853  
FXUS02 KWBC 150658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT THU MAY 15 2025  
 
VALID 12Z SUN MAY 18 2025 - 12Z THU MAY 22 2025  
 
***HEAT BUILDS ACROSS THE SOUTHERN PLAINS WHILE LATE SEASON SNOW IS  
EXPECTED FOR THE ROCKIES***  
 
   
..GENERAL OVERVIEW  
 
A TRANSITION TO A MORE AMPLIFIED PATTERN IS EXPECTED AS A LEADING  
UPPER LOW OVER THE NORTHEASTERN U.S. BRIEFLY DEEPENS AND THEN MOVES  
OUT, A LARGE-SCALE TROUGH DIGS SOUTHWARD OVER THE WEST, AND A  
RIDGE BUILDS NORTHWARD BETWEEN THOSE TROUGHS OVER THE  
PLAINS AND MIDWEST STATES. THE MOST SIGNIFICANT WEATHER DURING THE  
PERIOD WILL LIKELY BE ASSOCIATED WITH THE WESTERN UPPER TROUGH AND  
ITS REFLECTION AT THE SURFACE AS A FRONTAL SYSTEM MOVES THROUGH  
THE INTERMOUNTAIN WEST. THIS UPPER TROUGH WILL INDUCE LEE  
CYCLOGENESIS OVER THE CENTRAL/SOUTHERN PLAINS DURING THE SUNDAY-  
MONDAY TIMEFRAME AS THE SYSTEM EJECTS EASTWARD OVER THE PLAINS.  
THE AMPLIFIED, BLOCKY PATTERN WILL ALSO RESULT IN THE SLOWER  
PROGRESSION OF THE INDIVIDUAL SYSTEMS LEADING TO MULTIPLE DAYS OF  
PRECIPITATION OVER THE WESTERN AND THEN CENTRAL U.S., AS WELL AS  
LINGERING PRECIPITATION OVER THE NORTHEAST THIS WEEKEND.  
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT  
 
THE 00Z MODEL GUIDANCE SUITE TODAY CONTINUES TO OFFER VERY GOOD  
SYNOPTIC SCALE AGREEMENT FOR THE UPCOMING WEEKEND, WITH A MULTI-  
DETERMINISTIC MODEL BLEND SUFFICING AS A STARTING POINT IN THE  
FORECAST PROCESS FOR SUNDAY INTO MONDAY, AND SLIGHTLY MORE  
WEIGHTING APPLIED TO THE ECMWF/GFS SOLUTIONS. IN GENERAL, THE CMC  
SOLUTION IS A LITTLE LESS AMPLIFIED THAN THE OTHER GUIDANCE WITH  
THE STORM SYSTEM EJECTING EAST ACROSS THE PLAINS, AND THIS REMAINS  
THE CASE GOING INTO NEXT THURSDAY AS THE LOW PRESSURE SYSTEM  
REACHES THE OHIO VALLEY. MORE IN THE WAY OF MODEL DIFFERENCES EXIST  
WITH THE NEXT SHORTWAVE REACHING THE PACIFIC NORTHWEST BY THURSDAY,  
WITH THE ENSEMBLE MEANS SERVING AS A GOOD STARTING POINT THERE.  
THE WPC FORECAST TRENDED TOWARDS HALF ENSEMBLE MEANS BY THE MIDDLE  
TO END OF NEXT WEEK WHICH SHOWED BETTER CONSISTENCY AND SMOOTHED  
OUT THE SMALLER SCALE DIFFERENCES.  
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
THE ACTIVE WEATHER PATTERN WITH THE STRONG SURFACE LOW DEVELOPING  
OVER THE WESTERN HIGH PLAINS WILL LEAD TO INCREASING SHOWERS AND  
THUNDERSTORMS FOR A WIDE EXPANSE FROM THE DAKOTAS TO THE MIDWEST,  
AND EXTENDING ACROSS PORTIONS OF TEXAS AND OKLAHOMA. PROLONGED  
ADVECTION OF GULF MOISTURE COMBINED WITH AN INCREASINGLY DYNAMIC  
LATE SPRING STORM SYSTEM WILL FUEL THE DEVELOPMENT OF MULTIPLE  
MESOSCALE CONVECTIVE COMPLEXES, AND THE GREATEST CONCENTRATION OF  
THESE WILL LIKELY BE OVER PORTIONS OF MISSOURI AND ARKANSAS. A  
SLIGHT RISK AREA WILL BE VALID FOR THE DAY 4 PERIOD SUNDAY WHERE  
THE HIGHEST CONFIDENCE EXISTS FOR EXCESSIVE RAINFALL. EVEN THOUGH A  
BROAD MARGINAL RISK AREA WILL BE IN PLACE FOR DAY 5/MONDAY, IT IS  
VERY LIKELY THAT PORTIONS OF THAT OUTLOOK AREA WILL EVENTUALLY NEED  
A SLIGHT RISK AS THE EVENT GETS CLOSER. SEVERE THUNDERSTORMS ARE  
ALSO LIKELY TO DEVELOP ACROSS PORTIONS OF THE CENTRAL PLAINS.  
 
