149  
FXUS63 KAPX 020137  
AFDAPX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GAYLORD MI  
937 PM EDT SAT AUG 1 2015  
   
UPDATE
 
 
ISSUED AT 937 PM EDT SAT AUG 1 2015  
 
A FEW STRAGGLING SHOWERS CONTINUE IN EASTERN UPPER. IN THE PAST  
HOUR THE SUPERIOR LAKE BREEZE HAS BEEN ACTIVE...WHILE CONVECTION  
A BIT TO THE SOUTH HAS FADED. REGARDLESS...WHAT/S LEFT OF THIS  
ACTIVITY LOOKS TO EXIT OVER THE NEXT HOUR.  
 
LOW LEVEL FLOW CONTINUES TO SLOWLY BACK AROUND AS SURFACE RIDGING  
TO OUR SOUTH SHIFTS SLIGHTLY EAST. BUT THIS FLOW NEVER REALLY  
GETS CRANKING TONIGHT. 850MB WINDS REACH NEAR 30KT LATE OVER  
NORTHERN IOWA/CENTRAL WI...BUT BY THEN THOSE WINDS HAVE VEERED  
ALMOST WESTERLY. THIS IS FAR FROM AN IDEAL SET-UP TO SUSTAIN AN  
MCS INTO THE REGION LATE. THERE IS ALSO ALMOST NO CONVECTION TO  
SPEAK OF UPSTREAM...AT LEAST NOT YET. WE ARE SEEING SOME SHOWER  
ACTIVITY INCREASE OVER CENTRAL/NORTHERN SUPERIOR...AS THE  
SOUTHERN EDGE OF THE DOME OF COLD MARINE AIR (EASTERN LAKE  
SUPERIOR BUOY AIR TEMP NEVER HIT 50F TODAY) ACTS AS A PSUEDO-WARM  
FRONT.  
 
ACTIVITY ON SUPERIOR WILL DEVELOP SE-WARD WITH TIME WITH THE  
SLOWLY VEERING WINDS...AND REMAINS ON PACE TO PERHAPS BRING RAIN  
TO EASTERN UPPER (CHIPPEWA CO ESPECIALLY) AFTER 2AM. ALSO...DO  
STILL EXPECT SOME SHRA/TSRA TO GET GOING WEST OF LAKE MI AS THE  
LOW LEVEL JET STRENGTHENS OUT THAT WAY. BUT THIS ALSO MAY NOT  
HAPPEN UNTIL AFTER 2 AM. THIS COULD STILL MANAGE TO PUSH SOME  
SHRA/TSRA INTO NW LOWER VERY LATE...AS THE GOING FORECAST  
INDICATES. HOWEVER...WILL TEND TO DECREASE POPS.  
 
NO OTHER MAJOR CHANGES.  
 

 
   
NEAR TERM
 
(THIS EVENING THROUGH TONIGHT)  
ISSUED AT 317 PM EDT SAT AUG 1 2015  
 
HIGH IMPACT WEATHER POTENTIAL: A FEW THUNDERSTORMS THROUGH  
TONIGHT...GUSTY WINDS POSSIBLE WITH ANY STORMS THAT DEVELOP.  
 
PATTERN SYNOPSIS/EXPECTED EVOLUTION: PARADE OF SHORT WAVE TROUGHS  
AROUND LARGE HUDSON BAY GYRE CONTINUES WITH ONE WAVE SLIDING EAST OF  
THE AREA THIS AFTERNOON AND ANOTHER UPSTREAM WAVE PROGGED TO MOVE  
NORTH OF SUPERIOR TONIGHT. THIS SECOND WAVE WILL PLAY A KEY ROLE IN  
PUSHING A COLD FRONT INTO THE NORTHERN LAKES ON SUNDAY.  
 
PRIMARY FORECAST CHALLENGES: EVOLUTION OF LINGERING DAYTIME  
CONVECTION INTO EARLY EVENING. POTENTIAL DEVELOPMENT OF SHOWER/TSTM  
AFTER MIDNIGHT OVER WESTERN PARTS OF THE AREA UNDER INCREASING  
WARM ADVECTION PATTERN.  
 
LATE AFTERNOON/TONIGHT...LINGERING DIURNAL ACTIVITY MAINLY CLOSER TO  
LAKE HURON SHOULD DISSIPATE EARLY AS INSTABILITY WANES AND MESO-  
SCALE LAKE CIRCULATIONS/LOW LEVEL CONVERGENCE DIMINISHES.  
 
TONIGHT...SHORTWAVE PASSING NORTH OF SUPERIOR WILL HELP TO INDUCE  
LOW LEVEL WARM AIR ADVECTION AND ISENTROPIC UPGLIDE. BEST LOW LEVEL  
JET INITIALLY WILL FOCUS CONVECTION OVER IOWA/MINNESOTA/WRN  
WISCONSIN...WITH THIS ACTIVITY GRADUALLY SHIFTING EAST INTO THE  
WESTERN LAKES TOWARD 12Z AS LOW LEVEL SOUTHWEST FLOW STRENGTHENS.  
INCREASING ELEVATED INSTABILITY DEVELOPING AS WELL WITH INCREASING  
THREAT OF SHOWERS/STORMS AFTER 08-09Z...ESPECIALLY WEST OF US-131 IN  
NORTHERN LOWER.  
 

