438
FXUS02 KWBC 291832
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT THU MAY 29 2025
VALID 12Z SUN JUN 01 2025 - 12Z THU JUN 05 2025
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
AN AMPLIFIED SPLIT-FLOW PATTERN CONTINUES TO PRODUCE LOWER THAN
AVERAGE PREDICTABILITY IN THE MEDIUM RANGE PERIOD, PARTICULARLY FOR
DAY 5 AND BEYOND. WHILE MOST OF THE DETERMINISTIC MODELS HAVE A
DECENT HANDLE ON THE OVERALL LARGE SCALE PATTERN ACROSS THE
CONTINENTAL U.S., RUN-TO-RUN CHANGES OF TIMING, POSITION, AND
STRENGTH OF SMALLER SCALE FEATURES ARE STILL LEADING TO DOWNSTREAM
IMPACTS ON FRONTAL SYSTEMS, QPF, AND OTHER SENSIBLE WEATHER. THE
TWO LARGEST SOURCES OF UNCERTAINTY STEM FROM THE HANDLING OF
TROUGHING ALONG THE WEST AND EAST COASTS WITH THE POTENTIAL FOR
THOSE TROUGHS TO CLOSE OFF INTO CLOSED LOWS. AS ALLUDED TO ABOVE,
THERE ARE SEVERAL SHORTER WAVELENGTH FEATURES EMBEDDED WITHIN THESE
TROUGHS WHICH ARE CHANGING BOTH THE SPATIAL AND TEMPORAL EVOLUTION
(TO VARYING DEGREES) WITH EVERY MODEL CYCLE.
FOR THIS WPC FORECAST PACKAGE, A COMPOSITE BLEND FEATURING THE 00Z
ECMWF, 00Z CMC, 00Z UKMET, 00Z EC ENSEMBLE MEAN AND 06Z GEFS
ENSEMBLE MEAN WAS FAVORED, WITH THE WEIGHTING OF ENSEMBLE MEANS
INCREASING FROM 30 PERCENT ON DAY 3 TO 50 PERCENT BY DAY 5 AND 60
PERCENT FOR DAYS 6 AND 7. THE 00Z AND 06Z DETERMINISTIC RUNS OF THE
GFS WERE NOT CONSIDERED FOR THE COMPOSITE BLEND DUE TO BEING MUCH
TOO STRONG AND SLOW WITH A SHORTWAVE/VORT MAX DESCENDING DOWN THE
EASTERN FLANK OF A WESTERN U.S. RIDGE AT THE START OF THE PERIOD,
NEGATIVELY AFFECTING THE REMAINDER OF ITS FORECAST RUN (WITH
RESPECT TO THE OTHER SOURCES OF GUIDANCE UTILIZED IN THE BLEND).
THE LARGE PERCENTAGE OF ENSEMBLE MEANS USED FOR THE LATTER HALF OF
THE FORECAST PERIOD OFFERED TO SMOOTH OUT SOME OF THE SMALLER SCALE
DIFFERENCES, OFFERING STABILITY AND ACCEPTABLE CONTINUITY TO THE
PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A SERIES OF SHORTWAVES WILL CONTINUE TO DIG INTO AN AMPLIFIED
UPPER TROUGH WORKING SLOWLY OFF THE EAST COAST AND POTENTIALLY
DEVELOPING A SEPARATED CLOSED LOW. A WAVY TRAILING FRONT WILL
SETTLE NEARBY FROM THE WESTERN ATLANTIC SOUTHWESTWARD TO THE GULF.
WHILE UNCERTAIN LOWS COULD ACT TO BRING SOME ACTIVITY FROM THE
COASTAL AREAS UP THE EASTERN SEABOARD SUNDAY AND INTO NEXT WEEK,
PARTICULAR RUNOFF ISSUES MAY DEVELOP WITH TIME FOR SOUTH FLORIDA
URBAN AREAS GIVEN DEEPER LOWER LATITUDE MOISTURE AVAILABILITY AND
SUPPORT TO MONITOR.
GUIDANCE CONTINUES TO OVERALL FAVOR UPPER TROUGH AMPLIFICATION
WITH MULTIPLE SYSTEMS INTO THE WEST ALONG WITH LEAD EJECTION OF A
SOUTHERN STREAM CLOSED SYSTEM FROM OFFSHORE BAJA THROUGH THE
SOUTHWEST INTO THE ROCKIES. THIS TRANSITION WILL ACT TO PROVIDE
RELIEF FROM WEEKEND HEAT OVER PORTIONS OF THE WEST WITH THE
BUILDING OF A MUCH MORE UNSETTLED AND INCREASINGLY WET FLOW PATTERN
FARTHER INLAND AND DOWNSTREAM OVER THE INTERMOUNTAIN WEST AND
ESPECIALLY THE NORTHERN ROCKIES THROUGH MIDWEEK. DESPITE THE
CALENDAR FLIPPING INTO JUNE, THIS PATTERN WILL SUPPORT A THREAT FOR
ENHANCED MOUNTAIN SNOW IN THE HIGHEST ELEVATIONS OF THE NORTHERN
ROCKIES. FAVORABLE UPPER SUPPORT, FRONTAL TRANSLATION, AND
ANOMALOUS MOISTURE ALONG WITH DOWNSTREAM CYCLO-/FRONTOGENESIS OVER
THE PLAINS SHOULD ALSO ACT TO ENHANCE PRECIPITATION AND AN EMERGING
CONVECTIVE PATTERN FROM PORTIONS OF THE NORTHERN ROCKIES TO THE
NORTHERN PLAINS BY DAY 5/MONDAY. DESPITE GUIDANCE SHIFTING AROUND A
BIT, INCREASING CONVECTIVE/QPF TRENDS SUPPORT THE INTRODUCTION OF
A BROAD MARGINAL RISK ERO FROM PORTIONS OF MINNESOTA AND THE
DAKOTAS TO SOUTHEAST WYOMING AND NORTHEAST COLORADO WITH THIS
AFTERNOON'S UPDATE.
MILLER/SCHICHTEL
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page