Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 040007
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
807 PM EDT THU SEP 3 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 PM EDT THU SEP 3 2015

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS LOWER
MICHIGAN THROUGH SATURDAY. THE CLOUDS AND SHOWERS WILL HOLD HIGHS
AROUND 80 FRIDAY BEFORE THE TEMPERATURE CLIMBS BACK TO THE MID 80S
FOR THE REMAINDER OF THE HOLIDAY WEEKEND. COOLER WEATHER IS EXPECTED
BY THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 330 PM EDT THU SEP 3 2015

FORECAST CONCERNS DEAL WITH THE CONVECTIVE POTENTIAL THROUGH
SATURDAY.

RADAR IMAGERY SHOWS A COUPLE OF BROKEN LINES OF CONVECTION. THE
FIRST EXTENDS FROM MOUNT PLEASANT WEST TO NEWAYGO COUNTY. THE SECOND
IS FARTHER SOUTH FROM NEAR ST JOHNS TO MIDDLEVILLE. THE SOUTHERN
LINE APPEARS TO BE NEAR A WEAK COLD FRONT THAT IS WASHING OUT.
FARTHER NORTH A WELL DEFINED CIRCULATION ASSOCIATED WITH AN UPPER
LOW THAT WILL LINGER OVER LOWER MICHIGAN THROUGH SATURDAY. SBCAPE
AROUND 2500 J/KG COUPLED WITH SHEAR AROUND 30 KTS IS ENABLING A FEW
STORMS TO BECOME ORGANIZED. AS THE SUN SETS WE/LL LOSE SOME
INSTABILITY AND THE CONVECTION SHOULD WANE A BIT. HOWEVER THE UPPER
LOW/TROUGH WILL LINGER OVER THE CWA THROUGH SATURDAY. SHEAR VALUES
AROUND 15KTS ARE PROGD FRIDAY ACROSS THE CWA SO WE DON/T ANTICIPATE
SVR STORMS BUT CAN`T RULE OUT A STRONG ONE OR TWO DUE TO DECENT
INSTABILITY.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 330 PM EDT THU SEP 3 2015 IMPACT WEATHER IN THE EXTENDED
PERIOD CENTERS AROUND THE SLOW MOVING FRONT THAT MAY BRING COPIOUS
RAINS FROM MONDAY TO EARLY WEDNESDAY.

ONLY A FEW TWEAKS WERE MADE TO THE BLENDED FORECAST...MAINLY TO SLOW
THE FRONT DOWN A BIT EARLY IN THE WEEK PER THE SLOWER 12Z ECMWF THEN
END THE CHANCE FOR POPS LATE WEDNESDAY WHICH THE 12Z GUIDANCE AGREES
ON. GIVEN THE LONG DURATION AND HIGH PWATS...WOULD NOT BE SURPRISED
TO SEE WIDESPREAD 2 TO 3 INCH RAINFALL FROM MONDAY TO EARLY
WEDNESDAY.

TEMPERATURES ON MONDAY WILL BE TRICKY AS HIGH COULD BE ANYWHERE FROM
AROUND 80 TO NEAR 90 DEPENDING ON HOW EXTENSIVE THE CLOUDS ARE. WENT
MIDDLE OF THE ROAD FOR NOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 806 PM EDT THU SEP 3 2015

I AM THINKING ALL TAF SITES WILL BECOME IFR TONIGHT AND IMPROVE TO
MVFR CIGS AT BEST BY MIDDAY FRIDAY. I DO NOT EXPECT MUCH RAIN
THROUGH JUST A LOT OF LOW CLOUDS AND FOG.

CURRENTLY THE CONVECTIVE BOUNDARY THAT HAS BEEN FIRING
THUNDERSTORMS MOST OF THE DAY IS MOVING SOUTH OF I-94. THIS IS
MORE THAN JUST A COOL POOL EVENT...THERE IS A COLD FRONT
ASSOCIATED WITH AN UPPER LOW THAT WILL BE IN NO HURRY GO GO
ANYWHERE. SINCE THE UPPER LOW WILL NOT BE MOVING MUCH IN THE NEXT
24 HOURS... WE WILL STAY IN THE COOL AIR. ALSO WORRY OF NOTE IS
ALL THE IFR CIGS WITH STRATUS CLOUDS CURRENTLY OCCURRING NORTH OF
I-96. THIS TO IS RELATED TO THE UPPER LOW. MY SPIN IS THE STRATUS
WILL EXPAND OVERNIGHT AND FOG WILL DEVELOP. THE QUESTION IS WHICH
HAPPENS FIRST. IF THE STRATUS GETS TO THE TAF SITES FIRST THERE
WILL LIKELY NOT BE DENSE FOG BY MORNING. IF THE STRATUS COMES IN
LATER...THEN THERE WILL BE TIME FOR THE FOG TO BECOME DENSE. AT
THIS POINT IT WOULD SEEM THE I-94 TAF SITES ARE FAR ENOUGH AWAY
FROM THE STRATUS TO ALLOW DENSE FOG TO FROM. TAF SITES NEAR TO
I-96 MAY GET THE STRATUS FIRST. EITHER WAY WE HAVE IFR IN THE
MORNING AT ALL TAF SITES. SINCE THE UPPER LOW IS GOING NO WHERE
FAST...I AM THINKING THE LOW CLOUDS WILL BE SLOW TO BURN OFF
(STATIONARY FRONT IMPACTS).

&&

.MARINE...
ISSUED AT 330 PM EDT THU SEP 3 2015

WINDS AND WAVES WILL REMAIN ON THE LIGHT SIDE TONIGHT AND FRIDAY DUE
TO THE WEAK PRESSURE GRADIENT. LIGHT NORTH WINDS TONIGHT WILL BECOME
ONSHORE FRIDAY. SCATTERED THUNDERSTORMS ARE POSSIBLE THROUGH
SATURDAY.


&&

.HYDROLOGY...
ISSUED AT 1110 AM EDT THU SEP 3 2015

NO IMMEDIATE CONCERNS TO BE AWARE OF TODAY REGARDING RIVER
FLOODING.

HEAVY RAINFALL ASSOCIATED WITH THUNDERSTORM ACTIVITY WILL QUICKLY
PASS THROUGH THE AREA THIS MORNING AND THROUGH EARLY AFTERNOON.
PONDING MAY OCCUR ON ROADWAYS AND LOW LYING AREAS IN AND AROUND
THE HEAVIER RAINFALL. MUCH OF THE HEAVIER ACTIVITY WILL VACATE
THE REGION BY MID AFTERNOON.

THE NEXT 7 DAYS REMAINS ACTIVE AND INCLUDES MULTIPLE CHANCES FOR
RAIN. 7 DAY AREA AVERAGE RAINFALL OF ONE TO TWO INCHES IS POSSIBLE
WITH LOCALLY HIGHER AMOUNTS IN THE VICINITY OF THUNDERSTORMS.
RECENT DRY WEATHER AND LOW RIVER LEVELS...COUPLED WITH THE
PIECEWISE FASHION OF THE RAINFALL...SHOULD ALLOW FOR THE GROUND TO
SOAK UP MUCH OF THE ONSET OF MOISTURE. RUNOFF THEREAFTER IS
LIKELY TO BE HANDLED WELL BY RIVERS...AS THEY HAVE PLENTY OF ROOM
TO TAKE ON ADDITIONAL WATER.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...OSTUNO
AVIATION...WDM
HYDROLOGY...JAM
MARINE...04


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