Severe Thunderstorm Warning 59, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
644 AM EDT MON SEP 9 2013

LATEST UPDATE...
UPDATE/AVIATION

.SYNOPSIS...
ISSUED AT 338 AM EDT MON SEP 9 2013

A WARM FRONT WILL LIFT NORTH ACROSS SOUTHWEST MICHIGAN TODAY.  IT
WILL BRING A FEW SHOWERS AND MAYBE A THUNDERSTORM...MAINLY THIS
MORNING.  THEN HOT AND HUMID CONDITIONS CAN BE EXPECTED TONIGHT AND
TUESDAY.  MANY AREAS INLAND FROM LAKE MICHIGAN WILL REACH INTO THE
90S ON TUESDAY.  THEN A COLD FRONT IS EXPECTED TO SAG INTO THE AREA
TUESDAY NIGHT AND WEDNESDAY BRINGING A RETURNED CHANCE OF RAIN AND
TEMPERATURES RETREATING INTO THE 80S.

MUCH COOLER WEATHER...WITH TEMPERATURES IN THE 60S AND 70S...IS
EXPECTED FOR THE LATTER PART OF THE WEEK.  THERE COULD BE ANOTHER
CHANCE FOR RAIN BY SUNDAY.

&&

.UPDATE...
ISSUED AT 635 AM EDT MON SEP 9 2013

BAND OF SHOWERS AND THUNDERSTORMS FROM NEAR SHELBY THROUGH GRAND
RAPIDS DOWN TO BATTLE CREEK WAS ADVANCING EAST. POPS WERE RAISED
EARLY THIS MORNING TO ACCOUNT FOR THIS. BY MID MORNING MOST OF THE
RAIN SHOULD BE GONE.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 338 AM EDT MON SEP 9 2013

WARM ADVECTION SHOWERS...AND POSSIBLE THUNDER...WILL BE MOVING
THROUGH THE CWA THROUGH THE FIRST HALF OF THE DAY.  RAISED POPS TO
LIKELY OVER THE NW CWA...BUT THIS IS MAINLY THROUGH ABOUT MID
MORNING.  THE PCPN SHOULD BECOME MORE ISOLATED OR EVEN END THIS
AFTERNOON AS THE WARM FRONT MOVES NORTH ACROSS THE CWA.

BEHIND THE FRONT HUMIDITY LEVELS WILL INCREASE MAKING FOR A STEAMY
NIGHT.  TEMPS SHOULD REMAIN IN THE 70S FOR ALL BUT THE FAR NORTH.
DECIDED TO ADD A 30 POP TO THE FAR NE CWA AS THE CAP WILL NOT BE AS
STRONG THERE.  THE REST OF THE CWA WILL BE WITHIN THE WARM SECTOR
AND SHOULD BE MAINLY PCPN FREE.

VERY HOT AND HUMID DAY EXPECTED FOR TUESDAY.  LOW TO MID 90S LOOK
LIKELY FOR THE SE HALF OF THE CWA...WITH UPPER 80S TO AROUND 90 NW
DUE TO A SLIGHTLY COOLING SW WIND COMING OFF OF LAKE MICHIGAN.

THE COLD FRONT SAGS IN BY TUESDAY NIGHT.  HOWEVER IT WEAKENS AS IT
DOES SO...AS IT BECOMES MORE PARALLEL TO THE UPPER FLOW.  THIS
SHOULD RESULT IN THE NORTHERN CWA HAVING THE BEST CHC FOR PCPN.  THE
FRONT CONTINUES TO WASH OUT INTO WEDNESDAY.  WITH THIS IN MIND...IT
MAY NOT RAIN MUCH ACROSS ACROSS AREAS SOUTH OF I-96.  ALSO WITH THE
FRONT SAGGING IN SLOWLY...I TWEAKED TEMPS UPWARD OVER THE SE CWA
FOR WED WHERE TEMPS MAY APPROACH 90 AGAIN.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 338 AM EDT MON SEP 9 2013

THE MAIN CHALLENGES IN THE LONG TERM DEALS WITH HOW COLD THE
TEMPERATURES WILL BECOME AND THE CHANCES FOR RAIN.

MODELS ARE IN DECENT AGREEMENT IN SHOWING STRONGER COLD AIR
ADVECTION THURSDAY INTO THURSDAY  NIGHT.  THE 850 MB THERMAL TROUGH
ARRIVES THURSDAY NIGHT WITH VALUES OF ROUGHLY 6 TO 8 DEGREES C.  THE
SURFACE PRESSURE GRADIENT IS SHOWN TO WEAKEN THURSDAY NIGHT.  SO THE
COMBINATION OF DECREASING WINDS AND A CHILLY AIRMASS IN PLACE SHOULD
ALLOW FOR TEMPERATURES FALLING INTO THE 30S DURING THIS PERIOD.
WILL NEED TO MONITOR THE FROST POTENTIAL...ESPECIALLY NORTH AND EAST
OF GRAND RAPIDS.  THESE COOLER 850 MB TEMPERATURES SHOULD HOLD
DAYTIME  HIGHS IN THE 60S FOR MOST LOCATIONS FOR FRIDAY.

ANY WARM AIR ADVECTION WILL BE SLOW TO DEVELOP...SO SATURDAY IS
LIKELY TO END UP COOLER THAN NORMAL AS WELL.  MID LEVEL RIDGING
PUSHES IN BY THE END OF THE DAY.

MODELS ARE IN FAIRLY GOOD AGREEMENT CONCERNING THE ARRIVAL OF AN
UPPER TROUGH SUNDAY.  THIS PROGRESSIVE SYSTEM HAS ENOUGH AMPLITUDE
TO WARRANT THE MENTION OF SHOWERS ON SUNDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 635 AM EDT MON SEP 9 2013

IFR WILL REMAIN POSSIBLE WHERE THE HEAVIER STORMS OCCUR. TAFS WILL
REFLECT THIS. BY 15Z THE STORMS SHOULD BE EAST OF KLAN. VFR
CONDITIONS WILL STILL BE FORECASTED FOR THIS AFTERNOON AS MIXING
DEVELOPS WITH THE HEATING SUPPORTING SOME INCREASE IN THE CLOUD
BASES THROUGH THE AFTERNOON. WILL NEED TO MONITOR THE LOW CLOUD
FORMATION LATER TONIGHT AS LOW LEVEL RH VALUES INCREASE. WINDS
WILL INCREASE LATER TONIGHT...BUT LOOKS LIKE THE GUSTS OVER 25
KNOTS WILL HOLD OFF UNTIL AFTER 12Z TUE.

&&

.MARINE...
ISSUED AT 338 AM EDT MON SEP 9 2013

SOUTHWEST FLOW WILL GRADUALLY INCREASE INTO TONIGHT AHEAD OF THE
COLD FRONT.  A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED BY LATE
TONIGHT AND CONTINUE THROUGH MUCH OF TUESDAY.  WINDS AND WAVES
SHOULD DIMINISH TUESDAY NIGHT AS THE FRONT MOVES IN.

&&

.HYDROLOGY...
ISSUED AT 338 AM EDT MON SEP 9 2013

AREAS OF HEAVY RAIN THIS MORNING MAY LEAD TO SOME URBAN AND POOR
DRAINAGE FLOODING. ISOLATED AMOUNTS MAY APPROACH 3 INCHES.  THE
STORMS WILL PUSH EAST OF LANSING BY 15Z. MUCH LESS IN THE WAY OF
RAIN IS FORECASTED FOR THE AFTERNOON AND EVENING.

&&

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

UPDATE...MJS
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...JK
MARINE...JK

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