Severe Thunderstorm Warning 46, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
726 PM EDT FRI JUL 19 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 356 PM EDT FRI JUL 19 2013

A COLD FRONT WILL PRESS THROUGH SOUTHWEST LOWER MICHIGAN TONIGHT
WHICH WILL BE PRECEDED BY SHOWERS AND THUNDERSTORMS. SOME OF THE
STORMS THIS EVENING MAY BE SEVERE WITH DAMAGING WINDS AND TORRENTIAL
RAINS. THE SHOWERS AND STORMS WILL MOVE SOUTH INTO INDIANA AND OHIO
SATURDAY MORNING. A REFRESHING COOLER AND DRIER AIR MASS WILL SETTLE
INTO THE STATE FOR THE WEEKEND. HIGHS WILL BE CLOSER TO NORMALS FOR
THIS TIME OF YEAR WITH LOWER 80S ON SATURDAY AND AROUND 80 ON SUNDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 356 PM EDT FRI JUL 19 2013

STILL A COMPLEX CONVECTIVE EVOLUTION IN PLACE...WITH A PRE FRONTAL
CONVERGENCE ZONE RESULTING IN SCATTERED THUNDERSTORM DEVELOPMENT AT
THIS TIME FROM NEAR HOLLAND EAST TO IONIA. THESE STORMS WILL
CONTINUE TO DEVELOP AS MIXED LAYER CAPE VALUES ARE ON THE ORDER OF
2000 J/KG AT THIS TIME. TWO MAIN CORRIDORS OF INSTABILITY ARE IN
PLACE ONE POOLED NEAR THE FRONT OFF TO THE NORTH WHICH STRETCHES
FROM NORTHERN LAKE MICHIGAN INTO CENTRAL WISCONSIN. THE OTHER AREA
OF EVEN HIGHER INSTABILITY IS NOSED INTO SOUTH CENTRAL LOWER
MICHIGAN FROM GRR SOUTH AND EAST. THIS ZONE IS IN PLAY DUE TO THE
FACT THAT THE SOUTHWEST FLOW IS NOT OFF THE LAKE HERE.

DYNAMICS REMAIN A FACTOR AS THE MID LEVEL SHORTWAVE TROUGH EDGES IN
ALONG WITH AN ENTRANCE REGION TO A 250MB JET STREAK. REALLY ALL
INGREDIENTS ARE IN PLACE...MOISTURE...INSTABILITY AND LIFT. ENVISION
THE CURRENT LINE CONTINUING TO DEVELOP WITH SOME SEVERE WIND GUSTS
EMBEDDED. THE FRONT TO THE NORTH WILL BE THE WILD CARD BUT EXPECT TO
SEE A LINEAR LINE OF STORMS FORM ALONG IT AND PROGRESS SOUTH. THESE
STORMS MAY BE MOVING INTO CENTRAL LOWER MICHIGAN IN THE 7-9PM TIME
RANGE. SEVERE WEATHER WITH THESE IS POSSIBLE BUT THERE IS A SOLID
LAKE SHADOW OF WEAKER INSTABILITY THERE.

MAIN THREAT CONTINUES TO BE DAMAGING WINDS AS STRONG SYNOPTIC SCALE
FLOW IS IN PLACE IN THE 850-500MB LAYER.

COOLER AND DRIER AIR WILL BRING QUIET WEATHER SATURDAY INTO SUNDAY.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 356 PM EDT FRI JUL 19 2013

COOLER PATTERN TO PERSIST WITH NEAR NORMAL TO SLIGHTLY BELOW NORMAL
TEMPERATURES LOOKING MORE LIKELY THROUGH NEXT WEEK. THIS MEANS HIGHS
IN THE UPPER 70S TO LOWER 80S WITH LOWS IN THE LOWER 60S. THERE WILL
BE SCATTERED CHANCES FOR SHOWERS AND THUNDERSTORMS ESPECIALLY DURING
THE FIRST HALF OF NEXT WEEK...BUT OVERALL NO ORGANIZED SIGNIFICANT
WEATHER EXPECTED MONDAY THROUGH FRIDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 726 PM EDT FRI JUL 19 2013

THE BIG QUESTION IS DOES A LINE OF STORMS FORM JUST AHEAD OF THE
FRONT OR NOT? CURRENTLY SCATTERED STORMS ARE TRYING TO ORGANIZE
NEAR MBL...WHICH IS JUST AHEAD OF THE COLD FRONT. THE TIMING TOOL
TAKES THAT TO MKG BY 0430Z AND TO THE I-94 TAF SITES BY 11Z. THIS
SEEMS TO SLOW... THE LATEST HRRR REDEVELOPS STORMS OVER SOUTHERN
LAKE MICHIGAN BY 01Z AND HEADS THOSE STORMS OUT OF THE CWA BY 04Z.
SINCE THERE IS A JET SPEED MAX THAT COMES THROUGH THE AREA IN THE
03Z TIME FRAME... IT WOULD SEEM THERE IS A GOOD CHANCE THE STORMS
COULD YET BETTER ORGANIZE. SO NOT HAVING ANYTHING SOLID TO TRACK
INTO THE TAF SITES...I KEPT THE VCTS GOING 09Z AT MOST OF THE TAF
SITES. BEHIND THE FRONT SKIES WILL CLEAR SO MOST OF SATURDAY
SHOULD BE CLEAR WITH A NORTHWEST WIND AROUND 10 KNOTS.

