154
FXUS63 KGRB 210347
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1047 PM CDT FRI SEP 20 2019
UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE
SHORT TERM
TONIGHT AND SATURDAY
ISSUED AT 248 PM CDT FRI SEP 20 2019
THE MAIN FOCUS IN THE SHORT-TERM PORTION OF THE FORECAST WILL BE THE
POTENTIAL FOR SHOWERS AND THUNDERSTORMS SATURDAY AFTERNOON.
TEMPERATURES WILL REMAIN ABOVE NORMAL AND HUMID CONDITIONS WILL
LINGER INTO THE WEEKEND.
TONIGHT: A SURFACE RIDGE AND UPPER-LEVEL RIDGE WILL DRIFT SLOWLY OFF
TO THE EAST OF THE AREA TONIGHT, ALLOWING MORE MOIST SOUTHERLY FLOW
TO LIFT NORTHWARD. WEAK WAA WILL INCREASE ON THE MORE SOUTHERLY
RETURN FLOW, ALONG WITH THE MOISTURE, ALLOWING FOR ISENTROPIC
UPGLIDE TO KICK IN ACROSS THE AREA. WHILE OVERALL FORCING IS WEAK,
THERE COULD BE VERY LIGHT DRIZZLE OVERNIGHT. WHILE NOT OVERLY
CONFIDENT IN THE DRIZZLE OR LIGHT SHOWERS, THE MOST LIKELY LOCATION
FOR THIS TO OCCUR WOULD BE ACROSS THEN NORTHWOODS AREA AS MOISTURE
LOOKS TO BE A BIT DEEPER UP THAT WAY. FOG FORMATION IS STILL
POSSIBLE TONIGHT; HOWEVER, THE SOUTH WINDS ARE EXPECTED TO INCREASE,
ALLOWING SOME OF THE MOISTURE TO MIX UP INTO A LOW STRATUS DECK.
THIS SHOULD HELP TO LIMIT THE DENSE FOG POTENTIAL TONIGHT. OVERNIGHT
LOWS WILL BE MAINLY IN THE 60S.
SATURDAY: AS THE HIGH PRESSURE CENTER SHIFTS EASTWARD, LOW PRESSURE
OVER THE NORTHERN PLAINS WILL APPROACH FROM THE WEST. ALOFT, A
DEEPER LONG WAVE TROUGH, ACROSS MUCH OF THE WEST HALF OF THE U.S.,
WILL SHIFT SLOWLY TO THE EAST THROUGH SATURDAY AFTERNOON. SOME
SHORTWAVE ENERGY FLOWING AROUND THE THIS TROUGH WILL SLIDE THROUGH
THE AREA BY LATE SATURDAY MORNING INTO THE AFTERNOON HOURS. AT THE
SAME TIME, WAA ADVECTION WILL INCREASE AS A WEAK SURFACE TROUGH/WARM
FRONT LIFTS NORTHWARD. ISENTROPIC UPGLIDE WILL STEADILY INCREASE
INTO THE EARLY AFTERNOON HOURS AS WELL. ALL OF THIS POINTS TOWARD
ENOUGH LIFT TO TOUCH OF SHOWERS AND THUNDERSTORMS ACROSS THE AREA
BEGINNING LATE SATURDAY MORNING, THEN LINGERING INTO THE AFTERNOON.
INSTABILITY VALUES LOOK TO BE AROUND 1000 J/KG ACROSS THE AREA WITH
SHEAR VALUES EXPECTED TO BE AROUND 30 KTS DURING PEAK HEATING. THE
BETTER INSTABILITY/SHEAR IS EXPECTED TO REMAIN WEST OF THE AREA,
CLOSE TO THE DEEPER TROUGH AXIS. THAT BEING SAID, IT IS POSSIBLE
THAT A FEW OF THE THUNDERSTORMS COULD BECOME STRONG DURING THE
AFTERNOON HOURS AND AN ISOLATED SEVERE STORM CAN'T BE COMPLETELY
RULED OUT. THE MAIN THREAT WOULD BE VERY HEAVY RAINFALL UNDER ANY OF
THE STRONGER STORM, BUT GUSTY WINDS AND SMALL HAIL WOULD ALSO BE
POSSIBLE, MAINLY ACROSS CENTRAL WI. INCREASING SOUTH WINDS WILL
ALLOW WAVES TO BUILD ALONG THE LAKE MICHIGAN, LEADING TO DANGEROUS
SWIMMING CONDITIONS SATURDAY AFTERNOON. HIGHS WILL ONCE AGAIN BE
ABOVE NORMAL WITH MOST LOCATIONS WARMING INTO THE MID TO UPPER 70S.
