687
FXUS02 KWBC 060659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SAT APR 6 2024
VALID 12Z TUE APR 09 2024 - 12Z SAT APR 13 2024
...HEAVY RAIN AND FLASH FLOODING CONCERNS WILL INCREASE IN THE
SOUTHERN U.S. NEXT WEEK...
..OVERVIEW
THE OVERWHELMING FOCUS OF THE FORECAST WILL BE ON AN UPPER LOW
EJECTING FROM THE SOUTHERN ROCKIES AND EVENTUALLY PHASING WITH
NORTHERN STREAM FLOW TO YIELD AN AMPLIFIED AND LARGER SCALE EASTERN
U.S. UPPER TROUGH BY LATE NEXT WEEK. WITH THIS EVOLUTION ALOFT,
EXPECT SURFACE LOW PRESSURE TO DEEPEN AS IT TRACKS FROM TEXAS OR
NEAR THE WESTERN GULF COAST NORTHEASTWARD THROUGH THE GREAT LAKES
AND INTO EASTERN CANADA. THERE WILL BE A COUPLE DAYS OR SO OF
PERSISTENT GULF INFLOW WHICH WILL INTERACT WITH THE UPPER
DYNAMICS/SURFACE FRONTS TO PRODUCE A MULTI-DAY HEAVY/EXCESSIVE
RAINFALL EVENT FROM PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY INTO THE SOUTHEAST. A BROAD AREA OF LESS EXTREME
BUT STILL POTENTIALLY SIGNIFICANT RAIN WILL BE POSSIBLE OVER SOME
AREAS FARTHER NORTH AS WELL AS ALONG MUCH OF THE EAST COAST. A
WESTERN U.S. UPPER RIDGE THAT REACHES THE PLAINS BY NEXT SATURDAY
SHOULD BRING A PRONOUNCED WARMING TREND TO THOSE AREAS, WHILE THERE
IS CONSIDERABLE UNCERTAINTY OVER DETAILS OF PACIFIC ENERGY MOVING
INTO WESTERN NORTH AMERICA AROUND THE END OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FOR THE UPPER LOW EJECTING FROM THE SOUTHERN ROCKIES AND SUBSEQUENT
PHASING WITH NORTHERN STREAM FLOW, 12Z/18Z GUIDANCE STILL SHOWED
QUITE A BIT OF SPREAD BUT THE NEW 00Z RUNS SEEM TO BE SHOWING SOME
CONSOLIDATION. OVER RECENT RUNS THE GFS/GEFS HAVE TENDED TO BE ON
THE FASTER SIDE WITH THE OVERALL EVOLUTION WHILE THE CMC HAS BEEN A
SLOW EXTREME. THE 00Z GFS/GEFS ARE STILL SOMEWHAT FAST BUT A TAD
SLOWER THAN THE 18Z VERSION, WHILE CMC/UKMET DETAILS ARE
GRAVITATING CLOSER TO THE ECMWF (INCLUDING THE NEW 00Z RUN) THAT
HAS BEEN FAIRLY CONSISTENT THUS FAR WITH AN INTERMEDIATE TIMING.
THE 12Z ECMWF-INITIALIZED MACHINE LEARNING MODELS (MLS) FAVORED
SLOWER TIMING THAN THE GFS AS WELL, BUT WITH A VARIETY OF IDEAS FOR
SPECIFICS BEYOND THAT. OVERALL PREFERENCE BASED ON THE 12Z/18Z
GUIDANCE WAS TO STAY FAIRLY CLOSE TO CONTINUITY GIVEN THE ONGOING
SPREAD, WHICH LED TO GREATER EMPHASIS ON THE 12Z ECMWF AFTER
TUESDAY WITH SOME INPUT OF OTHER MODELS/ENSEMBLE MEANS TO ACCOUNT
FOR DETAIL UNCERTAINTY.
