749
FXUS02 KWBC 141859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT WED MAY 14 2025
VALID 12Z SAT MAY 17 2025 - 12Z WED MAY 21 2025
***HEAT BUILDS ACROSS THE SOUTHERN PLAINS WHILE LATE SEASON SNOW IS
EXPECTED FOR THE ROCKIES***
..GENERAL OVERVIEW
A WELL-ORGANIZED LOW PRESSURE SYSTEM THAT WILL INITIALLY BE OVER
THE NORTHERN GREAT LAKES ON SATURDAY WILL LIKELY DEVELOP A TRIPLE
POINT LOW OVER NEW ENGLAND BY SUNDAY BEFORE MOVING OFFSHORE,
BRINGING WIDESPREAD RAIN TO THE NORTHEAST STATES. OUT WEST, AN
AMPLIFIED UPPER TROUGH DEVELOPS OVER THE GREAT BASIN AND THIS SPURS
SURFACE CYCLOGENESIS ACROSS THE CENTRAL PLAINS BY MONDAY,
SUPPORTING WIDESPREAD COVERAGE OF SHOWERS AND THUNDERSTORMS FROM
THE WESTERN HIGH PLAINS TO THE MID-SOUTH TO START NEXT WEEK. THIS
SURFACE LOW THEN TRACKS IN THE GENERAL DIRECTION OF THE GREAT LAKES
BY NEXT WEDNESDAY, WHILE A WEAKER DISTURBANCE AFFECTS THE
NORTHWESTERN STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
UPDATED 00/06Z MODEL GUIDANCE REMAINS IN GENERALLY GOOD AGREEMENT
REGARDING THE SYNOPTIC SCALE PATTERN ACROSS THE CONUS THIS WEEKEND
AND INTO EARLY/MID-NEXT WEEK. AN INCREASINGLY AMPLIFIED PATTERN IS
EXPECTED AS A LEADING UPPER-LOW OVER THE NORTHEASTERN U.S. BRIEFLY
DEEPENS AND LINGERS OVER THE VICINITY, A LARGE-SCALE TROUGH DIGS
SOUTHWARD OVER THE WEST, AND A RIDGE BUILDS NORTHWARD IN BETWEEN
OVER THE PLAINS/MIDWEST. THE MOST SIGNIFICANT WEATHER DURING THE
PERIOD WILL LIKELY BE TIED TO THE WESTERN UPPER-TROUGH AND ITS
REFLECTION AT THE SURFACE AS A FRONTAL SYSTEM MOVES THROUGH THE
INTERMOUNTAIN WEST WITH EVENTUAL LEE CYCLOGENESIS OVER THE
CENTRAL/SOUTHERN PLAINS DURING THE SUNDAY-MONDAY TIMEFRAME AS THE
SYSTEM EMERGES ONTO THE PLAINS. THE AMPLIFIED, BLOCKY PATTERN WILL
ALSO RESULT IN THE SLOW 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. GUIDANCE THEN INDICATES LEADING ENERGY WITH
THE WESTERN TROUGH WILL EVENTUALLY LIFT NORTHEASTWARD OVER THE
MIDWEST/GREAT LAKES BY MID-WEEK. THERE IS SOME DISAGREEMENT ON THE
TIMING OF POTENTIAL UPSTREAM SHORTWAVE ENERGY FROM THE NORTHEASTERN
PACIFIC DROPPING SOUTHWARD OVER THE NORTHWEST U.S./SOUTHWESTERN
CANADA WITH A COLD FRONT AT THE SURFACE, THOUGH THIS LOOKS TO HAVE
MODEST SENSIBLE WEATHER IMPACTS AT THIS TIME.
THE UPDATED WPC FORECAST INITIALLY USES A COMPOSITE BLEND OF THE
00Z ECMWF/UKMET/CMC AND 06Z GFS BEFORE REMOVING THE CONTRIBUTION
FROM THE CMC GIVEN SOME MORE SIGNIFICANT DIFFERENCES IN THE
FORECAST, SPECIFICALLY A FASTER DEPARTURE OF THE UPPER-LOW OVER THE
NORTHEAST EAST INTO THE ATLANTIC AND A MORE AGGRESSIVE DEPICTION
OF SECONDARY NORTHERN STREAM ENERGY OVER THE NORTHWEST/SOUTHWESTERN
CANADA. A CONTRIBUTION FROM THE 00Z ECENS AND 06Z GEFS MEAN IS
ADDED FOLLOWING THE REMOVAL OF THE TIME-LIMITED UKMET GIVEN THE
TYPICAL INCREASING SMALL-SCALE DIFFERENCES IN THE DETERMINISTIC
GUIDANCE. THE UPDATED BLEND NOT SURPRISINGLY MAINTAINS GOOD
CONTINUITY WITH THE PRIOR FORECAST GIVEN GOOD RUN-TO-RUN
CONSISTENCY IN THE MODELS, WITH THE LARGEST DIFFERENCE IN THE
UPDATED FORECAST BEING A MODESTLY SLOWER NORTHEASTWARD PROGRESSION
OF THE CENTRAL U.S. SYSTEM FROM THE PLAINS TO MIDWEST/GREAT LAKES
BY MID- WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS INCREASE IN COVERAGE AND INTENSITY FROM
THE SOUTHERN PLAINS AND EXTENDING TO THE MID-SOUTH OVER THE WEEKEND
WITH ENHANCED MOISTURE CONVERGENCE NEAR A QUASI-STATIONARY FRONTAL
BOUNDARY AND AHEAD OF A DEVELOPING WAVE OF LOW PRESSURE NEAR THE
TEXAS PANHANDLE. THE GUIDANCE SUGGESTS MULTIPLE ROUNDS OF
CONVECTION ACROSS THE REGION, BUT DIFFER ON QPF PLACEMENT, SO A
BROAD MARGINAL RISK AREA IS VALID FOR PORTIONS OF THIS REGION ON
BOTH SATURDAY AND SUNDAY. ANOMALOUS MOISTURE COMBINED WITH LOW
FLASH FLOOD GUIDANCE VALUES ACROSS PARTS OF THE NORTHEAST ALLOWED
FOR THE CONTINUATION OF A MARGINAL RISK AREA FOR THE DAY 4/SATURDAY
ERO FOR THIS REGION AHEAD OF A DEPARTING FRONT AND REDEVELOPMENT
OF LOW PRESSURE OFFSHORE, AND MOISTURE LINGERS ACROSS EASTERN MAINE
WHERE A MARGINAL RISK IS PLANNED FOR SUNDAY.
