678
FXUS02 KWBC 290700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST MON JAN 29 2024
VALID 12Z THU FEB 01 2024 - 12Z MON FEB 05 2024
...LARGE SCALE SYSTEM LIKELY TO SPREAD PRECIPITATION ACROSS MUCH
OF THE WEST THIS WEEK AND THEN THE GULF COAST BY THE WEEKEND...
..OVERVIEW
MOST GUIDANCE STILL SHOWS THE DEVELOPMENT OF A BLOCKY REGIME OVER
THE COMING WEEK. A PACIFIC UPPER TROUGH REACHING THE WEST LATE
THIS WEEK WILL BECOME NEGATIVELY TILTED BY FRIDAY, FOLLOWED BY THE
SOUTHERN PART OF THE TROUGH ELONGATING EASTWARD AND BREAKING OFF
AN UPPER LOW THAT UNDERCUTS A PERSISTENT PLAINS INTO CANADA UPPER
RIDGE DURING NEXT WEEKEND. THIS FEATURE IS LIKELY TO SUPPORT A
GULF COAST STORM THAT MAY BE RATHER DEEP FOR A TRACK THAT FAR
SOUTH. TOWARD NEXT SUNDAY-MONDAY, A SOUTHERN STREAM PACIFIC
SYSTEM MAY APPROACH CALIFORNIA, WITH A LOT OF UNCERTAINTY OVER
WHAT ROLE LINGERING TROUGH ENERGY NEAR THE NORTHERN HALF OF THE
WEST COAST MAY PLAY. MEANWHILE MOST MODELS/ENSEMBLES MAINTAIN THE
IDEA OF A DEEPENING NORTHEAST UPPER TROUGH WITH ANCHORING LOW.
STRONG AND MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC TROUGH WILL
SUPPORT AREAS OF HEAVY RAIN/MOUNTAIN SNOW OVER CENTRAL-SOUTHERN
CALIFORNIA INTO THURSDAY. THEN A BROAD AREA OF RAIN/SNOW WILL
LIKELY EXTEND FARTHER INLAND OVER THE WEST WITH RAIN DEVELOPING
OVER PARTS OF THE PLAINS BY FRIDAY-SATURDAY. THIS MOISTURE,
SUPPORTING POTENTIALLY HEAVY RAINFALL, SHOULD THEN STREAM ACROSS
THE GULF COAST AND SOUTHEAST/FLORIDA. THE NORTHEAST MAY SEE SOME
PRECIPITATION MOSTLY IN THE FORM OF SNOW LATE IN THIS WEEK AND
INTO THE WEEKEND DUE TO THE DEEPENING UPPER TROUGH AND ASSOCIATED
SURFACE SYSTEM.
..GUIDANCE/PREDICTABILITY ASSESSMENT
COMPARISON OF 12Z/18Z OPERATIONAL MODELS/ENSEMBLES ALONG WITH 12Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS LED TO A GUIDANCE
PREFERENCE CONSISTING OF VARIOUS WEIGHTS OF THE 12Z/18Z GFS AND
00Z-12Z/28 ECMWF DURING THE FIRST HALF OF THE PERIOD AND SOME
INCLUSION OF THE 18Z GEFS/12Z ECENS BY SUNDAY-MONDAY.
THERE IS STILL A FAIR AMOUNT OF SPREAD FOR EXACTLY HOW QUICKLY AND
DEEPLY THE NORTHEAST UPPER TROUGH EVOLVES, WITH THE
FLATTER/EASTWARD CMC-CMCENS A NOTABLE EXTREME COMPARED TO OTHER
GUIDANCE (INCLUDING THE MACHINE LEARNING MODELS). THE OVERALL
AVERAGE OF MOST AGREEABLE MODELS/MEANS HAS BEEN TRENDING DEEPER
OVER RECENT DAYS. 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.
LATEST TRENDS SEEM TO BE NAVIGATING TOWARD THE MIDDLE OR
SOUTH-CENTRAL PART OF THE PRIOR GUIDANCE SPREAD, AS THE GFS HAS
NUDGED A LITTLE NORTH FROM EARLIER SOUTHERN SOLUTIONS WHILE THE
PREVIOUSLY NORTHWARD CMC HAS ADJUSTED TO THE SOUTH. INCREASED
SPREAD VERSUS 24 HOURS AGO IN THE 12Z ECMWF-INITIALIZED MACHINE
LEARNING MODELS TEMPERS CONFIDENCE IN SPECIFICS FOR NOW.
ALONG THE WEST COAST BY 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 12Z ECMWF-INITIALIZED MACHINE LEARNING MODELS SUGGEST
THE SURFACE SYSTEM COULD APPROACH CALIFORNIA MORE QUICKLY THAN IN
SOME OPERATIONAL MODEL RUNS--MORE SIMILAR TO THE GEFS/CMCENS MEANS.
..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. SYSTEM PROGRESSION SHOULD BE SUFFICIENT TO YIELD LOWER
PRECIPITATION TOTALS THAN FORECAST OVER NORTHERN CALIFORNIA ON
WEDNESDAY. HOWEVER 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 NEW DAY 4 EXCESSIVE RAINFALL
OUTLOOK PLANS TO INTRODUCE A SLIGHT RISK AREA OVER THAT REGION
WITHIN THE EXISTING MARGINAL RISK AREA. IT IS ALSO WORTH NOTING
THAT THIS SETUP HAS PERSISTED WELL IN THE GUIDANCE OVER THE PAST
DAY AND AT LEAST ONE FIRST-GUESS GUIDANCE SOURCE SUGGESTS AT LEAST
A SLIGHT RISK THREAT LEVEL. AS RAIN AND HIGHER ELEVATION SNOW OF
VARYING INTENSITY SPREADS THROUGH THE WEST, THERE IS SOME SIGNAL
FOR RELATIVELY GREATER ENHANCEMENT OVER SOUTH-CENTRAL ARIZONA ON
DAY 5/FRIDAY BUT THE CORRESPONDING ERO DEPICTS NO RISK AREA AS
THIS ACTIVITY SHOULD REMAIN LOCALIZED AND FAIRLY WELL BELOW FLASH
FLOOD GUIDANCE VALUES. THE SAME IS THE CASE FOR DEVELOPING
RAIN/THUNDERSTORMS OVER TEXAS, BUT THIS REGION MERITS MONITORING
AS A SLIGHTLY FASTER TREND IN DEVELOPMENT WOULD YIELD HIGHER
TOTALS.
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 CENTRAL-SOUTHERN ROCKIES/HIGH
PLAINS. 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 BUT WITH LOW CONFIDENCE IN
SPECIFICS.
THE EASTERN PACIFIC/CALIFORNIA EVOLUTION BY 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. 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.
UPPER TROUGHING/EMBEDDED LOW OVER THE NORTHEAST AND POTENTIAL
SURFACE DEVELOPMENT MAY PRODUCE SOME PRECIPITATION OVER THE REGION
FROM LATE WEEK THROUGH THE WEEKEND. MOST OF THIS PRECIPITATION
SHOULD BE SNOW FROM FRIDAY ONWARD. THERE WILL BE A COUPLE DAYS
WITH NORTHERN NEW ENGLAND SEEING 10-30 PERCENT PROBABILITIES FOR
SEEING 0.25 INCH LIQUID IN THE FORM OF SNOW.
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
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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