Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 310538
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
138 AM EDT SUN AUG 31 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 220 PM EDT SAT AUG 30 2014

AN AREA OF LOW PRESSURE WILL TRACK NORTHEAST THROUGH THE GREAT
LAKES REGION THIS EVENING PRODUCING SCATTERED SHOWERS AND
THUNDERSTORMS. A WEAK AREA OF HIGH PRESSURE WILL MOVE IN FOR
SUNDAY WITH MAINLY A DRY AND WARM DAY EXPECTED. A COLD FRONT
PUSHES IN FROM THE WEST ON MONDAY. THIS SYSTEM COULD TRIGGER
STRONG TO SEVERE THUNDERSTORMS THAT WOULD PERSIST INTO THE EVENING.

&&

.UPDATE...
ISSUED AT 959 PM EDT SAT AUG 30 2014

NO MAJOR CHANGES TO THE FORECAST THIS EVENING. WE HAVE FRESHENED
UP THE GRIDS AND ZONES TO ACCOUNT FOR THE LATEST RADAR TRENDS.
PCPN IS SHIFTING GRADUALLY TO THE SE AS EXPECTED. SEVERE WEATHER
THREAT IS VERY LIMITED WITH THE HEATING OF THE DAY LOST.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 220 PM EDT SAT AUG 30 2014

THE MAIN CONCERN DEALS WITH THE POTENTIAL FOR SEVERE WEATHER
THIS AFTERNOON AND EVENING ALONG WITH ON MONDAY. SPC MESO PAGE
SHOWS SURFACE BASED CAPE VALUES AROUND 2000 J/KG AND MLCAPE VALUES
OF AROUND 1000 J/KG. ENOUGH INSTABILITY FOR STORMS TO DEVELOP
AIDED BY THE LIFT FROM AN APPROACHING MID LEVEL WAVE. EFFECTIVE
BULK SHEAR AROUND 35 KNOTS AND 0 TO 1 KM SHEAR AROUND 15 KNOTS.
SO A RISK FOR SEVERE WEATHER EXISTS WITH DAMAGING WINDS THE
PRIMARY RISKS...ALONG WITH A SMALL RISK FOR A TORNADO. SO FAR THE
CELLS HAVE STRUGGLED TO KEEP PERSISTENT UPDRAFTS...BUT THAT COULD CHANGE.
SLIGHT RISK CONTINUES.

STORMS WILL WEAKEN BY MIDNIGHT. LESS IN THE WAY OF CONVECTION
EXPECTED LATER TONIGHT THROUGH SUNDAY WITH NO REAL FORCING AROUND.
STILL SOME DAYTIME STORMS COULD POP UP ON SUNDAY GIVEN THE DECENT
HEATING.

STRONG TO SEVERE STORMS ARE A POSSIBILITY ON MONDAY. RIGHT
ENTRANCE REGION OF AN UPPER JET MOVES IN DURING THE DAY WITH
STRONGER INSTABILITY PRESENT. MODELS SHOW THE STRONGER DEEP LAYER
SHEAR ARRIVING IN THE EVENING. ITS POSSIBLE WE COULD SEE SCATTERED
TO NUMEROUS AFTERNOON STORMS DEVELOPING WITH A FEW SEVERE IN THE
AFTERNOON FOLLOWED BY THE ARRIVAL OF A WEAKENING SQUALL LINE
MOVING IN FROM WISCONSIN IN THE EVENING. TIMING WILL LIKELY
DETERMINE HOW MUCH IF ANY SEVERE WEATHER OCCURS. SLIGHT RISK FOR
PARTS OF THE REGION CONTINUES.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 220 PM EDT SAT AUG 30 2014

MORE OF A ZONAL FLOW ARRIVES FOR THE MIDDLE OF NEXT WEEK. THIS
WILL SUPPORT WARMER TEMPERATURES. IT COULD BE UNSETTLED AS WELL
ESPECIALLY WEDNESDAY NIGHT INTO THURSDAY. HARD TO TIME INDIVIDUAL
SHORTWAVES GIVEN THE FAST FLOW THAT WILL BE PRESENT. WILL KEEP THE
RISK FOR SOME STORMS GOING THEN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 138 AM EDT SUN AUG 31 2014

THE MAIN CONCERN WITH THE 06Z FCSTS WILL BE FOG/LOW CLOUD
POTENTIAL FOR THIS MORNING. SHOWERS AND STORMS HAVE DROPPED SOUTH
AND WILL ONLY AFFECT KJXN FOR THE NEXT HOUR OR TWO BEFORE MOVING
OUT/ENDING.

FOG/LOW CLOUDS THEN BECOME THE MAIN FOCUS. LOW CLOUDS ARE ALREADY
SPREADING IN FROM THE NORTH TOWARD KMKG AND KGRR. WE EXPECT THAT
THEY WILL EVENTUALLY EXPAND OVER THOSE TERMINALS BY 10-11Z.
FURTHER SOUTH WHERE THERE WAS MORE RAIN AND AHEAD OF THE
FRONT...WE EXPECT LOW CLOUDS TO DEVELOP THERE. THIS IS ALREADY
BECOMING EVIDENT AT KAZO. IFR AND LIFR CIGS ARE LIKELY...AND SOME
FOG WILL BE POSSIBLE WITH THE LIGHT WINDS RIGHT AT THE SFC AND
MOIST AIR MASS.

THIS WILL ALL GRADUALLY LIFT SUN MORNING TO VFR CONDITIONS. WITH
THE FRONT STILL IN THE VICINITY...A FEW SHOWERS MAY POP UP DOWN
SOUTH IN THE AFTERNOON. EVERYONE SHOULD CLEAR OUT THIS EVENING.

&&

.MARINE...
ISSUED AT 220 PM EDT SAT AUG 30 2014

BEACH HAZARDS AND SMALL CRAFT ADVISORIES CONTINUE. SOME GUSTS OVER
25 KNOTS ON THE LAKESHORE. WAVES STILL RUNNING 3 TO 5 FEET BUT
THEY WILL DIMINISH AS WITH WINDS SETTLE DOWN THIS EVENING.


&&

.HYDROLOGY...
ISSUED AT 220 PM EDT SAT AUG 30 2014

PWAT VALUES OVER 1.75 INCHES SUPPORT LOCALLY HEAVY RAIN. STORMS
HAVE BEEN MOVING QUICKLY AND THUS THE DURATION HAS BEEN LIMITED.
WITH SEVERAL ROUNDS OF STORMS POSSIBLE MONDAY INTO MONDAY
NIGHT...WILL NEED TO MONITOR THE HEAVY RAIN POTENTIAL ESPECIALLY
WITH PWAT VALUES UNSEASONABLY HIGH AND STRONGER FORCING MOVING IN.
ELEVATED RISK FOR LOCALLY EXCESSIVE RAIN EXISTS.

&&

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

$$

UPDATE...NJJ
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...MJS
AVIATION...NJJ
HYDROLOGY...MJS
MARINE...MJS






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