683
FXUS02 KWBC 091913
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
313 PM EDT WED JUL 9 2025
VALID 12Z SAT JUL 12 2025 - 12Z WED JUL 16 2025
...HEAVY RAIN WITH FLASH FLOODING POTENTIAL IN THE SOUTHERN
PLAINS...
..OVERVIEW
A FAIRLY TYPICAL SUMMER PATTERN IS FORECAST ACROSS THE LOWER 48
DURING THIS WEEKEND INTO NEXT WEEK, WITH THE MAIN JET STREAM OVER
THE NORTHERN TIER (ANCHORED BY A NORTH-CENTRAL CANADA UPPER LOW)
PUSHING SHORTWAVES AND FRONTS THROUGH THE NORTH-CENTRAL U.S. TO
NORTHEAST. MEANWHILE WEAK SHORTWAVES CAUSE MINOR DISTURBANCES IN
THE LARGE SUBTROPICAL RIDGE ACROSS THE SOUTHERN TIER CAUSING SUMMER
HEAT. THESE SHORTWAVES, SURFACE FRONTS, AND INSTABILITY CREATED BY
HOT AND MOIST AIR WILL CAUSE RAIN AND THUNDERSTORM CHANCES FOR THE
CENTRAL AND EASTERN U.S., WITH A PARTICULAR FOCUS IN THE SOUTHERN
PLAINS OVER THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS REASONABLY AGREEABLE ON THE LARGE SCALE PATTERN,
INCLUDING TROUGHING STRETCHING INTO THE NORTHERN/CENTRAL PLAINS TO
THE NORTH OF SUBTROPICAL RIDGING. BUT MODELS DIFFER IN THE
PLACEMENT OF THE SHORTWAVES ON ANY GIVEN DAY, WHICH AFFECTS
SENSIBLE WEATHER PARAMETERS LIKE FRONTAL PLACEMENT AND QPF. THE
FIRST MODEL CONCERN WAS THE 00Z UKMET, WHICH HAD A SHORTWAVE THAT
SPUN UP A RELATIVELY STRONG SURFACE LOW IN THE UPPER MIDWEST AT THE
START OF THE PERIOD SATURDAY UNLIKE OTHER GUIDANCE. THUS THE EARLY
PART OF THE FORECAST PERIOD WAS BASED ON A BLEND OF THE 00Z ECMWF,
00/06Z GFS, AND LESSER 00Z CMC.
INTO EARLY NEXT WEEK, MODELS SHOW JUST MINOR TIMING DIFFERENCES
WITH THE FIRST TROUGH MOVING INTO THE NORTHEAST. BEHIND THAT SYSTEM
THERE IS MORE SPREAD WITH A POSSIBLE NEXT TROUGH OVER ALBERTA OR SO
AND POKING INTO THE INTERIOR NORTHWEST AROUND MONDAY. GFS AND ECMWF
RUNS HAVE PERSISTENTLY SHOWN THE TROUGH IN THIS POSITION MONDAY
BEFORE IT MAY SLIGHTLY DEEPEN AS IT MOVES EASTWARD. HOWEVER, THERE
IS A LOWER PROBABILITY SOLUTION FOR FLATTER FLOW THERE AND THE
TROUGHING DEVELOPING FARTHER EAST OVER WESTERN ONTARIO OR SO. CMC
RUNS AND A SIGNIFICANT PROPORTION OF AI/ML MODELS SHOW THIS.
ENSEMBLE SPREAD PLOTS, ESPECIALLY ONES INCLUDING THE AI MODELS,
INDICATE NOTABLE SPREAD NEAR THE U.S./CANADA BORDER WITH THIS.
