052
FXUS02 KWBC 140659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM 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
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 AND SLIGHTLY MORE WEIGHTING APPLIED TO THE
ECMWF/GFS SOLUTIONS. GUIDANCE AGREES WELL WITH ANOTHER TROUGH
AMPLIFYING OVER THE WEST THIS WEEKEND, WITH AN EVENTUAL CLOSED LOW
LOCATED OVER/NEAR THE CENTRAL GREAT BASIN. THIS LOW WILL EVENTUALLY
LIFT NORTHWARD INTO THE NORTH-CENTRAL U.S. EARLY NEXT WEEK BUT
WITH PLENTY OF UNCERTAINTY IN ENERGY DISPERSION WITHIN AND AROUND
LOW WHICH WOULD HAVE IMPLICATIONS ON SENSIBLE WEATHER ACROSS THIS
REGION. THE WPC FORECAST TRENDED TOWARDS HALF ENSEMBLE MEANS BY THE
MIDDLE OF NEXT WEEK WHICH SHOWED BETTER CONSISTENCY AND SMOOTHED
OUT THE SMALLER SCALE DIFFERENCES.
..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 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.
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.
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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