062
FXUS02 KWBC 050700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM 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
FOR THE UPPER TROUGH CROSSING THE CENTRAL/EASTERN U.S. AND
ASSOCIATED SURFACE DEVELOPMENT, CONFIDENCE REMAINS HIGH IN A
SIGNIFICANT SYSTEM BUT STILL MUCH LOWER FOR THE FINER DETAILS DUE
TO DEPENDENCE ON MULTIPLE PIECES OF LOWER-PREDICTABILITY EMBEDDED
SHORTWAVE ENERGY. OVER THE PAST DAY OR SO THE GUIDANCE HAS BEEN
REFINING ITS EVOLUTION TOWARD AN UPPER LOW DEVELOPING OVER OR NEAR
THE GREAT LAKES BY AROUND SUNDAY AND THEN CONTINUING EASTWARD
ACROSS THE NORTHEAST. MODELS/MEANS ARE SPLIT AS TO WHETHER THERE
MAY BE TWO SEPARATE SURFACE WAVES OR JUST ONE DOMINANT SURFACE LOW
CROSSING THE EAST BEFORE LOW PRESSURE EMPHASIS SHIFTS TO
ALONG/OFFSHORE THE NEW ENGLAND COAST. WITH SOME EXPECTED
DIFFERENCES, THE 12Z ECMWF-INITIALIZED MACHINE LEARNING MODELS
GENERALLY FAVORED A TWO-WAVE EVOLUTION THAT MOST CLOSELY RESEMBLED
THE 18Z GEFS/12Z CMCENS MEANS. THIS SCENARIO IS ALSO CLOSER TO
WPC CONTINUITY. ALONG THE WEST COAST, MOST GUIDANCE (MINUS THE
NEW 00Z UKMET AGREES FAIRLY WELL WITH SHORTWAVE DETAILS INTO
SUNDAY). THEN THE OPERATIONAL MODEL RUNS AND ENSEMBLES HAVE BEEN
DIVERGING FOR STRENGTH AND TIMING OF TRAILING SHORTWAVES WITH NO
WELL-DEFINED CLUSTERING YET TO BE SEEN AMONG THE DYNAMICAL
GUIDANCE AND MACHINE-LEARNING MODELS. A MODEL/MEAN BLEND SEEMS TO
OFFER THE BEST REFLECTION OF THE LARGE SCALE PATTERN WHILE WAITING
FOR BETTER AGREEMENT WITH THE SPECIFICS. GUIDANCE COMPARISONS
AMONG THE 12Z/18Z SOLUTIONS AND CONTINUITY CONSIDERATIONS LED TO
UPDATING THE FORECAST WITH AN OPERATIONAL MODEL BLEND ON DAY 3,
THEN A TREND TO INCORPORATE SOME WEIGHT OF THE 18Z GEFS/12Z CMCENS
MEANS WITH THE MODELS AROUND MID-PERIOD, FOLLOWED BY A NEARLY HALF
MODEL/HALF MEANS LATER IN THE FORECAST (ADDING IN THE 12Z ECENS AT
THIS POINT AS WELL).
..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 MAINTAINED THE 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 SOUTHWESTERN PART OF THE AREA A BIT PER GUIDANCE SIGNALS AND
CONSISTENCY WITH THE FORECAST OF GREATER INSTABILITY OVER THE
CENTRAL GULF COAST REGION. 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.
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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