Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221157
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
757 AM EDT THU SEP 22 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Thu Sep 22 2016

Showers will gradually move into and through the region tonight and
on Friday as a front slips south through the state. The front is
located across Northern Lower Michigan this morning and will move
off to the south of the state Friday night. A few thunderstorms are
possible as well especially this afternoon across Central Lower
Michigan. A slight cooling trend is expected into the weekend.

&&

.SHORT TERM...(Today through Saturday)
Issued at 330 AM EDT Thu Sep 22 2016

The main focus in the short term continues to be associated with
chances for precipitation near a front that is draped through the
region. The front is located over Northern Lower Michigan this
morning. It will gradually work its way south over the next 24 to 36
hours and the precipitation will move southward with it.

A key component in our precipitation chances is the western upper
trough clearly seen this morning in the water vapor imagery. As this
upper trough moves through the inter mountain west and towards the
plains the next 36 hours, surface low pressure will shift west in
the plains towards it. In doing so, the front will sag south through
the Great Lakes allowing high pressure to build in into the weekend.
The low level jet and high instability will refocus well west of the
area as well, out in the plains states.

What this means of Southwest Lower Michigan is we will see a fair
amount of cloud cover the next couple days as the front gradually
sags south through the area. Showers are expected with the front
with a few thunderstorms possible as well. Convective threat overall
is lower though given the lack of instability. In general have a lot
of chance pops in the forecast on the order of 30-50 percent. As we
head into Friday night and Saturday not anticipating much in the way
of significant precipitation as the front will be south of the area
and losing definition.

Temperatures will be modulated by the cloud cover both today and on
Friday.  Still expecting 80s today in the south however, given a
front off to the north and weak southerly flow. Thinking the
convective debris cloud will thin this afternoon. In general though,
a gradual cooling trend is expected through the short term more
towards normal values for this time of year.

.LONG TERM...(Saturday night through Wednesday) Issued at 330 AM EDT
Thu Sep 22 2016

A slow moving low pressure system near NW Minnesota will be the main
weather focus during the long term.

Some fairly big differences between the gfs and ecmwf exist late in
the weekend. The ecmwf is much more progressive with the upper
trough, while the gfs develops a closed low. the result is the ecmwf
is much quicker to push the front through compared to the gfs.
There`s a fairly large upper trough over the East Coast which may
help to slow the system down. As such will maintain the 30 pop
through much of the forecast from Sunday through Wednesday.
Instability is fairly low through this time so the forecast shows
mainly showers vs tsra.  High temps in the mid 70s will be a few
degree above normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 757 AM EDT Thu Sep 22 2016

Mainly VFR weather is expected the next 24 hours. Ceilings today
will generally be above 12000ft, lowering to around 4000ft
tonight. Mainly dry conditions are expected today at the TAF sites
with some scattered showers possible tonight. Any light fog will
dissipate by 15z this morning.

&&

.MARINE...
Issued at 330 AM EDT Thu Sep 22 2016

Winds and waves will remain below advisory criteria through
Saturday. Weak southerly flow will be in place today ahead of a
frontal boundary that will eventually drop south the next 24 hours.
Winds tonight into Friday will turn easterly/off shore and remain
that way into Saturday. Waves will likely peak on Friday behind the
front but given the easterly flow the highest waves will be well off
shore. 1 to 3 footers and below will be common in our nearshore
waters the next few days.


&&

.HYDROLOGY...
Issued at 326 PM EDT Wed Sep 21 2016

As much as 1.5 inches of rain fell in several areas north of I-96
Wednesday morning, but river rises are limited. Additional chances
for rainfall will stay mainly north of I-96 the next few days.
Excessive rainfall is not expected through the weekend.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...Duke
HYDROLOGY...CAS
MARINE...Duke



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