607
FXUS02 KWBC 051901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST MON FEB 05 2024
VALID 12Z THU FEB 08 2024 - 12Z MON FEB 12 2024
..OVERVIEW
A BROAD RELOADING UPPER TROUGH SHOULD HOLD ON OVER THE WEST INTO
SATURDAY, BEFORE BEGINNING TO SLOWLY SHIFT EASTWARD AS UPPER
RIDGING TRIES TO BUILD IN NEAR THE WEST COAST NEXT SUNDAY-MONDAY.
THE TROUGH WILL KEEP THIS REGION QUITE ACTIVE WITH ROUNDS OF LOWER
ELEVATION RAINS AND MOUNTAIN SNOW, INCLUDING POSSIBLY A COUPLE OF
WEAK ATMOSPHERIC RIVERS INTO CALIFORNIA. PRECIPITATION IS
CERTAINLY FORECAST TO BE LOWER THAN IN THE SHORT RANGE THOUGH.
MEANWHILE, A STRONG UPPER RIDGE SHIFTING OUT OF THE CENTRAL U.S.
WILL CONTINUE TO SUPPORT WELL ABOVE NORMAL TEMPERATURES THAT COULD
BE RECORD-SETTING ACROSS THE PARTS OF THE UPPER MIDWEST ON
THURSDAY-FRIDAY BEFORE IT BECOMES SUPPRESSED AND SHIFTS EASTWARD
WITH TIME. A FAIRLY STRONG STORM SYSTEM TRACKING OUT OF THE
NORTHERN PLAINS/UPPER MIDWEST THURSDAY ONWARD WILL PRODUCE SOME
COLD SECTOR SNOW AND BRISK WINDS. THEN ADDITIONAL
SHORTWAVES/ENERGY FROM THE MEAN UPPER TROUGH OVER THE WEST WILL
PERIODICALLY EJECT INTO THE CENTRAL U.S. THERE IS SIGNIFICANT
UNCERTAINTY OVER HOW ASSOCIATED SYSTEMS WILL REFLECT AT THE
SURFACE TO THE EAST OF THE ROCKIES, BUT THE GENERAL PATTERN
APPEARS FAVORABLE FOR INCREASING RAINFALL ACROSS THE
MID-SOUTH/SOUTHEAST BY LATE WEEK OR WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
SHORTWAVE DIFFERENCES WITHIN THE WESTERN U.S. UPPER TROUGH
CONTINUE TO ARISE FAIRLY EARLY IN THE PERIOD. MODEL/ENSEMBLE
SPREAD EVENTUALLY BECOMES COMPOUNDED BY DIFFERENCES WITH A COUPLE
PACIFIC SHORTWAVES THAT MAY TRY TO PASS AROUND OR THROUGH THE MEAN
RIDGE NEARING THE WEST COAST, ONE POSSIBLY APPROACHING THE PACIFIC
NORTHWEST/WESTERN CANADA AROUND SATURDAY AND ANOTHER BY MONDAY.
LATEST GFS RUNS SHEAR OUT THE FIRST PACIFIC SHORTWAVE MORE THAN
OTHER GUIDANCE WHILE THERE IS LITTLE COHERENCE AMONG GUIDANCE FOR
THE SECOND, WITH THE MEANS SHOWING A VAGUE HINT OF A WEAKENING
SHORTWAVE. DOWNSTREAM OVER THE LOWER 48, GUIDANCE DIVERGES FOR THE
CHARACTER OF ENERGY EJECTING FROM THE WEST AND THUS VARIES AMONG
EACH OTHER AND FROM RUN TO RUN FOR THE SURFACE EVOLUTION. THE 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS ALSO VARY FOR THE
DETAILS, HIGHLIGHTING THE RELATIVELY LOW PREDICTABILITY OF SOME
ASPECTS OF THIS OVERALL PATTERN, BUT GENERALLY FAVOR REASONABLE
PROGRESSION OF THE NORTHERN STREAM FLOW AND SUPPRESSED TRAILING
FRONTAL WAVINESS ACROSS THE SOUTHERN TIER IN RESPONSE TO A
MODERATELY SLOW SHORTWAVE EJECTING FROM THE WEST BUT NO PHASING
WITH THE NORTHERN STREAM. THIS SURFACE PATTERN IS CLOSEST IN
PRINCIPLE TO THE ENSEMBLE MEANS AND 00Z ECMWF LATE IN THE PERIOD.
