Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 301736
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
136 PM EDT SAT AUG 30 2014

LATEST UPDATE...
UPDATE

.SYNOPSIS...
ISSUED AT 327 AM EDT SAT AUG 30 2014

A LOW PRESSURE SYSTEM TRACKING THROUGH THE NORTHERN GREAT LAKES
WILL DRAG A COLD FRONT THROUGH THE SOUTHWEST LOWER MICHIGAN
TONIGHT. PERIODS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY
INTO THIS EVENING AHEAD OF THE COLD FRONT. IT WILL BE WARM AND
HUMID TODAY TOO. SUNDAY WILL FOR THE MOST PART BE PARTLY CLOUDY
WITH A SLIGHT CHANCE OF AN AFTERNOON THUNDERSTORM. IT WILL
CONTINUE TO BE WARM AND HUMID. A COLD FRONT PUSHING INTO THE AREA
ON LABOR DAY WILL BRING THE RISK FOR SEVERE STORMS IN THE
AFTERNOON. WARM AND HUMID CONDITIONS WILL CONTINUE.

&&

.UPDATE...
ISSUED AT 136 PM EDT SAT AUG 30 2014

INSTABILITY WAS BUILDING SLOWLY AS THE CLOUD COVER WAS ERODING
THIS AFTERNOON. MLCAPE VALUES NEAR 500 JKG WITH MUCAPE VALUES UP
OVER 1500 J/KG AND EFFECTIVE SHEAR VALUES ARE AROUND 35 KNOTS.
STORMS BEGINNING TO DEVELOP AND A FEW COULD CONTAIN DAMAGING WIND
GUSTS AS INSTABILITY TRIES TO INCREASE. MID LEVEL WAVE MOVING IN
FROM WI WILL HELP TO TRIGGER ADDITIONAL STORMS. CONVECTION WILL
DECREASE THIS EVENING AS THE INSTABILITY WEAKENS.

UPDATE ISSUED AT 1032 AM EDT SAT AUG 30 2014

SATELLITE IMAGERY SHOWS DIMINISHING CLOUDS ACROSS LAKE MI. BASED
ON THE MOVEMENT...WE SHOULD SEE A PERIOD OF SUN THIS AFTERNOON.
AS A RESULT THE UPDATE FEATURES MORE SUNSHINE IN THE GRIDS. THIS
HEATING SUPPORTS THUNDERSTORMS DEVELOPING. WITH A LOW LEVEL JET
MOVING IN...THE STORMS COULD BECOME NUMEROUS. WILL KEEP THE HIGHER
POPS GOING FOR THE AFTERNOON. WILL NEED TO MONITOR THE SEVERE
POTENTIAL AS DEEP LAYER SHEAR CLIMBS ABOVE 30 KNOTS. HRRR RUC
SHOWS VERY LITTLE CONVECTION AFTER 19Z DESPITE THE ARRIVAL OF A
MID LEVEL WAVE.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 327 AM EDT SAT AUG 30 2014

WE HAVE TWO PERIODS OF CONVECTION TO WATCH IN THE SHORT TERM
FORECAST. THE THUNDERSTORMS AHEAD OF THE WEAK COLD FRONT THAT
COMES THROUGH THE AREA TONIGHT... THEN THE POSSIBLY SEVERE STORMS
ON LABOR DAY AS A STRONG JET STREAM INTERACTS WITH THE COLD FRONT
DURING MAX HEATING.

A QUICK OVERVIEW OF WHAT IS HAPPENING ON THE LARGER SCALE IS THE
SHEARING OUT SOUTHERN STREAM WAVE WE HAVE BEEN WATCHING FOR OVER
A WEEK NOW COMES THROUGH THE AREA TODAY. THE MODELS ALL SHOW THE
327 MB WAVE DEVELOPING A CLOSED UPPER LOW BY MID AFTERNOON. THE
ASSOCIATED DYNAMICS OF THE UPPER JET STREAM AND CORRESPONDING LOW
LEVEL JET WILL BRING THUNDERSTORMS TO THE AREA TODAY. THAT SYSTEM
MOVES OUT OF THE AREA LEAVING A SHORTWAVE RIDGE IN THE AREA
SUNDAY. THIS WILL RESULT IN QUIET WEATHER INTO SUNDAY NIGHT.
FINALLY A STRONG PACIFIC STORM BRINGS A NORTHERN STREAM WAVE INTO
THE AREA ON LABOR DAY. THIS WILL BRING STRONG JET DYNAMICS WITH IT
AND WILL RESULT IN A STRONG LOW LEVEL RESPONSE TO THE ASSOCIATED
COUPLED JET CORE MOVING THROUGH ON LABOR DAY.

AS FOR TODAY...THERE WILL BE TWO PERIODS OF CONVECTION. THE FIRST
WAVE IS ASSOCIATED WITH A INCREASE IN DEEP MOISTURE AND IS
LARGELY THE SYSTEM WARM FRONT COMING THROUGH. THIS HAS A LOW LEVEL
JET ASSOCIATED WITH IT AND THE AXIS OF THAT JET WILL BE FROM BTL
TO MBS BY MID MORNING. THIS WILL HELP DEVELOP STORMS OVER WESTERN
LOWER MICHIGAN THAT WILL MOVE EAST ACROSS THE STATE DURING THE
DAY. THEN THERE IS A SECOND LOW LEVEL JET ASSOCIATE WITH THE MAIN
UPPER WAVE. IT COMES ONTO SOUTHWEST MICHIGAN THIS AFTERNOON AND
INCREASE TO 35 TO 40 KNOTS NEAR LANSING BY 2 PM. THAT WILL DEVELOP
A SECOND AREA OF CONVECTION OVER WESTERN LOWER MICHIGAN THAT WILL
ALSO MOVE EAST BY LATE AFTERNOON. BY THEN MIX LAYER CAPES COULD BE
1500 J/KG SO AND THERE COULD BE AS MUCH AS 30 KNOTS OF EFFECT DEEP
LAYER SHEAR SO SOME STORMS MAY BE STRONG.

