783
FXUS02 KWBC 010700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST THU FEB 01 2024
VALID 12Z SUN FEB 04 2024 - 12Z THU FEB 08 2024
...SOUTHERN TIER SYSTEM LIKELY TO SPREAD HEAVY RAIN ACROSS PARTS
OF THE SOUTHEAST THROUGH AT LEAST SUNDAY...
...ANOTHER STRONG WEATHER SYSTEM INCREASINGLY LIKELY TO IMPACT
CALIFORNIA BY EARLY NEXT WEEK AND EVENTUALLY SPREAD ACROSS MORE OF
THE WEST...
..OVERVIEW
WITH SOME PERSISTENT DETAIL DIFFERENCES, GUIDANCE CONTINUES TO
SHOW AN ACTIVE WEATHER PATTERN FOR THE WEST AT LEAST THROUGH
MIDWEEK. EXPECT A LARGE SCALE POSITIVELY TILTED MEAN TROUGH TO
PROMOTE A STRONG SOUTHWESTERLY FLOW OF MOISTURE INTO THE WEST OVER
A MULTI-DAY TIME FRAME, WITH HEAVIEST RAIN/MOUNTAIN SNOW LIKELY TO
FOCUS OVER CALIFORNIA. 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
TRACKING FROM THE SOUTHERN PLAINS THROUGH THE SOUTHEAST DURING
SUNDAY-MONDAY WILL SUPPORT A STRONG SURFACE SYSTEM AND A HEAVY
RAINFALL THREAT ACROSS THE SOUTHERN TIER. ADDITIONALLY, A STRONG
UPPER RIDGE CENTERED OVER THE UPPER MIDWEST/GREAT LAKES FROM THE
WEEKEND INTO MONDAY SHOULD MERGE WITH ANOTHER RIDGE BUILDING IN
ACROSS THE SOUTHWEST TO YIELD A SOUTHERN PLAINS INTO GREAT LAKES
RIDGE BY MIDWEEK. THESE RIDGES WILL SUPPORT WELL ABOVE NORMAL
TEMPERATURES OVER MUCH OF THE CENTRAL U.S. HOWEVER THE FLOW ALOFT
OVER THE NORTHEAST HAS BECOME MORE UNCERTAIN IN LATEST MODEL RUNS,
WITH A WIDE POTENTIAL SPREAD BETWEEN THE UPPER RIDGE MOVING IN
FROM THE WEST OR REINFORCEMENT OF UPPER TROUGHING OVER OR JUST
EAST OF THE REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE GUIDANCE PROVIDES HIGH CONFIDENCE IN THE OVERALL WEST COAST
TROUGH ALONG WITH THE GENERAL EASTWARD DRIFT AND EVENTUAL
BROADENING LATER IN THE PERIOD, GUIDANCE IS HAVING A VERY
DIFFICULT TIME RESOLVING INDIVIDUAL UPPER FEATURES (INITIAL ENERGY
THAT MAY CONSOLIDATE AROUND SUNDAY-MONDAY PLUS ONE OR MORE
NORTHERN STREAM FEATURES THAT MAY DROP INTO THE UPPER TROUGH).
THIS IS LEADING TO SIGNIFICANT SPREAD AND RUN-TO-RUN VARIABILITY
FOR THE SURFACE SYSTEM EXPECTED TO AFFECT CALIFORNIA EARLY IN THE
WEEK. IN GENERAL THE STRONGEST SIDE OF THE SOLUTION ENVELOPE FOR
LOW PRESSURE HAS TRENDED WEAKER WITH THE 00Z UKMET/ECMWF TRENDING
MORE STRUNG OUT WITH THE OVERALL AREA OF LOW PRESSURE. THERE HAD
BEEN A SIGNAL IN SOME GUIDANCE FOR THE PARENT LOW TO LINGER ALONG
THE WEST COAST FOR A WHILE, POSSIBLY EVEN DRIFTING SOUTHWARD,
VERSUS CONTINUED NORTHEAST PROGRESSION. RECENT ECMWF-INITIALIZED
MACHINE LEARNING MODELS HAVE BEEN FAIRLY CONSISTENT IN BEING ON
THE FASTER SIDE OF THE DYNAMICAL MODEL SPREAD AND THE 00Z
GFS/ECMWF TRENDS LEAN IN THAT DIRECTION FOR NORTHWARD PROGRESSION
(BUT PERHAPS A LITTLE EAST OF THE ML MODELS). SHORTWAVE DETAIL
ISSUES PLAGUE THE REST OF THE FORECAST OVER THE WEST AS WELL, BUT
THERE IS BETTER THAN AVERAGE MODEL/ENSEMBLE SUPPORT FOR LOW
PRESSURE TO DEVELOP OVER THE PLAINS BY MID-LATE WEEK. THE 12Z/18Z
GFS AND 12Z ECMWF PROVIDED THE BEST COMPARISON TO ENSEMBLES IN
GENERAL, WITH THE UKMET FAST/CMC SLOW.
