078  
FXUS02 KWBC 271853  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
253 PM EDT TUE MAY 27 2025  
 
VALID 12Z FRI MAY 30 2025 - 12Z TUE JUN 03 2025  
 
19Z UPDATE: THE 12Z MODEL GUIDANCE FEATURES GOOD SYNOPTIC SCALE  
AGREEMENT ACROSS THE CONTINENTAL U.S. FOR FRIDAY, ALTHOUGH THE CMC  
BECOMES A BIT MORE AMPLIFIED WITH THE UPPER TROUGH DEVELOPING NEAR  
THE EAST COAST GOING INTO SATURDAY. OVER THE WEEKEND, THE GFS AND  
TO A LESSER EXTENT THE GEFS MEAN IS A LITTLE FASTER WITH THE  
ARRIVAL OF THE SHORTWAVE ACROSS THE PACIFIC NORTHWEST. BY EARLY  
NEXT WEEKEND, GREATER MODEL SPREAD EXISTS ACROSS SOUTH-CENTRAL  
CANADA AS THE SHORTWAVE ENERGY FROM THE PACIFIC NORTHWEST WORKS ITS  
WAY EASTWARD. THE DEVELOPING UPPER LOW OVER THE INTERMOUNTAIN WEST  
BY NEXT TUESDAY IS WELL REPRESENTED BY THE GUIDANCE, ALTHOUGH THERE  
ARE LATITUDINAL DIFFERENCES WHICH ARE NOT UNUSUAL AT THIS TIME  
RANGE. THE PREVIOUS DISCUSSION IS APPENDED BELOW FOR REFERENCE.  
 
HAMRICK  
--------------------  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES CONTINUE TO SHOW A REASONABLY SIMILAR MEDIUM  
RANGE LARGER SCALE PATTERN EVOLUTION OVER THE LOWER 48 AND  
VICINITY. HOWEVER, COMPLEX SYSTEM AND STREAM PHASING INTERACTIONS  
HAVE AGAIN LED TO AN INCREASE IN SMALLER SCALE VARIANCES,  
ESPECIALLY EMANATING FROM ENERGY TRANSFERS FROM A NORTH-CENTRAL  
U.S./MIDWEST CLOSED LOW TO AN UPPER TROUGH OVER THE EAST. FORECAST  
SPREAD REMAINS GREATER THAN NORMAL FOR THESE SYSTEMS FROM THE  
START OF THIS FORECAST PERIOD ONWARD. ACCORDINGLY, FAVOR A MORE  
COMPATIBLE 18 UTC GEFS AND 12 UTC ECMWF/CANADIAN ENSEMBLE MEANS  
BLEND THAT TENDS TO MITIGATE SMALLER SCALE DIFFERENCES CONSISTENT  
WITH INDIVIDUAL SYSTEM PREDICTABILITY. WPC PRODUCT CONTINUITY IS  
DECENTLY MAINTAINED WITH THIS STRATEGY, WITH A SOLUTION IN LINE  
WITH A COMPOSITE OF LATEST 00 UTC GUIDANCE.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE PATTERN WILL BE IN TRANSITION INTO LATER THIS WEEK INTO THE  
WEEKEND AS A SERIES OF LEAD DIGGING SHORTWAVES AND SECONDARY  
SYSTEMS IN MULTIPLE STREAMS ACT TO CARVE OUT A COOLING AND  
WET/UNSETTLING AMPLIFIED UPPER TROUGH OVER THE EAST AS A TRAILING  
AND RAINFALL FOCUSING FRONT WORKS OFFSHORE THE SOUTH INTO THE GULF.  
THE BULK OF UPPER TROUGH ENERGY LIFTS OUT INTO NEXT WEEK, BUT WITH  
UPSTREAM ENERGIES STILL DIGGING UPSTREAM TO CARVE OUT A RENEWED BUT  
LESS ENERGETIC UPPER TROUGH POSITION OVER THE EAST.  
 
A MAIN SURFACE LOW WILL LIFT OVER EASTERN CANADA FRIDAY INTO THE  
WEEKEND, WHILE FRONTAL AND SECONDARY BOUNDARIES TRAIL DOWN OVER THE  
EAST, THE SOUTH AND INTO THE GULF TO FOCUS LINGERING AND WAVE  
ENHANCING SHOWERS AND THUNDERSTORMS LOCALLY. THE WPC DAY 4/FRIDAY  
EXCESSIVE RAINFALL OUTLOOK SHOWS A MARGINAL THREAT AREA FROM THE  
EAST-CENTRAL GULF COAST AND NORTH-CENTRAL FLORIDA UP THROUGH THE  
COASTAL CAROLINAS. ADDITIONALLY, A NEW MARGINAL RISK AREA IS  
PLANNED FOR PORTIONS OF THE NORTHERN MID-ATLANTIC FOR DAY 4, AND A  
NEW MARGINAL RISK FOR DAY 5 ACROSS PORTIONS OF NEW ENGLAND WITH  
MODEL QPF TRENDING HIGHER DURING THESE TIME PERIODS.  
 
MEANWHILE, UPPER RIDGING WILL PREVAIL OVER MUCH OF A WARMED WEST  
INTO THE WEEKEND AS A SOUTHERN STREAM CLOSED LOW SLOWLY WORKS  
TOWARD THE SOUTHWEST. HOWEVER, AMPLE NORTHERN STREAM EASTERN  
PACIFIC UPPER TROUGH AMPLIFICATION AND SOUTHEASTWARD APPROACH INTO  
THIS WEEKEND AND SUBSEQUENT STEADY INLAND PROGRESSION BREACH INTO  
THE WEST, ALONG WITH THE EJECTION OF THE LEAD SOUTHERN STREAM  
CLOSED SYSTEM, WILL ACT TO PROVIDE RELIEF FROM THE HEAT OVER THE  
WEST WITH THE BUILDING OF MUCH MORE UNSETTLED AND INCREASINGLY  
WIDESPREAD WET FLOW PATTERN SPREADING INCREASINGLY INLAND AND DOWNSTREAM  
TO THE INTERMOUNTAIN WEST AND ESPECIALLY THE NORTHERN ROCKIES.  
 
IN THE WEST, A BUILDING UPPER RIDGE WILL LEAD TO AN EXPANDING AREA  
OF HEAT FROM THE INTERMOUNTAIN WEST INTO THE WEST COAST STATES  
THIS WEEK INTO THE WEEKEND, WITH TEMPERATURES RISING UPWARDS TO 10  
TO 20 DEGREES ABOVE NORMAL. THIS IN PARTICULAR MAY LEAD TO A  
HAZARDOUS HEAT FOCUS FOR THE CALIFORNIA CENTRAL VALLEY INTO DESERT  
SOUTHWEST LATE WEEK/WEEKEND. ABOVE NORMAL TEMPERATURES CLOSER TO  
10-15 DEGREES ABOVE NORMAL SHOULD EXPAND TO THE NORTH-CENTRAL U.S.  
AS THE PERIOD PROGRESSES.  
 
SCHICHTEL/HAMRICK  
 
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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