402
FXUS02 KWNH 160727
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 AM EDT WED SEP 16 2026
VALID 12Z FRI SEP 18 2026 - 12Z TUE SEP 22 2026
...HEAVY RAINFALL THREATENS THE UPPER MIDWEST/GREAT LAKES AND
NORTHEAST THIS WEEKEND...
..OVERVIEW
A TROUGH WILL PRODUCE HEAVY RAINFALL ACROSS PORTIONS OF THE
UPPER MIDWEST/GREAT LAKES AND POTENTIALLY THE NORTHEAST THIS
WEEKEND. MEANWHILE, THE PASSAGE OF A CENTRAL U.S. TROUGH SHOULD
REDUCE HEAVY RAINFALL CONCERNS OVER THE SOUTHWEST AND SOUTHERN
PLAINS/ROCKIES THIS WEEKEND BEFORE AN EAST PACIFIC DISTURBANCE
RENEWS MONSOON STORMS ACROSS THE REGION EARLY NEXT WEEK. A MID-
LEVEL DISTURBANCE MEANDERING AROUND THE FLORIDA PENINSULA SHOULD
GENERATE MULTIPLE DAYS OF HEAVY RAINFALL ACROSS SOUTHERN FLORIDA
BEGINNING THIS WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODELS ARE IN RELATIVELY GOOD AGREEMENT ON THE
EVOLUTION OF THE NORTHERN STREAM PATTERN DURING THE MEDIUM RANGE
PERIOD. WHERE MODELS DIVERGE FROM ONE ANOTHER ARE OVER THE FLORIDA
PENINSULA WITH THE TIMING OF A RETROGRADING CLOSED MID-LEVEL
DISTURBANCE, AS WELL AS THE TIMING AND AMPLITUDE OF A TROUGH MOVING
INTO THE SOUTHWEST EARLY NEXT WEEK.
A GENERAL MODEL BLEND CONSISTING OF THE AVAILABLE DETERMINISTIC
(MINUS THE UKMET) AND AI MODELS WAS USED ON DAY 3. THE CANADIAN
BEGINS TO DIVERGE FROM THE EURO-GFS SUITE CONSENSUS ON DAY 4 SO
IT'S REMOVED FROM THE BLEND. THE ENSEMBLE MEANS ARE INTRODUCED ON
DAY 6 AND MAKE UP A MAJORITY OF THE BLEND THROUGH DAY 7 DUE TO
UNCERTAINTIES IN THE SOUTHWEST.
..WEATHER/HAZARDS HIGHLIGHTS
A POTENT LOW PRESSURE SYSTEM WILL BRING ROUNDS OF THUNDERSTORMS
AND HEAVY RAINFALL TO PORTIONS OF THE NORTH-CENTRAL U.S. LATER
THIS WEEK. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
SPREAD INTO PARTS OF THE UPPER MIDWEST/GREAT LAKES, WHERE A SLIGHT
RISK (AT LEAST 15 PERCENT CHANCE) OF EXCESSIVE RAINFALL IS IN
EFFECT ON SATURDAY. THUNDERSTORMS AND HEAVY RAINFALL FOCUS SHOULD
EXPAND INTO THE OHIO VALLEY AND NORTHEAST ON SUNDAY, BEFORE
DROPPING SOUTH INTO THE MID-ATLANTIC BY EARLY NEXT WEEK.
SHORTWAVE DISTURBANCES STREAMING NORTH THROUGH THE
SOUTHWEST/SOUTHERN PLAINS WILL GENERATE A LITTLE BIT MORE
CONVECTION OVER NEW MEXICO ON FRIDAY BEFORE AN AMPLIFYING TROUGH
SHIFTS THE UNSETTLED WEATHER INTO THE CENTRAL/SOUTHERN PLAINS THIS
WEEKEND. AN EAST PACIFIC TROUGH MOVING INTO THE SOUTHWEST SHOULD
REIGNITE MONSOONAL MOISTURE OVER NEW MEXICO LEADING TO HEAVY
RAINFALL CONCERNS BY EARLY NEXT WEEK. SLOT CANYONS AND DRY WASHES
ARE ESPECIALLY SUSCEPTIBLE TO FLASH FLOODING FROM ANY STORMS THAT
DEVELOP.
AN ANOMALOUS RIDGE WILL HAVE ITS FINAL DAY OF GENERATING
WIDESPREAD RECORD
BREAKING TEMPERATURES IN THE SOUTHERN PLAINS, LOWER MISSISSIPPI
VALLEY AND TENNESSEE VALLEY ON SATURDAY BEFORE CONDITIONS BEGIN TO
MODERATE ACROSS THE REGION EARLY NEXT WEEK.
KEBEDE
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES
ARE AT:
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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