968
FXUS02 KWBC 061859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM 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 REMAINS SOME UNCERTAINTY OVER THE DETAILS OF PACIFIC ENERGY
MOVING INTO WESTERN NORTH AMERICA AROUND THE END OF THE WEEK,
GUIDANCE HAS TRENDED TOWARDS INCREASING PRECIPITATION CHANCES
SPREADING INLAND FROM THE PACIFIC NORTHWEST INTO THE ROCKIES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE TRENDS HAVE REMAINED SIMILAR OVERNIGHT WITH RESPECT TO THE
HANDLING OF A SPLIT STREAM PATTERN OVER THE CENTRAL/EASTERN U.S.
EARLY IN THE FORECAST PERIOD FOR THE MIDDLE OF NEXT WEEK. THE
UPDATED 00Z/06Z GUIDANCE SHOWS THE ECMWF/CMC/UKMET RETAINING A
SLOWER EASTWARD PROGRESSION OF A SOUTHERN STREAM UPPER TROUGH/CLOSED
LOW MOVING EASTWARD FROM THE SOUTHWEST TOWARDS THE MISSISSIPPI
VALLEY TUESDAY-THURSDAY COMPARED TO THE MORE RECENT RUNS OF THE
GFS, WHICH HAVE BEEN TRENDING FASTER. THE ECMWF/CMC ALSO HAVE A
SIMILAR HANDLE ON THE EVENTUAL EVOLUTION/PHASING OF THE SOUTHERN
STREAM SYSTEM WITH THE NORTHERN STREAM OVER THE MIDWEST/SOUTHEAST
MID- TO LATE NEXT WEEK, CONTINUING A SLOWER PROGRESSION OF THE
SOUTHERN STREAM ENERGY WITH A MORE AMPLIFIED TROUGH APPROACHING THE
EAST COAST COMPARED TO THE GFS. THE EVOLUTION IN THE 00Z ECENS/CMC
MEANS IS SIMILAR TO THEIR DETERMINISTIC COUNTERPARTS, WITH THE
GEFS MEAN SIMILAR TO THE GFS. THE SUITE OF 00Z EC AI MODELS AS WELL
AS THE ICON FOLLOW A SIMILAR EVOLUTION EARLY TO THE
ECMWF/CMC/UKMET CLUSTER. THE EC AI FORECASTS DO START TO SHOW
INCREASING UNCERTAINTY AS THE STREAMS PHASE, THOUGH IN GENERAL DUE
TEND TO BE MORE AMPLIFIED AND SLOWER. THE UPPER-TROUGH PROGRESSION
SPEEDS UP IN THE ICON, THOUGH IT REMAINS MORE AMPLIFIED.
THERE IS MORE UNCERTAINTY UPSTREAM OVER THE WEST AND EASTERN
PACIFIC INTO LATER NEXT WEEK. THE GUIDANCE SHOWS A SIMILAR OVERALL
PICTURE, WITH A WEAK SOUTHERN STREAM SYSTEM APPROACHING CALIFORNIA
AND LEAD NORTHERN STREAM SHORTWAVE ENERGY MOVING INTO THE NORTHWEST
AHEAD OF AN UPPER TROUGH/LOW OVER THE NORTHEASTERN PACIFIC. RUN-
TO-RUN CONSISTENCY AND ALREADY INCREASING UNCERTAINTY IN THE
DETAILS AT THIS TIME FRAME LEADS TO LESS CONFIDENCE IN THE EXACT
EVOLUTION, AND THE EC AI MODELS ALSO DEPICT SOME VARIANCE IN THE
SOLUTIONS. THE 00Z GEFS MEAN IS ALSO RATHER NEUTRAL COMPARED TO THE
OTHER DETERMINISTIC/ENSEMBLE GUIDANCE. HOWEVER, DECENT CLUSTERING
IN REGARDS TO THE OVERALL PATTERN SUGGESTS LEANING TOWARDS A
POTENTIALLY STRONGER SYSTEM. THIS DOES BRING A NOTABLE INCREASE IN
PRECIPITATION CHANCES/QPF FROM THE PACIFIC NORTHWEST INTO THE GREAT
BASIN/ROCKIES LATER NEXT WEEK.