LONG TERM
SATURDAY NIGHT THROUGH FRIDAY
ISSUED AT 248 PM CDT FRI SEP 20 2019
THE CURRENT HIGHLY-AMPLIFIED MEAN FLOW CONSISTING OF A WESTERN
CONUS UPPER TROUGH/EASTERN CONUS UPPER RIDGE TO GRADUALLY
TRANSITION TO A FLATTER, NEAR ZONAL FLOW EARLY NEXT WEEK. THIS
WILL BRING A COOLER/LESS HUMID REGIME TO NORTHEAST WI. HOWEVER,
MODELS CONTINUE TO SHOW A NEW UPPER TROUGH TO DIG ACROSS THE
WESTERN CONUS LATE WEEK AND ALLOW THE UPPER RIDGE TO BUILD ALONG
THE EAST COAST. THIS PATTERN LOOKS SIMILAR TO OUR CURRENT SYNOPTIC
SET-UP WHICH SHOULD TRANSLATE TO ABOVE NORMAL TEMPERATURES, AS
WELL AS A MORE ACTIVE WEATHER SCENARIO.
THE COLD FRONT IS FORECAST TO PUSH EAST INTO THE REGION SATURDAY
NIGHT, REACHING CENTRAL WI TOWARD DAYBREAK. PLENTY OF MOISTURE TO
BE IN PLACE (DEW POINTS IN THE 60S) AND WHEN COMBINED WITH
PERSISTENT WAA AND LIFT FROM THE FRONT, SHOWERS/THUNDERSTORMS
APPEAR LIKELY DURING THE EVENING HOURS. INSTABILITY REMAINS
MARGINAL (MUCAPES 500-1000 J/KG), BUT SHEAR IS STRONGER (30-45
KNOTS) SO A FEW OF THE STORMS MAY BE ON THE STRONGER SIDE. SEVERE
THREAT APPEARS LIMITED, MAINLY DUE TO A LACK OF MID-LEVEL FORCING
AS THE UPPER TROUGH TO BE MOVING INTO ONTARIO. IF ANYTHING, HEAVY
RAIN MAY BE THE BIGGEST CONCERN. THE PRECIPITATION MAY TEND TO
DIMINISH OVER NORTH-CENTRAL WI AFTER MIDNIGHT AS THE FRONT MOVES
THROUGH. MIN TEMPERATURES TO RANGE FROM THE UPPER 50S NORTH-
CENTRAL WI, MIDDLE TO UPPER 60S EAST-CENTRAL WI.
THERE CONTINUES TO BE UNCERTAINTY AS TO HOW LONG TO HANG ON TO THE
PRECIPITATION CHANCES ON SUNDAY. ON ONE HAND, SOME MODELS LINGER
SHOWERS/THUNDERSTORMS OVER EASTERN WI SUNDAY MORNING AS THE COLD
FRONT MOVES BY, THEN DRY THINGS OUT FOR THE AFTERNOON. ON THE
OTHER HAND, SOME MODELS PUSH THE INITIAL PRECIPITATION OUT OF THE
AREA SUNDAY MORNING, ONLY TO HAVE ADDITIONAL SHOWERS/STORMS
DEVELOP IN THE AFTERNOON AS A SURFACE WAVE RIDES NORTHEAST ALONG
THE COLD FRONT. HARD TO DISPROVE EITHER SOLUTION AT THIS TIME,
THUS HAVE KEPT CHANCE POPS IN THE FORECAST FOR EAST-CENTRAL WI
THROUGH THE ENTIRE DAY, SLIGHT CHANCE POPS FOR CENTRAL/FAR
NORTHEAST WI AND DRY CONDITIONS FOR NORTH-CENTRAL WI. ONSET OF CAA
ON GUSTY WEST WINDS WILL ONLY ALLOW MAX TEMPERATURES TO REACH THE
MIDDLE 60S NORTH-CENTRAL, WHILE EASTERN WI GETS TO AROUND 70
DEGREES.
THE CHANCE FOR SHOWERS/THUNDERSTORMS COULD VERY WELL CONTINUE INTO
SUNDAY NIGHT AS A TRAILING SHORTWAVE TROUGH LIFTS NORTHEAST INTO
THE GREAT LAKES REGION. ONCE AGAIN, EAST-CENTRAL WI WOULD BE MOST
SUSCEPTIBLE OF SEEING PRECIPITATION, SO HIGHER POPS PLACED THERE.
MORE CLOUDS WILL PREVENT TEMPERATURES FROM FALLING AS FAR AS
ORIGINALLY THOUGHT WITH READINGS DIPPING INTO THE MIDDLE TO UPPER
40S NORTH, LOWER 50S SOUTH. WE FINALLY GET A BREAK IN THE RAIN
CHANCES ON MONDAY AS THE SHORTWAVE TROUGH EXITS THE REGION AND IS
REPLACED BY A RIDGE OF HIGH PRESSURE. LOOK FOR INCREASING SUNSHINE
THROUGH THE DAY WITH TEMPERATURES NEAR NORMAL AND LOWER HUMIDITY
LEVELS.