&&

.MARINE...
ISSUED AT 356 PM EDT FRI JUL 19 2013

A COMPLEX MARINE SCENARIO IS IN PLACE WITH AN ONGOING HIGH WAVE
EVENT IN PROGRESS. WAVES OF 4 TO 7 FEET ARE COMMON PLACE IN THE
NEARSHORE AREA AT THIS TIME. THE WIND WILL DIMINISH TONIGHT AND THE
WAVES WILL DAMPEN OUT AS WELL...SUBSIDING BELOW SMALL CRAFT ADVISORY
CRITERIA AFTER MIDNIGHT. A HIGH SWIM HAZARD RISK WILL CONTINUE
THROUGH SUNSET.

THE COMPLICATING FACTOR IS IT APPEARS ANOTHER HIGH WAVE EVENT WILL
FOLLOW QUICKLY ON THE HEELS OF THIS ONE TOMORROW AFTERNOON IN THE
NORTHERLY FLOW BEHIND THE COLD FRONT. WILL HOLD OFF ON ISSUING A
BEACH HAZARDS STATEMENT AND SMALL CRAFT ADVISORY FOR SATURDAY INTO
SATURDAY NIGHT...LETTING THIS ONE END FIRST. A CLOSER LOOK WILL BE
TAKEN AT TOMORROWS EVENT BY THE MID SHIFT.

&&

.HYDROLOGY...
ISSUED AT 356 PM EDT FRI JUL 19 2013
LOCAL FLOODING POTENTIAL WILL CONTINUE UNTIL THE FRONT AND THEREFORE
STORM THREAT IS SOUTH OF THE AREA. BY SATURDAY MORNING THE FRONT
SHOULD BE SOUTH OF SOUTHWEST LOWER MICHIGAN. ANY STORMS THIS EVENING
AND TONIGHT GIVEN A VERY MOIST AIRMASS IN PLACE WILL BE CAPABLE OF
TORRENTIAL DOWNPOURS. LOCALIZED FLOODING IS VERY POSSIBLE IN AN AIR
MASS SUCH AS THIS. WIDESPREAD HEAVY AREAL RAINFALL IS NOT EXPECTED
HOWEVER. SO...A FLASH FLOOD TYPE THREAT WILL EXIST THIS EVENING AND
TONIGHT BUT WIDESPREAD RIVER ISSUES ARE NOT ANTICIPATED GIVEN THE
LOCAL NATURE OF THE HEAVY RAINS. A COOLER AND DRIER AIR MASS WILL
PUSH INTO THE AREA FOR SATURDAY AND SUNDAY.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT UNTIL 11 PM EDT THIS EVENING FOR MIZ037-
     043-050-056-064-071.

     HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MIZ037>040-043>046-
     050>052-056>059-064>067-071>074.

LM...SMALL CRAFT ADVISORY UNTIL 4 AM EDT SATURDAY FOR LMZ844>849.

&&

SYNOPSIS...DUKE
SHORT TERM...DUKE
LONG TERM...MACZKO
AVIATION...WDM
HYDROLOGY...DUKE
MARINE...DUKE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1251 PM EDT FRI JUL 19 2013

MIZ037>040-043>046-050>052-056>059-064>067-071>074-200900-
MASON-LAKE-OSCEOLA-CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-
MONTCALM-GRATIOT-OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-
INGHAM-VAN BUREN-KALAMAZOO-CALHOUN-JACKSON-
1251 PM EDT FRI JUL 19 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST LOWER
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

HEAT INDEX WILL ONCE AGAIN CLIMB TO AROUND 100 DEGREES DURING
THE AFTERNOON AND EARLY EVENING HOURS. THIS WILL RESULT IN AN
INCREASED RISK FOR HEAT EXHAUSTION OR HEAT STROKE.

A THREAT FOR SEVERE THUNDERSTORMS EXIST AREA WIDE THROUGH THIS
EVENING. THE MAIN TIME FRAME OF CONCERN WILL BE BETWEEN
3 PM AND 10 PM. DAMAGING WINDS AND TORRENTIAL RAINS WILL BE THE MAIN
THREATS. TO A LESSER EXTENT HAIL WILL BE POSSIBLE AND AN ISOLATED
TORNADO CANNOT BE RULED OUT. THE PRIMARY STORM MOTION WILL BE
QUICKLY OFF TO THE EAST AROUND 40 MPH.

TODAY WILL BE A WINDY DAY WITH GUSTS UP TO 40 MPH POSSIBLE.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

ADDITIONAL THUNDERSTORMS WILL BE POSSIBLE EARLY NEXT WEEK. SEVERE
WEATHER IS NOT FORECASTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THROUGH THIS EVENING.

LMZ844>849-200900-
ST JOSEPH TO SOUTH HAVEN MI-SOUTH HAVEN TO HOLLAND MI-
HOLLAND TO GRAND HAVEN MI-GRAND HAVEN TO WHITEHALL MI-
WHITEHALL TO PENTWATER MI-PENTWATER TO MANISTEE MI-
1251 PM EDT FRI JUL 19 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST LOWER
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SEVERE THUNDERSTORMS WILL BE POSSIBLE TODAY INTO THIS
EVENING. WIND GUSTS OVER 50 KNOTS...LARGE HAIL AND FREQUENT LIGHTNING
WILL BE THE MAIN RISKS.

A HIGH SWIM HAZARD RISK IS IN PLACE FOR OUR ENTIRE LAKESHORE THIS
AFTERNOON AND EVENING WITH LARGE WAVES AND DANGEROUS CURRENTS
EXPECTED.

WINDS AND WAVES WILL BE HAZARDOUS TO SMALL CRAFT THROUGH THIS
EVENING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

ADDITIONAL THUNDERSTORMS WILL BE POSSIBLE EARLY NEXT WEEK. SEVERE
WEATHER IS NOT FORECASTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THROUGH THIS EVENING.

MJS DUKE

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