281
FXUS02 KWBC 300700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST TUE JAN 30 2024
VALID 12Z FRI FEB 02 2024 - 12Z TUE FEB 06 2024
...LATE WEEK INTO WEEKEND SYSTEM TO SPREAD SIGNIFICANT
PRECIPITATION ACROSS MUCH OF THE WEST AND THEN THE PLAINS AND GULF
COAST/SOUTHEAST...
...ANOTHER STRONG WEATHER SYSTEM INCREASINGLY LIKELY TO IMPACT
CALIFORNIA LATE THIS WEEKEND INTO EARLY NEXT WEEK...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW AN EVOLVING OMEGA BLOCK PATTERN ALOFT,
WITH VARYING DEGREES OF MEAN TROUGHING ALONG OR OFFSHORE THE WEST
COAST AND OVER THE CANADIAN MARITIMES WHILE AN UPPER RIDGE
PREVAILS OVER THE UPPER MIDWEST/GREAT LAKES. THERE WILL BE THE
ADDED WRINKLE OF LATE WEEK WESTERN U.S. UPPER TROUGH ENERGY
BREAKING OFF AN UPPER LOW THAT TRACKS ACROSS THE SOUTHERN TIER
DURING THE WEEKEND INTO EARLY NEXT WEEK. THE LARGE SCALE PATTERN
WILL PROMOTE EPISODES OF SIGNIFICANT PRECIPITATION AND POTENTIALLY
OTHER ACTIVE WEATHER ACROSS THE WEST, WITH HIGHEST TOTALS LIKELY
TO BE OVER CALIFORNIA WITH A LATE WEEKEND INTO EARLY NEXT WEEK
SYSTEM AND THE SOUTHERN TIER WITH THE SYSTEM CROSSING THE REGION
DURING THE WEEKEND. MEANWHILE, THE FORECAST PATTERN WOULD SUPPORT
PERSISTENCE OF MUCH ABOVE NORMAL TEMPERATURES OVER THE UPPER
MIDWEST AND VICINITY IN CONTRAST TO COOL DAYTIME HIGHS OVER THE
SOUTHWEST/CALIFORNIA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AS HAS BEEN THE CASE OVER RECENT DAYS, MOST GUIDANCE SHARES
GENERAL THEMES FOR THE LARGE SCALE PATTERN BUT WITH SOME EMBEDDED
SPREAD AND RUN-TO-RUN ADJUSTMENTS. ONE NOTABLE TREND OVER THE
PAST DAY HAS BEEN FOR GUIDANCE TO SHIFT EASTWARD SOMEWHAT FOR THE
UPPER MIDWEST/GREAT LAKES RIDGE AND DOWNSTREAM TROUGH/POTENTIAL
EMBEDDED UPPER LOW, WITH THE LATTER NOW MORE LIKELY SETTLING OVER
OR NEAR THE CANADIAN MARITIMES INSTEAD OF NEW ENGLAND. THE
ECMWF-INITIALIZED MACHINE LEARNING MODELS THAT HAD INITIALLY BEEN
MOST AGGRESSIVE WITH THE NORTHEAST TROUGHING/LOW HAVE ALSO SHIFTED
EASTWARD SOME, BUT THEIR 12Z CYCLE STILL OFFERS SOME POTENTIAL FOR
TROUGHING TO LINGER IN MORE AMPLIFIED FORM THAN MOST DYNAMICAL
GUIDANCE BY EARLY NEXT WEEK. MEANWHILE THE GUIDANCE HAS BEEN
WAFFLING FOR THE PRECISE LATITUDE AND SPEED OF THE UPPER LOW AND
ASSOCIATED SURFACE SYSTEM CROSSING THE SOUTHERN TIER. CONSENSUS
OF 12Z/18Z MODELS AND ENSEMBLES HAS RETURNED BACK TO WHERE IT WAS
TWO DAYS AGO AFTER DRIFTING A LITTLE SOUTH FOR A TIME. THE NEW
00Z GFS/UKMET STRAY ON THE FASTER AND SOUTHERN SIDE OF THE SPREAD.
WHAT BECOMES OF THIS SYSTEM UPON REACHING THE WESTERN ATLANTIC
EARLY NEXT WEEK IS STILL SOMEWHAT UNCERTAIN GIVEN THE SPREAD AND
INCONSISTENCY FOR TROUGHING TO THE NORTH. ALONG THE WEST COAST,
RECENT DAYS OF MODEL RUNS HAVE VARIED FOR EVOLUTION OF LOW
PRESSURE OFF THE PACIFIC NORTHWEST. CURRENTLY THE GFS/ECMWF/UKMET
AND ENSEMBLE MEANS CLUSTER TOWARD A SOUTHWARD DRIFT FRIDAY INTO
THE WEEKEND WITH THE CMC TRENDING WEAKER/EASTWARD. THEN THERE IS A
FAIRLY GOOD CONSENSUS TOWARD POSITIVELY TILTED UPPER TROUGHING
COMPOSED OF LINGERING PACIFIC NORTHWEST COAST TROUGHING AND AN
INCOMING SOUTHERN STREAM PACIFIC FEATURE. DETAILS ARE STILL VERY
MURKY HOWEVER, SO CONFIDENCE REMAINS QUITE LOW REGARDING THE
STRENGTH AND TRACK OF ASSOCIATED LOW PRESSURE THAT COULD BE QUITE
DEEP/NORTH (GFS/ECMWF) OR SLOWER (PER CMC RUNS THAT HAVE BEEN
SHOWING LESS PHASING ALOFT). ECMWF-INITIALIZED MACHINE LEARNING
MODELS HAVE BEEN FAVORING THE FASTER SIDE OF THE SPREAD FOR THE
PRIMARY SURFACE SYSTEM. AT THIS POINT PREFERENCES FAVOR AN
INTERMEDIATE SOLUTION UNTIL BETTER CLUSTERING EMERGES.
