080
FXUS02 KWBC 240712
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
312 AM EDT SUN MAR 24 2024
VALID 12Z WED MAR 27 2024 - 12Z SUN MAR 31 2024
...HEAVY RAIN THREAT ACROSS THE SOUTHEAST MAY CONTINUE INTO MIDWEEK...
...ROUNDS OF HEAVY RAIN AND SNOW POSSIBLE ACROSS MUCH OF THE WEST
THROUGH THE PERIOD...
..OVERVIEW
A COLD FRONT OR TWO PUSHING AHEAD OF A BROAD UPPER TROUGH IN THE
CENTRAL-EASTERN U.S. AND EVENTUAL ATLANTIC SURFACE LOW DEVELOPMENT
WILL HELP FOCUS RAINFALL FOR PORTIONS OF THE EASTERN SEABOARD FOR
THE LATTER HALF OF THE WORKWEEK. THIS ACTIVITY COULD BE
PARTICULARLY HEAVY FOR PORTIONS OF FLORIDA AND GEORGIA INTO THE
CAROLINAS. MEANWHILE, ONE OR MORE PACIFIC SYSTEMS SHOULD BRING
INCREASING TOTALS OF RAIN AND MOUNTAIN SNOW TO THE WEST COAST
STATES AND THEN INTO THE ROCKIES MID-LATE WEEK INTO NEXT WEEKEND.
INCREASING MOISTURE MAY COMBINE WITH SHORTWAVES IN THE NORTH-
CENTRAL TO EAST-CENTRAL U.S. FRIDAY-SUNDAY, THOUGH WITH AMPLE
UNCERTAINTY IN THE DETAILS OF PRECIPITATION PLACEMENT AND TYPE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST GUIDANCE AGREES IN PRINCIPLE FOR THE LARGE SCALE UPPER
PATTERN EVOLUTION, WITH CENTRAL-EASTERN U.S. UPPER TROUGHING TAKING
ON A MORE NEGATIVE TILT BY FRIDAY-SATURDAY AS IT REACHES THE EAST
COAST/WESTERN ATLANTIC WHILE DEEPENING MEAN TROUGHING BECOMES
ESTABLISHED NEAR THE WEST COAST. THE MOST PROMINENT FORECAST ISSUES
INVOLVE THE EAST COAST/WESTERN ATLANTIC EVOLUTION LATE THIS WEEK,
ALONG WITH INDIVIDUAL FEATURES WITHIN THE WEST COAST TROUGH PLUS
EJECTING ENERGY AND ITS INFLUENCE ON CENTRAL U.S. SURFACE WAVINESS.
FOR THE LATE WEEK EAST COAST EVOLUTION, GUIDANCE CONTINUES TO VARY
WITH THE DETAILS OF ENERGY ALOFT. HOWEVER, THE PAST COUPLE OF
MODEL CYCLES HAVE AT LEAST SHOWN SOME CONVERGENCE AWAY FROM
SOLUTIONS SHOWING SEPARATE CLOSED LOW DEVELOPMENT ALOFT. IN TERMS
OF THE SURFACE LOW, THE GFS RUNS SEEM TO ALIGN THE BEST WITH THE
ENSEMBLE MEANS WHILE THE ECMWF (BOTH 12Z AND NEW 00Z RUNS) APPEAR
QUITE SLOW/SOUTH.
CLUSTERING IS STILL GOOD FOR THE STRONG STORM FORECAST TO BE
OFFSHORE THE PACIFIC NORTHWEST BY THURSDAY. THERE IS INCREASING
SPREAD BOTH ALOFT AND AT THE SURFACE BY FRIDAY, AS ENERGY ROUNDING
THE BASE OF THE UPPER LOW ALREADY IN PLACE CAUSES POTENTIAL FOR A
SURFACE LOW FARTHER SOUTH TO TAKE OVER FOR THE NORTHERN ONE.
ENSEMBLE MEANS INDICATE ONE SURFACE LOW IN BETWEEN BUT THIS COULD
BE DUE TO AVERAGING OUT ENSEMBLE MEMBERS SHOWING BOTH LOWS. MOST
DETERMINISTIC GUIDANCE BRIEFLY SHOW TWO LOWS. REGARDLESS, AN UPPER
TROUGH WITH AN EMBEDDED LOW IS MOST LIKELY TO REACH THE VICINITY OF
CALIFORNIA BY THE WEEKEND, ALONG WITH A LOW AT THE SURFACE. THE
ECMWF OPERATIONAL RUN AND MANY OF ITS ENSEMBLE MEMBERS ARE SLOWER
THAN THE CMC/GFS SUITES. ECMWF-BASED AI MODELS ARE FASTER THAN THE
OPERATIONAL RUN, SO FAVORED A BLEND NOT AS SLOW AS THE EC ITSELF.
SHORTWAVES FARTHER EAST ARE VARIABLE BUT IN GENERAL DO NOT SEEM AS
FOCUSED IN THE NORTH-CENTRAL U.S. COMPARED TO SOME PREVIOUS MODEL
RUNS.
THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND EARLY IN
THE PERIOD, AND WITH REASONABLE CLUSTERING FOR THE LARGE SCALE
FEATURES WAS ABLE TO MAINTAIN A MAJORITY DETERMINISTIC BLEND
THROUGH DAY 6. BY DAY 7 THE GEFS AND EC ENSEMBLE MEANS REACHED JUST
OVER HALF THE BLEND.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT OR TWO AND DEVELOPING LOW PRESSURE AT THE SURFACE
COMBINING WITH A STRONG JET AND ITS RIGHT ENTRANCE REGION TO THE
EAST OF AN UPPER TROUGH WILL SUPPORT POTENTIALLY HEAVY RAIN ACROSS
PORTIONS OF THE SOUTHEAST/CAROLINAS ON WEDNESDAY. THOUGH RECENT
MODEL GUIDANCE HAS BACKED OFF SOME FROM SOME OF THE EXTREMELY HIGH
RAIN TOTALS FROM A DAY AGO, INGREDIENTS ARE IN PLACE FOR SOME
LOCALLY HEAVY RAIN THAT COULD CAUSE FLOODING ISSUES. A MARGINAL
RISK REMAINS IN PLACE IN THE WEDNESDAY EXCESSIVE RAINFALL OUTLOOK,
AND AN EMBEDDED SLIGHT RISK CANNOT BE RULED OUT IN FUTURE UPDATES.
SOME POTENTIALLY HEAVY RAIN COULD LINGER INTO THURSDAY, CURRENTLY
MOST LIKELY OVER EASTERN NORTH CAROLINA, BUT WITH CONTINUED
UNCERTAINTY. WILL START WITH A MARGINAL RISK THERE WITH WHAT SEEMS
TO BE A COMPROMISE IN COVERAGE OF THE GUIDANCE (SOME SHOW HEAVY
RAIN WELL WEST AND SOUTH OF THE MARGINAL, WHILE SOME REALLY ONLY
HIT THE OUTER BANKS). THERE IS ALSO A BROAD RANGE OF POSSIBLE
OUTCOMES FOR HOW MUCH RAINFALL EXTENDS INTO THE MID-
ATLANTIC/NORTHEAST MID-LATE WEEK, DEPENDING ON THE EVOLUTION AND
TRACK OF WESTERN ATLANTIC LOW PRESSURE. IN THIS FORECAST CYCLE,
PRECIPITATION HAS TRENDED DOWN THERE IN FAVOR OF A FOCUS OFFSHORE.
THE SURFACE LOW MAY PRODUCE A PERIOD OF BRISK WINDS OVER NEW
ENGLAND.
DEEPER MOISTURE STARTS TO STREAM INTO THE WEST COAST BY WEDNESDAY
AS UPPER TROUGHING AND LOW PRESSURE APPROACH. RAIN RATES COULD BE
HIGH ENOUGH TO BE CONCERNING FOR FLOODING ACROSS PORTIONS OF
CALIFORNIA INTO WESTERN OREGON, SO THE DAY 5 ERO SHOWS A MARGINAL
RISK THERE FOR WEDNESDAY. HEAVY SNOW IS LIKELY INTO THE
CASCADES/SIERRA NEVADA AND TOWARD THE NORTHERN ROCKIES BEGINNING
WEDNESDAY. COASTAL/LOWER ELEVATION RAIN TOTALS LOOK TO LESSEN BY
THURSDAY BUT SNOW IS FORECAST TO EXPAND INTO THE INTERMOUNTAIN WEST
THURSDAY AND BEYOND. THEN MODEL TRENDS HAVE CONTINUED TO INDICATE THAT
CALIFORNIA MAY SEE INCREASING HEAVY PRECIPITATION BY FRIDAY INTO
THE WEEKEND BASED ON WHERE AN EASTERN PACIFIC UPPER LOW/TROUGH SETS
UP AND DIRECTS A POSSIBLE ATMOSPHERIC RIVER INTO THE STATE. THIS
SOUTHERN SHIFT WOULD ALSO BRING PRECIPITATION INTO THE CENTRAL
GREAT BASIN AND SOUTHWEST FOR THE WEEKEND. FARTHER EAST, SHORTWAVES
GENERALLY RIDING ALONG THE NORTHERN SIDE OF A CENTRAL U.S. RIDGE
COULD COMBINE WITH MOISTURE TO PRODUCE SOME LIGHT TO MODERATE
PRECIPITATION FRIDAY INTO THE WEEKEND ACROSS THE NORTH-CENTRAL
U.S. AND GREAT LAKES REGION AND OHIO VALLEY. CONFIDENCE IS LOW FOR
WHERE PRECIPITATION WILL OCCUR AS WELL AS THE PRECIPITATION TYPES.
COLDER THAN AVERAGE TEMPERATURES BY 15-20 DEGREES ARE LIKELY TO
REMAIN INTO MIDWEEK FOR THE NORTH-CENTRAL PLAINS, WITH SOME GRADUAL
MODERATION BUT REMAINING ON THE COOLER SIDE INTO THE WEEKEND. COOL
TEMPERATURES BUT WITH LESSER ANOMALIES ARE FARTHER SOUTH IN THE
CENTRAL U.S. WEDNESDAY, BUT THEN A NOTABLE WARMING TREND IS
EXPECTED THERE AS UPPER RIDGING BUILDS. THE SOUTH-CENTRAL PLAINS
INTO MISSISSIPPI VALLEY CAN EXPECT TEMPERATURES AROUND 10-15
DEGREES ABOVE AVERAGE BY FRIDAY-SATURDAY AND CLOSER TO 20 DEGREES
ABOVE AVERAGE BY SUNDAY. THIS BRINGS 70S AND 80S INTO KANSAS AND
MISSOURI. MEANWHILE IN THE WEST, NEAR TO ABOVE NORMAL LOWS BUT
NEAR TO BELOW NORMAL HIGHS ARE FORECAST, CONSISTENT WITH THE CLOUDS
AND PRECIPITATION THERE.
TATE
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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