ACROSS THE ROCKIES, EXPECT ADDITIONAL CHANCES FOR LATE SEASON SNOW
FOR THE CENTRAL AND NORTHERN ROCKIES BY SUNDAY INTO EARLY NEXT
WEEK AS THE NEXT UPPER TROUGH AND SHORTWAVE MOVES IN, WITH THE
POTENTIAL FOR OVER A FOOT OF ACCUMULATION FOR SOME OF THE HIGHEST
MOUNTAIN RANGES. WIDESPREAD MODERATE TO LOCALLY HEAVY RAINFALL
SEEMS LIKELY TO DEVELOP ACROSS THE GREAT BASIN OVER THE WEEKEND AND
INTO THE NORTH-CENTRAL U.S. EARLY NEXT WEEK IN RESPONSE TO THE
DEVELOPING UPPER LOW WHICH WILL CONTINUE TO BE MONITORED. A
MARGINAL RISK AREA IS PLANNED FOR SUNDAY/DAY 5 ACROSS PORTIONS OF
EASTERN NEVADA, SOUTHWEST UTAH, AND NORTHERN ARIZONA WHERE SLOW
MOVING CONVECTION ASSOCIATED WITH THE UPPER LOW MAY RESULT IN SOME
LOCALIZED FLOODING ACROSS THE HIGH DESERT. ANOTHER AREA OF ENHANCED
RAINFALL IS LOOKING MORE LIKELY ACROSS THE NORTHWESTERN HIGH
PLAINS ON SUNDAY AS WELL WITH INCREASED MOISTURE FLUX TO THE NORTH
OF THE DEVELOPING SURFACE LOW EJECTING EAST FROM THE ROCKIES, AND A
MARGINAL RISK AREA IS ALSO PLANNED FOR THIS AREA ON SUNDAY. EXPECT
BOTH A SEVERE WEATHER AND HEAVY RAINFALL THREAT WITH THE PLAINS
SYSTEM DURING THE SUNDAY TO TUESDAY TIMEFRAME GIVEN SEASONABLY
SUFFICIENT MOISTURE, INSTABILITY, AND SHEAR FOR MAY. THE SEVERE
WEATHER RISK CURRENTLY LOOKS TO BE GREATEST ACROSS PORTIONS OF THE
CENTRAL/SOUTHERN PLAINS, WITH A BROADER HEAVY RAINFALL THREAT
ARCING AHEAD OF THE SYSTEM FROM THE NORTHERN PLAINS SOUTHEASTWARD
INTO THE MISSOURI AND UPPER/MIDDLE MISSISSIPPI RIVER VALLEYS. GUSTY
WINDS ARE ALSO LIKELY GIVEN THE STRENGTH OF THE WESTERN SYSTEM,
PARTICULARLY OVER PORTIONS OF THE DESERT SOUTHWEST SATURDAY, AND
ALSO POSSIBLY ALONG THE FOOTHILLS OF THE ROCKIES AND HIGH PLAINS
SUNDAY-MONDAY.
EARLY SEASON EXCESSIVE HEAT IS EXPECTED ACROSS CENTRAL AND
SOUTHERN TEXAS THROUGH THE UPCOMING WEEKEND WITH HIGHS EXCEEDING
100 DEGREES NEAR THE RIO GRANDE AND INTO MUCH OF CENTRAL TEXAS, AND
HEATRISK REACHING THE MAJOR TO EXTREME CATEGORY FOR SOME OF THESE
AREAS. THIS WILL LIKELY SET ADDITIONAL RECORD HIGH TEMPERATURES FOR
THESE AREAS, AND OVERNIGHT LOWS WILL STRUGGLE TO FALL BELOW 75
DEGREES FOR MANY OF THESE SAME AREAS. IN CONTRAST, CHILLY
CONDITIONS ARE LIKELY FOR THE INTERMOUNTAIN WEST AND NORTHERN
ROCKIES/PLAINS WITH HIGHS RUNNING 10 TO PERHAPS 20 DEGREES BELOW
AVERAGE FOR MANY AREAS FROM ARIZONA TO IDAHO WITH THE UPPER LEVEL
TROUGH AND INCREASED CLOUD COVER.
PUTNAM/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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