Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 020422
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1222 AM EDT SUN AUG 2 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 255 PM EDT SAT AUG 1 2015

QUIET WEATHER WILL CONTINUE THROUGH THIS EVENING BEFORE THINGS
BECOME A BIT MORE UNSETTLED ACROSS THE AREA LATER TONIGHT. A ROUND
OF STORMS WILL BECOME POSSIBLE TOWARD DAYBREAK ON SUNDAY. A FEW
STORMS WILL REMAIN POSSIBLE DURING THE DAY ON SUNDAY...BEFORE A
POTENTIALLY STRONG TO SEVERE LINE OF STORMS MOVES THROUGH SUNDAY
EVENING.

STORMS WILL COME TO AN END LATE SUNDAY NIGHT...WITH A SHOWER
REMAINING POSSIBLE ON MONDAY. MUCH COOLER AIR WILL MOVE IN BEGINNING
ON MONDAY AND LAST THROUGH MUCH OF THE UPCOMING WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 255 PM EDT SAT AUG 1 2015

OUR MAIN FOCUS OF THE FCST IS ON THE SEVERE WX POTENTIAL FOR LATE
SUN INTO THE OVERNIGHT HOURS ON SUN. THE POTENTIAL CONTINUES TO
INCREASE FOR ALL OF THE CWFA.

VERY QUIET WEATHER...ALBEIT A BIT BREEZY THIS AFTERNOON THROUGH THIS
EVENING. A COUPLE OF SHOWERS PRETTY MUCH MISSED THE AREA TO THE
NE...JUST CLIPPING FAR NE CLARE COUNTY THIS AFTERNOON. THE SHORT
WAVE RESPONSIBLE FOR THOSE SHOWERS IS NOW MOVING EAST OF THE
AREA...SO DRY WEATHER IS EXPECTED THE REST OF TODAY WITH SOME
SUBSIDENCE BUILDING IN.

THE POTENTIAL FOR SHOWERS AND STORMS WILL INCREASE DURING THE LATER
PORTION OF TONIGHT...ESPECIALLY ACROSS THE NW. THESE SHOWERS AND
STORMS WILL DEVELOP AT THE NOSE OF A 30-35 KNOT LLJ MOVING IN LATER
TONIGHT AHEAD OF A SHORT WAVE CURRENTLY COMING INTO THE DAKOTAS. WE
ARE EXPECTING THAT THESE STORMS WILL REMAIN MOSTLY SUB-SEVERE AS
THEY WILL BE ELEVATED IN NATURE...AND INSTABILITY PROFILES ARE NOT
REAL STRONG. THESE WILL TRAVEL ACROSS MAINLY THE NRN AND CENTRAL
PORTIONS OF THE CWFA THEN SUN MORNING.

WE WILL SEE A CHC OF A FEW STORMS SUN AFTERNOON...HOWEVER THIS WILL
BE A RELATIVE LULL IN THE ACTIVITY. THE SHORT WAVE COMING IN EARLY
IN THE MORNING WILL BE EXITING AND WE SHOULD SEE SOME WEAK RIDGING
BEHIND THIS. THE LLJ WILL REMAIN ACROSS THE AREA HELPING TO
SUPPLY CONTINUED INSTABILITY...SO STORMS WILL REMAIN POSSIBLE.

THE TIME FRAME WE ARE MOST CONCERNED ABOUT IS AFTER 6 PM SUN UNTIL
ABOUT 2 AM MON MORNING. WE WILL SEE SOME SEMBLANCE OF A SHORT WAVE
APPROACH THE AREA AROUND 00Z MON FROM THE NW. THIS WILL HELP PUSH A
FAIRLY ROBUST SFC COLD FRONT INTO THE AREA. AHEAD OF THIS
FRONT...MODELS ARE IN GOOD AGREEMENT IN ADVECTING 2000+ J/KG OF MU
CAPE INTO THE AREA TOWARD AND AFTER 00Z MON WITH A STRENGTHENING LLJ
OVERHEAD HELPING THIS CAUSE.

MODELS ALL PRETTY MUCH AGREE IN DEVELOPING A SQUALL LINE TO OUR
NW...AND PUSHING IT THROUGH THE CWFA BY ABOUT 06-07Z. THIS LINE WILL
HAVE SOME GOOD 0-3KM SHEAR AVAILABLE TO HELP SUSTAIN THE LINE WITH
THE INSTABILITY. FCST SOUNDINGS INDICATE THAT 40-50 KNOTS OF WIND
AROUND 2-5K FT WILL BE AVAILABLE TO TAP...TO HELP WITH THE BIGGEST
THREAT OF DAMAGING WINDS. LOW LEVEL WIND FIELDS ALSO INDICATE SOME
DECENT VEERING WITH HEIGHT DUE TO THE LLJ. THIS COULD HELP TO
PRODUCE ISOLATED TORNADOES ALONG THE MAIN SQUALL LINE. THE STABLE
LAYER IS WEAK...AND WITH THE INSTABILITY PRESENT AND FORCING...THE
SEVERE THREAT IS LEGITIMATE. LOCALLY HEAVY RAIN WILL ALSO BE LIKELY
WITH PWATS AROUND 1.50 TO 1.75 INCHES.

