Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 181745

Area Forecast Discussion
National Weather Service Grand Rapids MI
145 PM EDT THU AUG 18 2016


Issued at 330 AM EDT Thu Aug 18 2016

A southerly flow of air will gradually bring in an increasing humid
airmass of the next few days. Isolated storms are possible today in
the southwest corner of the state. As a cold front approaches the
area on Friday a better chance for showers and storms exists.
Finally, on Saturday a low will move along the front through the
Great Lakes region bringing with it more widespread showers and
storms. Severe weather will be possible Saturday into Saturday night.
Cooler and less humid air will work into the area for Sunday on
strong northwest winds. Highs will top out in the 80s Today and on


.SHORT TERM...(Today through Saturday)
Issued at 330 AM EDT Thu Aug 18 2016

Main focus in the short term is on thunderstorm chances and the
possibility for severe weather on Saturday. Chances for showers and
storms will ramp up each day as we head from today through Saturday.

Today`s storms will be isolated in nature and based on convection
allowing models be rooted in the higher instability air of the
southwest corner of the state. Essentially from GRR to the south and
west. Today will be a high CAPE low shear pulse type of environment,
and therefore not expecting severe weather. Not expecting
precipitation tonight after the loss of daytime heating and the lack
of a trigger.

Friday a cold front from the west will approach although there will
not be much in the way of mid level support. Shear remains low but
CAPE values continue to climb as low level moisture increases in the
southwest flow. Expect a higher concentration of storms on Friday,
with all areas standing a chance at rainfall. Only used chance pops
at this point but could see needing to raise them some.

Chances for showers and storms increase further from Friday night
into Saturday. A strong cold front will be pushing into Southwest
Lower Michigan Saturday afternoon at peak heating. Expecting a lot
of cloud cover which may tend to limit instability a bit. Dynamics
are much better on Saturday as a mid level shortwave is working in
from the west. The LLJ and deep layer shear are supportive of severe
weather. The question mark will be the amount of instability. Severe
weather is not a certainty given the instability factor but we will
need to keep an eye on Saturday afternoon and evening given the
strengthening low and associated wind fields.

.LONG TERM...(Saturday night through Wednesday)
Issued at 330 AM EDT Thu Aug 18 2016

The extended period begins with a low pressure pulling off to the
northeast of Lower Michigan and strong height falls across the Great
Lakes as an upper trough extending from a deep closed low across
Hudson Bay moves in.

Steady rains should be clearing the eastern zones Sunday morning
with some diurnal enhancement of showers through Sunday as lapse
rates become steep. Temperatures should be held to the lower 70s in
strong low level cold advection and clouds holding on through the

Sfc ridging builds in on Sunday night and continues into mid-week
with slowly warming temperatures as the upper trough flattens and
moves east. Sfc ridging Sunday night should allow for some clearing
and a touch of Fall in the air with lows by Monday morning in the
40s up north. Sfc high is overhead Monday night with good
radiational cooling conditions and lows again in the 40s to lower


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 145 PM EDT Thu Aug 18 2016

I expect VFR conditions to hold through the evening but later in
the night expect a period of MVFR CIGS as the low level moisture moves
in. The low clouds should mix out by late morning which will then
allow VFR conditions to return to the area.

There is a outside chance of a thunderstorm this evening for the
western TAF sites as instability and moisture moves in but it
will be dry at mid levels so any storm that tries to form should
not last all that long.

On Friday the warm front will try to pushes northward through the
area. That could mean scattered thunderstorms too. At this point
it looks to me like most of the storms will be well north of here
Friday (over Northern Lower Michigan mostly). Since the risk of
storms seems low to me I did not put VCTS in any of the TAFs.


Issued at 330 AM EDT Thu Aug 18 2016

A southwesterly gradient will be in place through Saturday,
gradually strengthening with time. Conditions may be near advisory
levels beginning Friday into Friday night especially as the gradient
tightens. Saturday into Saturday night it look like advisory
criteria conditions at least are likely. Wind Saturday afternoon
into Saturday night may rise into the Gale category as the low
deepens as it passes by.

Bottom line, after fairly quiet conditions from today into this
evening a generally ramping up of winds and waves are expected.
Headlines look likely as we head into the weekend.


Issued at 541 PM EDT Wed Aug 17 2016

Flood warnings continue for Sycamore Creek at Holt in Ingham County
and for the Portage River near Vicksburg in Kalamazoo County. Rivers
have crested or are expected to crest soon. Widespread heavy rain is
not expected this week but, there will be periods of showers and
thunderstorms. Basin average precipitation will not be significant
given the more scattered nature of the rains. Rivers will likely
begin falling after crests over the next few days. Additional
precipitation for the weekend will need to be monitored given very
saturated soils that will not be able to absorb much rain.


.GRR Watches/Warnings/Advisories...


LONG TERM...Ostuno
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