Severe Thunderstorm Warning 6, NWS Marquette, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
346 PM EDT WED JUN 26 2013

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 345 PM EDT WED JUN 26 2013

WV LOOP INDICATES GENERAL WESTERLY FLOW ACROSS THE CONUS. 12Z RAOBS
SHOW ELONGATED CLOSED OFF UPPER LOW SASKATCHEWAN TO MANITOBA. AT THE
SFC...STATIONARY FRONT EXTENDS FROM SFC LOW OVER SOUTHERN MANITOBA
TO SOUTHERN QUEBEC. COLD FRONT...MAINLY SIGNALING ARRIVAL OF DRIER
AIR AT H85...IS PRESSING INTO EASTERN MINNESOTA. SO FAR TODAY...SHRA
AND TSRA HAVE BEEN CONFINED TO EASTERN MN DUE TO PVA FM SHORTWAVE
AND H85 TEMP ADVECTION. OTHER SHRA/TSRA ARE AFFECTING NORTHERN IOWA
INTO NORTHERN ILL IN AREA WHERE MCV DECAYED OVERNIGHT. HAS BEEN
ANOTHER WARM AND HUMID AFTN OVER UPR MICHIGAN WITH TEMPS IN MANY
AREAS WELL INTO THE 80S AND DWPNTS IN THE 60S.

SHRA/TSRA TRENDS MAIN ISSUE INTO THIS EVENING. COUPLE OF WEAKER
SHORTWAVES COMING TOGETHER OVER CWA CURRENTLY. AS THESE SHORTWAVES
AND LINE OF SHRA/TSRA RUN INTO THE ROBUST INSTABILITY IN THE AREA
RIGHT NOW /MLCAPES NEAR 2000J/KG AND SFC BASED CAPES OVER 3000 J/KG/
WOULD THINK INTENSITY WILL BE MAINTAINED IF NOT INCREASE SOME OVER
CURRENT INTENSITY.  MAY SEE COVERAGE INCREASE SOME TOO THROUGH
AROUND 00Z BEFORE WEAKENING CONVERGENCE AND INSTABILITY LESSEN THE
POTENTIAL. EVEN WITH THESE SHORTWAVES AND ASSOCIATED LIFT...LARGER
SCALE UPPER LEVEL WINDS ARE NOT THAT STRONG /H7 WINDS 15-20KT AND H5
WINDS 20-25 KTS/ SO DEEP LAYER SHEAR IS WEAK. THUS FAR STORM TRENDS
UPSTREAM INDICATE THIS WITH PULSE TYPE BEHAVIOR. EXPECT SIMILAR
SETUP OVER AT LEAST WEST HALF OF CWA INTO THE EVENING. PULSE SVR
TSRA CERTAINLY POSSIBLE WITH DEGREE OF INSTABILITY PRESENT. DRY
AIR ALOFT REFLECTED IN DCAPE VALUES WELL OVER 1000J/KG INDICATE THAT
ANY STRONGER/ORGANIZED STORM COULD PRODUCE SEVERE WIND GUSTS. THE
GUSTY WINDS ALONG WITH HEAVY DOWNPOURS APPEAR TO BE MAIN HAZARD WITH
TSRA LATE THIS AFTN INTO THE EVENING. STRONG STORM EARLIER UPSTREAM
ALSO PRODUCED NICKEL SIZED HAIL...SO PROBABLY CANNOT RULE THAT OUT
EITHER. JUST SHOULD NOT BE THE MAIN HAZARD.

LATER THIS EVENING AND EVEN OVERNIGHT...SHRA/TSRA STILL POSSIBLE
AS UPPER TROUGH/PV ANAMOLY CURRENTLY SLIDING ACROSS ND DIGS INTO
UPR GREAT LAKES REGION AND COMBINES WITH STEEPER MID-LEVEL LAPSE
RATES AND H85 CONVERGENCE/WARM AIR ADVECTION. ENHANCED LIFT COULD
ALSO OCCUR AS UPR MICHIGAN WILL BE IN LEFT EXIT OF STRONG JET
STREAK FROM WESTERN CANADA INTO UPPER MISSISSIPPI RIVER VALLEY.
MAJORITY OF SHRA/TSRA SHOULD SPREAD TO THE EASTERN CWA ALONG AND
DOWNSTREAM OF HIGHER H85 DWPNT. EVEN AS SFC TROUGH SHIFTS WINDS TO
MORE WRLY...HIGHER SFC DWPNT LINGERS...LEADING TO ANOTHER WARM
NIGHT WITH MOST LOCATIONS STAYING AOA 60 DEGREES.