HOWEVER THE 12Z CMC/ECMWF NOW SHOW MORE PHASING ALOFT AND BRING
THE TRAILING SYSTEM INTO THE OHIO VALLEY/GREAT LAKES LATE IN THE
PERIOD--A SCENARIO THAT HAS APPEARED IN ONE OR MORE PRIOR
OPERATIONAL MODEL RUNS.
GIVEN THE LOWER THAN AVERAGE CONFIDENCE IN THE FORECAST, THE
OPERATIONAL MODEL BLEND EMPLOYED EARLY IN THE PERIOD (WHICH
ALREADY BLENDS OUT THE LOWEST-PREDICTABILITY SHORTWAVE DETAILS)
TRANSITIONED TOWARD THREE-FOURTHS GEFS/ECENS MEAN WEIGHT WITH
LINGERING 00Z ECMWF INPUT BY THE END OF THE PERIOD NEXT MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
GENERAL BROAD TROUGHING OVER THE SOUTHWEST SHOULD KEEP THE WESTERN
U.S. PERIODICALLY ACTIVE WITH WIDESPREAD LOWER ELEVATION
RAIN/MOUNTAIN SNOWS INTO NEXT WEEKEND. BEST SNOW POTENTIAL SHOULD
BE OVER THE FAVORED TERRAIN OF THE FOUR CORNERS STATES. ADDITIONAL
ROUNDS OF RAIN AND MOUNTAIN SNOWS COULD COME INTO CALIFORNIA
THURSDAY-FRIDAY, THOUGH WITH VERY LOW CONFIDENCE ON EXACT AMOUNTS
AND LOCATIONS OF HEAVIEST PRECIPITATION. GIVEN EXTREME RAINFALL
ACROSS MUCH OF CALIFORNIA RECENTLY, THE AREA IS MORE SENSITIVE
THAN USUAL TO ADDITIONAL RAINFALL, BUT THE FACT THAT ANY DIGGING
DYNAMICS ALOFT SHOULD TAKE AN ALONG-COAST OR INLAND PATH SHOULD
REDUCE THE HEAVY PRECIPITATION THREAT. GUIDANCE SPREAD FOR
SHORTWAVE DETAILS ALOFT AND RESULTING QPF KEEPS CONFIDENCE TOO LOW
TO DEPICT ANY RISK AREAS IN THE DAYS 4-5 EXCESSIVE RAINFALL
OUTLOOKS VALID FROM THURSDAY THROUGH FRIDAY NIGHT. PRECIPITATION
MAY CLEAR OUT OF MUCH OF THE INTERMOUNTAIN WEST BY SATURDAY, BUT
ONE OR MORE PROGRESSIVE SYSTEMS COULD BRING EPISODES OF LIGHT TO
MODERATE TOTALS TO THE PACIFIC NORTHWEST.
FAIRLY STRONG LOW PRESSURE TRACKING NORTHEASTWARD FROM THE
NORTHERN PLAINS SHOULD PRODUCE AN AREA OF MEANINGFUL SNOW TO THE
WEST OF THE STORM TRACK THIS THURSDAY, WITH BEST POTENTIAL FOR AT
LEAST 0.25 INCH LIQUID IN THE FORM OF SNOW OVER EASTERN MONTANA
THROUGH NORTH DAKOTA. WINDS COULD BE STRONG ENOUGH TO PRODUCE SOME
BLOWING AND DRIFTING OF THE SNOW. THE TRAILING COLD FRONT SHOULD
FOCUS MOISTURE AND SOME WEAK INSTABILITY TO PRODUCE RAIN ACROSS
THE MID-SOUTH. RAIN RATES AND AMOUNTS ON THURSDAY DO NOT LOOK HIGH
ENOUGH TO CAUSE FLOODING ISSUES GIVEN FAIRLY PROGRESSIVE MOVEMENT.
