673
FXUS02 KWBC 281816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
115 PM EST SUN JAN 28 2024
VALID 12Z WED JAN 31 2024 - 12Z SUN FEB 04 2024
...LARGE SCALE SYSTEM LIKELY TO SPREAD PRECIPITATION ACROSS MUCH
OF THE WEST THIS WEEK WITH HIGHEST TOTALS EXPECTED OVER
CALIFORNIA...
..19Z UPDATE
THERE IS GOOD OVERALL SYNOPTIC AGREEMENT AMONG THE GFS/ECMWF/UKMET
MODELS THROUGH THE END OF THE WEEK WITH ONLY MINOR MESOSCALE
DIFFERENCES NOTED, SO A GENERAL BLEND OF THOSE MODELS SUFFICES AS
A GOOD STARTING POINT IN THE FORECAST PROCESS. THE CMC WAS OUT OF
PHASE WITH THAT OVERALL FLOW PATTERN ACROSS THE EASTERN U.S. AND
STRAYED FROM THE MODEL CONSENSUS AS EARLY AS THURSDAY, SO THE 00Z
RUN WAS NOT USED FOR THIS FORECAST. MORE NOTEWORTHY DIFFERENCES
ARE EVIDENT BY NEXT SUNDAY AS THE LOW PRESSURE SYSTEM NEAR THE
GULF COAST TRACKS SOUTH OF A CLOSED HIGH CENTERED OVER THE
NORTH-CENTRAL STATES. THEREFORE, THE ENSEMBLE MEANS WERE INCREASED
TO ABOUT 40 PERCENT ALONG WITH SOME PREVIOUS WPC CONTINUITY FOR
NEXT WEEKEND. NO MAJOR CHANGES WERE NEEDED FOR THE UPDATED DAY 4
AND 5 EXCESSIVE RAINFALL OUTLOOKS. THE PREVIOUS DISCUSSION IS
APPENDED BELOW FOR REFERENCE. /HAMRICK
..OVERVIEW
GUIDANCE CONTINUES TO SHOW THE LARGE SCALE PATTERN BECOMING MORE
BLOCKY BY LATER THIS WEEK AND NEXT WEEKEND. EXPECT UPPER RIDGING
TO SETTLE OVER THE CENTRAL U.S. WHILE EXTENDING NORTH INTO CANADA,
AS A PACIFIC UPPER TROUGH REACHING THE WEST BECOMES NEGATIVELY
TILTED BY FRIDAY. THE SOUTHERN PART OF THE TROUGH WILL LIKELY
CONTINUE ELONGATING EASTWARD AND BREAK OFF AN UPPER LOW THAT
UNDERCUTS THE CENTRAL U.S. RIDGE NEXT WEEKEND. SOME LINGERING
UPPER TROUGHING/POSSIBLE EMBEDDED LOW SHOULD LINGERING NEAR THE
NORTHERN-CENTRAL WEST COAST THROUGH THE WEEKEND. MEANWHILE EAST
COAST MEAN TROUGHING WILL COMPRISE ONE SHORTWAVE PASSING THROUGH
AROUND MIDWEEK AND THEN REINFORCING ENERGY ARRIVING FARTHER NORTH
TOWARD THE END OF THE WEEK AND LIKELY PERSISTING THROUGH THE
WEEKEND. STRONG AND MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC
TROUGH WILL SUPPORT AN ATMOSPHERIC RIVER EVENT WHOSE FOCUS SHOULD
BE MOST PRONOUNCED OVER NORTHERN CALIFORNIA ON WEDNESDAY AND
FARTHER SOUTH BY THURSDAY. A BROAD AREA OF RAIN/SNOW WILL LIKELY
EXTEND FARTHER INLAND OVER THE WEST AFTER WEDNESDAY AND RAIN
SHOULD DEVELOP OVER PARTS OF THE PLAINS BY FRIDAY OR SATURDAY.
