498
FXUS02 KWBC 060704
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST TUE FEB 06 2024
VALID 12Z FRI FEB 09 2024 - 12Z TUE FEB 13 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 AGAIN AND A COUPLE
OF STRONG SYSTEMS PUSH THROUGH THE EAST PACIFIC. THE TROUGH WILL
CONTINUE TO KEEP THIS REGION QUITE ACTIVE WITH ROUNDS OF LOWER
ELEVATION RAINS AND MOUNTAIN SNOW, INCLUDING POSSIBLY A COUPLE OF
WEAK ATMOSPHERIC RIVERS INTO THE WEST COAST. 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 GREAT LAKES-NORTHEAST
ON FRIDAY-SATURDAY BEFORE IT BECOMES SUPPRESSED AND SHIFTS
EASTWARD OFF THE COAST. A FAIRLY STRONG STORM SYSTEM TRACKING OUT
OF THE GREAT LAKES ON FRIDAY 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 WESTER U.S. UPPER TROUGH AND HOW
THE TROUGH EVOLVES AND EVENTUALLY PUSHES EASTWARD CONTINUES TO
PRESENT THE MOST UNCERTAINTY DURING THE MEDIUM RANGE PERIOD. AS
EARLY AS FRIDAY-SATURDAY, THERE ARE NOTABLE DIFFERENCES IN
SHORTWAVE ENERGY THAT DIGS SOUTHWARD ALONG THE WEST COAST AND HOW
THAT BECOMES ABSORBED INTO THE MEAN TROUGH. MODELS HAVE SHOWN
BETTER AGREEMENT FOR A MUCH MORE AMPLIFIED (WITH A POSSIBLE BRIEF
CLOSED LOW) OVER THE SOUTHWEST THIS COMING WEEKEND, BUT AS THAT
SOUTHERN STREAM ENERGY MOVES INTO THE SOUTH-CENTRAL PLAINS AND
POSSIBLY INTERACTS WITH NORTHERN STREAM ENERGY DROPPING OUT OF
CENTRAL CANADA PRESENTS SIGNIFICANT UNCERTAINTY IN THE PATTERN
EVOLUTION ACROSS THE MIDWEST/EAST EARLY NEXT WEEK. THROUGH THE NEW
00Z RUN TONIGHT, THE GFS SHOWS DISTINCT SEPARATION BETWEEN THE TWO
SYSTEMS, WITH THE NORTHERN STREAM SYSTEM OUT RUNNING THE SOUTHERN
STREAM AND A STRONG LOW PRESSURE SYSTEM THAT TRACKS ACROSS THE
SOUTHEAST AND EVENTUALLY OFF THE MID-ATLANTIC COAST. PRIOR RUNS OF
THE ECMWF AND CMC ON THE OTHER HAND SHOWED MORE INTERACTION IN THE
TWO STREAMS RESULTING IN A SHARP SHORTWAVE/AMPLFIED TROUGH AND
STRONG SURFACE LOW THAT TRACKS NORTHWARD INTO THE MIDWEST AND OFF
THE NORTHEAST COAST AT THE SAME TIME. HOWEVER, THE NEW 00Z RUNS
(AVAILABLE AFTER WPC FORECAST GENERATION) TONIGHT CAME MORE IN
LINE WITH THE GFS SCENARIO (THOUGH WILDLY DIFFERENT IN TIMING OF
THE SYSTEM). STILL TOO EARLY TO SUGGEST THIS MAY BE A TREND, BUT
IT WILL NEED TO BE WATCHED AS IT WOULD HAVE SENSIBLE WEATHER
IMPACTS. BOTH THE GEFS AND ECENS ENSEMBLES SHOW A LOT OF
UNCERTAINTY, WITH THE RESULTING MEAN FORECAST QUITE WEAK AND
WASHED OUT. GIVEN THE UNCERTAINTY, THE WPC LATE PERIOD FORECAST
USED A BLEND OF THE ENSEMBLE MEANS, WITH SOME ATTEMPTS TO ADD A
LITTLE SYSTEM DEFINITION FROM YESTERDAYS 12Z ECMWF. THIS DID
RESULT IN NOTICEABLE CHANGES TO PREVIOUS WPC CONTINUITY, WITH THE
DEPICTION OF A MORE DEFINED WAVE/SYSTEM GIVEN THE BETTER MODEL
SUPPORT. EITHER WAY, A VERY LOW CONFIDENCE FORECAST ACROSS THE
EASTERN THIRD OF THE COUNTRY EARLY NEXT WEEK WITH PLENTY OF TIME
FOR MODEL SWINGS AND VARIABILITY.
ELSEWHERE, THERE IS A LOT OF UNCERTAINTY AS WELL WITH POTENTIAL
FOR A COUPLE OF WEAKER SHORTWAVES TO IMPACT THE WEST COAST
SUNDAY-TUESDAY, BUT QUESTIONS ARISE WITH HOW MUCH THESE ARE ABLE
TO DISRUPT/GET THROUGH THE OVERALL MEAN RIDGE THAT TRIES TO BUILD
BACK IN OVER THE WEST. A BLEND OF THE ENSEMBLE MEANS HELPED TO
SMOOTH OUT THESE DIFFERENCES AND WAS A GOOD STARTING POINT FOR THE
FORECAST OUT WEST LATE PERIOD.
..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
THROUGH 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 ON THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
VALID ON FRIDAY. 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 WILL BE TRACKING OUT OF THE GREAT LAKES
ON FRIDAY, THOUGH WITH STILL SOME LINGERING SNOW AND GUSTY WIND
THREAT ON THE BACKSIDE OF THE SYSTEM. THE TRAILING COLD FRONT
SHOULD FOCUS MOISTURE AND SOME WEAK INSTABILITY TO PRODUCE RAIN
ACROSS THE MID-SOUTH, ESPECIALLY INTO THE WEEKEND AIDED BY
SHORTWAVE ENERGY OUT OF THE SOUTHWEST. THIS MAY INCREASE POTENTIAL
FOR TRAINING/REPEAT SHOWERS AND THUNDERSTORMS OVER SOME AREAS, BUT
WITH STILL A LOT OF SPREAD IN THE DETAILS AND CORRESPONDING
LOCATION/MAGNITUDE/TIMING OF THE 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. DESPITE THE PRESENCE OF ANAMOLOUS MOISTURE AND SOME
INSTABILITY, CONFIDENCE REMAINS TOO LOW THOUGH 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 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, BUT HIGHLY UNCERTAIN
AND DEPENDENT ON THE EXACT TRACK OF THE VERY UNCERTAIN LOW
PRESSURE SYSTEM OUT OF THE SOUTH-CENTRAL STATES.
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 GREAT
LAKES/MIDWEST 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 ON 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.
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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