486
FXUS63 KGRB 140720
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
220 AM CDT THU AUG 14 2025
FORECAST DISCUSSION FOR ROUTINE MORNING FORECAST ISSUANCE
KEY MESSAGES
- RELATIVELY TYPICAL LATE SUMMER WEATHER EXPECTED THROUGH FRIDAY
WITH A SLIGHT CHANCE OF SHOWERS (LESS THAN 25%) OVER NORTH-
CENTRAL WI LATE TONIGHT AND FRIDAY.
- PERIODS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED FROM LATE
FRIDAY NIGHT THROUGH MONDAY. STRONG TO SEVERE THUNDERSTORMS MAY
BE POSSIBLE AT TIMES, PARTICULARLY FROM LATE FRIDAY NIGHT
THROUGH SATURDAY NIGHT.
- THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ON SATURDAY. THERE
IS A 20-40% CHANCE OF RAINFALL GREATER THAN 1 INCH ACROSS THE
ENTIRE AREA.
DISCUSSION
ISSUED AT 218 AM CDT THU AUG 14 2025
SHORT TERM...TODAY...TONIGHT...AND FRIDAY
THE LATEST RAP ANALYSIS AND SATELLITE/RADAR IMAGERY INDICATE A
SURFACE RIDGE AXIS POSITIONED ACROSS THE WESTERN GREAT LAKES EARLY
THIS MORNING. OVER FAR NORTHEAST WISCONSIN, AREAS OF STRATO-CU
ARE PRESENT, WHILE PATCHY FOG, MOST WIDESPREAD OVER NORTH-CENTRAL
WISCONSIN, IS REDUCING VISIBILITIES ELSEWHERE. MEANWHILE, WARM
ADVECTION IS OCCURRING OVER THE NORTHERN PLAINS TO NORTHERN
MISSISSIPPI VALLEY, SPURRED ON BY A ROBUST 45 KT LOW-LEVEL JET,
WHERE SHOWERS AND THUNDERSTORMS ARE CURRENTLY ONGOING. AS
SHORTWAVE ENERGY AND WARM ADVECTION ADVANCE EASTWARD AHEAD OF A
COLD FRONT, LIGHT PRECIPITATION CHANCES WILL BE THE PRIMARY FOCUS
THROUGH FRIDAY AFTERNOON.
HIGH PRESSURE WILL GRADUALLY SLIDE EAST OF THE REGION TODAY,
ALLOWING FOR A SHIFT IN THE SYNOPTIC PATTERN. WEAK WARM ADVECTION
WILL BEGIN TO MOVE INTO WESTERN AND CENTRAL WISCONSIN, LEADING TO
INCREASING MID-LEVEL CLOUDS ABOVE 7000 FT. IN ADDITION, FAIR
WEATHER CONVECTIVE CLOUDS ARE EXPECTED TO BEGIN POPPING UP BY LATE
MORNING OR MIDDAY ACROSS THE AREA. DESPITE THESE DEVELOPMENTS,
THE BEST CHANCES FOR RAIN SHOULD REMAIN WEST OF OUR FORECAST AREA
THROUGH THE DAY.
WARM AIR AND MOISTURE ADVECTION WILL CONTINUE TONIGHT AS RAIN
CHANCES CREEP CLOSER TO THE AREA. LIGHT RAIN COULD REACH AS FAR
EAST AS NORTH-CENTRAL WISCONSIN BY LATE TONIGHT, BUT FOR NOW, THE
BULK OF OUR FORECAST AREA IS EXPECTED TO REMAIN DRY. THIS IS DUE
TO THE AXIS OF HIGHER PRECIPITABLE WATER AND ELEVATED INSTABILITY
REMAINING PRIMARILY OVER WESTERN WISCONSIN DURING THIS PERIOD.
ON FRIDAY, INCREASING SOUTHWEST FLOW WILL COMBINE WITH RISING
INSTABILITY AHEAD OF AN APPROACHING COLD FRONT. THE AXIS OF HIGHER
PRECIPITABLE WATER IS FORECAST TO SPREAD ACROSS NORTH-CENTRAL
WISCONSIN. FURTHERMORE, ELEVATED INSTABILITY WILL INCREASE ABOVE A
MID-LEVEL CAP, WHICH IS EXPECTED TO BE CENTERED AROUND 6,000
FEET. GIVEN THESE CONDITIONS, SMALL CHANCES OF SHOWERS HAVE BEEN
ADDED TO THE FORECAST, PRIMARILY OVER CENTRAL AND NORTH-CENTRAL
WISCONSIN ON FRIDAY. TEMPERATURES WILL BE WARMER, WITH HIGHS IN
THE LOWER TO MIDDLE 80S, AND ACCOMPANIED BY HIGHER HUMIDITY.
LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY
THE LONG-TERM PATTERN WILL BE HIGHLIGHTED BY MEAN TROUGHING
OFFSHORE OF BRITISH COLUMBIA AND SUB-TROPICAL RIDGING ACROSS THE
GREAT LAKES AT THE START OF THE PERIOD. THIS OVERALL PATTERN IS
EXPECTED TO GRADUALLY RETROGRADE OVER THE NEXT WEEK, WHICH WILL
ULTIMATELY BRING THE REGION INTO A NORTHWEST FLOW ALOFT BY TUESDAY
AND WEDNESDAY.
AUGMENTED BY A RETROGRADING SUB-TROPICAL RIDGE AND A MODEST LOW-
LEVEL JET UP TO 35 KNOTS, A WARM AND UNSTABLE AIRMASS WILL SURGE
INTO THE REGION AHEAD OF A SLOW-MOVING COLD FRONT ON FRIDAY NIGHT.
MASS CONVERGENCE ON THE NOSE OF THE LOW- LEVEL JET OVER EAST-
CENTRAL MINNESOTA IS THE MOST PROBABLE LOCATION FOR INITIAL
MESOSCALE CONVECTIVE SYSTEM (MCS) ACTIVITY. DEEP LAYER WIND
TRAJECTORIES WOULD THEN MOVE THIS ACTIVITY EASTWARD INTO NORTH-
CENTRAL WISCONSIN LATE ON FRIDAY NIGHT. CONFIDENCE IN THE EXACT
PLACEMENT OF THIS INITIAL MCS ACTIVITY REMAINS RELATIVELY LOW, BUT
A FAVORABLE PATTERN FOR ORGANIZED CONVECTION WILL NONETHELESS
EXIST.
ADDITIONAL MCS ACTIVITY COULD THEN OCCUR ON SATURDAY AS A SHARP
INSTABILITY GRADIENT IS FORECAST TO DEVELOP OVER CENTRAL
WISCONSIN. SURFACE-BASED INSTABILITY VALUES OF 2000-3000 J/KG
COMBINED WITH DEEP LAYER SHEAR OF 25-30 KNOTS PROVIDE A ROBUST
PARAMETER SPACE FOR STRONG TO SEVERE THUNDERSTORMS. THIS IS
REFLECTED IN MACHINE LEARNING GUIDANCE, WHICH PEGS SEVERE
PROBABILITIES IN THE 15-30% RANGE OVER CENTRAL AND EAST-CENTRAL
WISCONSIN ON SATURDAY. BECAUSE OF THESE FAVORABLE PARAMETER SPACE
AND SYNOPTIC CONDITIONS, LATE FRIDAY NIGHT THROUGH SATURDAY NIGHT
APPEARS TO BE THE MOST FAVORABLE TIME FOR STRONG TO SEVERE STORMS,
ALONG WITH THE POTENTIAL FOR HEAVY RAINFALL.
THERE ARE SOME ENSEMBLE PROBABILITIES SHOWING A SIGNAL FOR 2-3
INCHES OF RAINFALL (UP TO 10% CHANCE) FROM EAST-CENTRAL MINNESOTA
TO NORTH- CENTRAL WISCONSIN, INDICATING A POTENTIAL FOR HEAVY
RAINFALL AND FLOODING. THE PROBABILITY OF RAINFALL GREATER THAN 1
INCH STANDS AT 20-40%. WPC ALSO INDICATES A SLIGHT RISK OF
EXCESSIVE RAINFALL ACROSS MUCH OF THE AREA ON SATURDAY.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 955 PM CDT WED AUG 13 2025
FEW-SCT CU AND STRATOCU LINGER THROUGH THE NIGHT, ESPECIALLY OVER
FAR NORTHEAST WI. MAY ALSO SEE HIGHER CLOUDS FROM THE WEST. FOG
IS POSSIBLE LATE TONIGHT WITH HIGH PRESSURE OVERHEAD, ESPECIALLY
OVER CENTRAL AND NORTH-CENTRAL WHERE COOLEST TEMPS ARE EXPECTED.
KEPT THE MENTION OF LIFR VSBY AT RHI AND IFR/MVFR AT AUW/CWA.
PATCHY, BRIEF MVFR GROUND FOG COULD OCCUR ELSEWHERE. HINT THAT
SMOKE OVER NORTHERN LAKE MICHIGAN AND LOWER MICHIGAN MAY TRY TO
SHIFT ACROSS NORTHEAST WI IN THE MORNING. MAY NEED TO ADD TO TAFS
EVENTUALLY BASED ON UPSTREAM OBSERVATIONS. NOT CLEAR CUT THOUGH.
LIGHT AND VARIABLE WINDS TONIGHT WILL BECOME SOUTHERLY ON
THURSDAY.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....MPC/MPC
AVIATION.......JLA
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