Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 300729
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
329 AM EDT SAT AUG 30 2014

LATEST UPDATE...
SYNOPSIS/SHORT TERM/LONG TERM/MARINE

.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.


&&

.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 OVER 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 REUSTL IN A STRONG LOW LEVEL RESPONSE TO THE ASSOCIATED
COUPLED JET CORE MOVING THROUGH 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 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 153 AM EDT SAT AUG 30 2014

PCPN/CONVECTION TRENDS ARE THE MAIN CONCERNS FOR THE 06Z FCST
PERIOD. THE DETAILS IN THE CONVECTION TRENDS ARE STILL A BIT
UNCERTAIN THROUGH MOST OF THE PERIOD. WE CAN NOT RULE OUT A POP UP
SHOWER OR EVEN STORM REALLY AT ANY POINT THROUGH ABOUT 01-02Z SUN.

THERE DO LOOK TO BE TWO BETTER OPPORTUNITIES. THE FIRST WILL START
AFFECTING KMKG AROUND 09Z OR SO AND THEN SPREAD TO THE EAST. THIS
WILL LIKELY BE MORE SHOWERS THAN STORMS...SO WE HAVE GONE WITH
VCSH AND A TEMPO GROUP. THE SECOND IS AFTER 18Z THIS AFTERNOON AS
THE CENTER OF THE SYSTEM MOVES IN AND HEATING OF THE DAY STARTS TO
HELP POP SHOWERS AND STORMS.

WE BELIEVE AS THE LOW STARTS TO MOVE EAST OF THE AREA AFTER ABOUT
01-02Z SUN...PCPN WILL END. WE COULD SEE SOME RESIDUAL MVFR CIGS
HOLD IN THEN THROUGH THE END OF THE FCST PERIOD.


&&

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

WE WILL BE LEAVING THE MARINE AND BEACH HEADLINES AS IS THIS
MORNING. WINDS ARE UP NEAR SMALL CRAFT ADVISORY CRITERIA AT MANY
LOCATIONS ALONG THE COAST. WAVES ARE A BIT MORE MARGINAL...HOWEVER
THEY SHOULD BUILD A BIT AS THE FLOW GOES FROM OFFSHORE TO MORE
ONSHORE THIS AFTERNOON. WINDS WILL REMAIN UP THROUGH THE DAY TODAY
BEFORE THEY DIMINISH THIS EVENING AND TONIGHT.

ANOTHER GOOD POTENTIAL OF STRONGER WINDS LOOKS POISED TO MOVE IN ON
MON WITH THE STRONGER WINDS AHEAD OF THE COLD FRONT. SMALL CRAFT
ADVISORIES AND BEACH HAZARDS STATEMENTS LOOK LIKELY FOR MON.

&&

.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 THROUGH THIS EVENING FOR MIZ037-043-050-
     056-064-071.

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

&&

$$

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






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