRENDS
SEEM TO BE NAVIGATING TOWARD THE MIDDLE OR SOUTH-CENTRAL PART OF
THE PRIOR GUIDANCE SPREAD. ALONG THE WEST COAST BY SUNDAY INTO
NEXT MONDAY, THERE IS DECENT AGREEMENT THAT A SOUTHERN STREAM
PACIFIC SYSTEM SHOULD BE COMING INTO THE PICTURE BUT WITH A LOT OF
SPREAD FOR SPECIFICS. THIS IS DUE IN PART FROM VARIOUS IDEAS FOR
HOW ENERGY WITHIN THE LINGERING UPPER TROUGH ALONG THE
NORTHERN-CENTRAL WEST COAST COULD INTERACT. IN GENERAL THE LATEST
MODEL GUIDANCE HAS SPED UP THE TIMING OF THIS SYSTEM, REACHING THE
CA COAST BY SUNDAY/SUNDAY NIGHT INTO MONDAY AND COULD LEAD TO A
VARIETY OF WEATHER IMPACTS.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER TROUGH AND LEADING FRONTAL SYSTEM REACHING THE WEST
COAST BY THE START OF THE PERIOD WILL SUPPORT A STRONG SOUTHERLY
FLOW OF ENHANCED MOISTURE AND BRING A PERIOD OF SIGNIFICANT
RAINFALL AND HIGH ELEVATION SNOW TO CENTRAL/SOUTHERN CALIFORNIA ON
THURSDAY. GUIDANCE CONTINUES TO SHOW SOME INSTABILITY ACCOMPANYING
THE ACTIVITY ALONG THE SOUTHERN CALIFORNIA COAST, WHICH COMBINED
WITH TERRAIN ENHANCEMENT COULD PRODUCE SOME INTENSE RAIN RATES
ALONG THE TRANSVERSE RANGES IN PARTICULAR AS THE SYSTEM IS MOVING
THROUGH. THEREFORE THE DAY 4 EXCESSIVE RAINFALL OUTLOOK MAINTAINS
THE SLIGHT RISK AREA OVER THAT REGION FOR POSSIBLE EXCESSIVE
RAINFALL AND ITS IMPACTS INCLUDING FLASH FLOODING, DEBRIS FLOWS,
MUDSLIDES PARTICULARLY IN AREAS OF STEEP TERRAIN OR BURN SCARS.
THE ENERGY WITH THE SYSTEM THEN QUICKLY MOVES EASTWARD THROUGH
SOUTHERN ARIZONA LATE IN THE DAY 4 ERO PERIOD AND WHILE SOME
LOCALLY HEAVY RAINFALL MAY OCCUR, THE INTENSITY AND DURATION
(ALONG WITH SOME MODEL UNCERTAINTY) OF THE RAINFALL AND RATES LOOK
TO BE LOW ENOUGH TO LIMIT ANY FLASH FLOOD CONCERNS AS OF NOW.
HOWEVER, ONCE THE SYSTEM REACHES THE SOUTHERN PLAINS, IT TAPS INTO
SOME GULF MOISTURE WITH DEVELOPING SOUTHERLY LOW LEVEL FLOW. THIS
WILL LIKELY BRING A PERIOD OF SHOWERS AND THUNDERSTORMS OVER TX
INTO SOUTHERN OKLAHOMA LATE IN THE DAY 5 ERO PERIOD. GIVEN THE
FASTER TIMING AND INCREASING MODEL AGREEMENT FOR POSSIBLE 1-2" OF
RAINFALL, A MARGINAL RISK WAS INTRODUCED FOR THIS AFTERNOON
UPDATE.
