684
FXUS02 KWBC 011858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT THU MAY 1 2025
VALID 12Z SUN MAY 04 2025 - 12Z THU MAY 08 2025
...BLOCKY PATTERN WITH CLOSED LOWS OVER THE WEST AND THE EAST WITH
AREAS OF HEAVY RAINFALL POTENTIAL...
..OVERVIEW
THE FORECAST CONTINUES TO CALL FOR A BLOCKY PATTERN OVER THE LOWER
48 NEXT WEEK. THE DOMINANT FEATURES WILL BE TWO CLOSED UPPER LOWS,
ONE OVER THE WEST/SOUTHWEST AND ONE OVER THE EAST, THAT WILL BOTH
SLOWLY DRIFT AROUND WEAKENING THROUGH WEDNESDAY/THURSDAY. THESE
SYSTEMS ARE EXPECTED TO PRODUCE AREAS OF SIGNIFICANT RAINFALL OVER
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, NORTHEAST, AND MID-
ATLANTIC AND HIGH ELEVATION SNOWS IN THE WEST. EVENTUALLY, THE
EASTERN UPPER LOW SHOULD INTERACT WITH A NORTHERN STREAM TROUGH
THAT WILL SWING ACROSS SOUTHERN CANADA, RESULTING IN THE LOW BEING
SWEPT UP TOWARDS THE CANADIAN MARITIMES LATE NEXT WEEK. THE WESTERN
LOW WILL LIKELY REMAIN ISOLATED AS IT DRIFTS EAST OVER THE PLAINS
AND WEAKENS ON WEDNESDAY. THE REMNANTS OF THE WESTERN LOW MAY
EVENTUALLY COMBINE WITH ANOTHER TROUGH DEVELOPING OVER THE EAST
COAST LATE THURSDAY INTO FRIDAY. BY WEDNESDAY, ANOTHER TROUGH AND
FRONTAL SYSTEM WILL APPROACH THE WEST COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THE OVERALL
PATTERN. THERE HAVE BEEN SOME SHIFTS IN THE GUIDANCE SINCE THE
OVERNIGHT FORECAST THAT WILL AFFECT THE SENSIBLE WEATHER, THE MOST
IMPACTFUL ONE BEING AN EASTWARD SHIFT IN THE UPPER LOW/SURFACE
FRONTAL SYSTEM THAT WILL BRING RAIN TO THE PLAINS TUESDAY THROUGH
THURSDAY. THIS EASTWARD SHIFT IS DUE TO A SLIGHTLY MORE WESTWARD
POSITION OF THE WESTERN UPPER LOW, WHICH WILL BRING HEAVY RAIN
FURTHER INTO TEXAS AND OKLAHOMA THAN THE PREVIOUS FORECAST. THERE
IS CONSIDERABLY MORE UNCERTAINTY IN THE EAST, WHICH WILL DEPEND ON
HOW THE UPPER LOW INTERACTS WITH THE NORTHERN STREAM. THE 06Z GFS
CONTINUED TO BE THE OUTLIER WITH A FLATTER AND FASTER NORTHERN
STREAM THAT INTERACTS VERY LITTLE WITH THE UPPER LOW, WHILE ALL
OTHER GUIDANCE IS STILL DEPICTING A MORE AMPLIFIED NORTHERN STREAM
THAT ABSORBS THE EASTERN LOW EVENTUALLY. FOR THE AFTERNOON
FORECAST, THE AMPLIFIED NORTHERN STREAM CONSENSUS WAS USED, WHICH
ALSO MAINTAINS CONTINUITY FROM THE OVERNIGHT FORECAST AND IS IN
LINE WITH NEW 12Z GUIDANCE.