 
   
SHORT TERM
 
(SUNDAY THROUGH TUESDAY)  
ISSUED AT 317 PM EDT SAT AUG 1 2015  
 
...UNSETTLED WITH A RISK FOR BENEFICIAL RAINFALL THEN TURNING  
COOLER...  
 
HIGH IMPACT WEATHER POTENTIAL: RISK FOR SEVERE THUNDERSTORMS  
ACROSS LOWER MICHIGAN SUNDAY.  
 
PATTERN SYNOPSIS/ANTICIPATED EVOLUTION: BROAD LOW AMPLITUDE UPPER  
TROUGH OVER THE NE QUADRANT OF THE CONUS WILL SHARPEN BY EARLY IN  
THE UPCOMING WORK WEEK AS A SHORT WAVE DROPS SEWD...AND A STRONGER  
UPPER LOW EVENTUALLY TAKES SHAPE OVER EXTREME NRN ONTARIO. AN  
ASSOCIATED SURFACE WAVE WILL BRING A RISK FOR SHOWERS AND STORMS TO  
THE REGION SUNDAY AND SUNDAY NIGHT /SOME OF THESE STORMS COULD BE  
SEVERE/. IN THE WAKE OF THIS SYSTEM...COOLER AIR WILL OVERSPREAD THE  
GREAT LAKES MONDAY AND TUESDAY AS AFOREMENTIONED UPPER TROUGH HOLDS  
FIRM. THIS WILL ALSO MAINTAIN A RISK FOR SCATTERED SHOWERS.  
 
SUNDAY AND SUNDAY NIGHT...PREVIOUSLY REFERENCED H5 SHORT WAVE  
INITIALLY OVER FAR NRN MN EARLY SUNDAY WILL DROP SEWD INTO THE WRN  
GREAT LAKES DURING THE DAY. THIS WILL BE ASSOCIATED WITH DECENT  
UPPER HEIGHT FALLS...AND AN IMPRESSIVE SURFACE WAVE THAT IS FORECAST  
TO CROSS THE REGION BY SUNDAY NIGHT. WSW LLJ IS EXPECTED TO SUPPORT  
ONGOING CONVECTION EARLY SUNDAY /POSSIBLY AN MCS/ SOMEWHERE OVER THE  
WRN GREAT LAKES /WRN LOWER MI?/. THE USUAL QUESTIONS WILL THEN COME  
INTO PLAY FOR THE REST OF THE DAY...NAMELY WILL CONVECTION SUSTAIN  
ITSELF SUNDAY MORNING AS IT MOVES INTO THE AREA...AND WHAT IMPACT  
WILL THE CONVECTION AND/OR ITS DEBRIS HAVE ON DESTABILIZATION LATER  
IN THE DAY? ADDITIONALLY...MODELS NOT IN GOOD AGREEMENT REGARDING  
PLACEMENT OF WARM FRONT EXPECTED TO SLOWLY LIFT NE ACROSS THE  
REGION. GFS PUSHES WARM FRONT WELL NORTH TOWARD THE TIP OF THE  
MITT...WHILE NAM KEEPS FRONT OVER CENTRAL LOWER. THIS WILL IMPACT  
AREAS THAT DESTABILIZE...AS WELL AS LOW LEVEL SHEAR. IN SPITE OF  
THESE UNCERTAINTIES...MODEL SOUNDINGS SUPPORT MLCAPES AROUND 2000  
J/KG OVER SRN PARTS OF FORECAST AREA...AS H5 WINDS INCREASE TO  
AROUND 50 KTS BY LATE AFTERNOON. UPSHOT...EXPECT A COUPLE ROUNDS OF  
THUNDERSTORMS SUNDAY INTO SUNDAY EVENING BEFORE SURFACE FRONT  
PASSES. STRONG TO LOCALLY SEVERE STORMS NOT OUT OF THE QUESTION  
/SOUTH OF PETOSKEY-ALPENA LINE/ WITH DAMAGING STRAIGHT LINE WINDS  
LIKELY TO BE THE MAIN THREAT.  
 
MONDAY AND TUESDAY...LOW LEVEL CAA EXPECTED...AS UPPER TROUGH  
SETTLES IN ACROSS THE REGION. IN FACT...H8 TEMPS ARE FORECAST TO  
DROP TO AROUND +5C OVER THE FAR NRN GREAT LAKES BY LATE TUESDAY  
/PERHAPS SUPPORTING SOME SUBTLE LAKE INFLUENCES/. WITH SAID UPPER  
TROUGH...WEAK RIPPLES IN THE FLOW CONTRIBUTING TO SURFACE  
TROUGHINESS/CONVERGENCE...AND DAYTIME HEATING...A SMALL RISK FOR  
SHOWERS SEEMS WARRANTED BOTH DAYS FOR PARTS OF FORECAST AREA. HIGHS  
EACH DAY WILL RANGE FROM THE 60S NORTH TO THE LOW-MID 70S SOUTH.  
 

