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889
FXUS63 KGRR 221148
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
748 AM EDT Sat Jul 22 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sat Jul 22 2017

Low pressure and a humid air mass will bring considerable
cloudiness and scattered showers and thunderstorms through the
weekend. Less humid weather and mainly clear conditions are
expected for early next week as high pressure builds in.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Jul 22 2017

Warm front/instability has struggled to advance north due to
widespread convection persisting from ne IA to nrn IL/IN. Have
therefore continued theme of lowering pops/qpf, although recently
identified MCV near BEH will bring showers and a few tstms to at
least the I-94 corridor over the next few hours.

After passage of the showers this morning on nrn fringes of the
stronger convection south of Michigan, prospects for new
convection look slim this afternoon and evening due to extensive
cloudiness persisting and a capping inversion noted in the fcst
soundings.

For tonight, a few showers and tstms associated with approaching
upper low/shortwave trough may impact areas north of I-96 after
06Z. With high dew points around 70 lingering, areas of fog are
possible tonight into Sunday morning if/where pockets of clearing
develop.

Upper trough will be over the region on Sunday and associated
lift/colder air aloft will contribute to destabilization for the
afternoon/evening hours. However as low level wly/nwly flow
develops/strengthens over wrn lwr MI, better afternoon instability
and sfc convergence should be mainly east of our area. Risk of
stronger storms should therefore favor eastern lwr MI, mainly east
of U.S. 127.

Drier air/sfc ridging moves in Sunday night and Monday, leading
to more comfortable conditions.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Jul 22 2017

We are looking at a fairly quiet and tranquil long term period this
coming week, along with seasonable temperatures. There looks to be
only one period where there are legitimate rain chances.

We will start out with dry conditions at the beginning of the long
term Mon night. This dry period will last at least through Tue.
Upper ridge axis situated to our west on Monday will slip east of
the area by Tue evening. Sfc ridging with a Canadian origin will
bring a comfortable air mass to the area through Tuesday.

Rain chances will gradually increase as early as Tue night, likely
peaking on Wed. We still expect an upper low to traverse Srn Canada
through mid-week that will eventually push a sfc front down into the
area. This front coming from Canada will not have significant
moisture with it. Also there is not a strong direct Gulf flow ahead
of it. It could come through at peak heating, which is probably the
best thing going for it.

There is some disagreement with how quick the front sinks south of
the area. Solutions range from Wed evening through Thu afternoon.
The thought is that a little quicker solution is preferred with a
nice Canadian ridge pushing it through. We will keep a chc of rain in
through Wed night, then dry out the forecast. Comfortable temps will
be reinforced behind the front for the end of the week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 747 AM EDT Sat Jul 22 2017

MVFR cigs becoming more widespread this morning, with some areas
of IFR cigs along I-94. Scattered showers ending and cigs lifting
toward VFR levels after 18Z.

Areas of fog/stratus developing after 06z tonight, with IFR or
lower conditions likely becoming more widespread after 09z
tonight.


&&

.MARINE...
Issued at 330 AM EDT Sat Jul 22 2017

Winds/waves remaining below advisory criteria this weekend
although a fog risk will exist due to high dew points over the
cooler waters, particularly tonight and Sunday morning. Period of
stronger northerly flow/cold advection could send waves to
heights close to advisory criteria Sunday night into early Monday.


&&

.HYDROLOGY...
Issued at 330 PM EDT Fri Jul 21 2017

The favored region for locally heavy rainfall through early Saturday
will be south of I-96 and particularly near the MI/IN border. Hi res
models have trended further south with thunderstorm activity
overnight into Saturday morning due to poor handling of earlier
convection. Therefore, the risk for heavy rainfall has shifted
accordingly. Localized flooding will still be possible where any
storms persist. This may be more of a concern near I-94 and toward
the MI/IN border. Rises of small rivers and streams will be possible
but it is not looking like the main stem rivers will have any big
issues unless convective trends change significantly.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...NJJ
AVIATION...Meade
HYDROLOGY...Hoving
MARINE...Meade