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Area forecast discussion 
National Weather Service Grand Rapids Michigan
805 am EDT Friday Jul 31 2015

Latest update...
marine

Synopsis...
issued at 314 am EDT Friday Jul 31 2015

Today and Saturday are expected to be dry. Breezy conditions once
again will occur today much like yesterday. Sunday will feature
increasing cloudiness with some showers and thunderstorms possible
especially across west central lower Michigan during the morning and
afternoon...with more widespread rainfall possible Sunday night.

&&

Short term...(today through sunday)
issued at 314 am EDT Friday Jul 31 2015

Main focus is on the chance for thunderstorms on Sunday. An upper
low over Hudson Bay will meander south and amplify a longwave trough
across the eastern half of the Continental U.S.. split h250 jets over the
Midwest will create a zone of divergence over the Great Lakes. A 30-
35 knots low level jet noses in during the day while warm air advection and a
h850 thermal gradient develops over the lower peninsula.

With modest middle level winds...deep layer shear will not be
spectacular but will at least Register in the 30-35 kts range mainly
for the central and northern County Warning Area...with lesser readings across the
south. Surface based cape off the European model (ecmwf) does increase to 1000-2000 j/kg
during the day. Precipitable water values are expected to nose upward but do not
look extremely high. Showers and thunderstorms will likely get going
across WI/Illinois during the first half of the day and spread east during
the afternoon. The GFS and Gem are a bit quicker than the European model (ecmwf) with
developing precipitation over the area...which may stabilize the atmosphere
and reduce the risk for thunderstorms during the afternoon.

Outside of Sunday...dry weather dominates today and Saturday. Winds
will once again be noticeable today...with similar sustained speeds
and gusts probable. The ground is quite dry at this point for the
central and northern County Warning Area. Breezy conditions today may create
somewhat of a higher risk for spreadable fires...although dew point
readings will not be critically low. Still...something to be mindful
of if there are any Burns planned.

Long term...(sunday night through thursday)
issued at 314 am EDT Friday Jul 31 2015

A low pressure system and cold front will bring rain and
thunderstorms Sunday night into early Monday. It is noted that
overall short to medium range guidance trends suggest a somewhat
faster frontal passage such that the best chance for storms may come
Sunday night with dry weather for most of Monday.

Raised probability of precipitation some for Sunday night based on short to medium range
guidance trends the past 24 hours. Potentially moderate instability
will develop out ahead of this system Sunday. A few strong to severe
storms are possible Sunday night with decent instability potentially
in place and forcing from the low pressure and cold front and
increasingly favorable upper dynamics and increasing deep layer
shear.

A cooler and drier airmass will advect in behind that system for the
early to middle portion of next week as the upper level trough
becomes more entrenched into the Great Lakes region. In fact high
temperatures Tuesday through Thursday will likely only reach the 70s with
mins mainly in the 50s.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 709 am EDT Friday Jul 31 2015

Gusty west winds are the main impact to aviation today with
westerly breezes gusting into the 20-25 knots range...which will
subside toward sunset. Little in the way of cloud cover expected.



&&

Marine...
issued at 803 am EDT Friday Jul 31 2015

Small Craft Advisory and beach hazards statement in effect through the evening.
Waves already 2 to 3 feet this morning and should gain another 1-2
feet in height this afternoon. Whitecaps are visible on the
Muskegon webcam. Felt this was close enough of a call to issue the
Small Craft Advisory for the rest of today.

&&

Hydrology...
issued at 1232 PM EDT Thursday Jul 30 2015

River levels continue to fall and are expected to continue to fall
for at least the next week as rainfall amounts are not expected to
be enough to cause the rivers to start rising.

&&

GRR watches/warnings/advisories...
Michigan...Beach hazards statement until 8 PM EDT this evening for miz037-
043-050-056-064.

Lm...Small Craft Advisory until 8 PM EDT this evening for lmz845>849.

&&

$$

Synopsis...Hoving
short term...Hoving
long term...Laurens
aviation...Hoving
hydrology...wdm
marine...Hoving

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