Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 011149
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
749 AM EDT MON SEP 1 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EDT MON SEP 1 2014

A COLD FRONT WILL MOVE INTO THE GREAT LAKES REGION FROM THE WEST
LATER TODAY AND INTO TONIGHT. SHOWERS AND THUNDERSTORMS ARE EXPECTED
TO DEVELOP OVER SOUTHWEST LOWER MICHIGAN FROM THE LATE MORNING HOURS
PERSISTING INTO THE EVENING. SOME OF THE STORMS FROM THE MIDDAY
HOURS THROUGH THE EVENING MAY BE SEVERE WITH LARGE HAIL AND STRONG
WINDS. SHOWERS AND STORMS WILL GRADUALLY TAPER OFF TONIGHT
FROM NORTH TO SOUTH AS THE FRONT DROPS SOUTHWARD INTO INDIANA. DRY
WEATHER IS THEN EXPECTED FOR THE MOST PART FROM TUESDAY THROUGH
WEDNESDAY. CHANCES FOR SHOWERS AND STORMS INCREASE ONCE AGAIN
WEDNESDAY NIGHT THROUGH FRIDAY AS A LOW PRESSURE SYSTEM TRAVERSES
THE AREA. TEMPERATURES THIS WEEK WILL BE NEAR TO ABOVE NORMAL WITH
HIGHS IN THE UPPER 70S TO 80S ALL WEEK. A COOL DOWN IS EXPECTED NEXT
WEEKEND BEHIND A COLD FRONT THAT MOVES THROUGH ON FRIDAY.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 330 AM EDT MON SEP 1 2014

MAIN FORECAST ISSUE IS DETERMINING THE THREAT FOR SEVERE WEATHER
TODAY FROM LATE MORNING INTO THE EVENING HOURS. FEEL THE THREAT FOR
SEVERE WEATHER IS THERE TODAY...BUT IT IS NOT A CERTAINTY BY ANY
MEANS. THERE ARE FACTORS BOTH FOR AND AGAINST SEVERE STORMS TODAY.
HOWEVER...THERE IS ENOUGH GOING FOR IT TO CONTINUE TO FORECAST THE
THREAT.

IN TERMS OF THE PARAMETERS THAT ARE GOING FOR THIS EVENT...WE HAVE A
STRONG SHORTWAVE PIVOTING OUR DIRECTION FROM THE PLAINS. THIS WILL
RESULT IN SOLID WIND FIELDS...30-35 KNOT LLJ...40-55 KNOT MID LEVEL
JET RESULTING IN 0-6KM SHEAR ON THE ORDER OF 40 KNOTS THIS
AFTERNOON. SO...WIND FIELDS WILL BE STRONG ENOUGH FOR SEVERE WEATHER
AND THE DEEP LAYER SHEAR IS FAVORABLE FOR ORGANIZATION. SURFACE DEW
POINT SHOULD SURGE BACK INTO THE LOWER 70S AT MOST PLACES THIS
AFTERNOON. ALSO...SOLID 850MB MOISTURE TRANSPORT IS ONGOING FROM 15Z
THROUGH 00Z OR SO.

THE QUESTION MARKS WITH THIS EVENT ARE THAT THE MAIN SHORTWAVE IS
PIVOTING NORTHEAST TOWARDS LAKE SUPERIOR...AS WELL AS THE AREA BEING
IN THE RIGHT EXIT REGION OF THE UPPER LEVEL JET. HENCE...THE BEST
DYNAMICS WILL BE NORTH OF OUR AREA TODAY. INSTABILITY IS A QUESTION
GIVEN THE AMOUNT OF DEBRIS CLOUDS THAT WILL BE TRYING TO PRESS IN
FROM THE WEST AS WELL AS THE FACT THAT THE EVENT MAY GET GOING
BEFORE PEAK HEATING. FEEL THE LOW LEVEL MOISTURE ADVECTION COUPLED
WITH MID LEVEL COOLING SHOULD PROVIDE DECENT CAPE VALUES THOUGH ON
THE ORDER OF 1000-2000 J/KG.