THIS MOISTURE SHOULD THEN STREAM INTO THE SOUTHEAST. AN AREA OF
MOSTLY LIGHT PRECIPITATION SHOULD ACCOMPANY A MODEST MIDWEEK EAST
COAST SYSTEM WHILE THE NORTHEAST MAY SEE SOME PRECIPITATION MOSTLY
IN THE FORM OF SNOW LATE IN THE WEEK AND NEXT WEEKEND AS
REINFORCING ENERGY ALOFT SETTLES INTO THE MEAN TROUGH POSITION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AS HAS BEEN THE CASE RECENTLY, MOST ASPECTS OF THE WESTERN U.S.
PATTERN (AT LEAST THROUGH FRIDAY) ARE MORE STABLE AND AGREEABLE
THAN FOR DETAILS OVER THE EAST. LEADING HEIGHT FALLS WITH THE
UPPER TROUGH ARRIVING INTO THE WEST STILL BECOME A LITTLE FASTER
IN THE CMC BUT OTHERWISE A CONSENSUS APPROACH LOOKS GOOD THROUGH
FRIDAY. THEN GUIDANCE FAIRLY RAPIDLY DIVERGES REGARDING THE PATH
OF A POTENTIAL UPPER LOW EXPECTED TO BREAK OFF FROM THE SOUTHERN
PART OF THE WESTERN TROUGH. LATEST CMC RUNS REPRESENT THE
NORTHERN EXTREME OVER THE CENTRAL PLAINS WHILE THE NEW 00Z GFS HAS
BECOME A SOUTHERN EXTREME JUST OFFSHORE THE WESTERN GULF COAST AS
OF EARLY NEXT SUNDAY, AND THE 12Z ECMWF STRAYS TO THE FAST SIDE
NEAR THE GULF COAST (ADJUSTED BACK TO SLOWER TIMING IN THE NEW 00Z
RUN). A COMPOSITE OF THE 12Z/18Z GFS, 00Z/27 ECMWF, AND 18Z
GEFS/12Z ECENS MEANS SEEM TO PROVIDE THE BEST INTERMEDIATE
STARTING POINT AT THIS TIME. WORTH MONITORING IS A POTENTIAL
SOUTHWARD TREND AS THE 12Z ECMWF-INITIALIZED MACHINE LEARNING
MODELS LEANED ALONG OR JUST NORTH OF THE GULF COAST FOR THE UPPER
LOW TRACK.
OVER THE EAST, THE LEADING SYSTEM ON WEDNESDAY IS GRADUALLY COMING
INTO BETTER AGREEMENT WITH MOST SOLUTIONS DEPICTING RAPID
PROGRESSION INTO THE ATLANTIC AFTER EARLY WEDNESDAY. CMC RUNS ARE
A NOTABLE SLOW EXTREME COMPARED TO THIS EMERGING MAJORITY. BEHIND
THIS SYSTEM, INDIVIDUAL MODEL RUNS CONTINUE TO BE QUITE DIVERSE
AND ERRATIC REGARDING HOW UPSTREAM SOUTHERN CANADA ENERGY MAY
AMPLIFY INTO THE NORTHEASTERN U.S. WITH THE ECMWF-INITIALIZED
MACHINE LEARNING MODELS BECOMING MORE EMPHATIC ABOUT AN UPPER LOW
REACHING OVER OR NEAR NEW ENGLAND BY NEXT WEEKEND, LATEST GFS RUNS
AND 00Z/27 ECMWF MATCH THAT IDEA THE BEST OVERALL WITHIN A
FAVORABLY COMPARABLE GEFS/ECENS MEAN TROUGH. THE 12Z/27 ECMWF WAS
A SOUTHWEST EXTREME WITH THE UPPER LOW WHILE THE CMC/CMCENS HAVE
BEEN SHIFTING THE OVERALL TROUGH AXIS FARTHER EAST. THE NEW 00Z
ECMWF HAS DIFFERENT DETAILS THAN SOME OTHER SOLUTIONS BUT DOES
ULTIMATELY ACHIEVE A NEW ENGLAND UPPER LOW BY NEXT SUNDAY.
