639
FXUS02 KWBC 051857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 PM EST TUE MAR 05 2024
VALID 12Z FRI MAR 08 2024 - 12Z TUE MAR 12 2024
...WET PATTERN FOR PARTS OF THE EASTERN U.S., ESPECIALLY ACROSS
THE SOUTH...
...MULTI-DAY UNSETTLED PERIOD ALONG THE NORTHERN-CENTRAL WEST
COAST STARTING LATE THIS WEEK...
..OVERVIEW
ONE PROMINENT FOCUS OF THE FORECAST WILL BE ON AN UPPER TROUGH
TRACKING OUT OF THE ROCKIES ON FRIDAY, SUPPORTING A VIGOROUS
SURFACE SYSTEM THAT WILL SPREAD A BROAD AREA OF MOISTURE ACROSS
THE EASTERN HALF OF THE COUNTRY FROM LATE THIS WEEK THROUGH THE
WEEKEND AFTER PRODUCING SOME SNOW/LOW ELEVATION RAIN OVER THE
SOUTHERN HALF OF THE ROCKIES. THE BEST POTENTIAL FOR SNOW WITH
THIS EASTERN U.S. SYSTEM WILL BE OVER NEW ENGLAND BY THE WEEKEND.
THERE WILL BE A BROADENING DRIER TREND WITH TIME BEHIND THIS
SYSTEM. MEANWHILE A MEAN TROUGH ALOFT SETTING UP NEAR THE WEST
COAST WILL BRING A SERIES OF SHORTWAVES AND SURFACE FRONTS INTO
THE REGION, LEADING TO PERSISTENT RAIN/HIGHER ELEVATION SNOW ALONG
THE NORTHERN-CENTRAL WEST COAST LATE THIS WEEK INTO NEXT WEEK.
SOME OF THE MOISTURE FROM THESE SYSTEMS WILL LIKELY REACH THE
NORTHERN ROCKIES BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MOST CONSEQUENTIAL AREA OF UNCERTAINTY IN THE MEDIUM RANGE IS
AT THE BEGINNING OF THE PERIOD OVER THE SOUTHEAST. SMALL
DIFFERENCES IN THE 500MB PATTERN OVER THE PLAINS/MISSISSIPPI
VALLEY IS REFLECTED IN THE VARIOUS MODELS' QPF AXES OVER THE
SOUTHEAST ON DAYS 3/4. THE 00Z UKMET AND CMC BOTH HAVE SHORTWAVE
ENERGY AMPLIFYING NOTABLY MORE THAN THE OTHER GUIDANCE OVER THE
MISSISSIPPI VALLEY ON DAY 4. THUS A GENERAL MODEL BLEND FAVORING
THE 00Z EURO AND 06Z GFS WITH LESS WEIGHTING FOR THE 00Z CMC AND
UKMET WAS UTILIZED FOR DAYS 3 AND 4.
THE 00Z EURO AND 06Z GFS DETERMINISTIC AND ENSEMBLE MEANS WERE
FAVORED WITH SOME 00Z CANADIAN SPRINKLED IN ON DAY 5 SINCE THEY
ALL CLUSTERED FAIRLY WELL AROUND A PHASING SOLUTION FOR THE
NORTHERN AND SOUTHERN STREAMS. THE EVOLUTION OF AN EAST PAC TROUGH
PROPAGATING THROUGH THE GULF OF ALASKA THIS WEEKEND IS STILL VERY
MUCH IN FLUX WITH PLENTY OF SPREAD IDENTIFIED BY THE ENSEMBLE
GUIDANCE. IN FACT THE ECE SEEMS TO BE THE ONLY ENSEMBLE TO DEPICT
A TROUGH WHILE THE GEFS AND CMCE HAVE A ZONAL PATTERN PRESENT. A
BLEND FAVORING THE 06 GFS/GEFS IS USED WITH SOME LESSER WEIGHTED
00Z EC/ECE/CMC/CMCE USED ON DAY 6 DUE THE CONTINUED UNCERTAINTY
AROUND THIS EAST PAC EVOLUTION. THERE'S REASONABLE AGREEMENT WITH
RESPECT TO THE DEEP UPPER LOW OVER THE NORTHEAST ON DAY 6. THINGS
TEND TO AMPLIFY ENOUGH IN THE GEFS AND CMCE MEANS TO SUGGEST A
TROUGH WILL BE PRESENT OVER THE WEST COAST BY DAY 7, ALTHOUGH
THERE REMAINS PLENTY OF SPREAD AMONG THE CANADIAN ENSEMBLE MEMBERS.
