382
FXUS02 KWBC 271816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 PM EDT SUN APR 27 2025
VALID 12Z WED APR 30 2025 - 12Z SUN MAY 04 2025
...HEAVY RAINFALL THREAT OVER THE SOUTHERN HALF OF THE PLAINS
CONTINUING INTO WEDNESDAY...
..OVERVIEW
THE COMBINATION OF AN EJECTING SOUTHERN ROCKIES SHORTWAVE AND
UPSTREAM ENERGY WILL SUPPORT DEVELOPING PLAINS/MIDWEST LOW PRESSURE
THAT SHOULD REACH SOUTHEASTERN CANADA BY FRIDAY. THIS SYSTEM WILL
LIKELY PRODUCE ITS HEAVIEST RAIN OVER PARTS OF THE SOUTHERN PLAINS
ON WEDNESDAY BEFORE SPREADING A BROADER AREA OF SOMEWHAT LOWER
RAINFALL TOTALS ACROSS THE EAST LATER IN THE WEEK. THE UPPER TROUGH
AND POSSIBLE EMBEDDED UPPER LOW FORECAST TO SETTLE OVER EASTERN
NORTH AMERICA BY NEXT WEEKEND SHOULD BE ONE COMPONENT OF WHAT
GUIDANCE SUGGESTS WILL BECOME A MORE BLOCKY LARGE SCALE PATTERN
ALSO CONSISTING OF AN ARRIVING WEST COAST TROUGH CLOSING OFF ITS
OWN LOW WHILE A RIDGE SETS UP OVER THE CENTRAL U.S. THE WESTERN
SYSTEM WILL SPREAD RAIN AND HIGH ELEVATION SNOW ACROSS THE REGION
LATE WEEK THROUGH THE WEEKEND WHILE SOME AREAS OF RAIN WILL ALSO BE
POSSIBLE OVER THE CENTRAL/SOUTHERN PLAINS IN THAT TIME FRAME.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST SUITE OF MODEL AND ENSEMBLE GUIDANCE CONTINUES TO SHOW
ABOVE AVERAGE AGREEMENT ON THE LARGE SCALE EVOLUTION DURING THE
MEDIUM RANGE PERIOD, BUT PLENTY OF UNCERTAINTY IN THE DETAILS OF
INDIVIDUAL SYSTEMS. THERE CONTINUES TO BE SOME VARIABILITY WITH
DETAILS OF THE INITIAL DEVELOPING SYSTEM FORECAST TO TRACK FROM THE
PLAINS/MIDWEST THROUGH SOUTHEASTERN CANADA DURING MID-LATE WEEK.
SOME MODELS SHOW A COUPLE WEAKER EMBEDDED SHORTWAVES/ENERGY, BUT
THE MORE NOTICEABLE DIFFERENCE IS THE 00Z ECMWF WHICH WAS FASTER
THAN CONSENSUS AS THE SYSTEM MOVES THROUGH THE NORTHEAST. WPC
PREFERS A SLOWER APPROACH, CLOSER TO CONTINUITY AND THE ENSEMBLE
MEANS AND THUS TRENDED THE LATE PERIOD BLEND AWAY FROM THE ECMWF
FOR THIS SYSTEM.
THE DEEPENING TROUGH WHICH EVENTUALLY CLOSES OFF AN UPPER LOW OVER
THE WEST NEXT WEEKEND IS SHOWING BETTER CONSISTENCY AND TIMING.
THERE ARE SOME SMALLER SCALE DETAILS TO BE WORKED OUT, WHICH MAY
TAKE UNTIL THE SHORT RANGE TO RESOLVE. A GENERAL MODEL BLEND WITH
THE ENSEMBLE MEANS SEEMS TO WORK WELL AS A STARTING POINT FOR THIS
SYSTEM.
..WEATHER/HAZARDS HIGHLIGHTS
THE GENERAL SIGNAL FOR HEAVY RAINFALL OVER AND NEAR THE SOUTHERN
PLAINS ON WEDNESDAY HAS BEEN FAIRLY CONSISTENT IN LATEST MODEL
RUNS/FIRST-GUESS FIELDS, AS SURFACE WAVINESS DEVELOPS ALONG A
STALLED FRONT IN RESPONSE TO AN EJECTING ROCKIES SHORTWAVE.
