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Area forecast discussion 
National Weather Service Grand Rapids Michigan
1046 am EDT Friday Aug 1 2014

Latest update...

issued at 328 am EDT Friday Aug 1 2014

No significant weather is expected through the weekend and into
early next week. The area will continue to see a chance of a few
showers and storms during the afternoon and early evening hours
through Saturday. The best chance will be found away from Lake
Michigan. A dry day is expected on Sunday...before the chance of a
few showers and storms will become possible once again. Temperatures
will be closer to average compared to the cool weather from earlier
this week.


Short term...(today through sunday)
issued at 328 am EDT Friday Aug 1 2014

No changes to the going forecast through the day on Sunday.

The best threat of storms in the short term will be during the day
today. This is partially due to the greatest amount of instability
expected with temperatures inching up into the 80s with dew points inching
up toward 60. It is also expected as middle levels cool a tad...and a
wave slowly moving across the region. The best threat of a few
stronger storms is also expected today. Convective available potential energy are expected to
increase up to around 1500 j/kg. A good deal of this cape will be in
the -10c to -30c layer to help with good hail production. Deep layer
shear will be lacking with values below 20 knots pointing toward
pulse type storms.

We will see the chance of storms continue for the day on Sat...however
the coverage and strength will likely be a little lower compared to
today. The upper trough axis will shift east of the state...although
slightly cool middle levels will remain. Lower to middle 80s and 60 degree
dew points will produce 500-1000 j/kg of cape. The main focus on Sat
will likely be lake breezes converging down the middle of the lower
peninsula from lakes Michigan and Huron.

We have continued with a dry forecast for the day on sun. We will see
short wave ridging overhead early and then slowly shift east of the
area during the day on sun. Forecast soundings show this ridging
supplying a good deal of subsidence to the area...capping any
potential of vertical development. We can not entirely rule out a
renegade shower/storm popping on the lake breeze with the light flow
in place...however the chance is too low at this time to include in the

Long term...(sunday night through thursday)
issued at 328 am EDT Friday Aug 1 2014

The primary weather concern for this forecast period is the threat
of widespread rain/thunderstorms nearly each day from Monday through
Thursday. Little question no heat waves are on the way... nor would
I expect any unseasonably strong surges of cold air during this time

Overall the longwave trough over eastern Canada and the eastern
Continental U.S. Continues with little change through this coming week. What
needs to be watched through is model trends for how deep the next
upper level trough becomes. We have two recurving typhoons in the
western Pacific and if you remember the recurving of neoguri (cat 4)
the first week of July and the recurving of matmo (cat 2) both lead
to significant periods of cold weather within about a week of their
recurving. We now have Halong about to recurve. I have to believe
the European model (ecmwf) 01/00z run...which shows a deeper eastern upper level
trough than the GFS in the Wednesday/Thursday time frame... is mover correct.
That would lead to two period of thunderstorms... Monday into
Tuesday as that next northern stream cold front comes through and
again Thursday/Friday as the next upstream shortwave moves into the
longwave trough over the eastern Continental U.S..

For now though I keep chance probability of precipitation through the extended period since
it is possible the GFS would be correct and the front would not get
as far south at the latest European model (ecmwf) suggests it will. However do not be
surprised to see our forecast probability of precipitation for Wednesday lower over time and
cooler temperatures come into the forecast then too.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 720 am EDT Friday Aug 1 2014

MVFR fog will quickly burn off as the sun heats the air this
morning. By 14z all sites should be VFR. There is enough
instability for afternoon thunderstorms. With a west winds most of
the convection will be closer to lan. Tonight skies should clear
and winds will be light. Some MVFR fog is possible.


issued at 1041 am EDT Friday Aug 1 2014

Overall looks like good boating conditions on the lake through the
weekend. Outside of a localized thunderstorm...conditions will
feature winds mostly under 15 knots...low wave heights and warming
water temperatures.


issued at 258 PM EDT Thursday Jul 31 2014

Basin average quantitative precipitation forecast stays minimal through the end of the week. Thus
not significant river rises expected. Isolated storms could
locally produce up to a half inch of rain.


GRR watches/warnings/advisories...


short term...njj
long term...wdm

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