ALL OF THAT MOVES OUT LATE THIS EVENING AND SHORTWAVE RIDING
FOLLOWS SUNDAY. HOWEVER THERE IS STILL SOME INSTABILITY EVEN THOUGH
THE MID LEVELS (ABOVE 850 MB) IS RATHER DRY. I ADDED A SMALL
CHANCE OF AFTERNOON THUNDERSTORMS MOSTLY SOUTH OF I-96 IN THE
AFTERNOON FOR THAT.

THE MAIN STORY IS MONDAY WHEN THE UPPER LEVEL WAVE MOVES INTO VERY
UNSTABLE AIR. THE LOW LEVEL JET ON THE GFS IS FOCUSED ON SOUTHWEST
LOWER MICHIGAN IN THE AFTERNOON AND SHOWS OVER 3270 J/KG OF CAPE.
SO THERE IS REAL POTENTIAL FOR SEVERE STORMS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 327 AM EDT SAT AUG 30 2014

THE MAIN FOCUS OF THE LONG TERM REMAINS ON THE SYSTEM THAT WILL BE
AFFECTING THE AREA DURING THE FIRST PART OF NEXT WEEK. THE FRONT
LOOKS TO START OUT MON EVENING TO OUR WEST YET. THIS WILL KEEP THE
THREAT OF STORMS IN THE FCST...ALTHOUGH THE THREAT OF SEVERE WEATHER
WILL BE DIMINISHING AS DIURNAL INSTABILITY WILL BE ON THE WANE A
BIT.

A RESIDUAL CHC OF SHOWERS AND STORMS WILL BE LEFT IN FOR THE DAY ON
TUE. THE FRONT LOOKS TO SINK JUST SOUTH OF THE AREA AND STALL OUT.
HOW FAR SOUTH IT STALLS IS UNCERTAIN WITH THE GFS A BIT FURTHER
SOUTH...AND THE EURO KEEPING IT CLOSER TO THE AREA. THIS FRONTAL
POSITION WILL BE IMPORTANT AS ANOTHER WAVE LOOKS TO MOVE THROUGH THE
REGION AND COULD BRING ANOTHER ROUND OF RAIN TO THE AREA ON TUE.

THE AREA SHOULD DRY OUT FOR WED WITH A RIDGE OF HIGH PRESSURE
BUILDING INTO THE AREA. THIS RIDGE WILL BE FAIRLY FLAT IN NATURE AND
WILL BE SHORT LIVED. A TROUGH EXPECTED TO COME ONSHORE OVER THE
PACIFIC NW DURING THE TUE TIME FRAME WILL PUSH A FRONTAL SYSTEM SE
INTO THE AREA LATE IN THE WEEK. PCPN CHCS WILL START ON THU AS A
WARM FRONT MOVES THROUGH THE AREA. THE COLD FRONT THEN FOLLOWS FOR
THE DAY ON FRI.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 732 AM EDT SAT AUG 30 2014

WHILE IT SHOWERS AND ISOLATED THUNDERSTORMS WILL BE AROUND TODAY
IT WOULD SEEM THE LOW LEVELS ARE DRY ENOUGH THAT CIGS/VSBY WILL
LARGELY BE VFR. I PUT VCTS THIS AFTERNOON AS IT IS EXPECTED SOME
CONVECTION WILL BE AROUND AHEAD OF THE WEAK COLD FRONT BUT THE
ACTIVITY WILL NOT BE CONCENTRATED ENOUGH TO NAIL DOWN THE TIMING
AT THIS POINT. TONIGHT ONCE THE FRONT COMES THROUGH IT WILL STALL
AND WINDS WILL BECOME LIGHT. I WOULD EXPECT LOW CIGS AND SOME IFR
FOG TO DEVELOP TOWARD SUNRISE SUNDAY.


&&

.MARINE...
ISSUED AT 1032 AM EDT SAT AUG 30 2014

WAVES RUNNING 3 TO 5 FEET ALONG THE LAKESHORE. GIVEN THE VEERING
FLOW WITH GUSTS UP AROUND 25 KNOTS...HAZARDOUS CONDITIONS WILL
PERSIST INTO THE AFTERNOON. WINDS AND WAVES WILL GRADUALLY
DIMINISH LATER THIS AFTERNOON AND INTO THE EVENING.


&&

.HYDROLOGY...
ISSUED AT 307 PM EDT FRI AUG 29 2014

HEAVY RAIN IS A RISK THROUGH SATURDAY. VERY MOIST AIRMASS WILL ADVECT
INTO MI AS PWAT VALUES GENERALLY CLIMB ABOVE 1.5 INCHES. GIVEN THE
LACK OF DIRECTIONAL SHEAR...WE COULD SEE SOME TRAINING WHICH MAY
LEAD TO THE STORMS PERSISTING. IF THIS ENDS UP OCCURRING...SOME
LOCATIONS COULD EASILY SEE OVER 2 INCHES OF RAIN.

&&

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

LM...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...MJS
MARINE...MJS






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