Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 291929
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
329 PM EDT FRI AUG 29 2014

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

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

AN AREA OF LOW PRESSURE WILL TRACK NORTHEAST THROUGH THE GREAT
LAKES REGION TONIGHT THROUGH SATURDAY. THIS SYSTEM WILL PRODUCE
AREAS OF SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL. A
WEAK AREA OF HIGH PRESSURE WILL TEMPORARILY MOVE IN FOR SUNDAY
LEADING TO MAINLY DRY WEATHER. THE RISK FOR THUNDERSTORMS RETURNS
FOR MONDAY AS A WEAK COLD FRONT TRACKS EASTWARD THROUGH THE STATE.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 307 PM EDT FRI AUG 29 2014

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE TIMING AND
COVERAGE OF ANY SHOWERS AND THUNDERSTORMS. THE UPPER LOW NEAR
KANSAS CITY TRACKS NORTHEAST THROUGH SATURDAY. DEEPER MOISTURE
ARRIVES HERE IN SOUTHWEST LOWER MI DURING THIS TIME AND THE
ATMOSPHERE REMAINS UNSTABLE. SO WITH SOME FORCING...MOISTURE AND
INSTABILITY WE WILL SEE A RISK FOR THUNDERSTORMS INTO SATURDAY
NIGHT. THE LOW LEVEL JET WILL LIKELY FOCUS THE STORMS. AROUND 12Z
SAT WE SEE SOME LOW LEVEL CONVERGENCE ASSOCIATED WITH THE LOW
LEVEL JET THAT IT APPEARS WILL HELP CREATE NUMEROUS SHOWERS AND
THUNDERSTORMS. FOR THAT REASON I FEATURED THE HIGHEST POPS FOR SATURDAY.

WE WILL DRY OUT SAT NIGHT INTO SUNDAY AS THE WAVE OF LOW PRESSURE
PULLS AWAY.





.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 307 PM EDT FRI AUG 29 2014

ANOTHER COLD FRONT SHOULD BE COMING THROUGH MONDAY NIGHT.  SHOWERS
AND STORMS SHOULD BE ON THE INCREASE THROUGH MONDAY.  THERE IS AN
OUTSIDE CHANCE THAT A FEW STORMS COULD BE SEVERE...BUT MAINLY THIS
APPEARS TO BE A WET SYSTEM WITH PRECIPITABLE WATER VALUES AROUND
1.75 INCHES.  WILL MAINTAIN THE LIKELY POPS...AND EXPAND THEM ACROSS
THE ENTIRE CWA FOR MONDAY.  THE FRONT SEEMS TO HAVE SLOWED DOWN A
BIT ON THE MEDIUM RANGE MODELS...SO HAVE EXTENDED THE CHANCE POPS
INTO TUESDAY.

WE SHOULD HAVE A MOSTLY DRY PERIOD FROM TUESDAY NIGHT THROUGH
THURSDAY AS HIGH PRESSURE DRIFTS THROUGH.  AFTER A SLIGHT COOL DOWN
TUESDAY AND WEDNESDAY...TEMPS SHOULD REBOUND AGAIN FOR THURSDAY AS
RETURN SOUTHERLY FLOW KICKS IN.  THURSDAY SHOULD BE THE WARMEST DAY
OF THE WEEK...IN THE LOWER TO MID 80S.  THEN THERE ARE SOME MODELS
DIFFERENCES IN TIMING...BUT IT APPEARS ANOTHER COLD FRONT ARRIVES
THURSDAY NIGHT OR FRIDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 153 PM EDT FRI AUG 29 2014

WIDELY SCATTERED THUNDERSTORMS CAN NOT BE COMPLETED RULED OUT ANY
TIME OVER THE NEXT 24 HOURS...HOWEVER I ATTEMPTED TO SHOW WHEN
STORMS WOULD BE THE MOST LIKELY WITHIN THE 18Z TAFS.

INSTABILITY WILL BUILD THROUGH THIS AFTERNOON...HOWEVER THERE IS
NOT A FOCUSED TRIGGER TO START ANYTHING SIGNIFICANT...SO LEFT
STORMS OUT OF THE TAFS UNTIL AFTER 01Z...HOWEVER AN ISOLATED
STORM IS POSSIBLE PRIOR TO THAT. THERE IS A LOW LEVEL JET THAT
DEVELOPS THIS EVENING AND MOVES IN TOWARD SOUTHERN LAKE MICHIGAN.
I HAVE STORMS IN THE TAFS AT AZO AND BTL...BUT FURTHER NORTH AND
EAST ANY STORMS SHOULD WEAKEN...SO ONLY HAVE SHOWERS ELSEWHERE.
ANY STORMS SHOULD DIMINISH AFTER MIDNIGHT AS THE INSTABILITY
LESSENS.

ANOTHER ROUND OF STORMS WILL BECOME POSSIBLE AGAIN THROUGH
MID/LATE SATURDAY MORNING AND INTO EARLY AFTERNOON ACROSS THE
ENTIRE AREA AS INSTABILITY SHOULD INCREASE AGAIN ALONG WITH A
MORE FAVORABLE PUSH OF MOISTURE.

VFR WITH PATCHY MVFR IS EXPECTED OVER THE NEXT 24 HOURS OUTSIDE OF
ANY STORMS.


&&

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

WITH A LOW LEVEL JET MOVING IN TONIGHT WINDS WILL
INCREASE...ESPECIALLY OVER LAKE MI. IT IS A GOOD SETUP FOR WAVES
OVER 3 FEET AS THE WINDS VEER FROM SOUTHEAST TO SOUTHWEST. THE
LONGER FETCH SUPPORT HIGHEST WAVES GENERALLY NORTH OF HOLLAND.
THE LOW LEVEL JET PULLS OUT LATER SATURDAY. THIS WILL ACT TO
SUPPORT DECREASING WAVE HEIGHTS.

&&

.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 FROM 8 PM EDT THIS EVENING THROUGH
     SATURDAY EVENING FOR MIZ037-043-050-056-064-071.

LM...SMALL CRAFT ADVISORY UNTIL 11 PM EDT SATURDAY FOR LMZ848-849.

     SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 PM EDT
     SATURDAY FOR LMZ844>847.

&&

$$

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





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