Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 290407
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1210 AM EDT FRI MAY 29 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 326 PM EDT THU MAY 28 2015

AN EASTWARD MOVING COLD FRONT WILL GENERATE SHOWERS AND
THUNDERSTORMS FRIDAY INTO SATURDAY. COLDER AIR BEHIND THE FRONT MAY
RESULT IN SOME FROST ACROSS PORTIONS OF CENTRAL LOWER MICHIGAN
SUNDAY NIGHT. HIGH TEMPERATURES WILL ONLY REACH THE 60S SATURDAY AND
SUNDAY BEFORE WARMER AIR RETURNS EARLY NEXT WEEK. THE THUNDERSTORMS
THAT DEVELOP FRIDAY AND SATURDAY WILL HAVE THE POTENTIAL FOR
GENERATING HEAVY RAINFALL.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 326 PM EDT THU MAY 28 2015

FORECAST CONCERNS DEAL WITH THE CONVECTIVE POTENTIAL LATE TONIGHT
THROUGH SATURDAY.

CLEAR SKIES WILL GIVE WAY TO SOME HIGH CLOUDS TONIGHT AS A COLD
FRONT MOVES EAST FROM THE PLAINS. FRIDAY MORNING SHOULD BE MOSTLY
DRY. THE UPPER SUPPORT WITH THE FRONT ARE PROGD TO REMAIN ACROSS
IOWA AND WISCONSIN FRIDAY. THAT SUGGESTS TO ME THAT THE DRIER ECMWF
MAY BE A BETTER SOLUTION THAN THE WETTER GFS. SHRA/TSRA SHOULD
INCREASE FRIDAY AFTERNOON AND THEN CONTINUE INTO SATURDAY AS THE
COLD FRONT MOVES THROUGH THE CWA. SHORT RANGE MODELS SHOW THE FRONT
MOVING THROUGH THE CWA SATURDAY AFTERNOON. SHEAR VALUES FRIDAY
MORNING NORTH OF MUSKEGON ARE 30+ KTS...HOWEVER INSTABILITY IS LOW.
BY THE TIME THE INSTABILITY INCREASES DURING THE AFTERNOON THE SHEAR
DECREASES A BIT. HOWEVER FORECAST SOUNDINGS SHOW STEEP LAPSE RATES
AROUND 7.5 C/KM. THERE MAY BE A NARROW WINDOW EARLY TO MID AFTERNOON
ACROSS THE CENTRAL CWA WHERE A FEW OF THE STORMS COULD BE STRONG.
SPC HAS THE ENTIRE CWA IN A MARGINAL RISK FOR SEVERE STORMS FRIDAY.

PCPN WILL DIMINISH LATE SATURDAY AFTERNOON/EVENING AS THE FRONT
MOVES THROUGH AND SATURDAY AND SUNDAY WILL BE COOLER WITH HIGHS IN
THE 60S. ADDED FROST TO THE GRIDS OVER THE NRN CWA SUNDAY NIGHT AS
LOWS WILL FALL INTO THE 30S UNDER MOSTLY CLEAR SKIES.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 326 PM EDT THU MAY 28 2015

FAIRLY QUIET WEATHER IN THE EXTENDED. A COOL SFC HIGH WILL HOLD SWAY
AT THE START WITH FROST FORMATION POSSIBLE ACROSS THE NORTHERN THIRD
OF THE FORECAST AREA SUNDAY NIGHT. THE HIGH WILL MOVES EAST EARLY IN
THE WEEK WITH A MOIST RETURN FLOW SETTING UP BY WEDNESDAY.

SOME SHOWERS AND POSSIBLY THUNDER CAN BE EXPECTED ACROSS THE
SOUTHERN ZONES BY WEDNESDAY AFTERNOON IN AREA OF WEAK ISENTROPIC
ASCENT AND THIS SHOULD EXPAND NORTHWARD ON THURSDAY WITH CONTINUED
MOISTURE RETURN AND SFC BASED INSTABILITY ON THE INCREASE. SEVERE
THREAT WILL BE LIMITED BY VERY WEAK SHEAR WITH ANY THUNDERSTORMS
EXPECTED TO BE SHORT LIVED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY)
ISSUED AT 1210 AM EDT FRI MAY 29 2015

VFR CONDITIONS WILL CONTINUE OVERNIGHT THROUGH FRIDAY. SFC WINDS
WILL STRENGTHEN TO 10 TO 20 KTS FROM THE SOUTH BY MID MORNING.
ISOLATED RAIN SHOWERS WILL GRADUALLY DEVELOP LATE FRIDAY MORNING
INTO THE AFTERNOON. A FEW THUNDERSTORMS ARE POSSIBLE BY LATE FRIDAY
AFTERNOON AS INSTABILITY INCREASES.

MAINLY VFR CONDITIONS SHOULD CONTINUE FRIDAY EVENING WITH SHOWERS
AND A FEW THUNDERSTORMS. BRIEF IFR/MVFR CONDITIONS ARE POSSIBLE IN
HEAVIER SHOWERS AND ANY THUNDERSTORMS BUT PREVAILING CONDITIONS
SHOULD REMAIN VFR THROUGH LATE FRIDAY EVENING.

&&

.MARINE...
ISSUED AT 326 PM EDT THU MAY 28 2015

A WEAK PRESSURE GRADIENT WILL RESULT IN LOW WAVE HEIGHTS TONIGHT.
SOUTH WINDS AHEAD OF THE COLD FRONT WILL RESULT IN WAVES BUILDING TO
1 TO 3 FEET NORTH OF GRAND HAVEN FRIDAY.


&&

.HYDROLOGY...
ISSUED AT 1220 PM EDT THU MAY 28 2015

TOTAL QPF FRIDAY THROUGH SATURDAY WITH THE NEXT ROUND OF SHOWERS
AND THUNDERSTORMS CONTINUES TO TREND DOWNWARD AT AROUND AN INCH
OR LESS. GIVEN THAT BASE FLOWS ARE NEAR NORMAL IN THE GRAND RIVER
BASIN AND BELOW NORMAL IN THE KALAMAZOO BASIN...WE EXPECT MODEST
RISES WITH SOME SITES PERHAPS REACHING BANKFULL BUT NOTHING OF
GREAT SIGNIFICANCE. THE COMING WEEK LOOKS DRY WHICH SHOULD ALLOW
LEVELS TO FALL ONCE AGAIN.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...OSTUNO
AVIATION...LAURENS
HYDROLOGY...TJT
MARINE...04


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