BASED ON GUIDANCE COMPARISONS OVER THE COURSE OF THE PERIOD, DAY 3
WEDNESDAY STARTED WITH A MODEL COMPOSITE INCLUDING A SPLIT OF
OLDER 00Z/12Z ECMWF RUNS AND 12Z/18Z GFS RUNS WITH SOME 12Z UKMET
AND MINIMAL 12Z CMC INCLUSION. THEREAFTER, THE BLEND FIRST
EXCLUDED THE CMC AND THEN EVENTUALLY PHASED OUT 12Z ECMWF INPUT
WHILE INCORPORATING ONLY 30 PERCENT WEIGHT OF 18Z GEFS/12Z ECENS
MEANS AS THE 12Z ECMWF AND TWO GFS RUNS TOGETHER ALREADY COMPARED
FAIRLY WELL TO THE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER TROUGH AND LEADING FRONTAL SYSTEM APPROACHING THE WEST
COAST AROUND MIDWEEK WILL SUPPORT A STRONG SOUTHERLY FLOW OF
ENHANCED MOISTURE AND LIKELY BRING A PERIOD OF SIGNIFICANT
RAINFALL AND HIGH ELEVATION SNOW TO THE WEST COAST STATES. DURING
THE PERIOD COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS
(EARLY WEDNESDAY THROUGH THURSDAY NIGHT), GUIDANCE HAS BEEN
CONSISTENT IN BRINGING THE HEAVIEST RAINFALL TO NORTHERN
CALIFORNIA AROUND WEDNESDAY WHEN A SLIGHT RISK AREA REMAINS AS
CARRIED OVER FROM THE PRIOR DAY 5 OUTLOOK. THIS OUTLOOK STILL
CORRESPONDS TO THE BEST OVERLAP OF GUIDANCE SIGNALS WITHIN
PERSISTENT TIMING SPREAD, THOUGH NOW WITH A LITTLE CLOSER
AGREEMENT AMONG THE GFS/ECMWF/UKMET AND THE GEFS/ECENS VERSUS THE
CMC/CMCENS THAT ARE STILL A LITTLE FASTER. THE SURROUNDING
MARGINAL RISK AREA REFLECTS AN INTERMEDIATE TIMING OF SIGNIFICANT
BUT LESS EXTREME RAINFALL POTENTIAL. THERE IS ALSO A MARGINAL
RISK AREA OVER THE OLYMPIC PENINSULA IN WESTERN WASHINGTON IN THE
DAY 4 OUTLOOK WITH GUIDANCE STILL SHOWING SOME RELATIVE QPF MAXIMA
WITH WET FROM PRIOR DAYS' RAINFALL. BY DAY 5/THURSDAY, EXPECT THE
BEST PRECIPITATION FOCUS TO SHIFT FARTHER SOUTH OVER CALIFORNIA AS
THE UPPER TROUGH AXIS NEARS THE COAST. A MAJORITY OF HEAVY QPF
OVER THE SIERRA NEVADA SHOULD BE IN THE FORM OF SNOW, LEAVING
AREAS NEAR THE SOUTHERN CALIFORNIA COAST AS THE REGION OF INTEREST
FOR EXCESSIVE RAINFALL POTENTIAL. CURRENT PLAN IS TO INTRODUCE A
MARGINAL RISK AREA OVER AND SOUTH OF THE TRANSVERSE RANGES, WITH
SOME ACCELERATION OF THE MOISTURE BAND RELATIVE TO DAY 4 HELPING
TO TEMPER AMOUNTS SOMEWHAT. HOWEVER THE GFS/ECMWF SUGGEST THERE
MAY BE SOME INSTABILITY WITH THIS ACTIVITY, SO THERE COULD BE
POTENTIAL FOR FAIRLY INTENSE RAIN RATES OVER FAVORED
SOUTHWARD-FACING TERRAIN. A NARROWING OF EXISTING TIMING SPREAD
AND BETTER RESOLUTION IN THE SHORT-TERM MODELS OVER THE COMING
DAYS COULD EVENTUALLY HELP TO DEFINE ANY POTENTIAL EMBEDDED SLIGHT
RISK AREA. FARTHER INLAND, EXPECT A BROAD AREA OF MOISTURE TO
SPREAD ACROSS THE WEST FROM THURSDAY INTO THE WEEKEND AND PRODUCE
RAIN/HIGHER ELEVATION SNOW. SOUTHWARD-FACING TERRAIN SHOULD SEE
THE HIGHEST TOTALS OVER THE WEST, WHILE PORTIONS OF THE CENTRAL
AND/OR SOUTHERN ROCKIES INTO HIGH PLAINS COULD EVENTUALLY SEE
EASTERLY ENHANCEMENT AS ELONGATING UPPER TROUGH ENERGY FORMS A
CLOSED LOW OVER OR JUST BEYOND THE FOUR CORNERS REGION. THEN A
FAIRLY STRONG SYSTEM MOST LIKELY CONTINUING EASTWARD ACROSS THE
SOUTHERN TIER SHOULD EXTEND RAINFALL FROM THE CENTRAL-SOUTHERN
PLAINS THROUGH THE SOUTHEAST, WITH SOME OF THIS RAIN POTENTIALLY
HEAVY.