ANOMALOUS MOISTURE AND SUFFICIENT INSTABILITY WILL FURTHER
CONTRIBUTE TO THE HEAVY RAINFALL THREAT. THE DAY 4 ERO REMAINED
FAIRLY CLOSE TO CONTINUITY WITH BOTH THE SLIGHT RISK AREA
ENCOMPASSING PARTS OF TEXAS/OKLAHOMA AND WESTERN
ARKANSAS/SOUTHWESTERN MISSOURI AND THE SURROUNDING MARGINAL RISK
AREA. ACCELERATION OF THE SURFACE LOW AND TRAILING COLD FRONT
DURING DAY 5/THURSDAY SHOULD TEMPER RAINFALL TOTALS SOMEWHAT, BUT
THERE MAY STILL BE POCKETS OF RAIN RATES SUFFICIENT TO CAUSE RUNOFF
ISSUES (ESPECIALLY WHERE THERE ARE WETTER GROUND CONDITIONS
LEADING INTO THE EVENT). THUS THE DAY 5 ERO INTRODUCES A BROAD
MARGINAL RISK AREA FROM PORTIONS OF THE TENNESSEE VALLEY INTO THE
GREAT LAKES. THE STORM PREDICTION CENTER IS ALSO MONITORING FOR
SEVERE THREATS ON WEDNESDAY FOR PARTS OF NORTHERN TEXAS. CHECK THE
SPC OUTLOOKS FOR THE LATEST INFO ON SEVERE THREATS.
RAIN SHOULD CONTINUE ACROSS THE EAST ON FRIDAY WITH MOSTLY LIGHT
TO MODERATE TOTALS. MOST AREAS SHOULD SEE A DRIER TREND FOR THE
WEEKEND BUT AN UPPER TROUGH ON THE DEEPER/MORE PERSISTENT SIDE OF
THE SPREAD COULD PRODUCE SOME DIURNALLY FAVORED SHOWERS OVER THE
NORTHEAST. MEANWHILE AREAS OF RAIN WITH VARYING INTENSITY SHOULD
DEVELOP OVER THE CENTRAL/SOUTHERN PLAINS LATE WEEK INTO THE
WEEKEND, AND THE SYSTEM PUSHING INTO THE WEST WILL SPREAD RAIN AND
HIGH ELEVATION SNOW INTO THE REGION. LOCATIONS FROM THE PACIFIC
NORTHWEST INTO THE GREAT BASIN SHOULD SEE RELATIVELY HIGHER TOTALS.
BETWEEN THESE PRECIPITATION AREAS, SOME LIGHT ACTIVITY WILL BE
POSSIBLE FROM THE SIERRA NEVADA INTO CENTRAL ROCKIES MID-LATE WEEK
DUE TO WEAK SHORTWAVE ENERGY.
MOST OF THE EAST EXCEPT FOR FAR NORTHERN AREAS SHOULD SEE ABOVE
NORMAL TEMPERATURES MID-LATE WEEK WITH SOME PLUS 10-15F ANOMALIES.
COLD FRONTAL PASSAGE AND ARRIVAL OF UPPER TROUGHING SHOULD BRING
TEMPERATURES DOWN TO NEAR OR BELOW NORMAL DURING THE WEEKEND.
MEANWHILE ABOVE NORMAL TEMPERATURES WILL PROGRESS FROM THE
NORTHWEST INTO THE NORTHERN/CENTRAL PLAINS DURING THE PERIOD,
CORRESPONDING TO MOVEMENT OF AN UPPER RIDGE. SOME PLUS 10-20F
ANOMALIES WILL BE POSSIBLE OVER NORTHERN LOCATIONS MAINLY DURING
THURSDAY-SATURDAY. THEN THE WEST WILL TREND SIGNIFICANTLY COLDER
NEXT WEEKEND WITH THE ARRIVAL OF A DEEP UPPER TROUGH/POSSIBLE LOW,
BRINGING HIGHS DOWN TO 5-15F BELOW NORMAL.
SANTORELLI/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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