142
FXUS02 KWBC 231859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT SAT MAR 23 2024
VALID 12Z TUE MAR 26 2024 - 12Z SAT MAR 30 2024
..HEAVY RAIN THREAT ACROSS THE SOUTHEAST TUESDAY-WEDNESDAY
...HEAVY RAIN AND SNOW POSSIBLE ACROSS MUCH OF THE WEST BY MIDWEEK
AND BEYOND...
..OVERVIEW
AS SNOW STARTS TO EXIT THE UPPER MIDWEST ON TUESDAY, THE MAIN
FOCUS FOR POTENTIALLY HAZARDOUS WEATHER WILL BE MUCH FARTHER SOUTH,
AS HEAVY RAIN AND THUNDERSTORMS ARE LIKELY AHEAD OF A COLD FRONT
TRACKING ACROSS THE SOUTHEASTERN U.S. TUESDAY-THURSDAY. THEN UPPER
TROUGHING THAT REACHES THE EAST LATE THIS WEEK SHOULD PROMOTE
WESTERN ATLANTIC SURFACE DEVELOPMENT BUT WITH CONTINUED UNCERTAINTY
FOR THE COVERAGE/MAGNITUDE OF PRECIPITATION AND WIND, ESPECIALLY
FOR THE NORTHEAST. 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. SOME OF THIS
MOISTURE MAY REACH THE NORTHERN PLAINS BY FRIDAY.
..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. BY THE END OF THE PERIOD,
DIFFERENCES BETWEEN PHASING OR HAVING A SEPARATE CLOSED LOW LEAD TO
WIDE DIFFERENCES IN ATLANTIC SURFACE LOW TRACK AND
PRECIPITATION/WIND EFFECTS FOR THE NORTHEAST. 00Z ECMWF-INITIALIZED
MACHINE LEARNING (ML) MODELS DID NOT OFFER MUCH HELP AS THEY VARIED
AS WELL, HIGHLIGHTING THE UNCERTAINTY OF THIS ASPECT OF THE
FORECAST. THE 06Z GFS/GEFS AND 00Z ECMWF/ECENS/CMC SEEMED TO
PROVIDE THE BEST CLUSTERING FOR THE TIME BEING.
CLUSTERING IS STILL GOOD FOR THE STRONG STORM FORECAST TO BE
OFFSHORE THE PACIFIC NORTHWEST BY THURSDAY. THE 00Z UKMET APPEARED
SOMEWHAT WEAK/FAST BUT THE NEW 12Z RUN COMPARES BETTER TO
CONSENSUS. HOWEVER MORE SPREAD AND VARIABILITY ARISE BY FRIDAY-
SATURDAY. MOST OF THE RECENT GUIDANCE THROUGH YESTERDAY HAD
ADVERTISED AN UPSTREAM PACIFIC SYSTEM DISPLACING THE THURSDAY
FEATURE, BUT 00Z THROUGH 12Z MODEL RUNS ARE SUGGESTING THAT
UPSTREAM ENERGY MAY SHEAR AROUND THE SOUTHWEST SIDE OF THE INITIAL
UPPER TROUGH, TRACKING SURFACE LOW PRESSURE MORE TOWARD CALIFORNIA.
EITHER WAY AN UPPER TROUGH WITH AN EMBEDDED LOW IS MOST LIKELY TO
REACH THE VICINITY OF CALIFORNIA BY DAY 7 SATURDAY. THE NEW 12Z
ECMWF HAS FURTHERED ITS DETAIL DIFFERENCES TO YIELD A SLOWER
TROUGH/LOW BY THIS TIME. FARTHER EAST, LATEST CHANGES HAVE LED TO A
WEAKER DEPICTION OF SHORTWAVE ENERGY EJECTING THROUGH THE
WESTERN/CENTRAL U.S. LATE IN THE WEEK--YIELDING A WEAKER SURFACE
SYSTEM. ML MODELS CONTINUE TO SHOW DIFFERENCES FOR WEST COAST
DETAILS AND MOST SUPPORT FAIRLY WEAK SURFACE WAVINESS OVER THE
CENTRAL U.S. BY THE END OF THE PERIOD.
THE UPDATED FORECAST STARTED WITH MAIN EMPHASIS ON THE 06Z GFS/00Z
ECMWF AND A LITTLE 00Z CMC FOR THE FIRST HALF OF THE PERIOD, WITH
THE UKMET STILL NOT COMPARING WELL TO CONSENSUS FOR SOME FEATURES.
THEN THE FORECAST INCORPORATED 40 PERCENT TOTAL 06Z GEFS/00Z ECENS
MEANS (WITH EVEN WEIGHT OF GFS/ECMWF/CMC RUNS) BY DAYS 6-7 FRIDAY-
SATURDAY. THIS PROVIDED AN INTERMEDIATE WAY OF BEGINNING THE
POTENTIAL TRENDS ALONG THE WEST COAST AND STARTED TO NUDGE A LITTLE
WEAKER WITH CENTRAL U.S. SURFACE WAVINESS.
..WEATHER/HAZARDS HIGHLIGHTS
SOME SNOW MAY LINGER ACROSS NORTHERN PARTS OF THE UPPER MIDWEST ON
TUESDAY AS THE SURFACE LOW TRACKS ACROSS THE UPPER GREAT LAKES.
