198
FXUS02 KWBC 190723
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
323 AM EDT FRI SEP 19 2025
VALID 12Z MON SEP 22 2025 - 12Z FRI SEP 26 2025
..DESERT SOUTHWEST HEAT NEXT WEEK
..OVERVIEW
THE MAIN PATTERN DRIVER DURING THE MEDIUM RANGE PERIOD WILL BE A
DEEPENING SHORTWAVE OVER THE NORTHWEST/ROCKIES ON MONDAY. THERE IS
STILL A LOT OF UNCERTAINTY IN HOW THIS EVOLVES AFTER MONDAY, BUT
THE CONSENSUS REMAINS FOR IT TO EVENTUALLY CLOSE OFF INTO A DEEP
UPPER LOW OVER THE CENTRAL PLAINS ON TUESDAY, THEN LINGER OVER/NEAR
THE MID-MISSISSIPPI VALLEY WEDNESDAY-FRIDAY. THIS WOULD FOCUS QPF
ALONG ANY ASSOCIATED FRONTS THROUGH THE OHIO VALLEY AND THE MID-
SOUTH. MEANWHILE, ANOTHER CUTOFF LOW OFF THE CALIFORNIA COAST
SHOULD EVENTUALLY GET PULLED NORTH AND ABSORBED BY ADDITIONAL
ENERGY INTO THE NORTHWEST LATE NEXT WEEK WHILE UPPER RIDGING OVER
THE SOUTHWEST LEADS TO A PERIOD OF TRIPLE DIGIT HEAT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
A LOT OF UNCERTAINTY IN THE GUIDANCE REGARDING A POSSIBLE OMEGA
BLOCK SET UP NEXT WEEK OVER THE CONUS FOR THE MEDIUM RANGE PERIOD.
THIS FEATURES AN UPPER LOW OVER CALIFORNIA, A LARGE CUT-OFF UPPER
LOW OVER THE CENTRAL U.S., AND A STRONG RIDGE IN BETWEEN. THE
MODELS SHOW GOOD AGREEMENT ON A DIGGING SHORTWAVE OVER THE
ROCKIES/HIGH PLAINS ON MONDAY, BUT A LOT OF QUESTIONS REGARDING
THIS EVOLUTION OF THIS THEREAFTER. THE PAST COUPLE OF RUNS OF THE
GFS HAVE SHOWN AN EVENTUAL UPPER LOW POSITION MUCH FARTHER NORTH
OVER THE CENTRAL U.S. AND MORE PROGRESSIVE LATER IN THE WEEK
THROUGH THE NORTHERN PLAINS INTO THE GREAT LAKES. THIS IS A RESULT
OF A MUCH LESS AMPLIFIED FLOW. THE ECMWF, UKMET, AND GENERALLY
ENSEMBLE MEANS SHOW A MUCH MORE AMPLIFIED FLOW WITH A LARGE CUT OFF
LOW OVER THE MISSISSIPPI VALLEY BY MID-WEEK AND LINGERING THERE
FOR SEVERAL DAYS. THE WPC FORECAST AND SENSIBLE WEATHER GRIDS WERE
WEIGHTED HEAVILY TOWARDS THE ECMWF AND ENSEMBLE MEANS, WHICH
MAINTAINS GOOD CONTINUITY WITH THE PREVIOUS FORECAST AS WELL. THE
00Z GUIDANCE TONIGHT ALSO FOLLOWS SUIT WITH PREVIOUS RUNS, WITH THE
CMC BEING CLOSER TO THE GFS SOLUTION.
..WEATHER/HAZARDS HIGHLIGHTS
WIDESPREAD RAIN LOOKS TO FOCUS ALONG SURFACE FRONTAL BOUNDARIES ON
MONDAY FROM THE NORTH- CENTRAL ROCKIES INTO THE PLAINS AND MIDWEST
ASSOCIATED WITH NORTHERN STREAM ENERGY ACROSS THE GREAT LAKES AND
THE EVENTUAL DEVELOPMENT OF A CLOSED LOW OVER THE CENTRAL U.S..
SHOWERS AND THUNDERSTORMS WILL BE SUPPORTED BY INCREASINGLY
ANOMALOUS MOISTURE, WITH PWS OF 1.5-1.75" MONDAY INTO TUESDAY. THIS
MOISTURE WHEN COMBINED WITH ADEQUATE INSTABILITY AND FORCING IS
SUFFICIENT FOR EXCESSIVE RAINFALL CONCERNS WITH SLOW MOVING
ACTIVITY/FLOW PARALLEL TO ANY BOUNDARIES. A MARGINAL RISK IS
HIGHLIGHTED FROM THE CENTRAL PLAINS INTO THE MIDWEST ON MONDAY ON
THE ERO. AS THE UPPER LOW BECOMES MORE DEFINED ON TUESDAY, RAINFALL
SHOULD INCREASE IN INTENSITY AND FOCUS MORE INTO THE CENTRAL
PLAINS AND MID- MISSISSIPPI VALLEY. A BROAD MARGINAL IS IN PLACE
FOR THE DAY 5/TUESDAY ERO. GUIDANCE GENERALLY IS TARGETING EASTERN
NEBRASKA INTO MISSOURI WITH THE HEAVIEST RAIN BUT UNCERTAINTY AND
DRY ANTECEDENT CONDITIONS PRECLUDE ANYTHING MORE THAN A MARGINAL
RIGHT NOW. THIS ACTIVITY WILL MOVE SLOWLY EASTWARD WITH TIME NEXT
WEEK INTO THE MID-SOUTH AND OHIO VALLEY AND EVENTUALLY PARTS OF THE
EAST LATE WEEK. ELSEWHERE, AN UPPER LOW NEAR CALIFORNIA EARLY IN
THE WEEK SHOULD RESULT IN SOME RAINFALL OVER THE STATE AND POSSIBLY
INTO THE SOUTHWEST. THE REST OF THE WEST SHOULD BE DRY UNDERNEATH
OF UPPER LEVEL RIDGING.
A STRONG SURFACE HIGH LINGERING ALONG THE NORTHEASTERN SEABOARD
INTO MONDAY SHOULD MAINTAIN COOL AIR DAMMING EAST OF THE
APPALACHIANS AND SOUTH THROUGH THE CAROLINA PIEDMONT. THIS RESULTS
IN NEAR TO BELOW NORMAL TEMPERATURES EAST OF THE APPALACHIANS.
TEMPERATURES SHOULD TREND A BIT WARMER LATER INTO THE WEEK AS
RIDGING BUILDS AHEAD OF THE CENTRAL U.S. UPPER LOW. AMPLIFYING
RIDGING OVER THE DESERT SOUTHWEST WILL LEAD TO A PERIOD OF WARMER
THAN AVERAGE TEMPERATURES. THIS HEAT MAY CHALLENGE HIGH TEMPERATURE
RECORDS WITH HIGHS INTO THE MID 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, LINGERING INTO THURSDAY WITH
TEMPERATURES BELOW NORMAL. UPPER RIDGING SHOULD BRING ABOVE NORMAL
TEMPERATURES TO PARTS OF THE WEST AS WELL.
SANTORELLI
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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