Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 181131
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
731 AM EDT THU SEP 18 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 246 AM EDT THU SEP 18 2014

A WEAK COLD FRONT WILL SLIP SOUTHWARD THROUGH LOWER MICHIGAN THIS
MORNING. HIGH PRESSURE WILL BUILD IN FROM THE NORTH BEHIND THIS
SYSTEM DRAWING DOWN A COOLER AIRMASS. THIS HIGH WILL THEN TRACK
EASTWARD TO NEW ENGLAND ON FRIDAY. SOUTHWEST WINDS AROUND THIS
SYSTEM WILL DRAW UP A MILDER AIRMASS FROM THE CENTRAL PLAINS FOR
FRIDAY AND SATURDAY. UNSETTLED WEATHER WILL ARRIVE OVER THE
WEEKEND AS A COLD FRONT TRACKS IN FROM THE WEST.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 246 AM EDT THU SEP 18 2014

THE MAIN CHALLENGES IN THE SHORT TERM DEAL WITH THE POTENTIAL FOR
SHOWERS WITH THE COLD FRONT SLIPPING DOWN FROM THE NORTH
TODAY...AND ALSO THE SEVERE WEATHER POTENTIAL FOR SATURDAY.

STILL LOOKS LIKE THE COLD FRONT SLIPPING SOUTHWARD THROUGH LOWER
MICHIGAN WILL END UP AS A DRY FRONTAL PASSAGE. THE MOISTURE WILL
MOSTLY BE CONFINED TO THE LOW LEVELS...AND LIFT WILL BE
WEAK...THUS THE LOW RISK FOR RAIN. CLOUDS WILL THICKEN UP ACROSS
MY NORTHERN COUNTIES AS THIS FRONT MOVES IN...BUT AS THE FRONT
WEAKENS OVER THE AREA TODAY...THE CLOUDS WILL ALSO DIMINISH. AS A
RESULT SOUTHERN COUNTIES ALONG INTERSTATE 94 COULD STAY MOSTLY TO
PARTLY SUNNY THROUGH THE DAY.

WILL NEED TO MONITOR THE SEVERE POTENTIAL FOR SATURDAY. LATEST
TRENDS FROM THE HIGH RES EURO SHOW STRENGTHENING DEEP LAYER SHEAR
VALUES OF 40 TO 60 KNOTS AND DECENT INSTABILITY WITH LIFTED INDEX
VALUES DOWN TO -6 DEG C. NOT ALL MODELS ARE IN AGREEMENT ON THIS
SCENARIO SO CONFIDENCE IS NOT THAT HIGH ON THE OCCURRENCE OF
SEVERE STORMS. WILL KEEP THE HIGH POPS GOING AND MENTION THE RISK
IN THE HAZARDOUS WEATHER OUTLOOK.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 246 AM EDT THU SEP 18 2014

THE COLD FRONT WILL BRING POTENTIAL FOR A FEW THUNDERSTORMS SATURDAY
EVENING AND LINGERING SHOWERS OVERNIGHT INTO SUNDAY. A COOLER
AIRMASS WILL MOVE IN BEHIND THE FRONT SUNDAY INTO EARLY NEXT WEEK.
HOWEVER IT IS NOTED THAT OVERALL MEDIUM RANGE GUIDANCE TRENDS ARE
MILDER FOR EARLY NEXT WEEK.

TEMPS MONDAY WILL AVERAGE AROUND 5 TO 10 DEGREES BELOW NORMAL BUT
TEMPS SHOULD RECOVER QUICKLY TO NEAR NORMAL FOR TUE/WED. DRY WEATHER
IS ANTICIPATED DURING THE EARLY TO MIDDLE PORTION OF NEXT WEEK AS A
LARGE SURFACE HIGH PRESSURE RIDGE BUILDS IN.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 721 AM EDT THU SEP 18 2014

PATCHES OF IFR HAD FORMED OVER PARTS OF SOUTHWEST LOWER MI SINCE
09Z. ONE WAS LOCATED OVER KY70...WHILE ANOTHER WAS AT KRMY. AT
THIS TIME IT APPEARS THAT THE IFR WILL LARGELY MISS THE SOUTHWEST
MI TAF SITES. A LARGER MVFR DECK OF CLOUDS WAS SLIPPING DOWN FROM
THE NORTH...AND THEY SHOULD MOVE IN BY 14Z FOR MANY OF THE TAF
SITES. THE CLOUDS WILL BREAK UP THIS AFTERNOON INTO THE EVENING
LEADING TO VFR CONDITIONS. A RISK FOR LOW CLOUDS AND FOG RETURNS
TONIGHT...MAINLY AFTER 09Z.

&&

.MARINE...
ISSUED AT 246 AM EDT THU SEP 18 2014

MARGINAL CONDITIONS FOR A SMALL CRAFT ADVISORY WILL EXIST THIS
MORNING. CURRENTLY WAVES ONLY AROUND 2 FEET OFF OF
LUDINGTON...HOWEVER THEY WILL BUILD SOMEWHAT AS THE NORTHEAST FLOW
STRENGTHENS. CONSIDERING THERE WILL ALSO BE COLD AIR ADVECTION...A
RISK FOR HAZARDOUS CONDITIONS WILL EXIST FOR THE LITTLE AND BIG
SABLE POINT REGION.

A MUCH GREATER CHANCE FOR MORE WIDESPREAD HAZARDOUS BOATING
CONDITIONS WILL ARRIVE FRI NIGHT AS SOUTH TO SOUTHWEST WINDS
STRENGTHEN AHEAD OF THE NEXT COLD FRONT.


&&

.HYDROLOGY...
ISSUED AT 246 AM EDT THU SEP 18 2014

RIVER LEVELS WILL REMAIN NEARLY STEADY INTO SATURDAY. THE ARRIVAL
OF A COLD FRONT AND ASSOCIATED SHOWERS AND THUNDERSTORMS WILL LEAD
TO LOCALIZED HEAVY RUNOFF...ESPECIALLY WHERE THE STORMS PERSIST
FOR AN HOUR OR TWO. THIS COULD LEAD TO SOME URBAN AND POOR
DRAINAGE ISSUES...BUT CONSIDERABLE RISES ON AREA RIVERS IS NOT
EXPECTED FROM THIS NEXT FRONTAL PASSAGE.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 10 AM EDT THIS MORNING FOR LMZ848-849.

&&

$$

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






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