NOT THROUGH WITH THE WARMER/HUMID WEATHER AND POP-UP SHRA/TSRA ON
THURSDAY. LEADING SHORTWAVE MOVES TO THE NORTH IN THE MORNING WHILE
ANOTHER WAVE DIGS IN MAINLY ACROSS NORTHERN WI MID-LATE AFTN. DAYTIME
HEATING SHOULD BOOST TEMPS BACK INTO THE 80S AGAIN...EXCEPT NEAR THE
LK SUPERIOR SHORELINE OVER WESTERN UPR MICHIGAN. WEAKER WEST BLYR
FLOW ALONG WITH DEVELOPING LK BREEZES COMBINE WITH MLCAPES NEARING
1000J/KG TO KICK OF SHRA/TSRA...ESPECIALLY IN FAVORED LK BREEZE
CONVERGENCE ZONE OF CNTRL UPR MICHIGAN. SHRA/TSRA WILL MOVE FM WNW
TO ESE. THUS WOULD EXPECT HIGHER POPS EARLY IN THE AFTN NCNTRL AND
SETTLING INTO THE SCNTRL CWA BY MID-LATE AFTN. DEEP SHEAR LIMITED TO
LESS THAN 20 KTS SO CHANCE OF ORGANIZED/STRONGER STORMS LOOKS
MARGINAL.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 345 PM EDT WED JUN 26 2013

THURSDAY NIGHT THROUGH SATURDAY MORNING...LOW PRESSURE PROGGED TO BE
CENTERED JUST NORTH OF LAKE SUPERIOR THURSDAY NIGHT IS EXPECTED TO
SHIFT SLOWLY SOUTHEASTWARD...REACHING THE LOWER GREAT LAKES BY
SATURDAY MORNING. AS THIS HAPPENS...THE ASSOCIATED UPPER LEVEL 500
MB TROUGH WILL ALSO SHIFT TO THE LOWER GREAT LAKES. SIGNIFICANT
MOISTURE WILL REMAIN IN PLACE THROUGH THIS TIME PERIOD...AS SHOWN BY
ANALYZING 1000-500MB RH VALUES...TO KEEP INTERMITTENT CHANCES OF
SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA. INSTABILITY LOOKS
TO REMAIN IN PLACE THROUGH MUCH OF THIS TIME PERIOD WITH THE NAM AND
GFS SHOWING VALUES AROUND 800-1000 J/KG THURSDAY NIGHT INTO
FRIDAY...DROPPING OFF FRIDAY NIGHT AS UPPER LEVEL TROUGH AXIS BEGINS
TO SHIFT TO THE SOUTH OF THE AREA. THE SEVERE WEATHER THREAT THROUGH
THIS TIME FRAME SEEMS FAIRLY LOW AT THIS POINT GIVEN THE LACK OF
DEEP LAYER SHEAR...ALONG WITH MARGINAL CAPE VALUES OF 100-150 J/KG
IN THE -10-30C TEMPERATURE RANGE ALOFT. MAY SEE SOME PEA SIZE HAIL
LATE THURSDAY EVENING INTO FRIDAY AFTERNOON...BUT DO NOT EXPECT MORE
THAN THAT AT THIS POINT. STORM MOTIONS ARE EXPECTED TO BE AROUND 10
TO 15 KNOTS WITH MINIMAL DCAPE...SO SEVERE WIND POTENTIAL WILL ALSO
BE REDUCED DURING THIS TIME PERIOD. THE OTHER ISSUE WILL BE FOG
POTENTIAL LINGERING OVER LAKE SUPERIOR AS STABLE LAYER NEAR THE LAKE
SURFACE PINS THE MOISTURE CLOSE TO THE SURFACE. THIS SHOULD LAST
THROUGH AT LEAST FRIDAY EVENING BEFORE COOLER AIR MOVES IN
ALOFT...HELPING TO WEAKEN THE TEMPERATURE INVERSION AS SHOWN BY
ANALYZING FORECAST SOUNDINGS.

