871
FXUS02 KWNH 180728
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 AM EDT THU SEP 18 2025
VALID 12Z SUN SEP 21 2025 - 12Z THU SEP 25 2025
..DESERT SOUTHWEST HEAT WAVE NEXT WEEK
..OVERVIEW
GUIDANCE IS COMING INTO AGREEMENT ON A POTENT TROUGH ENTERING THE
PACIFIC NORTHWEST SUNDAY, DIGGING AND AMPLIFYING OVER THE PLAINS ON
MONDAY, CLOSING OFF INTO A DEEP LOW TUESDAY OVER THE CENTRAL PLAINS
THEN LINGERING OVER THE CENTRAL STATES THROUGH MIDWEEK.
TROUGHING/UPPER LOW PRESSURE LINGERS ALONG/OFF THE CALIFORNIA COAST
AFTER BECOMING CUTOFF ON SUNDAY. OTHERWISE, DEEP RIDGING OVER THE
DESERT SOUTHWEST IS EXPECTED MONDAY THROUGH MIDWEEK SETTING UP A
HEAT WAVE. PERSISTENT TROUGHING OVER THE CENTRAL U.S. AHEAD OF THE
APPROACHING POTENT TROUGH SHOULD ALLOW LOCALLY HEAVY RAIN TO
LINGER SUNDAY AND MONDAY OVER THE SOUTHERN PLAINS AND MID-SOUTH.
COOL AIR DAMMING LINGERS OVER THE EASTERN SEABOARD THROUGH THE
CAROLINA PIEDMONT SUNDAY AND MONDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
00Z GUIDANCE CONSENSUS IS NOW ON BOARD WITH A DEEP CLOSED LOW OVER
THE CENTRAL U.S. BY TUESDAY. THE 12Z CMC/UKMET DID NOT HAVE THAT
FEATURE, BUT THE 00Z RUNS HAVE JOINED THE EC/GFS. POSITIONING OF
THIS CUTOFF LOW IS INHERENTLY UNCERTAIN, SO THAT WILL BE A KEY AREA
OF FOCUS OVER THE NEXT WEEK. THE TIMING OF THE POTENT TROUGH IS
GETTING BETTER WITH THE 00Z CONSENSUS TO HAVE THE TROUGH AXIS OVER
CENTRAL MONTANA BY 12Z MONDAY. THIS TROUGH WILL ALLOW THE LOW ALONG
THE CALIFORNIA COAST TO BECOME CUTOFF AND DRIFT OFFSHORE, THOUGH
ALL 00Z GUIDANCE EXCEPT THE UKMET HAS THE LOW BACK TO THE COAST BY
12Z TUESDAY. THE DESERT SOUTHWEST HAS DEEP RIDGING THROUGH NEXT
WEEK AS CHAMPIONED MOST BY THE EC (AS WELL AS THE EC-AIFS). THE WPC
FORECAST (WHICH USES 12Z/18Z GUIDANCE IN THE EVENING) HEAVILY
FAVORED THE EC/GFS WITH THEIR ENSEMBLE MEANS TO FILL THE BLEND
SINCE THE 12Z CMC/UKMET WERE NOT ON BOARD WITH THE CENTRAL U.S.
LOW. WPC QPF DAYS 4-7 FAVORS THE EC AND EC-AIFS TO ENHANCE THE
NBM.
..WEATHER/HAZARDS HIGHLIGHTS
CONVERGENCE OF GULF MOISTURE STREAMING NORTH TOWARD LINGERING
TROUGHING OVER THE NORTH-CENTRAL U.S. ALLOWS FOR SOME SLOWER
MOVING CLUSTERS OF LOCALLY HEAVY THUNDERSTORMS OVER PORTIONS OF
THE SOUTHERN PLAINS/MID-SOUTH SUNDAY AND MONDAY. DAY 4 AND 5
MARGINAL EROS ARE OVER THESE AREAS WITH ONLY A LITTLE EASTWARD
PROGRESSION, SUGGESTING THE RISK FOR REPEATING ACTIVITY. MOISTURE
BEGINS AS NOT THAT ANOMALOUS, BUT PW OF 1.5" INCREASING TO AROUND
1.75" COMBINED WITH ADEQUATE INSTABILITY AND FORCING IS SUFFICIENT
FOR EXCESSIVE RAINFALL CONCERNS WITH SLOW MOVING ACTIVITY/FLOW
PARALLEL TO ANY BOUNDARIES. FURTHER HEAVY RAIN AHEAD OF THE UPPER
LOW THAT CUTS OFF COULD OCCUR OVER SIMILAR AREAS LATER IN THE WEEK,
SO ATTENTION WILL NEED TO BE GIVEN TO THIS THREAT.
RIDGING SHIFTS NORTHEAST FROM THE MIDWEST ALLOWING MAX TEMPS OF
10-15 DEGREES ABOVE NORMAL TO SHIFT TO THE INTERIOR NORTHEAST.
MEANWHILE A STRONG SURFACE HIGH LINGERING ALONG THE NORTHEASTERN
SEABOARD SUNDAY AND MONDAY SHOULD MAINTAIN COOL AIR DAMMING EAST
OF THE APPALACHIANS AND SOUTH THROUGH THE CAROLINA PIEDMONT.
ONSHORE FLOW, SCATTERED CLOUDS, AND POSSIBLE SHOWERS WILL RESULT IN
BELOW NORMAL TEMPERATURES EAST OF THE APPALACHIANS.
AMPLIFYING RIDGING OVER THE DESERT SOUTHWEST WILL LEAD TO A
HEAT WAVE ACROSS THE DESERT SOUTHWEST EARLY THROUGH MID NEXT WEEK.
THIS HEAT MAY CHALLENGE HIGH TEMPERATURE RECORDS WITH HIGHS
SOARING INTO THE MID TO UPPER 100S FOR SOME LOCATIONS. DOWNSTREAM
OF THE RIDGE, A SERIES OF SHORTWAVES WILL LIKELY COMBINE TO FORM A
DEEP, CUTOFF MID-LEVEL LOW PRESSURE SYSTEM ACROSS THE CENTRAL U.S.
BY TUESDAY AND WEDNESDAY. THIS WILL LIKELY RESULT IN FAIRLY
WIDESPREAD UNSETTLED WEATHER WITH TEMPERATURES TRENDING NEAR TO
BELOW NORMAL.
JACKSON
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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