STORMS WILL MOVE OUT AFTER 06Z...LEAVING ONLY A CHC AS THE ACTUAL
FRONT FINISHES MOVING THROUGH. WE WILL SEE UPPER TROUGHING BUILD IN
FOR MON AND MON NIGHT. THIS WILL KEEP A LOW CHC OF A LIGHT RAIN
SHOWER IN. THE BETTER CHC WILL BE FURTHER NORTH...ABOVE THE JET CORE
WHICH WILL BE ACROSS CENTRAL LOWER. COOLER AIR WILL THEN BE IN PLACE.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 255 PM EDT SAT AUG 1 2015

PRETTY QUIET LONG TERM FORECAST REMAINS ON TRACK WITH COOLER
TEMPERATURES AND LITTLE CHANCE FOR WIDESPREAD PRECIPITATION. A FEW
POP UP SHOWERS THROUGH MID WEEK IN NORTHWEST FLOW ALOFT ARE NOT OUT
OF THE REALM OF POSSIBILITY...BUT NO ORGANIZED THREAT APPEARS LIKELY
THROUGH AT LEAST THURSDAY. MODELS HAVE BEEN SLOWING DOWN SYSTEM FOR
LATE IN THE WEEK...WITH PRECIPITATION CHANCES NOW LOOKING LIKE
FRIDAY INSTEAD OF THURSDAY AFTERNOON/NIGHT...BUT AGAIN NOTHING
SIGNIFICANT AT THIS TIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1218 AM EDT SUN AUG 2 2015

VFR CONDITIONS WILL CONTINUE OVERNIGHT THROUGH MOST OF SUNDAY.
ANY SCATTERED SHOWERS AND STORMS SUNDAY MORNING AND AFTERNOON WILL
MOST LIKELY STAY NORTH OF ALL THE TERMINALS. A COLD FRONT WILL
BRING WIDESPREAD RAIN AND THUNDERSTORMS LATE SUNDAY AFTERNOON
THROUGH SUNDAY EVENING.

THE STRONGEST STORMS COULD CONTAIN BRIEFLY VERY GUSTY WINDS IN
ADDITION TO FREQUENT LIGHTNING... HEAVY RAIN AND POSSIBLY SOME
HAIL. CONDITIONS COULD BRIEFLY DETERIORATE TO IFR/LIFR AS THE
THUNDERSTORMS MOVE THROUGH FROM NW TO SE SUNDAY EVENING.

&&

.MARINE...
ISSUED AT 255 PM EDT SAT AUG 1 2015

WE WILL BE ISSUING A SMALL CRAFT ADVISORY AND BEACH HAZARDS
STATEMENT FOR THE ENTIRE NEARSHORE EFFECTIVE LATE TONIGHT THROUGH
SUN NIGHT. LOW LEVEL WIND CORE WILL MOVE INTO THE AREA LATE TONIGHT
AND SUN MORNING. WHILE A LOT OF THIS WILL REMAIN 1-2K FT ABOVE THE
GROUND...WE EXPECT ENOUGH WIND WILL MAKE IT TO THE SFC TO CAUSE
HAZARDOUS CONDITIONS.

STORMS WILL BE POSSIBLE LATER TONIGHT UP NORTH. A FEW STORMS WILL BE
POSSIBLE DURING THE DAY ON SUNDAY. THE MAIN TIME OF CONCERN FOR
STORMS WILL BE SUNDAY EVENING AS A FAIRLY ROBUST LINE OF STORMS WITH
DAMAGING WINDS IS LOOKING MORE LIKELY.

WINDS WILL DIMINISH A BIT VERY LATE SUN NIGHT. WE EXPECT WINDS WILL
PICK UP MONDAY AS COLDER AIR MOVES IN. THE ADVISORY MAY NEED TO BE
EXTENDED IN TIME...DEPENDING ON THE TREND OF THE COLD FRONT PASSAGE.
NOT OUT OF THE QUESTION FOR MON NIGHT ARE THE POTENTIAL FOR SOME
WATERSPOUTS. STILL SOME TIME TO EVALUATE THAT CHANCE.


&&

.HYDROLOGY...
ISSUED AT 255 PM EDT SAT AUG 1 2015

LOCALLY HEAVY RAINFALL ON SUNDAY WILL BE THE MAIN HYDRO CONCERN OVER
THE NEXT WEEK. GIVEN THE RECENT DRY WEATHER... BASIN AVERAGE QPF OF
A HALF TO AROUND AN INCH SHOULD BE EASILY HANDLED BY THE LARGER
RIVER SYSTEMS. POTENTIAL EXISTS FOR MINOR HEAVY RAIN IMPACTS
INCLUDING ROAD PONDING AND RISES OF SMALLER CREEKS AND RIVERS...
PRIMARILY IF THUNDERSTORMS TEND TO PERSIST OVER A GIVEN AREA.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM 5 AM EDT EARLY THIS MORNING THROUGH
     MONDAY MORNING FOR MIZ037-043-050-056-064-071.

LM...SMALL CRAFT ADVISORY FROM 5 AM EARLY THIS MORNING TO 8 AM EDT
     MONDAY FOR LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MACZKO
AVIATION...LAURENS
HYDROLOGY...CAS
MARINE...NJJ



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