THE GUIDANCE AVERAGE LOOKS GOOD FOR THE SYSTEM TRACKING ACROSS THE
SOUTHEAST, WITH THE UKMET CONSISTENTLY ON THE SOUTHERN SIDE OF THE
SPREAD. OVER THE PAST DAY A NEW COMPLICATION HAS DEVELOPED
REGARDING THE ULTIMATE EVOLUTION/TRACK OF THIS SYSTEM OVER THE
WESTERN ATLANTIC, AS THE GFS/CMC NOW ARE MUCH MORE AGGRESSIVE TO
DIG TROUGH ENERGY SOUTH THROUGH NEW ENGLAND AND BEYOND BY TUESDAY
ONWARD. THOSE SOLUTIONS RESULT IN A FARTHER NORTH TRACK AND
GREATER WIND IMPACTS (IF NOT EVEN SOME PRECIPITATION) ALONG THE
NORTHERN EAST COAST. TELECONNECTIONS RELATIVE TO POSITIVE HEIGHT
ANOMALIES FORECAST OVER SOUTHERN CANADA, AS WELL AS THE 12Z
ECMWF-INITIALIZED ML MODELS, DO NOT FAVOR UPPER TROUGHING AS CLOSE
TO THE EAST COAST AS WHAT THE GFS/GEFS SUGGEST--BUT ALSO UPPER
RIDGING PERHAPS NOT REACHING QUITE AS CLOSE TO NEW ENGLAND AS IN
THE ECMWF/ECMWF MEAN. THUS A COMPROMISE LOOKS REASONABLE AT THIS
TIME.
AFOREMENTIONED GUIDANCE COMPARISONS LED TO UPDATING THE FORECAST
WITH A BLEND OF THE 12Z/18Z GFS AND 12Z ECMWF EARLY IN THE PERIOD
AND THEN TRANSITIONING TO INCLUDE 50-60 PERCENT TOTAL WEIGHT OF
THE 18Z GEFS/12Z ECENS MEANS AS DETAIL UNCERTAINTIES STEADILY
INCREASE.
..WEATHER/HAZARDS HIGHLIGHTS
SOME OF THE SPECIFICS CONTINUE TO BE UNCERTAIN BUT MOST GUIDANCE
STILL PROVIDES STRONG SUPPORT FOR THE IDEA OF A MULTI-DAY
ATMOSPHERIC RIVER EVENT AFFECTING CALIFORNIA FROM AROUND SUNDAY
INTO THE NEXT WORKWEEK. A POTENTIALLY STRONG SYSTEM THAT MAY
PRODUCE GUSTY WINDS SHOULD TRACK TO A POSITION JUST OFFSHORE
NORTHERN CALIFORNIA BY EARLY MONDAY, BRINGING THE LEADING SURGE OF
MOISTURE. SLOW MOVEMENT OF THE SUPPORTING UPPER TROUGH MAY PRODUCE
A CONTINUED SOUTHWESTERLY FLOW OF MOISTURE INTO THE REGION THROUGH
AT LEAST TUESDAY (WITH PRECIPITATION ENHANCEMENT POSSIBLY
GENERATED BY ONE OR MORE TRAILING FRONTAL WAVES) WHILE THE LEADING
EDGE OF THE MOISTURE BEGINS TO PUSH INTO THE SOUTHWEST/GREAT
BASIN. HEAVY SNOW FAVORING SOUTHWARD-FACING TERRAIN SHOULD ALSO
SPREAD INTO THE ROCKIES DURING THE EARLY-MID WEEK TIME FRAME.