HOWEVER, ONE OF THE BEST PERFORMING AI MODELS, THE EC-AIFS, IS
CLOSER TO THE OPERATIONAL GFS/EC. THUS WILL CONTINUE TO MONITOR BUT
LEAN TOWARD A GFS/EC (AND AIFS) SOLUTION FOR NOW. BY TUESDAY-
WEDNESDAY THERE IS ACTUALLY A BIT BETTER AGREEMENT AS THE TROUGH IS
OVER CENTRAL NORTH AMERICA NO MATTER WHERE IT DEVELOPS--THOUGH THE
06Z AND 12Z GFS RUNS APPEAR TOO STRONG WITH THE RESULTANT SURFACE
LOW IN SOUTH-CENTRAL CANADA. THROUGH THE MID TO LATE MEDIUM RANGE
PERIOD, REDUCED THE PROPORTION OF DETERMINISTIC MODELS IN FAVOR OF
THE GEFS/EC ENSEMBLE MEANS TO MINIMIZE INDIVIDUAL MODEL SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONTAL SYSTEM WILL PUSH THROUGH THE MIDWEST AND TRAIL ACROSS
THE SOUTH-CENTRAL PLAINS THIS WEEKEND. CONVECTION IS LIKELY AHEAD
OF IT WHERE MOISTURE AND INSTABILITY POOL, AND A LARGE DAY
4/SATURDAY MARGINAL RISK COVERS THE POTENTIAL FOR ISOLATED FLASH
FLOODING IN THESE AREAS. RELATIVELY GREATER CHANCES OF FLASH
FLOODING ARE CENTERED OVER OKLAHOMA OR SO, WHERE AN MCS IS LIKELY
TO DEVELOP AND TRAIN. MODEL GUIDANCE SHOWS SPREAD IN WHERE THIS
WILL SET UP. AI MODELS HAVE BEEN FAVORING A SOUTHEASTERN POSITION
CLOSER TO THE RED RIVER, AND THE 00/12Z ECMWF AND THE 12Z CMC ARE
TRENDING IN THIS SOUTHERLY DIRECTION. THUS STARTED TO LEAN TOWARD
THIS BY BROADENING THE SLIGHT SOUTHWARD ACROSS THE RED RIVER
COMPARED TO THE PREVIOUS ISSUANCE. MUCH THE SAME METEOROLOGICAL
SETUP IS LIKELY ON SUNDAY, BUT WITH THE FRONT PROGRESSING EASTWARD
ACROSS THE GREAT LAKES. THUS SHOW A MARGINAL RISK ALONG AND AHEAD
OF THE FRONT ON SUNDAY AS WELL. COMPARED TO THE PREVIOUS DAY 5 ERO,
EXPANDED THE MARGINAL NORTH INTO THE LOWER GREAT LAKES REGION
WHERE THE BEST FORCING AND STILL SUFFICIENT INSTABILITY IS, AND
EXPANDED WEST THROUGH THE SOUTHERN ROCKIES/HIGH PLAINS WITH A
PARTICULAR NOD TOWARD THE SENSITIVE BURN SCARS THERE. WILL CONTINUE
TO HOLD OFF ON ANY SLIGHT RISKS WITHOUT ANY CONSENSUS IN HEAVY
AMOUNTS AND THEIR POSITION.
FARTHER SOUTH, ABOVE NORMAL MOISTURE IS FORECAST TO MOVE INTO
FLORIDA ALONG WITH AMPLE INSTABILITY UNDERNEATH THE BROAD
SUBTROPICAL RIDGE. A MARGINAL RISK REMAINS IN PLACE FOR DAY
5/SUNDAY FOR MUCH OF THE PENINSULA FOR THE LOW END FLASH FLOODING
THREAT. THIS LOOKS TO LAST INTO AT LEAST MONDAY, AND CONVECTION MAY
INCREASE IN THE SOUTHEASTERN STATES BY TUESDAY AS A FRONT MOVES
CLOSER.
THE NEXT FRONT COMING INTO THE NORTH-CENTRAL U.S. MONDAY-TUESDAY
IS LIKELY TO CAUSE ADDITIONAL RAIN THERE MONDAY AND ESPECIALLY INTO
TUESDAY. DETAILS IN PLACEMENT AND AMOUNTS WILL VARY DEPENDING ON
THE EVENTUAL EVOLUTION OF THE TROUGH, SO STAY TUNED FOR FURTHER
DETAILS.
TEMPERATURE-WISE, THE WESTERN U.S. CAN EXPECT ABOVE NORMAL
TEMPERATURES AS UPPER RIDGING MOSTLY SETS UP TO THE WEST OF ROUNDS
OF TROUGHING. THIS PUTS HIGHS WELL INTO THE 100S AND 110S FOR THE
DESERT SOUTHWEST, AND NEARING/EXCEEDING 100F FARTHER NORTH IN
INTERIOR/LOWER ELEVATION AREAS OF THE GREAT BASIN. TEMPERATURES
COULD BE A FEW DEGREES COOLER THAN AVERAGE ESPECIALLY FOR HIGHS FOR
THE SOUTH-CENTRAL U.S. THIS WEEKEND AS CLOUDS AND RAIN HOLD
TEMPERATURES DOWN. THE SOUTHEAST SHOULD BE NEAR NORMAL TO A FEW
DEGREES ABOVE, FOR TYPICAL SUMMER HEAT AND HUMIDITY. TEMPERATURES
WILL GENERALLY BE 5-10 DEGREES ABOVE NORMAL IN THE GREAT LAKES TO
NORTHEAST. INTO NEXT WEEK, DEPENDING ON THE EVOLUTION OF THE NORTH-
CENTRAL U.S. TROUGH, TEMPERATURES MAY COOL NOTABLY, WITH HIGHS
PERHAPS ONLY IN THE 70S THROUGH THE NORTH-CENTRAL PLAINS FOR
TUESDAY/WEDNESDAY.
TATE
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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