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Area forecast discussion 
National Weather Service Grand Rapids Michigan
743 PM EDT Friday Jul 31 2015

Latest update...

issued at 309 PM EDT Friday Jul 31 2015

Quiet...warm...and breezy conditions can be expected the rest of
today and once again on Saturday. Rain chances will then begin to
increase late Saturday night and peak on Sunday and Sunday evening
as a frontal system moves through the area. Showers and
thunderstorms will be likely then...with some possibly becoming
somewhat strong.

Rain should move out early on Monday and clouds will break up.
Cooler temperatures will move in for much of the rest of next week
along with relatively drier conditions. Rain chances will increase
again late in the work week next week.


Short term...(this evening through Sunday night)
issued at 309 PM EDT Friday Jul 31 2015

Our main focus of the forecast is on the frontal system coming in
beginning late Sat night and continuing through the area through Sun

Not much to speak of through Sat evening with mainly dry conditions
expected through then. We will have a couple of short waves that
will pass by...just to the north of the area through Sat. It looks
like that the somewhat stabilizing influence of the wrly flow of off
Lake Michigan is combining with slightly mild temperatures aloft to limit
vertical development of cumulus. This is evident with showers staying
across northern lower and eastern lower. We expect similar conditions on Sat.
Conditions will once again be rather breezy in the afternoon with
decent mixing tapping 20-25 knots of wind aloft.

As mentioned above...precipitation chances will increase later Sat night across
the northwest and then shift southeast through the area through sun evening. We
will see a 35-40 knot low level jet approach late Sat night ahead of a cold
front just entering the upper Midwest. This will bring a nice
moisture surge to the area. This looks to be mainly elevated and
will initially affect the northwest portion of the County warning forecast severe chances
Sat night look minimal.

The low level jet will traverse the area during the day on sun...bringing a
better threat for showers and storms to the rest of the County warning forecast area. We
could be looking at some stronger storms possible if a couple of
things can occur. If the morning convection and clouds remain northwest...
we could see some early sun across the southeast to help destabilize the
atmosphere a bit more before storms would move through. Deep layer
shear is not impressive with around 30 knots or so. We are looking
at some speed good shear in the 0-3km layer with the low level jet moving
through that could make things interesting. A lot of uncertainty
remains...and we will continue to monitor the potential.

Best chance of storms will be into sun evening...before the low level jet pushes
southeast. The main front will not come through until late Sun night and some residual rain chances will remain through Sun night.

Long term...(monday through friday)
issued at 309 PM EDT Friday Jul 31 2015

Northwest flow aloft to keep comfortable temperatures and mostly dry
weather in place through the end of next week. Best shot for
widespread precipitation and maybe a few storms would be Thursday
and Thursday night. Otherwise...expect some lingering instability
showers early Monday and perhaps a few pop up showers Tuesday and
Wednesday as well. Temperatures through the end of next week should
remain slightly cooler than normal with afternoon highs generally in
the 70s.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 740 PM EDT Friday Jul 31 2015

Isolated showers across extreme northern portions of central
Michigan this evening are not expected to affect taf locations. A
few clouds may appear around kmkg...kgrr...and klan but VFR
conditions will prevail as the shortwave energy passes to the

Quiet weather will continue overnight into middle day Saturday...when
winds will increase again as surface pressure gradient tightens.


issued at 309 PM EDT Friday Jul 31 2015

We have trimmed a couple of zones from the southern portion of the Small
Craft Advisory/beach hazards statement with the afternoon forecast
package. Winds and waves are remaining close enough to criteria to
maintain the headlines north of Grand Haven. We have had a ship ob
off of big Sable report 5 feet and mkg buoy has maximum waves around 4 feet.
South of Grand Haven...conditions are just not bad enough to justify
keeping the headlines. All should be able to be dropped this evening.

There is another potential tomorrow for some breezy and wavy
conditions once again with decent winds aloft. Limited mixing over
the waters like today and less wind tomorrow than today points
toward no headlines anticipated. This will be monitored for a
possible headline.


issued at 309 PM EDT Friday Jul 31 2015

Most but not all river gauge sites have returned to near normal
streamflows. Main concern for precipitation over the next week is
Sunday. Basin average quantitative precipitation forecast of half to three-quarters of an inch
should not be enough to cause a problem on the larger rivers.
However... any thunderstorms that persist could produce locally
heavy rainfall which would lead to ponding of water and minor
impacts on smaller rivers and streams.


GRR watches/warnings/advisories...


short term...njj
long term...maczko

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