 
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 317 PM EDT SAT AUG 1 2015  
 
THE MAIN ISSUE FOR THE EXTENDED PERIOD WILL BE THE CHANCE FOR  
WEEKEND RAIN CHANCES. RIGHT NOW...SOLUTIONS RUN THE GAMUT FROM DRY  
TO A DECENT RAIN. THE PROBLEM LIES IN THE HANDLING OF THE PERSISTENT  
H5 RIDGING OUT WEST. THERE SEEMS TO BE OVERALL AGREEMENT WITH A  
SHORTWAVE MOVING THROUGH...OR NEAR...OUR REGION OVER THE WEEKEND.  
DIFFERENCES LIE WITH THE AMPLITUDE OF RIDGING TO OUR WEST. MORE  
AMPLIFIED RIDGING WILL HAVE THE BETTER FORCING FURTHER  
NORTH...BRINGING RAIN TO THE CWA. LESS AMPLIFIED SOLUTIONS RESULT IN  
THE SHORTWAVE TRACKING FURTHER SOUTH...AND WITH IT THE RAIN CHANCES.  
CURRENT BLENDED GUIDANCE IS FAVORING CHANCE POPS OVER THE WEEKEND AS  
SOME OF THE UNCERTAINTIES GET IRONED OUT. I AM NOT SOLD ON THIS JUST  
YET...AS THE MORE AMPLIFIED H5 RIDGE SOLUTIONS SEEM A BIT OVERDONE.  
WILL NOT REMOVE THE CHANCE POPS YET...BUT EXPECT SOLUTIONS WILL  
BEGIN TO MERGE WITH THE MORE FAVORABLE FORCING TO OUR SOUTH  
RESULTING IN A DRY WEEKEND FOR US. TEMPS LOOK TO BE BELOW NORMAL  
THROUGH THE PERIOD.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)  
ISSUED AT 739 PM EDT SAT AUG 1 2015  
 
SHRA/TSRA LIKELY SUNDAY.  
 
COLD FRONT MOVING ACROSS THE DAKOTAS WILL MOVE INTO NORTHERN MI  
LATE SUNDAY. SHRA/TSRA ARE EXPECTED TO DEVELOP AHEAD OF THE FRONT  
IN THE UPPER MS VALLEY TONIGHT. THESE WILL MOVE EAST  
OVERNIGHT...AND COULD REACH NORTHERN LOWER MI AT OR A BIT AFTER  
DAWN. BETTER CHANCE FOR PRECIP WILL BE LATER IN THE DAY...AFTER  
MORNING ACTIVITY HAS FADED OUT AND ALLOWED FOR SOME  
DESTABILIZATION. DIFFICULT TO NARROW THE DOWN THE BEST RELATIVELY  
NARROW WINDOW FOR TSRA CHANCES IN THE TAFS. FOR NOW...HAVE TSRA  
MENTIONED FOR A 4-HR WINDOW IN THE AFTERNOON/EARLY EVENING.  
 
LIGHT W TO SW SURFACE WINDS TONIGHT...INCREASING SUNDAY MORNING  
AND VEERING W VERY LATE IN THE DAY. LLWS OVERNIGHT AT PLN...WITH  
STRONGER WSW WINDS OFF THE SURFACE.  
 

 
   
MARINE
 
 
ISSUED AT 317 PM EDT SAT AUG 1 2015  
 
TONIGHT/SUNDAY...TIGHTENING GRADIENT WITH INCREASING SOUTHWEST  
WINDS LATE TONIGHT INTO SUNDAY IN ADVANCE OF APPROACHING COLD  
FRONT NORTH OF SUPERIOR. STRONGEST WINDS LIKELY FROM GRAND  
TRAVERSE LIGHT NORTHWARD TO THE STRAITS DUE TO COASTAL  
CONVERGENCE. SMALL CRAFT ADVISORIES ISSUED FOR NORTHERN PARTS OF  
LAKE MICHIGAN AND LAKE HURON STARTING LATE TONIGHT THROUGH SUNDAY.  
WINDS SHIFT AROUND TO THE NORTHWEST SUNDAY NIGHT AFTER FROPA WITH  
ADDITIONAL HEADLINES POSSIBLY NEEDED...ESPECIALLY LAKE HURON.  
 

 
   
APX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LH...SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM EDT SUNDAY FOR LHZ345-  
347>349.  
 
LM...SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM EDT SUNDAY FOR LMZ323-341-  
342-344>346.  
 
LS...NONE.  

 
 

 
 
UPDATE...JAZ  
NEAR TERM...KEYSOR  
SHORT TERM...SMITH  
LONG TERM...ALM  
AVIATION...JAZ  
MARINE...KEYSOR  
 
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