Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 170504
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1204 AM EST Fri Nov 17 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Thu Nov 16 2017

A quiet weather period is expected from this evening through Friday
midday as high pressure drifts east through the Great Lakes region.
A strengthening low will take shape over the Central Plains Friday
evening and move through our region on Saturday. Rain ahead of the
system will spread into the area Friday evening, with periods of
rain expected Friday night into Saturday morning. Some areas may see
rainfall totals of around an inch. A few rumbles of thunder are
possible Friday night into Saturday as well. It will become breezy
Saturday evening with some gusts along the lakeshore over 40 mph.
Some light snow showers are expected Saturday evening and Saturday
night as the cold air moves over Lake Michigan. Little in the way of
accumulation will occur.

&&

.UPDATE...
Issued at 1005 PM EST Thu Nov 16 2017

A couple changes to the forecast. The clouds were holding in
longer. Thus I bumped up the cloud cover along with the
temperatures.

With one small craft advisory event winding down...then a break
tonight followed by the next event...I went ahead and issued
another headline for Friday into Friday night.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EST Thu Nov 16 2017

Main focus in the short term is on the system forecast to swing
through the Southern Great Lakes on Saturday. A soaking rain, a few
storms and breezy conditions are expected. Precipitation will
changeover to some light snow showers on the backside the system
Saturday night.

The low is forecast to be around 990mb as it passes the Southern
Great Lakes on Saturday, deepening to around 980mb as it heads
toward Toronto and points east. The upstream high Saturday evening
is around 1030mb, so a decent gradient exists. Thinking we are
looking at Gales on Lake Michigan with gusts into the 40-50mph
possible near the lakeshore. Inland, the winds should be more in the
30-40 mph range. Impacts will likely be limited to some isolated to
scattered power outages, especially toward the lakeshore.

Rainfall will likely end up in the 0.50 to 1.00 range after the
event comes to an end Saturday evening. Highest totals are expected
along I-94. A few thunderstorms may be embedded within the
precipitation shield, but thinking the chances are not all that good
with a low passing off to our south. Have slight chance wording for
thunderstorms in the forecast for Friday night and Saturday morning.
The higher instability stays south of our area.

Rain should spread in late Friday afternoon and more likely Friday
evening. Periods of rain are then expected the remainder of Friday
night and through the day on Saturday. Some light snow may mix in
with the synoptic precipitation before it peels to the east Saturday
afternoon and evening. Little to no accumulation is expected.

Some lake effect will get going Saturday night in northwest flow.
Expecting snow showers off the lake up near the points and from
Holland south down the shore. Enough moisture and lift remain in
place for lake effect snow through the night with the best
conditions occurring at daybreak on Sunday near South Haven.
Moisture depth is somewhat shallow with the DGZ barely becoming
saturated. Envisioning some wind blown snow showers with a dusting
occurring in the better snow bands.

Otherwise, expect skies to become partly cloudy this evening, before
clouding back up again late with mid and high clouds.

.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EST Thu Nov 16 2017

Lake effect snow showers will linger in the cold air and cyclonic
flow on Sunday, mainly in the morning before surface ridging nudges
in from the west. Any accumulations should be minor since the deeper
moisture peels away quickly as the low pressure system continues to
race away to the northeast.

A period of tranquil/dry weather with seasonal temperatures is
expected next week, including the peak holiday travel period. A
split flow pattern aloft should keep the nrn stream systems up in
Canada and prevent any influxes of arctic air, while srn stream
moisture will remain down near the Gulf coast. There is a sfc cold
frontal passage late Tuesday, but we are on the tail end of it and
it looks to come through predominately dry and the cold advection
behind it is rather brief before ridging resumes.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1201 AM EST Fri Nov 17 2017

Quite a mix of vfr and mvfr cigs across Lower Michigan tonight.
It`s likely that MKG/GRR/LAN will see more vfr than mvfr and the
opposite for the other taf sites. We`re seeing an increase in low
level moisture later in the period ahead of low pressure that will
move across the state Friday night. Rain is in the tafs from late
afternoon through the rest of the period.

&&

.MARINE...
Issued at 330 PM EST Thu Nov 16 2017

Have decided to let the current Small Craft Advisory expire at 10pm
this evening, before we jump into the next one. It looks like we
will need another SCA in the increasing southerly flow on Friday.
The far south zone looks marginal, but the others look like a solid
SCA from at least mid morning on. South to southwest flow producing
SCA conditions will exist from Friday morning through Friday night.

Saturday morning the winds shift to the north-northwest and increase
to Gales. Waves will peak in the southerly flow up near the points
in the 7 to 10 foot range Friday evening. Wave may reach the 10 to
14 foot range Saturday evening near South Haven and St. Joe. With
waves of this height piers will be overtopped by water and some
moderate beach erosion is possible.


&&

.HYDROLOGY...
Issued at 1255 PM EST Thu Nov 16 2017

Wednesday`s rainfall totals were greatest through Central and
Northern Lower Michigan, while amount tapered off southeast toward
the Detroit area. Aside from Sycamore Creek near Holt, all sites
have experienced within bank rises or have show little impact.

Additional rises can be expected over the course of the weekend.
Primary concerns are the Sycamore Creek at Holt and the Looking
Glass River near Eagle. For this reason, Holt will remain under
an advisory, which was extended. The Looking Glass River is
forecast to rise above bankfull, pending realized precipitation
amounts. Precipitation totals could reach an inch in some places
late Saturday evening. Amounts will be greatest south of I-96.

Conditions become less active for the local area into the holiday
week, which should help mitigate flooding potential. Until then,
additional attention will be needed on area rivers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 7 AM this morning to 3 AM EST Saturday
     for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Meade
AVIATION...04
HYDROLOGY...JAM
MARINE...Duke


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