Small Craft Advisory 63, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
744 AM EDT FRI AUG 30 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 332 AM EDT FRI AUG 30 2013

A SLOW MOVING COLD FRONT WILL PASS THROUGH LOWER MICHIGAN THIS
EVENING. SHOWERS/STORMS ARE POSSIBLE AHEAD OF THE COLD FRONT.
ANOTHER STRONGER COLD FRONT WILL APPROACH SUNDAY WITH ANOTHER CHANCE
OF RAIN. TEMPERATURES WILL REMAIN IN THE MID 80S UNTIL MONDAY WHEN
MUCH COOLER AIR WILL FLOW SOUTH BEHIND THE FRONT. HIGHS IN THE 70S
ARE EXPECTED NEXT WEEK.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 332 AM EDT FRI AUG 30 2013

FORECAST CONCERNS DEAL WITH PCPN TRENDS THROUGH THE PERIOD.

DECAYING MCS WAS NOTED ON RADAR MOVING ACROSS NRN LWR AND JUST
CLIPPING THE FAR NRN CWA. THIS PCPN SHOULD BE EAST OF THE CWA BEFORE
9 AM.

A WEAK COLD FRONT STRETCHES FROM FAR WRN LAKE SUPERIOR SWWD INTO SE
SOUTH DAKOTA. SHORT RANGE MODELS PROG THIS FRONT TO MOVE ACROSS THE
SE CWA THIS EVENING. THUS WE/LL SEE SOME DIURNAL DESTABILIZATION
BEFORE FROPA. GIVEN THAT SHEAR VALUES ARE NOT HIGH CHANCES FOR STORM
ORGANIZATION IS FAIRLY LOW. HOWEVER...PRECIPITABLE WATER IS FAIRLY
HIGH...AROUND 1.85 INCHES...SO ANY STORMS THAT DEVELOP MAY PRODUCE
LOCALLY HEAVY RAINFALL. BUT SVR STORMS ARE NOT EXPECTED.

SATURDAY SHOULD BE DRY AS HIGH PRESSURE FILLS IN BEHIND THE FRONT.

A SHORT WAVE RIDING THE TOP OF THE UPPER RIDGE WILL PUSH A STRONGER
COLD FRONT TOWARD LOWER MICHIGAN SUNDAY. THERE/S A DECENT PUNCH OF
COLDER AIR BEHIND THIS FRONT. WE/LL KEEP CHC POPS IN THE GRIDS FOR
SCT TSRA THAT MAY DEVELOP AHEAD OF IT. OVERALL...I/M NOT OVERLY
BULLISH ON PCPN CHANCES THROUGH THE SHORT TERM. HOWEVER...WITH
ABUNDANT LOW LEVEL MOISTURE IN PLACE A WEAK COLD FRONT PASSING
THROUGH...SCT TSRA SEEMS LIKE THE WAY TO GO.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 332 AM EDT FRI AUG 30 2013

MODELS REMAIN IN GOOD AGREEMENT REGARDING THE TIMING OF THE COLD
FRONTAL PASSAGE ON SUNDAY NIGHT... BUT ARE NOT VERY AMBITIOUS WITH
QPF. THE SFC FRONT LOOKS WEAK WITH LIMITED CONVERGENCE AND NO LOW
LEVEL JET TO SPEAK OF... BUT THE H5 SHORTWAVE LOOKS IMPRESSIVE. WILL
KEEP POPS IN THE CHANCE CATEGORY FOR NOW.

ECMWF CONTINUES TO MORE AGGRESSIVE THAN THE GFS WITH THE STRENGTH OF
THE COLD ADVECTION ON LABOR DAY. EITHER WAY WE WILL SEE DEW POINTS
FALLING INTO THE 50S IN THE NORTHERLY FLOW WHICH WILL FEEL PLEASANT
AFTER SEVERAL DAYS OF HEAT AND HUMIDITY.

TUESDAY AND WEDNESDAY LOOK LIKE FINE WEATHER DAYS AS A LARGE SFC
HIGH DRIFTS FROM MINNESOTA TO INDIANA. THE ECMWF AND GFS ARE NOT IN
GOOD AGREEMENT AT ALL ON WEDNESDAY NIGHT AND THURSDAY. THE GFS IS
SHOWING WARM ADVECTION WITH H8 TEMPS IN THE MID TO UPPER TEENS WHILE
THE ECMWF HAS A SFC FRONT DROPPING DOWN FROM THE NORTH WITH H8 TEMPS
FALLING TO AROUND 4C. WILL CARRY A SLGT CHANCE FOR A SHOWER OR STORM
WED NIGHT WITH THE POTENTIAL ECMWF FRONT... BUT THE AIR MASS LOOKS
RATHER DRY AT THIS TIME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 745 AM EDT FRI AUG 30 2013

THE MAIN FOCUS IS TSTM POTENTIAL AND TIMING TODAY AND TONIGHT.
THE BEST THREAT OF TSTMS DOES NOT ARRIVE UNTIL AFTER ROUGHLY 21Z
THEN LINGERS THROUGH 06Z OR SO TONIGHT AS THE COLD FRONT MOVES
SLOWLY SOUTH THROUGH THE AREA.

THE COVERAGE OF STORMS ALONG THE FRONT SHOULD ONLY BE SCATTERED AT
BEST... AND THE HIGHEST COVERAGE OF STORMS WILL PROBABLY BE OVER
SE WISCONSIN/NRN ILLINOIS AS WELL AS OVER THE THUMB AREA OF LWR
MI. THESE TWO AREAS ARE WHERE THE MODELS SHOW THE BEST SFC
CONVERGENCE DEVELOPING LATER TODAY AND TONIGHT. WENT WITH ONLY
VCTS REMARKS IN THE SW MI TAFS.

ALSO OF CONCERN AVIATION WISE IS THE POTENTIAL FOR IFR STRATUS AND
FOG DEVELOPING AFTER ROUGHLY 09Z TONIGHT BEHIND THE COLD FRONT.
CONFIDENCE IS MEDIUM ON THIS... ESPECIALLY ALONG AND NORTH OF THE
I-96 CORRIDOR.

A PERIOD OF STRONGER SOUTHWEST SFC WINDS AROUND 12KT IS LIKELY FROM
MID MORNING THROUGH EARLY EVENING... PRECEDING THE COLD FRONT.

&&

.MARINE...
ISSUED AT 332 AM EDT FRI AUG 30 2013

SOUTH WINDS 10 TO 20 KNOTS WILL CAUSE WAVES TO BUILD TO 2 TO 4 FEET
NORTH OF PENTWATER TODAY. NORTH WINDS BEHIND THE COLD FRONT TONIGHT
COULD GENERATE 3 TO 5 FOOT WAVES AND A SCA MAY BE NEEDED TONIGHT
INTO SUNDAY.

&&

.HYDROLOGY...
ISSUED AT 332 AM EDT FRI AUG 30 2013
PRECIPITABLE WATER VALUES NEAR 1.85 INCHES COULD RESULT IN LOCALLY
HEAVY RAINFALL FROM ANY STORMS THAT DEVELOP LATER THIS AFTERNOON.
MOST AREAS LIKELY WON/T SEE RAIN HOWEVER.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

SYNOPSIS...93
SHORT TERM...93
LONG TERM...MEADE
AVIATION...MEADE
HYDROLOGY...93
MARINE...93

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