THE OTHER SIGNIFICANT ISSUE IN THE FORECAST INVOLVES PACIFIC FLOW
THAT REACHES WESTERN NORTH AMERICA TOWARD THE END OF NEXT WEEK.
ENSEMBLE SPAGHETTI PLOTS HAVE BEEN QUITE MESSY OVER THIS REGION THE
PAST COUPLE OF DAYS, WITH OPERATIONAL RUNS ALSO VARYING FOR THE
DEPTH AND TIMING OF A POTENTIAL SHORTWAVE. ISSUES INCLUDE THE
ULTIMATE PATH/EVOLUTION OF A GULF OF ALASKA UPPER LOW, WITH POOR
AGREEMENT FOR THAT PARTICULAR FEATURE. ADDING TO THE UNCERTAINTY,
MOST OF THE 12Z MLS ACTUALLY FAVORED A MORE AMPLIFIED AND SHARPER
UPPER TROUGH REACHING THE WEST BY NEXT SATURDAY VERSUS MOST OF THE
DYNAMICAL MODELS AND ENSEMBLE MEANS. THIS WOULD LEAD TO A SLOWER
NORTHERN TIER SURFACE SYSTEM AND FARTHER SOUTH PROGRESSION OF THE
TRAILING COLD FRONT OVER THE WEST. FOR NOW THE MANUAL FORECAST
DEPICTS THE FAIRLY CONSERVATIVE REPRESENTATION OF THE INCOMING
SHORTWAVE PER THE MAJORITY OF DYNAMICAL GUIDANCE BUT IT IS WORTH
WATCHING FOR ANY TREND TOWARD THE ML IDEAS.
..WEATHER/HAZARDS HIGHLIGHTS
THE PRIMARY FOCUS OF NEXT WEEK'S FORECAST FROM A HAZARD
PERSPECTIVE WILL CONTINUE TO BE A MULTI-DAY HEAVY RAINFALL THREAT
FROM PARTS OF THE SOUTHERN PLAINS EASTWARD AS THE UPPER LOW
TRACKING OUT OF THE SOUTHERN ROCKIES INTERACTS WITH A PERSISTENT
FLOW OF MOISTURE FROM THE GULF OF MEXICO AND ONE OR MORE LEADING
SURFACE FRONTS. THIS EVENT SHOULD ALREADY BE IN PROGRESS OVER THE
SOUTHEASTERN PLAINS/LOWER MISSISSIPPI VALLEY AS OF THE START OF
THE PERIOD EARLY TUESDAY, AND WILL LIKELY PERSIST/EXPAND
THEREAFTER. THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK VALID
TUESDAY- TUESDAY NIGHT MAINTAINS A SLIGHT RISK AREA EXTENDING FROM
NORTHEAST TEXAS TO THE SOUTHWEST CORNER OF TENNESSEE WITH A
SURROUNDING MARGINAL RISK AREA. THERE CONTINUES TO BE POTENTIAL FOR
AN UPGRADE TO AN EMBEDDED MODERATE RISK AREA IN THE SHORTER TERM IF
CONFIDENCE INCREASES IN OVERLAP OF TUESDAY'S HEAVY RAINFALL WITH
THAT OF THE PRIOR DAY. THE SURROUNDING MARGINAL RISK AREA ACCOUNTS
FOR LOWER-CONSENSUS IDEAS FROM VARIOUS GUIDANCE, INCLUDING THE GFS
BEING ON THE NORTHERN SIDE OF THE SPREAD WITH A SEPARATE ENHANCED
QPF AXIS, AND UKMET/CMC RUNS BEING CONSISTENTLY HEAVY WITH THEIR
RAINFALL AXIS OVER THE SOUTHERN HIGH PLAINS JUST TO THE NORTH OF
THE UPPER LOW TRACK. THE HEAVY RAIN THREAT SHOULD BEGIN TO PUSH
FARTHER EASTWARD BY MIDWEEK, WITH THE DAY 5 ERO VALID WEDNESDAY-
WEDNESDAY NIGHT DEPICTING A SLIGHT RISK AREA FROM PARTS OF THE