..WEATHER/HAZARDS HIGHLIGHTS
WHILE SOME DETAILS ARE YET TO BE RESOLVED, CONFIDENCE REMAINS HIGH
IN THE GENERAL THEME OF AN ACTIVE WEATHER PATTERN OVER EASTERN
HALF OF THE COUNTRY FROM LATE THIS WEEK INTO THE WEEKEND, AND
LIKELY CONTINUING INTO NEXT MONDAY OVER THE NORTHEAST. THE
COMBINATION OF UPPER TROUGHING THAT EMERGES FROM THE WEST AND
SEPARATE NORTHERN TIER ENERGY MAY SUPPORT ONE OR TWO VIGOROUS
SURFACE WAVES TRACKING FROM THE CENTRAL U.S. INTO THE
EAST/NORTHEAST FROM LATE THIS WEEK THROUGH THE WEEKEND. SURFACE
LOW PRESSURE SHOULD CONSOLIDATE INTO A STORM SYSTEM NEAR NEW
ENGLAND BY MONDAY AND THEN DEPART TO THE EAST. AS THE PLAINS
SYSTEM (WHETHER THE PRIMARY LOW OR THE SOUTHERN OF TWO WAVES)
TRACKS EAST/NORTHEAST BY FRIDAY-FRIDAY NIGHT AND LIFTS A LEADING
WARM FRONT NORTHWARD (WITH INTERACTING MOISTURE/INSTABILITY),
GUIDANCE IS PERSISTENT WITH ITS HEAVY RAINFALL SIGNAL OVER PARTS
OF THE SOUTH/SOUTHEAST. THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK
HAS A HIGHER-END SLIGHT RISK AREA COVERING LOCATIONS FROM AROUND
THE CENTRAL GULF COAST REGION INTO FAR WESTERN SOUTH CAROLINA,
WITH THE ONLY ADJUSTMENT FROM THE PRIOR DAY 5 ERO BEING TO EXPAND
THE NORTHWESTERN PART OF THE AREA A BIT PER GUIDANCE SIGNALS. THE
NORTHWESTERN PART OF THE SURROUNDING MARGINAL RISK AREA CONTINUES
TO ACCOUNT FOR A SIGNAL IN SOME OF THE GUIDANCE FOR A SECONDARY
AXIS OF ENHANCED RAINFALL FROM THE SOUTH-CENTRAL PLAINS
NORTHEASTWARD, NEAR THE SURFACE LOW TRACK. MEANINGFUL RAINFALL
COULD EXTEND FARTHER NORTH/NORTHEAST OF THE CURRENT MARGINAL RISK
AREA BUT IN THE ABSENCE OF INSTABILITY IN THE GUIDANCE THUS FAR.
DURING THE SATURDAY-SATURDAY NIGHT PERIOD COVERED BY THE DAY 5
ERO, GUIDANCE SHOWS ONE AREA OF ENHANCED RAINFALL POTENTIAL OVER
THE SOUTHEAST, REFLECTING EASTWARD CONTINUATION OF CONVECTION FROM
THE PREVIOUS 24 HOURS. THUS FAR THERE HAS BEEN SOME SPREAD AND
VARIABILITY FOR THE TIMING AND DETAILS OF CONVECTION (WITH
ECMWF/ECENS RUNS BEING SLOWEST) SO INITIALLY INTRODUCED A MARGINAL
RISK AREA WITH THE EXPECTATION THAT AN EMBEDDED SLIGHT RISK MAY
ARISE ONCE GUIDANCE CLUSTERING IMPROVES. THERE IS ANOTHER AREA OF
ENHANCED RAINFALL POTENTIAL ACROSS PARTS OF THE OHIO VALLEY/LOWER
GREAT LAKES/NORTHERN MID-ATLANTIC, BUT WITH LESS INSTABILITY
SUGGESTED. A MARGINAL RISK AREA OVER THIS REGION ACCOUNTS FOR A
COMBINATION OF MODEL QPF SIGNALS, AND OVER THE MID-ATLANTIC WET
GROUND CONDITIONS FROM SHORTER-TERM RAINFALL. A FEW POCKETS OF
SNOW WILL BE POSSIBLE ON THE NORTHERN PERIPHERY OF THE MOISTURE
SHIELD BUT WITH NEW ENGLAND EASILY SEEING THE BEST POTENTIAL FOR
MEANINGFUL SNOW. SOME LOCATIONS IN NEW ENGLAND MAY BE
SUFFICIENTLY COLD FOR SOME SNOW AS THE SYSTEM REACHES THE GREAT
LAKES/MID-ATLANTIC, AND THEN THE THE PATTERN WOULD BECOME
INCREASINGLY FAVORABLE FOR SNOW AS LOW PRESSURE EMPHASIS SHIFTS
MORE ALONG/OFFSHORE THE COAST BY AROUND LATE SUNDAY-MONDAY. THE
WINTER WEATHER OUTLOOK PROBABILITIES FOR AT LEAST 0.25 INCH LIQUID
IN THE FORM OF SNOW CURRENTLY EXCEED 50 PERCENT ACROSS PORTIONS OF
INTERIOR NEW ENGLAND FOR THE SUNDAY-SUNDAY NIGHT PERIOD. THIS
SYSTEM MAY PRODUCE SOME BRISK WINDS AS WELL.
