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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