WE GET ON THE BACKSIDE OF THE SURFACE RIDGE ON TUESDAY AND WITH A
RETURN FLOW TO DEVELOP, THIS WILL ALLOW FOR WAA TO OVERSPREAD WI.
LOOK FOR CLOUDS TO BE ON THE INCREASE THROUGH THE DAY AND IF
ENOUGH MOISTURE CAN ARRIVE, THERE CLOUD BE A LATE DAY SHOWER OR
THUNDERSTORM OVER NORTH-CENTRAL WI. MAX TEMPERATURES FOR TUESDAY
TO MAINLY BE IN THE UPPER 60S TO LOWER 70S. BY THE MIDDLE OF NEXT
WEEK, A BROAD/SHALLOW UPPER TROUGH TO STRETCH FROM THE PACIFIC
NORTHWEST TO THE GREAT LAKES. ABOVE THIS TROUGH WILL BE A FAST
(120-140 KNOT) UPPER JET THAT WOULD HELP CARRY SYSTEMS QUICKLY
ACROSS THE NORTHERN CONUS. ONE SUCH SYSTEM ARRIVES TUESDAY NIGHT
OR WEDNESDAY IN THE FORM OF A SHORTWAVE TROUGH AND A SURFACE COLD
FRONT. MODELS ALWAYS SEEM TO HAVE TIMING ISSUES WHEN A FAST JET/
PATTERN SHIFT OCCURS. HAVE MENTIONED SMALL POPS FOR BOTH PERIODS
UNTIL HIGHER CONFIDENCE CAN BE REACHED. MAX TEMPERATURES ON
WEDNESDAY TO BE IN THE MIDDLE 60S TO LOWER 70S.
PRECIPITATION CHANCES END WEDNESDAY NIGHT AS HIGH PRESSURE BUILDS
INTO THE AREA. AS THE HIGH PRESSURE SHIFTS TO OUR EAST ON
THURSDAY, MOISTURE WILL BE GATHERING TO THE WEST AS A NEW SYSTEM
ORGANIZES OVER THE PLAINS/MIDWEST. ANTICIPATE CLOUDS TO BEGIN
INCREASING THROUGH THE DAY WITH THE LEADING EDGE OF PRECIPITATION
APPROACHING WI TOWARD EVENING. MAX TEMPERATURES TO BE IN THE LOWER
TO MIDDLE 60S ON THURSDAY. AS A NEW UPPER TROUGH DIGS INTO THE
WESTERN CONUS LATE NEXT WEEK, DOWNSTREAM UPPER RIDGING BUILDS OVER
THE EAST COAST. A SOUTHWEST MEAN FLOW WILL DRAW GULF MOISTURE
NORTHWARD AS A WARM FRONT LIFTS NORTH THURSDAY NIGHT AND A SURFACE
LOW/COLD FRONT APPROACH WI ON FRIDAY. CHANCE OF SHOWERS/STORMS TO
BE ON THE INCREASE DURING THIS TIME WITH MAX TEMPERATURES ON
FRIDAY REACHING THE MIDDLE 60S TO AROUND 70 DEGREES.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 1047 PM CDT FRI SEP 20 2019
FOG AND LOW CLOUDS ARE LIKELY OVERNIGHT AT MTW/SUE/3D2/2P2/OCQ
AS MOISTURE FROM LAKE MICHIGAN MOVES INLAND. SCATTERED TO BROKEN CLOUDS
BETWEEN 2500 AND 4000 FEET ARE EXPECTED ELSEWHERE TONIGHT.
A WARM FRONT APPROACHING FROM THE SOUTHWEST WILL BRING SHOWERS AND
SCATTERED THUNDERSTORMS TO THE AREA SATURDAY, ESPECIALLY IN THE AFTERNOON
AND EVENING HOURS. MVFR OR IFR CONDITIONS ARE EXPECTED.
A COLD FRONT WILL MOVE THROUGH LATE SATURDAY NIGHT OR EARLY SUNDAY
MORNING, WITH VFR CONDITIONS BY MIDDAY SUNDAY.
GRB WATCHES/WARNINGS/ADVISORIES
BEACH HAZARDS STATEMENT FROM SATURDAY AFTERNOON THROUGH LATE
SATURDAY NIGHT FOR WIZ022-040-050.
SHORT TERM.....COOLEY
LONG TERM......KALLAS
AVIATION.......RDM
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