LOWER MISSISSIPPI VALLEY INTO GEORGIA. WHILE THE SYSTEM IS
BEGINNING TO ACCELERATE IN THIS TIME FRAME, GUIDANCE CONTINUES TO
SHOW SIGNIFICANT MAXIMUM TOTALS WITHIN WHAT MAY BE A LINE OF SOUTH
TO NORTH TRAINING CONVECTION. EXPECT A BROADER AREA OF MEANINGFUL
RAINFALL TO THE NORTH, WITH SOME POCKETS OF HEAVY RAINFALL
POSSIBLE, WITH AREAS OF MODERATE TO HEAVY RAIN REACHING THE EAST
COAST LATER IN THE WEEK. AT THAT TIME, THE BEST FOCUS FOR HEAVIEST
RAINFALL MAY BE NORTHWESTERN FLORIDA AND VICINITY PLUS PORTIONS OF
THE NORTHERN MID-ATLANTIC/NORTHEAST. THE DEEPENING STORM SYSTEM MAY
ALSO PRODUCE BRISK TO STRONG WINDS OVER SOME AREAS. THE STORM
PREDICTION CENTER IS ALSO MONITORING THE POTENTIAL FOR SEVERE
WEATHER WITH THIS SOUTHERN TIER EVENT. CHECK THEIR LATEST OUTLOOKS
FOR MORE INFORMATION.
THE UPPER LOW TRACKING THROUGH THE SOUTHERN ROCKIES MAY PRODUCE
SOME AREAS OF MEANINGFUL SNOW OVER HIGHER ELEVATIONS ON TUESDAY
WHILE THE NORTHWEST COULD SEE LINGERING LIGHT PRECIPITATION WITH A
FRONT REACHING THE AREA. AN UPPER SHORTWAVE AND SURFACE SYSTEM
REACHING THE NORTHWEST LATE IN THE WEEK MAY BRING SOME
PRECIPITATION TO THE REGION BUT STILL WITH LOW CONFIDENCE IN THE
DETAILS AT THIS TIME.
THE UPPER LOW CROSSING THE SOUTHERN ROCKIES/HIGH PLAINS TUESDAY
INTO WEDNESDAY WILL SUPPORT HIGH TEMPERATURES UP TO 10-20F BELOW
AVERAGE OVER THE REGION ON TUESDAY WITH SOME LINGERING BELOW NORMAL
READINGS LINGERING OVER THE SOUTHERN PLAINS INTO WEDNESDAY. TO THE
EAST OF THE UPPER LOW, A MAJORITY OF THE EASTERN HALF OF THE
COUNTRY WILL SEE ABOVE NORMAL TEMPERATURES, ESPECIALLY FOR MORNING
LOWS. THE NORTHEAST MAY BE ONE EXCEPTION, WITH NEAR TO BELOW NORMAL
TEMPERATURES DUE TO COOL HIGH PRESSURE BEHIND A BACKDOOR FRONT
THAT SETTLES INTO THE NORTHERN MID-ATLANTIC AROUND WEDNESDAY-
THURSDAY. PASSAGE OF A COUPLE FRONTS WILL BRING A COOLER TREND FROM
WEST TO EAST LATE IN THE WEEK. MEANWHILE AN UPPER RIDGE BUILDING
INTO THE WEST AND EVENTUALLY REACHING THE PLAINS WILL STEADILY
EXPAND COVERAGE OF PLUS 10-20F ANOMALIES DURING THE TUESDAY-
SATURDAY PERIOD. CONFIDENCE IN THE TEMPERATURE FORECAST OVER PARTS
OF THE WEST DECLINES BY THE END OF NEXT WEEK DUE TO UNCERTAINTY IN
AMPLITUDE/TIMING OF PACIFIC SHORTWAVE ENERGY AND SOUTHEASTWARD
EXTENT OF THE LEADING COLD FRONT.
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 (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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