THE SYSTEM CROSSING THE EAST INTO WEDNESDAY WILL PRODUCE AN AREA
OF MOSTLY LIGHT PRECIPITATION WHICH MAY BE SNOW OVER THE CENTRAL
APPALACHIANS/NORTHERN MID-ATLANTIC AND RAIN FARTHER SOUTH. THERE
IS STILL SOME UNCERTAINTY OVER THE EXACT MOISTURE COVERAGE. THEN
UPPER TROUGHING AND POTENTIAL SURFACE DEVELOPMENT MAY PRODUCE SOME
PRECIPITATION OVER THE NORTHEAST FROM LATE WEEK THROUGH THE
WEEKEND. MOST OF THIS PRECIPITATION SHOULD BE SNOW, BUT SOME RAIN
COULD BE POSSIBLE DEPENDING ON DETAILS WHICH REMAIN FAIRLY
UNCERTAIN.
THE NORTHERN-CENTRAL PLAINS INTO THE MIDWEST AND GREAT LAKES
SHOULD SEE THE MOST CONSISTENTLY ABOVE NORMAL TEMPERATURES DURING
THE PERIOD, WITH NORTHERN AREAS SEEING THE BEST POTENTIAL FOR
MULTIPLE DAYS OF MORNING LOWS UP TO 20-30F ABOVE NORMAL AND HIGHS
UP TO 15-25F ABOVE NORMAL. SOME DAILY RECORDS WILL BE POSSIBLE,
PRIMARILY FOR WARM LOWS. THE WEST WILL BE WARM INTO MIDWEEK WITH
LESS EXTREME ANOMALIES, GENERALLY UP TO PLUS 10-20F AND ESPECIALLY
FOR MORNING LOWS WHICH COULD HOLD ABOVE SOME DAILY RECORDS. THE
UPPER TROUGH MOVING IN WILL BRING A COOLING TREND FOR THE LATTER
HALF OF THE WEEK THROUGH NEXT WEEKEND WITH HIGHS OVER PORTIONS OF
CALIFORNIA AND SOUTHWEST U.S. UP TO 10-15F BELOW NORMAL
FRIDAY-SUNDAY. THE ABOVE NORMAL MIN TEMPERATURES WILL TAKE AN
EXTRA DAY OR SO TO TREND TOWARD NORMAL. OVER THE EAST, THE
SOUTHERN PART OF THE FLORIDA PENINSULA MAY SEE TEMPERATURES UP TO
A FEW DEGREES BELOW NORMAL MID-LATE WEEK BUT OTHERWISE EXPECT NEAR
TO ABOVE NORMAL TEMPERATURES. THERE IS CONTINUED UNCERTAINTY FOR
HIGHS OVER THE NORTHEAST BY NEXT WEEKEND, DEPENDING ON THE DEPTH
AND LOCATION OF UPPER TROUGHING AND A POSSIBLE EMBEDDED CLOSED
LOW. THERE IS BETTER CONFIDENCE IN ABOVE NORMAL MORNING LOWS OVER
THIS REGION.
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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