HOWEVER FROM FRIDAY INTO THE WEEKEND, SHORTWAVE ENERGY DIGGING
INTO THE SOUTHWEST COULD HELP TO SLOW DOWN THE CENTRAL/SOUTHERN
PART OF THE FRONT (WHICH MAY HAVE EMBEDDED WAVES) FOR A TIME AND
LEAD TO INCREASED POTENTIAL FOR TRAINING/REPEATING OF SHOWERS AND
THUNDERSTORMS OVER SOME AREAS. THERE IS A LOT OF SPREAD FOR THE
SHORTWAVE DETAILS AMONG THE GUIDANCE, WITH CORRESPONDING
DISPERSION IN LOCATION/MAGNITUDE/TIME FRAME OF HEAVIEST RAINFALL.
ENSEMBLES SUGGEST THE PRIMARY REGION THAT REQUIRES MONITORING
EXTENDS FROM THE TENNESSEE VALLEY INTO LOWER MISSISSIPPI VALLEY
AND SOUTHEAST. THIS OVERALL AREA HAS A MIX OF ANTECEDENT SOIL
MOISTURE CONDITIONS. CONFIDENCE REMAINS TOO LOW TO INTRODUCE ANY
RISK AREAS IN THE DAYS 4-5 EROS AT THIS TIME, BUT AGAIN THE
GENERAL PATTERN MAY ULTIMATELY SUPPORT A HEAVY RAINFALL EVENT
SOMETIME IN THE LATE WEEK/WEEKEND TIME FRAME. MEANWHILE, THE FAR
NORTHERN FRINGE OF THE SOUTHERN TIER MOISTURE SHIELD COULD PRODUCE
SOME SNOW FROM THE WEEKEND INTO EARLY NEXT WEEK.
THE UPPER RIDGE PROGRESSING FROM THE EASTERN U.S. INTO THE WESTERN
ATLANTIC LATE THIS WEEK WILL SUPPORT A BROAD AREA OF UNSEASONABLY
WARM TEMPERATURES WHICH WILL GRADUALLY SHIFT FROM THE
PLAINS/MISSISSIPPI VALLEY/GREAT LAKES TOWARD THE EAST COAST.
DEPARTURES FROM NORMAL SHOULD EVENTUALLY BECOME SOMEWHAT LESS
EXTREME WITH TIME. THE UPPER MIDWEST/GREAT LAKES SHOULD BE WARMEST
VERSUS NORMAL THURSDAY-FRIDAY WITH ANOMALIES UP TO PLUS 30-35F FOR
MORNING LOWS AND PLUS 20-30F FOR DAYTIME HIGHS, LEADING TO
WIDESPREAD DAILY TEMPERATURE RECORDS. BY THE WEEKEND EXPECT THE
EAST TO SEE LOWS OF 15-30F ABOVE NORMAL AND HIGHS 10-20F ABOVE
NORMAL WHILE THE CENTRAL U.S. TRENDS CLOSER TO NORMAL. IN
CONTRAST, THE SOUTHWEST U.S./CALIFORNIA SHOULD BE PERSISTENTLY
COOL, ESPECIALLY FOR DAYTIME HIGHS THAT MAY BE UP TO 10-15F BELOW
NORMAL INTO THE WEEKEND. THIS REGION SHOULD BEGIN TO SEE A
MODERATING TREND BY SUNDAY OR MONDAY. CLOUDS/PRECIPITATION OVER
THE WEST SHOULD KEEP MOST MORNING LOWS WITHIN A FEW DEGREES ON
EITHER SIDE OF NORMAL BUT A FEW LOCALIZED COOLER SPOTS ARE
POSSIBLE.
RAUSCH/SANTORELLI
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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