SHORT TERM CONVECTION ALLOWING MODELS ALL SHOW SOME ACTIVITY
SWEEPING EAST THROUGH THE FORECAST AREA FROM MIDDAY THROUGH THE
EVENING (NOON THROUGH 800 PM). FEEL THE BIGGEST THREAT FROM STORMS
TODAY IN OUR AREA WILL BE STRONG WINDS GIVEN THE WIND FIELDS IN
PLACE. NOT A SLAM DUNK BY ANY MEANS BUT WE WILL BE MONITORING STORMS
THROUGH THE EVENING FOR THE POTENTIAL FOR SEVERE WX. THE MODELS ALSO
SHOW SOMEWHAT OF LAKE SHADOW TO THE CONVECTION...BUT THIS MAY BE
MORE RELATED TO OUR LOCATION SOUTH OF THE BEST DYNAMICS.

OTHERWISE...THE SHORT TERM IS RELATIVELY QUIET. ANY STORMS THIS
EVENING SHOULD WORK SOUTH OF THE AREA OVERNIGHT. NOT OUT OF THE
REALM OF POSSIBILITIES FOR A FEW SHOWERS ON TUESDAY...BUT FELT THE
THREAT WAS SMALL ENOUGH TO GO DRY. TUESDAY NIGHT AND WEDNESDAY
SHOULD BE DRY WITH RIDGING IN PLACE AT THE SURFACE.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 AM EDT MON SEP 1 2014

THE MOST UNSETTLED WEATHER IN THE LONG TERM LOOKS TO OCCUR IN THE
FIRST COUPLE OF DAYS...FROM THE BEGINNING OF THE PERIOD WED NIGHT
INTO FRI NIGHT. THE LATEST TREND IS FOR A LITTLE MORE POSSIBLE PCPN
WED NIGHT INTO THU WITH THE PASSAGE OF THE WARM FRONT THROUGH THE
AREA. THIS LOOKS TO BE THE CASE DUE TO THE GRADIENT/LOW LEVEL JET
EXPECTED TO BE A LITTLE STRONGER WITH A STRONGER TROUGH MOVING IN.
HOW QUICKLY THE FRONT MOVES THROUGH WILL DICTATE HOW WARM WE GET ON
THU. IF THE FRONT MOVES QUICK ENOUGH...WE COULD HAVE A CHC TO WARM
TOWARD 90 WITH H850 TEMPS OF 20C ADVECTING IN. FOR NOW...WE HAVE
SETTLED WITH THE MID-UPPER 80S WITH THE UNCERTAINTY OF THE PCPN.

WE WILL SEE ANOTHER BATCH OF CONVECTION BE POSSIBLE THEN CENTERED
AROUND FRI AS THE COLD FRONT PUSHES THROUGH AND ENCOUNTERING THE
VERY WARM AND MOIST AIR MASS. WE COULD HAVE SOME ASSISTANCE VIA THE
RRQ OF AN UPPER JET TO OUR N/NE THAT WOULD SUPPLEMENT THE COLD
FRONTAL PASSAGE.

THE REMAINDER OF THE LONG TERM FROM SAT THROUGH SUN LOOKS TO BE
RATHER QUIET...YET COOL. WE WILL SEE A CANADIAN AIR MASS FILTER IN
BEHIND THE THU/FRI SYSTEM WITH A DECENT NNE LOW LEVEL FLOW USHERING
IT IN. THE UPPER FLOW WILL BE FROM THE NW AND A BIT OF A TROUGH WILL
BE OVER THE AREA. THE FAR ERN FLANK OF A SFC RIDGE WILL BE
BUILDING IN AS THE SYNOPTIC PATTERN OVER THE COUNTRY WILL FEATURE A
FAIRLY BROAD/EXPANSIVE UPPER RIDGE FROM THE ERN PACIFIC INTO THE
ROCKIES. THIS SHOULD KEEP THE AREA DRY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 749 AM EDT MON SEP 1 2014

COMPLICATED WEATHER SCENARIO IN PLACE THIS MORNING WITH STRATUS
MOVING NORTH THROUGH THE TAF SITES AND THE POTENTIAL FOR
THUNDERSTORMS LOOMING.

THE STRATUS AND FOG SHOULD GRADUALLY LIFT THROUGH THE COURSE OF
THE MORNING...BUT IT HAS BECOME FAIRLY EXTENSIVE ACROSS SOUTHERN
LOWER MICHIGAN. BY AFTERNOON...EXPECTING VFR CEILINGS AND VSBYS
OUTSIDE OF THUNDERSTORMS.