AS THE UPPER LEVEL ENERGY CROSSING THE SOUTHWEST/SOUTHERN ROCKIES
LIKELY BREAKS OFF AN UPPER LOW, THERE WILL BE A PERIOD OF EASTERLY
PRECIPITATION ENHANCEMENT ALONG THE ROCKIES/HIGH PLAINS WITH
WIDESPREAD ACCUMULATING SNOW FOR THE TERRAIN AREAS, SOME OF WHICH
COULD BE LOCALLY HEAVY/SIGNIFICANT. AS THE UPPER LOW CONTINUES
EASTWARD DURING THE WEEKEND, EXPECT HEAVIER RAINFALL TO SPREAD
ACROSS EASTERN TEXAS AND CONTINUE ALONG/NEAR THE GULF COAST INTO
THE SOUTHEAST AND FLORIDA. THE FAR NORTHERN PERIPHERY OF THE
PRECIPITATION SHIELD COULD CONTAIN A LITTLE WINTRY WEATHER ACROSS
PORTIONS OF THE SOUTHERN APPALACHIANS BUT WITH LOW CONFIDENCE IN
SPECIFICS.
THE EASTERN PACIFIC/CALIFORNIA EVOLUTION BY SUNDAY INTO EARLY NEXT
WEEK WILL REQUIRE CLOSE MONITORING. THE OVERALL PATTERN APPEARS
TO SUPPORT THE POTENTIAL FOR A SOMEWHAT HEAVIER AND/OR LONGER
DURATION ATMOSPHERIC RIVER EVENT FOR CENTRAL-SOUTHERN CALIFORNIA
THAN THE ONE FORECAST LATE THIS WEEK, WITH A SOMEWHAT MORE DIRECT
CONNECTION TO LOWER LATITUDE MOISTURE WITH BOTH HEAVY LOWER
ELEVATION RAINFALL AND HEAVY MOUNTAIN SNOW POSSIBLE. HOWEVER
THERE ARE SIGNIFICANT DETAIL UNCERTAINTIES THAT DO NOT HAVE GREAT
PREDICTABILITY A WEEK OUT IN TIME, SO CONFIDENCE IS LOW IN THE
DETAILS AT THIS TIME.
THE PERSISTENT UPPER RIDGE OVER AND NEAR THE NORTHERN PLAINS WILL
KEEP THE NORTHERN TIER QUITE WARM THROUGH THE PERIOD, WITH MORNING
LOWS UP TO 20-30F ABOVE NORMAL AND DAYTIME HIGHS 10-25F ABOVE
NORMAL. A FEW DAILY RECORDS WILL BE POSSIBLE FOR WARM LOWS.
OVERALL EXPECT THE COVERAGE OF WARMEST ANOMALIES TO DECREASE VERY
GRADUALLY WITH TIME. THE UPPER TROUGH MOVING INTO THE WEST WILL
BRING HIGH TEMPERATURES DOWN TO 5-15F BELOW NORMAL OVER THE WEST
COAST STATES/SOUTHWEST FROM LATE THIS WEEK ONWARD, WITH THE
COOLEST ANOMALIES MOST LIKELY OVER SOUTHERN CALIFORNIA INTO
ARIZONA. FARTHER EAST, THE SOUTHERN PART OF THE FLORIDA PENINSULA
MAY SEE TEMPERATURES UP TO SEVERAL DEGREES BELOW NORMAL INTO
THURSDAY FOLLOWED BY A REBOUND TO NORMAL FOR A TIME. PASSAGE OF
THE STRONG GULF COAST SYSTEM AROUND SUNDAY-MONDAY SHOULD DROP
DAYTIME HIGHS TO BELOW NORMAL LEVELS ACROSS THE SOUTHERN TIER.
THE NORTHEAST WILL SEE ABOVE NORMAL TEMPERATURES (ESPECIALLY FOR
MORNING LOWS) LATE THIS WEEK IN THE WARM SECTOR OF AN APPROACHING
FRONT. THEN INCREASING AGREEMENT ON A DEVELOPING DEEP
TROUGH/UPPER LOW OVER THE REGION SUGGESTS HIGH TEMPERATURES MAY
DECLINE TO MODERATELY BELOW NORMAL LEVELS BY THE WEEKEND.
RAUSCH/TAYLOR
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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