SATURDAY AFTERNOON THROUGH MONDAY MORNING...AS THE UPPER LEVEL LOW
AND SURFACE LOW OVER THE OHIO VALLEY SATURDAY AFTERNOON CONTINUES TO
SHIFT SOUTH AND EAST OF THE AREA...EXPECT BROAD SURFACE HIGH
PRESSURE OVER THE PLAINS TO BUILD SLOWLY EASTWARD INTO THE GREAT
LAKES REGION. NORTHERLY FLOW ON THE EAST SIDE OF THE HIGH WILL ALLOW
DRY AIR OVER CENTRAL CANADA TO SPILL SOUTHWARD INTO THE UPPER GREAT
LAKES REGION EFFECTIVELY ENDING THE CHANCE OF SHOWERS AND
THUNDERSTORMS SATURDAY AFTERNOON. THE SURFACE HIGH WILL CONTINUE TO
BUILD EASTWARD THROUGH THE WEEKEND AND REMAIN OVER HEAD THROUGH
MONDAY MORNING KEEPING CONDITIONS DRY ACROSS THE AREA. THROUGH THIS
TIME FRAME THE UPPER LEVEL 500MB TROUGH WILL REMAIN ENTRENCHED
ACROSS MUCH OF THE EASTERN U.S. WHILE A LARGE RIDGE AND HEAT WAVE
BEGINS BUILDING OVER MUCH OF THE WESTERN U.S.

MONDAY AFTERNOON THROUGH WEDNESDAY...THE MODELS CONTINUE TO KEEP THE
TROUGH PARKED OVER THE EASTERN HALF OF THE UNITED STATES WITH THE
RIDGE BUILDING OUT WEST. THE GFS/EC TRY TO CLOSE AN UPPER LEVEL LOW
OVER MUCH OF THE GREAT LAKES REGION THROUGH THIS TIME
FRAME...HOWEVER...CONSIDERABLE TIMING AND INTENSITY DIFFERENCE ARE
SHOWN BETWEEN THE MODELS AND FROM RUN TO RUN...THEREFORE WILL STICK
MAINLY WITH A CONSENSUS OF THE MODELS FOR THE EXTENDED. TRENDED DRY
FOR MONDAY NIGHT AS FORCING AND MOISTURE APPEARED TO STAY WELL TO
THE SOUTHEAST OF THE AREA.  IT DOES APPEAR IF COOLER WEATHER IS IN
STORE THROUGH THE EXTENDED WITH CONTINUED TROUGHING EXPECTED ACROSS
THE REGION.
&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 147 PM EDT WED JUN 26 2013

APPROACHING DISTURBANCE SHOULD BRING SHRA/SCT TSRA INTO UPPER MI
LATER THIS AFTN. ALREADY SEEING ISOLD SHRA POPPING UP UPSTREAM OF
CMX. MENTIONED MAINLY MVFR -SHRA WITH VCTS AT THE TAF SITES LATE
AFTN THROUGH EARLY EVENING AS THE DISTURBANCE ROLLS ACROSS. SINCE
THERE SHOULD BE SOME RAIN AT ALL THE TAF SITES...KEPT MENTION OF LGT
FOG OVERNIGHT TONIGHT. BEST SHOT OF IFR VSBY WILL BE AT CMX WITH EAST
WINDS OFF LK SUPERIOR. CHANCE OF ADDITIONAL SHRA/TSRA OVERNIGHT
TONIGHT BUT TOO MUCH UNCERTAINTY TO PUT IN TAFS AT THIS POINT. DID
PUT SHRA/TSRA MENTION IN FOR VERY LATE IN THE TAF PERIOD AT SAW ON
THURSDAY DUE TO LAKE BREEZE CONVERGENCE AND BUILDUP OF INSTABILITY.
&&

.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 345 PM EDT WED JUN 26 2013

OVERALL...WINDS ARE EXPECTED TO STAY BELOW 20 KTS THROUGH THE PERIOD
AS THE PRESSURE PATTERN REMAINS FAIRLY WEAK ACROSS THE AREA. WARM
MOIST AIR OVER THE UPPER GREAT LAKES WILL CONTINUE TO RESULT IN FOG
THROUGH FRIDAY.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&

SHORT TERM...JLA
LONG TERM...KEC
AVIATION...JLA
MARINE...JLA

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