WPCS MODEL BLEND CONSISTED OF THE 06Z GFS AND 00Z ECMWF/CMC/UKMET
FOR THE FIRST TWO DAYS. BY DAY 5 (TUESDAY), THE WEIGHT ON THE 06Z
GFS WAS REDUCED AND ENSEMBLE MEANS FROM THE GEFS AND ECENS WERE
ADDED TO THE BLEND IN INCREASING AMOUNTS THROUGH THE END OF THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
EARLY NEXT WEEK, TWO OCCLUDED FRONTAL SYSTEMS ARE EXPECTED TO
BRING MODERATE TO LOCALLY HEAVY RAINFALL TO PORTIONS OF THE WEST
AND EAST. IN THE WEST, ANOMALOUS MOISTURE ACCOMPANYING THE UPPER
LOW WILL SUPPORT HEIGHTENED PRECIPITATION FROM THE GREAT BASIN TO
THE CENTRAL AND SOUTHERN ROCKIES AND PLAINS. PRECIPITATION WILL BE
INITIALLY TRIGGERED BY THE SURFACE FRONTAL SYSTEM, WHICH WILL PUSH
ACROSS THE INTERMOUNTAIN WEST ON SUNDAY THEN BECOME STATIONARY OVER
THE PLAINS NEXT WEEK. ONCE THE SYSTEM STALLS, MOISTURE WILL
CONTINUOUSLY POOL OVER THE PLAINS, WHICH WILL LIKELY RESULT IN A
MULTI-DAY HEAVY RAINFALL EVENT ACROSS THE CENTRAL AND SOUTHERN
PLAINS. THE HEAVIEST PRECIPITATION IS FORECAST TO FALL OVER THE
SOUTHERN PLAINS MONDAY INTO TUESDAY, THEN SPREAD INTO THE LOWER
MISSISSIPPI VALLEY WEDNESDAY AND THURSDAY. PORTIONS OF THE PLAINS
STATES WILL BE ESPECIALLY VULNERABLE TO HEAVY RAIN/FLOODING DUE TO
RECENT HEAVY RAINS AND SATURATED SOILS. THIS ACTIVITY IS
HIGHLIGHTED IN THE DAY 4-5 EXCESSIVE RAINFALL OUTLOOKS (EROS) WITH
A MARGINAL RISK AREA ON SUNDAY AND A SLIGHT RISK AREA ON MONDAY
FOCUSED ON EASTERN NEW MEXICO AND THE TEXAS AND OKLAHOMA
PANHANDLES.
UNDER THE EASTERN UPPER LOW, THE FRONTAL SYSTEM WILL VERY SLOWLY
PUSH EAST ACROSS THE EAST COAST, RESULTING IN A STREAM OF ONSHORE
MOISTURE OVER THE MID-ATLANTIC AND NORTHEAST. THIS PATTERN WILL
RESULT IN PERSISTENT PRECIPITATION ACROSS THESE REGIONS THROUGH
TUESDAY. INITIALLY, RAINFALL COULD BE BENEFICIAL AND BRING SOME
RELIEF TO DROUGHT CONDITIONS, BUT REPEATED ROUNDS OF RAINFALL
COULD PRODUCE LOCALLY HEAVY TOTALS AND MAY RESULT IN LOCALIZED
FLOODING IN URBAN AND POOR DRAINAGE AREAS. THE DAY 4-5 EROS SHOW A
MARGINAL RISK AREA ACROSS THESE REGIONS ON BOTH SUNDAY AND MONDAY.
BY WEDNESDAY, THE FRONTAL SYSTEM SHOULD ACCELERATE TO THE EAST AS
THE UPPER LOW INTERACTS WITH THE NORTHERN STREAM, SHIFTING
PRECIPITATION FARTHER INTO THE NORTHEAST.
THE NORTHERN HIGH PLAINS IN PARTICULAR WILL SEE WELL ABOVE NORMAL
TEMPERATURES ON SUNDAY, WITH SOME PLUS 15-25 DEGREE ANOMALIES FOR
HIGHS. TEMPERATURES WILL STEADILY MODERATE AS THIS AREA OF WARMTH
MIGRATES EASTWARD EARLY NEXT WEEK. IN CONTRAST, THE UPPER LOW
TRACKING INTO THE SOUTHWEST WILL BRING MUCH COOLER TEMPERATURES TO
THE REGION. HIGHS SHOULD BE 10-20 DEGREES BELOW NORMAL ON SUNDAY-
MONDAY, WITH SOME RECORD COLD HIGHS POSSIBLE NEAR THE UPPER LOW'S
PATH. THE SOUTHWEST WILL SLOWLY TREND CLOSER TO NORMAL AFTER
MIDWEEK. PERSISTENT CLOUDS AND RAINFALL SHOULD KEEP THE SOUTHERN
HIGH PLAINS BELOW NORMAL FOR HIGHS AS WELL. THE NORTHWEST WILL SEE
A WARMER TREND NEXT WEEK, WITH SOME HIGHS REACHING 10-15 DEGREES OR
SO ABOVE NORMAL. OVER THE EAST, LOCATIONS UNDER AND SOUTHWEST OF
THE OHIO VALLEY UPPER LOW SHOULD SEE MODERATELY BELOW NORMAL HIGHS
SUNDAY-MONDAY AND THEN SOME MODERATION. THE NORTHEAST WILL TEND TO
SEE ABOVE NORMAL LOWS.
DOLAN/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page