AS FOR THUNDERSTORMS...THEY ARE ALREADY DEVELOPING ACROSS
PORTIONS OF NORTHERN ILLINOIS AND NORTHERN INDIANA. THE TREND
SHOULD BE FOR SCATTERED SHOWERS AND THUNDERSTORMS TO MOVE THROUGH
THE TAF SITES FROM 14Z OR SO THROUGH 23Z. TOO DIFFICULT TO NAIL
DOWN PREVAILING TIMING AT THIS POINT GIVEN THE HIT OR MISS NATURE
TO TODAY/S STORMS...SO HAVE VCTS WORDING IN ALL THE TAFS THIS
AFTERNOON.

OVERNIGHT...EXPECTING THE SHOWERS AND STORMS TO END WITH MVFR
CEILINGS TRYING TO SETTLE BACK IN.

IT WILL BECOME WINDY TODAY OUT OF THE SOUTH-SOUTHWEST...ESPECIALLY
FROM 15Z-23Z. WINDS FROM 200-220 AT 15-25 KNOTS SHOULD BE COMMON.

&&

.MARINE...
ISSUED AT 330 AM EDT MON SEP 1 2014

WE WILL BE KEEPING THE SMALL CRAFT ADVISORY AND BEACH HAZARDS
HEADLINES AS IS FOR THIS FCST CYCLE. WINDS WILL BE RAMPING UP THIS
MORNING AS THE SW GRADIENT STRENGTHENS OUT AHEAD OF THE INCOMING
COLD FRONT. THE WINDS AND WAVES SHOULD PEAK MID TO LATE AFTERNOON
BEFORE THEN COMING DOWN QUICKLY THIS EVENING AS THE GRADIENT WEAKENS
WITH THE ACTUAL FRONT.

THE NEXT POSSIBLE SET OF HEADLINES THAT MAY BE NEEDED FOR THE
NEARSHORE WATERS LOOKS TO START IN THE WED NIGHT/THU TIME FRAME AS
THE FLOW STRENGTHENS WITH A SURGE OF WARMER AIR WITH THE NEXT
FRONTAL SYSTEM POISED TO MOVE IN.


&&

.HYDROLOGY...
ISSUED AT 330 AM EDT MON SEP 1 2014

LOCALLY HEAVY RAIN IS CERTAINLY POSSIBLE TODAY GIVEN PRECIPITABLE
WATER VALUES SURGING TOWARDS 2 INCHES THIS AFTERNOON. THE RAIN WILL
BE CONVECTIVE IN NATURE THOUGH...SO ANY HEAVY RAIN WILL OCCUR IN
SWATHS AS OPPOSED TO BEING WIDESPREAD. RIVER LEVELS ARE ALL WITHIN
BANK...AND FORECAST BASIN AVERAGE RAINFALL AMOUNTS ARE ON THE ORDER
OF 0.20 TO 0.50 INCHES. THESE AMOUNTS SHOULD BE ABLE TO BE ABSORBED
BY THE RIVER SYSTEMS WITHOUT MUCH ISSUE.

TODAY/S ISSUE THOUGH WILL BE MONITORING THE SWATHS OF HEAVIER RAIN
THAT SWEEP THROUGH WITH THE STORMS. THINKING THE MOTION WILL BE
QUICK ENOUGH (NORTHEAST AT 35-45 MPH)...TO PREVENT MUCH OF AN ISSUE
WITH FLASH FLOODING.

NEXT GOOD CHANCE FOR RAIN WILL COME LATER THIS WEEK WITH A WARM
FRONT WEDNESDAY NIGHT INTO THURSDAY MORNING AND AGAIN FRIDAY AHEAD
OF A COLD FRONT. TOTAL RAINFALL WITH THIS SYSTEM COULD BE ON THE
ORDER OF A HALF INCH TO AN INCH.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR MIZ037-043-050-
     056-064-071.

LM...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LMZ844>849.

&&

$$

SYNOPSIS...DUKE
SHORT TERM...DUKE
LONG TERM...NJJ
AVIATION...DUKE
HYDROLOGY...DUKE
MARINE...NJJ






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