FOLLOWING THE PERSISTENT GUIDANCE MAJORITY THAT BRINGS MOISTURE
INTO CALIFORNIA EARLIER/EASTWARD VERSUS CMC RUNS, THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS INDICATE A SLIGHT RISK FROM ALONG/NEAR
THE TRANSVERSE RANGES NORTHWARD ALONG COASTAL CALIFORNIA, WITH THE
NORTHERN EXTENT SLIGHTLY LESS ON DAY 5/MONDAY AS THE BEST MOISTURE
AXIS DRIFTS A LITTLE EASTWARD. THE MARGINAL RISK EXPANDS FARTHER
INLAND, BUT OF COURSE NOT TO HIGHER ELEVATION AREAS OF THE SIERRA
NEVADA WHERE HEAVY SNOW IS LIKELY. PRECIPITATION SHOULD PERSIST
ESPECIALLY FOR SOUTHERN PORTIONS OF CALIFORNIA THROUGH AT LEAST
MIDWEEK BUT WITH GRADUALLY DECREASING TOTALS. THIS EVENT STILL
APPEARS LIKELY TO PRODUCE GREATER LOW ELEVATION RAIN/MOUNTAIN SNOW
TOTALS THAN THE PRECEDING EVENT DUE TO A LONGER DURATION OF
SOUTHWESTERLY FLOW ALOFT AND A MORE DIRECT CONNECTION WITH LOWER
LATITUDE MOISTURE. CONTINUE TO MONITOR FORECASTS FOR THIS TIME
FRAME AS SPECIFICS GRADUALLY BECOME BETTER RESOLVED. BY NEXT
WEDNESDAY-THURSDAY, LEADING HEIGHT FALLS ALOFT AND ASSOCIATED LOW
PRESSURE MAY DEVELOP PRECIPITATION OVER THE NORTHERN PLAINS.
THE UPPER LOW TRACKING FROM THE SOUTHERN PLAINS THROUGH THE
SOUTHEAST DURING SUNDAY-MONDAY WILL SUPPORT ASSOCIATED LOW
PRESSURE THAT WILL BE FAIRLY DEEP FOR SUCH A SOUTHERN TRACK.
EXPECT THIS SYSTEM TO PRODUCE SOME AREAS OF HEAVY RAINFALL ACROSS
THE SOUTHEAST DURING THE SUNDAY-SUNDAY NIGHT PERIOD COVERED BY THE
DAY 4 ERO. THE OUTLOOK MAINTAINS A BROAD MARGINAL RISK AREA OVER
THE SOUTHEAST, WITH LATEST GUIDANCE SIGNALS STILL SOMEWHAT DIFFUSE
FOR WHERE BEST RAINFALL FOCUS WILL BE, PRECLUDING INTRODUCTION OF
ANY EMBEDDED SLIGHT RISK. ONE REGION OF POTENTIALLY GREATER
INTEREST CONTINUES TO BE OVER PARTS OF GEORGIA/SOUTH CAROLINA
WHICH WILL BE JUST TO THE NORTH OF ONE OR MORE FRONTS THAT COULD
HELP TO FOCUS HEAVIER RAINFALL. GUIDANCE EXPECTATIONS FOR
INSTABILITY OVER THIS AREA DO NOT APPEAR PARTICULARLY IMPRESSIVE
THOUGH. SOME HEAVY RAINFALL COULD LINGER INTO MONDAY OVER OR NEAR
THE COAST OF THE CAROLINAS. CURRENT GUIDANCE IS NOT SHOWING A
COHERENT ENOUGH OF A SIGNAL TO RECOMMEND A MARGINAL RISK OVER THIS
LOCALIZED AREA IN THE NEW DAY 5 ERO BUT WILL CONTINUE TO MONITOR
FOR IMPROVED CLUSTERING IN UPCOMING MODEL RUNS. ONCE THE SURFACE
SYSTEM MOVES OFFSHORE, EXPECT A PERIOD OF STRONG WINDS
ALONG/OFFSHORE THE SOUTHEAST COAST AND POSSIBLY FARTHER NORTH AS
WELL.
THE UPPER RIDGE INITIALLY OVER AND NEAR THE UPPER MIDWEST AND THEN
BECOMING ALIGNED FROM THE SOUTHERN PLAINS THROUGH GREAT LAKES WILL
SUPPORT A BROAD AREA OF UNSEASONABLY WARM TEMPERATURES OVER THE
CENTRAL U.S. 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 10-15F 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 OVER THE NORTHEAST
FROM TUESDAY ONWARD HAVE GREATER UNCERTAINTY THAN MOST OTHER
AREAS. THE MOST LIKELY SCENARIO WOULD YIELD NEAR TO ABOVE NORMAL
TEMPERATURES AS UPPER RIDGING APPROACHES, BUT THERE IS LESSER
POTENTIAL FOR A NEARBY UPPER TROUGH/LOW TO KEEP TEMPERATURES
COLDER.
RAUSCH/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 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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