THE UPPER TROUGH MOVING THROUGH THE FOUR CORNERS REGION LATE THIS
WEEK WILL PRODUCE SNOW AND LOWER ELEVATION RAIN OVER THE SOUTHERN
HALF OF THE ROCKIES, FOLLOWED BY A DRIER TREND AS THE TROUGH
DEPARTS. THEN THE MEAN TROUGH ALOFT AND MULTIPLE EMBEDDED
SHORTWAVES/SURFACE FRONTS AFFECTING THE WEST COAST WILL PRODUCE
PERSISTENT RAIN AND MOUNTAIN SNOW FROM THE PACIFIC NORTHWEST INTO
NORTHERN CALIFORNIA FROM FRIDAY INTO NEXT WEEK. EARLY IN THIS
PERIOD THE PRECIPITATION TOTALS SHOULD BE IN THE LIGHT TO MODERATE
RANGE WITH HIGHEST TOTALS OVER THE OLYMPICS. CURRENTLY THERE IS
NOT A STRONG ENOUGH SIGNAL FOR ANY RISK AREA IN THE OLYMPICS
THROUGH THE DAY 5 PERIOD OF THE EXCESSIVE RAINFALL OUTLOOK
(SATURDAY-SATURDAY NIGHT). HOWEVER GUIDANCE SUGGESTS POTENTIAL
FOR SOMEWHAT HEAVIER (THOUGH NOT EXCEPTIONAL) AMOUNTS ALONG THE
NORTHERN-CENTRAL WEST COAST BY SUNDAY-MONDAY. BY EARLY NEXT WEEK
CONFIDENCE IN SPECIFICS DECREASES AS GUIDANCE DIVERGES FOR
SHORTWAVE/FRONTAL DETAILS. EXPECT MOISTURE FROM THESE SYSTEMS TO
START REACHING INTO THE NORTHERN ROCKIES BY EARLY NEXT WEEK WITH
MEANINGFUL SNOWFALL POSSIBLE.
SYSTEM PROGRESSION ACROSS THE LOWER 48 LATE THIS WEEK INTO THE
WEEKEND WILL BRING AN AREA OF MODERATELY BELOW NORMAL TEMPERATURES
(SOME HIGHS UP TO 10-15F BELOW AVERAGE) ACROSS THE WEST INTO THE
CENTRAL-SOUTHERN HIGH PLAINS FRIDAY-SATURDAY, WHILE WARMTH OVER
THE EASTERN HALF OF THE COUNTRY AS OF FRIDAY WILL GET CONFINED
MORE TOWARD THE EAST COAST BY THE WEEKEND. NEAR TO SLIGHTLY BELOW
NORMAL HIGHS SHOULD PREVAIL OVER THE EAST BY NEXT SUNDAY-MONDAY
BEFORE STARTING TO REBOUND. MEANWHILE THE PLAINS/MISSISSIPPI
VALLEY WILL TREND STEADILY WARMER BY SUNDAY-TUESDAY UNDER THE
INFLUENCE OF MEAN RIDGING ALOFT, WITH SOME NORTHERN LOCATIONS
POSSIBLY SEEING HIGHS UP TO 20-25F OR SO ABOVE NORMAL EARLY NEXT
WEEK. THE SERIES OF FRONTAL SYSTEMS REACHING THE WEST COAST FROM
THE WEEKEND INTO EARLY NEXT WEEK WILL PROMOTE SLIGHTLY BELOW
NORMAL DAYTIME HIGHS OVER THAT REGION AND MODERATELY ABOVE NORMAL
LOWS OVER MOST OF THE WEST.
KEBEDE/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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