THE UPDATED WPC FORECAST BLEND RELIED ON A COMBINATION OF THE 00Z
ECMWF/CMC/UKMET FOR THE EARLY TO MID-FORECAST PERIOD. INCREASING
CONTRIBUTIONS FROM THE 00Z ECENS AND CMC MEANS WERE ADDED FOR THE
LATER HALF OF THE PERIOD GIVEN INCREASING UNCERTAINTY IN THE
DETAILS WITH RESPECT TO THE EVOLUTION OF THE SYSTEM ENTERING THE
NORTHWEST. THE GFS WAS NOT INCLUDED GIVEN THE TIMING AND EVOLUTION
DIFFERENCES WITH RESPECT TO THE FIRST CENTRAL/EASTERN U.S. SYSTEM,
WITH NO CONTRIBUTION FROM THE GEFS MEAN EITHER GIVEN HOW IT
DIFFERED FROM THE ECENS AND CMC MEANS WITH RESPECT TO THE WESTERN
U.S. LATER IN THE PERIOD. THE TENDENCY OF THE EC AI MODELS AND THE
ICON TO MORE ALIGN WITH THE ECMWF/CMC/UKMET CLUSTER, ESPECIALLY IN
THE EARLY TO MID-FORECAST PERIOD, HELPED SUPPORT THIS UPDATED
BLEND. THIS ALSO GENERALLY TENDS TO FOLLOW CONTINUITY WITH THE
PRIOR FORECAST AS A SLOWER PROGRESSION OF THE SOUTHERN STREAM
SYSTEM HAS BEEN FAVORED.
..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 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. 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 THE ECMWF/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 SYNOPTIC PATTERN, INFLUX OF GULF
MOISTURE, AND DETERMINISTIC QPF AMOUNTS/ENSEMBLE EXCEEDANCE
PROBABILITIES SUGGEST THAT AN UPGRADE TO A MODERATE RISK IS LIKELY
AT SOME POINT. HOWEVER, THE OVERLAP IN THE GUIDANCE, PARTICULARLY
THE CURRENT DIFFERENCES BETWEEN THE MORE NORTHERLY GFS/GEFS MEAN
AND SOUTHERLY ECMWF/ECENS MEAN DO NOT PROVIDE ENOUGH CONFIDENCE IN
THE LOCATION OF THIS HIGHER THREAT AT THIS TIME. 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/ENSEMBLE EXCEEDANCE
PROBABILITIES WITHIN WHAT MAY BE A LINE OF SOUTH TO NORTH TRAINING
CONVECTION. SIMILAR TO DAY 4/TUESDAY, AN EVENTUAL UPGRADE TO A
MODERATE RISK LOOKS INCREASINGLY LIKELY IF FORECAST TRENDS REMAIN
THE SAME, WITH THE LOCALLY HIGHEST THREAT CURRENTLY EXTENDING FROM
SOUTHERN MISSISSIPPI NORTHEASTWARD THROUGH CENTRAL/SOUTHERN ALABAMA
AND INTO NORTHERN GEORGIA. AGAIN SIMILAR TO TUESDAY, GUIDANCE HAS
BEEN CONSISTENT IN DEPICTING A SEPARATE ENHANCED QPF AXIS TO THE
NORTH OF THE LOW TRACK FROM THE ARKLATEX NORTHEASTWARD THROUGH THE
OHIO VALLEY, THOUGH CONFIDENCE IN LOCATION AND AMOUNTS HERE IS
LOWER. 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 THIS TIME, THE BEST FOCUS FOR HEAVIER RAINFALL LOOKS TO BE
ACROSS NORTH FLORIDA AND ALONG THE APPALACHIANS NORTH THROUGH THE
MID-ATLANTIC INTO NEW ENGLAND. 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, PASSING FROM THE SOUTHERN PLAINS TUESDAY
EAST TO THE LOWER MISSISSIPPI VALLEY WEDNESDAY AND THE SOUTHEAST
THURSDAY. 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 LOOKS TO BRING SOME
PRECIPITATION CHANCES TO PORTIONS OF THE PACIFIC NORTHWEST, GREAT
BASIN, AND ROCKIES, INCLUDING LOWER ELEVATION RAIN AND HIGHER
ELEVATION SNOW, PARTICULARLY FOR THE CASCADES.
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 NEAR TO 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. COOLER TEMPERATURES LOOK TO SETTLE INTO
THE NORTHWEST BY LATE WEEK AS A COLD FRONT PASSES THROUGH THE
REGION.
PUTNAM/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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