683
FXUS02 KWBC 300657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT THU APR 30 2026
VALID 12Z SUN MAY 03 2026 - 12Z THU MAY 07 2026
..OVERVIEW
SEVERAL DISTURBANCES ROTATING AROUND A PERSISTENT UPPER LEVEL
CLOSED LOW CENTERED OVER ONTARIO AND QUEBEC WILL HELP TO REINFORCE
BROADLY DEEP TROUGHING ACROSS THE EASTERN U.S. FROM LATE THIS
WEEKEND THROUGH MUCH OF NEXT WEEK. THIS PATTERN WILL KEEP
CONDITIONS COOL AND UNSETTLED AT TIMES ACROSS PARTS OF THE UPPER
MIDWEST, GREAT LAKES, MID-ATLANTIC, AND NORTHEAST AS MULTIPLE
FRONTAL SYSTEMS MOVE THROUGH. MEANWHILE, WHAT'S LEFT OF A FRONTAL
BOUNDARY WILL CONTINUE TO BE A FOCUS FOR SHOWERS AND THUNDERSTORMS
ACROSS CENTRAL AND SOUTHERN FLORIDA SUNDAY INTO MONDAY. THEN
ANOTHER PACIFIC CLOSED LOW PUSHES INLAND EARLY NEXT WEEK, BRINGING
LOW ELEVATION SHOWERS AND THUNDERSTORMS ALONG WITH MOUNTAIN SNOW
SHOWERS TO PARTS OF THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO HAVE A VERY GOOD HANDLE ON THE
LARGE SCALE PATTERN EVOLUTION THROUGH THE PERIOD, FEATURING AN
INITIAL LARGE UPPER LOW AND BROAD TROUGHING ACROSS THE EASTERN
U.S., AND A REX BLOCK ACROSS THE WESTERN U.S. BY LATE IN THE
PERIOD, THE REX BLOCK BREAKS DOWN AS A CLOSED UPPER LEVEL PACIFIC
LOW PUSHES INLAND AND AN UPPER LEVEL RIDGE BUILDS IN FROM THE WEST.
DESPITE ABOVE AVERAGE AGREEMENT AMONGST THE MODELS, THERE ARE
STILL SOME SMALLER SCALE DIFFERENCES. THE MAIN SOURCES OF
UNCERTAINTY DEAL WITH SEVERAL SMALLER WAVES ROTATING AROUND THE
LARGE PRIMARY UPPER LOW SPINNING OVER SOUTHEAST CANADA, AS WELL AS
HOW QUICKLY THE CUT-OFF PACIFIC LOW PORTION OF THE REX BLOCK PUSHES
INLAND OVER THE SOUTHWEST. AN EQUAL MODEL COMPOSITE BLEND BETWEEN
THE ECMWF, GFS, CMC, UKMET, AND EC-AIFS SUFFICED FOR THE FIRST HALF
OF THE FORECAST PERIOD, WITH MORE WEIGHTING PLACED ON THE ENSEMBLE
MEANS FOR THE LATTER HALF. THIS APPROACH REMAINS IN LINE WITH THE
PREVIOUS WPC FORECAST AS WELL AS THE 01Z NBM, WHICH SERVED AS A
GOOD STARTING POINT FOR THE WPC DAY 4-7 FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
AS A LARGE UPPER LEVEL LOW SPINS OVER SOUTHEAST CANADA, MULTIPLE
DISTURBANCES ROTATING AROUND THE LOW ARE LIKELY TO PUSH A FEW COLD
FRONTS AND CHANCES FOR SHOWERS AND THUNDERSTORMS INTO THE UPPER
MIDWEST, GREAT LAKES, OHIO VALLEY, AND NORTHEAST SUNDAY INTO THE
MIDDLE OF NEXT WEEK. A LITTLE SNOW MAY EVEN MIX IN WITH THE RAIN
CLOSER TO THE U.S./CANADA BORDER. IN ADDITION TO SHOWER CHANCES,
THE FRONTS WILL BRING REINFORCING SURGES OF COOL AIR, KEEPING
TEMPERATURES NEAR TO BELOW SEASONAL NORMS. CHILLY NIGHTTIME LOWS
MAY ALSO LEAD TO FROST AND FREEZE CONCERNS OVER PARTS OF THE OHIO
VALLEY, MID-ATLANTIC, AND THE CENTRAL APPALACHIANS SUNDAY NIGHT
INTO EARLY MONDAY MORNING.
A COLD FRONT SAGGING SOUTHWARD ACROSS CENTRAL AND SOUTHERN FLORIDA
WILL BE A FOCUS FOR HEAVY RAIN ON SUNDAY. ANOMALOUS MOISTURE
POOLING ALONG THE FRONT COMBINED WITH INCREASING INSTABILITY WILL
LEAD TO THE DEVELOPMENT OF SCATTERED TO NUMEROUS CLUSTERS OF
SHOWERS AND THUNDERSTORMS, MAINLY DURING THE AFTERNOON AND EVENING.
THIS ACTIVITY MAY CONTAIN HEAVY RAINFALL RATES WHICH COULD LEAD TO
LOCALIZED POOR DRAINAGE AND URBAN FLOODING. AS A RESULT, THE DAY
4/SUNDAY MARGINAL RISK ERO REMAINS IN PLACE. WHILE SOME SHOWERS AND
STORMS ARE LIKELY TO LINGER INTO MONDAY, WANING COVERAGE AND
INTENSITY SHOULD KEEP ANY REMAINING FLOODING THREAT TO A MINIMUM.
THUS, NO ADDITIONAL MARGINAL RISK WAS INTRODUCED FOR THE NEW DAY
5/MONDAY ERO.
A SLOW-MOVING PACIFIC LOW SPINNING OFF THE COAST OF CALIFORNIA
WILL BEGIN TO PUSH INLAND ACROSS CALIFORNIA AND THE GREAT BASIN
DURING THE FIRST HALF OF NEXT WEEK. INCREASING MOISTURE AND
INSTABILITY AHEAD OF THIS LOW WILL SUPPORT SCATTERED LOW ELEVATION
SHOWERS AND STORMS ALONG WITH MOUNTAIN SNOW SHOWERS ACROSS PORTIONS
OF THE WEST MONDAY AND TUESDAY. AFTER SEVERAL DAYS OF UNSEASONABLE
WARMTH, TEMPERATURES TREND COOLER FOR THE FIRST HALF OF THE WEEK
GIVEN PLENTY OF SHOWERS AND CLOUDS AROUND. ONCE THE LOW MOVES OUT
MID TO LATE WEEK, A RIDGE BUILDS IN AND TEMPERATURES REBOUND BACK
ABOVE SEASONAL NORMS ONCE AGAIN.
MILLER
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, EXCESSIVE RAINFALL OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES ARE AT:
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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