12Z/18Z GUIDANCE COMPARISONS LED TO A STARTING BLEND OF MORE
12Z/18Z GFS/12Z ECMWF RELATIVE TO THE UKMET/CMC EARLY IN THE
PERIOD AND THEN TRANSITIONING TO SOME 18Z GEFS/12Z ECENS MEAN
INPUT WHILE PHASING OUT WHAT MINORITY COMPONENT OF THE CMC THERE
WAS EARLIER ON.
..WEATHER/HAZARDS HIGHLIGHTS
THE LEADING UPPER TROUGH MOVING INTO THE WEST WILL PRODUCE A BROAD
AREA OF RAIN AND HIGHER ELEVATION SNOW, WITH SIGNIFICANT
ACCUMULATIONS POSSIBLE FRIDAY-SATURDAY OVER MUCH OF THE NORTHERN
AND CENTRAL ROCKIES. THERE WILL ALSO BE SOME LINGERING
PRECIPITATION CLOSER TO THE WEST COAST DURING THAT TIME. THE
UPPER LOW BREAKING OFF FROM THE SOUTHERN PART OF THE TROUGH ALONG
WITH THE ASSOCIATED SURFACE SYSTEM MAY LEAD TO A PERIOD OF
EASTERLY PRECIPITATION ENHANCEMENT ALONG THE CENTRAL ROCKIES, AND
SHOULD BEGIN TO GENERATE RAIN AND THUNDERSTORMS OVER THE SOUTHERN
PLAINS BY FRIDAY OR FRIDAY NIGHT WITH LIGHTER TOTALS EXTENDING
INTO THE CENTRAL PLAINS. EASTWARD PROGRESSION OF THE SYSTEM OVER
THE WEEKEND WILL SPREAD SOME HEAVY RAINFALL ACROSS THE GULF COAST
AND SOUTHEAST. THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK COVERING
FRIDAY-FRIDAY NIGHT MAINTAINS THE PRIOR DAY 5 MARGINAL RISK AREA
COVERING MOST OF THE EASTERN HALF OF TEXAS INTO PARTS OF OKLAHOMA,
WITH GUIDANCE CONTINUING TO SIGNAL POTENTIAL FOR LOCALLY HEAVY
(THOUGH NOT EXCEPTIONAL) RAINFALL. THEN THE DAY 5 ERO DEPICTS A
SLIGHT RISK AREA ALONG THE CENTRAL GULF COAST WHERE THE BEST
INSTABILITY AND ENSEMBLE PROBABILITIES OF HIGHEST RAINFALL TOTALS
OVERLAP, WITH OPERATIONAL MODEL RUNS SHOWING HEAVY RAINFALL
POTENTIAL AS WELL. THE SURROUNDING MARGINAL RISK AREA EXTENDS
NORTH-NORTHWEST INTO SOUTHWESTERN MISSOURI AND SOUTHEASTERN
KANSAS, FOR LESS EXTREME RAINFALL TOTALS BUT WITH GROUND
CONDITIONS STARTING OUT ON THE DAMP SIDE. HEAVY RAINFALL
POTENTIAL SHOULD CONTINUE EASTWARD INTO THE SOUTHEAST/CAROLINAS BY
EARLY NEXT WEEK.
THE DETAILS REMAIN VERY UNCERTAIN BUT THE OVERALL FORECAST PATTERN
CONTINUES TO SHOW THE POTENTIAL FOR A SIGNIFICANT ATMOSPHERIC
RIVER EVENT TO AFFECT CALIFORNIA FROM AROUND SUNDAY INTO EARLY
NEXT WEEK. THERE ARE ALSO SOME SIGNALS THAT THE ASSOCIATED
SURFACE SYSTEM COULD BE FAIRLY STRONG, WHICH WOULD PRODUCE A
PERIOD OF STRONG WINDS. 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.
THE PERSISTENT UPPER RIDGE OVER AND NEAR THE UPPER MIDWEST WILL
SUPPORT A CORE OF PERSISTENTLY WELL ABOVE NORMAL TEMPERATURES OVER
THAT PART OF THE COUNTRY. RECENT GUIDANCE ADJUSTMENTS FOR
SPECIFICS OF THE UPPER PATTERN HAVE INCREASED POTENTIAL
TEMPERATURE ANOMALIES, WITH MORNING LOWS POSSIBLY AS WARM AS
25-35F ABOVE NORMAL EXCEEDING DAILY RECORDS FOR MULTIPLE DAYS.
EXPECT DAYTIME HIGHS TO BE LESS EXTREME, UP TO 15-25F ABOVE
NORMAL. SOME OF THIS WARMTH, ESPECIALLY FOR MORNING LOWS, WILL
EXTEND ACROSS A MUCH BROADER AREA BETWEEN THE ROCKIES AND
APPALACHIANS. IN CONTRAST THE SOUTHWEST U.S./CALIFORNIA SHOULD
SEE COOL DAYTIME HIGHS THROUGH THE PERIOD WITH SOME LOCATIONS UP
TO 10-15F BELOW NORMAL. CLOUDS/PRECIPITATION OVER THE WEST SHOULD
KEEP MORNING LOWS NEAR TO ABOVE NORMAL.
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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