MEANWHILE FARTHER SOUTH, AMPLE MOISTURE AND A STRONG JET ALOFT WILL
SUPPORT HEAVY RAIN. THIS IS LIKELY TO BE ONGOING IN PARTS OF THE
SOUTHEAST AS THE PERIOD BEGINS EARLY TUESDAY, WITH MODEL GUIDANCE
INDICATING A SQUALL LINE CROSSING MISSISSIPPI AND ALABAMA. THIS
COULD PRODUCE RAIN RATES THAT SUPPORT SLIGHT RISK LEVELS IN THE
EXCESSIVE RAINFALL OUTLOOK FOR TUESDAY, THOUGH AREAL COVERAGE OF
HEAVY QPF SEEMS TO BE LESS SO COMPARED TO MONDAY (NOW IN THE SHORT
RANGE). SOME ENHANCED RAIN POTENTIAL EXTENDING INTO TENNESSEE AND
KENTUCKY AND OVER TO THE SOUTHERN APPALACHIANS IS COVERED BY A
MARGINAL RISK. THEN ON WEDNESDAY, THE AXIS OF HEAVY RAIN CONTINUES
TO SHIFT EASTWARD AS THE COLD FRONT(S) PRESS TOWARD THE EASTERN
SEABOARD. MODELS STILL VARY FOR THE PLACEMENT AND AMOUNTS OF EAST
COAST RAINFALL AT THAT TIME BUT THE LATEST MODEL RUNS ARE NARROWING
THE SPREAD A BIT (12Z GFS LIGHTER THAN EARLIER RUNS, 00Z ECMWF
HEAVIER THAN THE 12Z/22 RUN). THE MARGINAL RISK AREA IN THE
WEDNESDAY EXCESSIVE RAINFALL OUTLOOK STILL REFLECTS THE SITUATION
WELL, WHILE THE COMBINATION OF MOISTURE AND INSTABILITY WOULD KEEP
THE DOOR OPEN TO THE POSSIBILITY OF AN EVENTUAL EMBEDDED SLIGHT
RISK AREA. MOST MODELS ARE SUGGESTING A SLIGHTLY QUICKER END TO
RAINFALL, SO THE AFTERNOON UPDATE NUDGED THE FAR WESTERN EDGE OF
THE DAYS 4-5 RISK AREAS A FRACTION TO THE EAST. SOME POTENTIALLY
HEAVY RAIN COULD LINGER INTO THURSDAY, CURRENTLY MOST LIKELY OVER
THE EASTERN CAROLINAS, BUT WITH CONTINUED UNCERTAINTY. 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. THIS
SYSTEM MAY PRODUCE A PERIOD OF BRISK WINDS OVER NEW ENGLAND AS
WELL.
FARTHER WEST, SOME SNOW IS LIKELY IN THE INTERMOUNTAIN WEST ON
TUESDAY. DEEPER MOISTURE STARTS TO STREAM INTO THE WEST COAST LATE
TUESDAY AND ESPECIALLY 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. LATEST
MODEL GUIDANCE MAINTAINS SUPPORT FOR THIS AREA. HEAVY SNOW IS
LIKELY IN HIGHER ELEVATIONS MIDWEEK AND BEYOND, STRETCHING INTO THE
INTERMOUNTAIN WEST AS WELL. STARTING IN THIS PAST NIGHT'S CYCLE,
GUIDANCE HAS STARTED TO SHIFT EAST PACIFIC SURFACE DETAILS BY LATE
IN THE WEEK. IF THE EMERGING TRENDS HOLD, DURATION OF SIGNIFICANT
PRECIPITATION OVER SOUTHWESTERN OREGON/NORTHERN CALIFORNIA WOULD BE
A LITTLE SHORTER AS BETTER EMPHASIS SHIFTS INTO THE SOUTHERN TWO-
THIRDS OR SO OF CALIFORNIA. FARTHER EAST, THERE IS A GENERAL
SIGNAL FOR PRECIPITATION TO EXPAND INTO THE NORTH-CENTRAL U.S.,
POSSIBLY IN THE FORM OF SNOW AGAIN, BY FRIDAY. HOWEVER PRECISE
TOTALS ARE FAIRLY UNCERTAIN AT THIS TIME.
MUCH COLDER THAN AVERAGE TEMPERATURES (MORE COMPARABLE TO JANUARY)
ARE LIKELY FOR THE NORTHERN AND CENTRAL HIGH PLAINS IN THE WAKE OF
THE STRONG PLAINS/MIDWEST STORM. HIGHS WILL ONLY BE IN THE 20S AND
30S FOR THESE AREAS ON TUESDAY. THE CENTRAL U.S. WILL SEE A
WARMING TREND GOING INTO THE MIDDLE AND LATE PART OF NEXT WEEK,
THOUGH MONTANA AND THE DAKOTAS WILL STILL REMAIN CHILLY BY LATE
MARCH STANDARDS. THE WEST SHOULD SEE GENERALLY COOLER THAN AVERAGE
HIGHS AND NEAR AVERAGE LOWS NEXT WEEK. THE EAST MAY SEE MIXED
ABOVE AND NEAR NORMAL TEMPERATURES UNTIL LATE WEEK WHEN THE
RELATIVE WARMTH FROM THE CENTRAL U.S. (HIGHS REACHING UP TO 10-15F
ABOVE NORMAL OVER THE CENTRAL PLAINS) EXPANDS EAST.
RAUSCH/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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