061
FXUS02 KWBC 152005
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
405 PM EDT THU MAY 15 2025
VALID 12Z SUN MAY 18 2025 - 12Z THU MAY 22 2025
...HEAT BUILDS ACROSS THE SOUTHERN PLAINS AND FLORIDA 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
LATEST MODEL GUIDANCE CONTINUES TO BE IN REASONABLE AGREEMENT, AT
LEAST ON THE LARGE SCALE, FOR THE AMPLIFYING TROUGH OVER THE WEST
INTO EARLY NEXT WEEK, BUT WITH SOME STRUGGLE ON THE DETAILS. THE
WPC FORECAST FOR TODAY WENT WITH A GENERAL MODEL COMPROMISE FOR THE
DAYS 3 (SUNDAY) - DAY 5 (TUESDAY) TIME PERIOD. AFTER THIS, THE CMC
WAS A LITTLE DIFFERENT WITH THE EVOLUTION OF THE TROUGH AS IT
EJECTS INTO THE MIDWEST, WITH THE ECMWF AND GFS MORE CONSISTENT
WITH EACH OTHER AND THE ENSEMBLE MEANS. ALSO SOME SIGNIFICANT
TIMING DIFFERENCES ACROSS THE NORTHWEST LATE PERIOD WITH SMALLER
SCALE AND WEAKER SHORTWAVES MOVING THROUGH THE FLOW. FOR THIS
REASON, IT SEEMED BEST TO TREND MORE TOWARDS THE ENSEMBLE MEANS FOR
THE LATE PERIOD, WITH SMALLER CONTRIBUTIONS FROM THE DETERMINISTIC
ECMWF AND GFS. THIS ALSO MAINTAINED FAIRLY GOOD CONSISTENCY WITH
THE PREVIOUS WPC FORECAST AS WELL.
..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 THE MIDDLE MISSISSIPPI
VALLEY. A SLIGHT RISK AREA CONTINUES FOR THE DAY 4 PERIOD SUNDAY
WHERE THE HIGHEST CONFIDENCE EXISTS FOR EXCESSIVE RAINFALL, WITH
SOME EXPANSION ACROSS MISSOURI FOR THIS AFTERNOONS UPDATE. FOR DAY
5, ALSO WENT AHEAD AND UPGRADED THE SAME GENERAL REGION AND INTO
SOUTHERN ILLINOIS TO A SLIGHT RISK GIVEN THE OVERLAP OF HEAVY
RAINFALL POTENTIAL WITH DAY 4. SEVERE THUNDERSTORMS ARE ALSO LIKELY
TO DEVELOP ACROSS PORTIONS OF THE CENTRAL PLAINS IN ASSOCIATION
WITH THIS ACTIVITY.
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.
SANTORELLI/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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