ELSEWHERE ACROSS THE CONTINENTAL U.S., EXPECT ADDITIONAL LATE  
SEASON SNOW FOR THE CENTRAL AND NORTHERN ROCKIES BY SUNDAY AND INTO  
MONDAY, WITH THE POTENTIAL FOR OVER A FOOT OF ACCUMULATION FOR  
SOME OF THE HIGHEST MOUNTAIN RANGES OF WYOMING AND COLORADO. FOR  
THE LOWER ELEVATIONS, A MARGINAL RISK AREA FOR EXCESSIVE RAINFALL  
WILL BE VALID FOR BOTH SUNDAY AND MONDAY ACROSS PORTIONS OF THE  
FOUR CORNERS REGION WHERE SLOW MOVING CONVECTION ASSOCIATED WITH  
THE UPPER LOW MAY RESULT IN SOME LOCALIZED FLOODING ACROSS THE HIGH  
DESERT. ACROSS THE NORTHEAST U.S., ANOMALOUS MOISTURE COMBINED  
WITH LOW FLASH FLOOD GUIDANCE VALUES ACROSS PARTS OF MAINE ALLOWED  
FOR THE CONTINUATION OF A MARGINAL RISK AREA FOR THE DAY  
4/SUNDAY ERO FOR THIS REGION OWING TO RE-DEVELOPMENT OF LOW  
PRESSURE OFFSHORE.  
 
THERE WILL BE A TEMPERATURE DICHOTOMY ACROSS THE COUNTRY SUNDAY  
INTO THE EARLY PART OF NEXT WEEK WITH THE AMPLIFIED UPPER LEVEL  
PATTERN IN PLACE. IT WILL BE QUITE CHILLY FOR THIS TIME OF YEAR  
ACROSS MUCH OF THE INTERMOUNTAIN WEST AND THE NORTHERN ROCKIES,  
WITH HIGHS 10-20 DEGREES BELOW MID-MAY CLIMATOLOGY. THIS ALSO HOLDS  
TRUE ACROSS MUCH OF ARIZONA AS WELL, FOLLOWED BY A MODERATION TREND  
BY TUESDAY AS THE UPPER LOW MOVES OUT. IN CONTRAST, IT WILL  
CONTINUE TO BE QUITE HOT ACROSS SOUTHERN TEXAS WITH HEAT RISK IN  
THE MAJOR CATEGORY MOST DAYS, AND IT WILL ALSO BE HOT AND HUMID FOR  
MUCH OF THE DEEP SOUTH AND INTO FLORIDA WITH HIGHS REACHING 90-95  
DEGREES AND PLENTY OF HUMIDITY.  
 
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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