Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 040422
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1222 AM EDT FRI SEP 4 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.

&&

.UPDATE...
ISSUED AT 838 PM EDT THU SEP 3 2015

I UPDATED OUR FORECAST AND GRIDS TO DROP THE MENTION OF
PRECIPITATION OVER MOST OF OUR CWA TONIGHT. AS I SEE IT THE
CONVECTIVE LINE CONTINUES TO SINK SOUTH WITH TIME AND SHOULD BE
OUT OF OUR CWA TOTALLY BY MIDNIGHT. THE RAP MODEL SHOWS THE 700 MB
LOW...CURRENTLY CENTERED NEAR LAKE HURON BY APN...MOVES SLOWLY
WESTWARD...REACHING TO NEAR TVC BY MORNING. THAT KEEPS MOST OF OUR
CWA IN THE DRY WESTERLY FLOW ALL NIGHT LONG. THE DEEP MOISTURE IS
EAST OF LANSING BY 9 PM. THE MOST UNSTABLE CAPE ON THE RAP13
MODEL DROPS SOUTH OVER TIME TOO... WHICH GOES ALONG WITH THE IDEA
OF NO SIGNIFICANT CONVECTION TONIGHT. ONLY AREAS NEAR THE 700 MB
LOW MAY SEE SOME LIGHT WRAP AROUND RAIN SHOWERS (NEAR AND NORTH OF
ROUTE 10).

AS FOR FOG DEVELOPING TONIGHT...THIS COULD BE A SIGNIFICANT
FORECAST ISSUE. THERE IS AN AREA OF THICK LOW CLOUDS DROPPING
SOUTH TO NEAR I-96...AS 0F 8 PM THIS EVENING.  DEPENDING ON JUST
HOW FAR SOUTH THEY GET WILL DECIDE HOW DENSE THE FOG GETS TONIGHT.
WITH ALL THE RAIN TODAY AND LIGHT WINDS IF THE SKIES STAYED MOSTLY
CLEAR WE COULD BE LOOKING AT DENSE FOG BY SUNRISE. LIKELY IF THIS
HAPPENS IT WOULD BE NEAR I-94.

&&

.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 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1212 AM EDT FRI SEP 4 2015

TRENDS WILL BE MONITORED FOR FOG DEVELOPMENT NOW THROUGH ABOUT
13Z. CURRENTLY THINKING THE LOW CLOUDS WILL BE MORE OF A PROBLEM
THAN FOG DEVELOPMENT FOR SITES LIKE MKG...GRR...AZO...AND BTL.
MODEL SOUNDINGS ARE NOT BULLISH ON FOG DEVELOPMENT AND EVEN THE
HOURLY LAMP GUIDANCE PRODUCTS ARE BACKING OFF A BIT ON THE VIS
REDUCTIONS. THAT SAID...THERE ARE POCKETS OF FOG NORTH OF LAN
WHERE BREAKS IN THE CLOUDS HAVE OCCURRED. WILL NEED TO KEEP TRACK
OF THE BREAKS OVERNIGHT. LOW CIGS LOOK QUITE LIKELY FOR MOST
LOCATIONS...PROBABLY GETTING DOWN TO A COUPLE HUNDRED FEET. WILL
STILL MENTION SOME LIGHT FOG FOR THE TAFS TO KEEP CONSISTENCY WITH
PREVIOUS THINKING...THOUGH WILL KEEP ABOVE 1/2SM FOR NOW.

&&

.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.
&&

$$

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



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