Gale Warning 32, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EST Fri Nov 13 2020

LATEST UPDATE...
Synopsis/Discussion/Marine

.SYNOPSIS...
Issued at 330 PM EST Fri Nov 13 2020

- Strong fall storm system to affect area this weekend

- Mainly dry work week with moderating temperatures

&&

.DISCUSSION...(This evening through next Friday)
Issued at 330 PM EST Fri Nov 13 2020

-- Strong fall storm system to affect area this weekend --

Multi faceted storm system to affect the area this weekend, with
rain, wind and some snow all expected on land. See the marine
section below for some significant lakeshore impacts.

As for the rain, it should break out in the southwest corner of
the state after 3pm Saturday and overspread the area through the
evening. Periods of wind driven rain can be expected Saturday
night. Cannot rule out a few rumbles of thunder, we are in the SPC
Day 2 general thunder, but instability is rather weak. Deep layer
CAPE is less than a couple of hundred joules, 850mb LIs are
mainly positive and 850mb dew points only reach +6C. I would like
to see more than 200 j/kg of CAPE, LIs that are negative and 850mb
dew points that are at least +8C. Given very strong forcing though
cannot rule out a few rumbles but nothing close to severe. The
HREF has a long lived cell moving through our southern CWA late
Saturday night so we will be watching for that. Rainfall looks to
be on the order of 0.50 to 1.00 inches in many areas. We should be
able to handle this without issue river and runoff wise.

Regarding the wind, we will certainly need headlines. The inland
areas look to be solid Wind Advisory potential, while the
lakeshore will be on the line between Advisory and Warning. Still
just a bit early to issue and neighboring offices wanted to wait
on a headline call, so we will as well. Most likely, tonight's
shifts will be making the call on both wind and lakeshore flood
headlines. I think we are trending towards needing a Lakeshore
Flood Warning and High Wind Warning on the lakeshore and a Wind
Advisory inland. The advisory/warning call is a tough one in both
regards on the lakeshore which is why giving it another 6-12 hours
is prudent here. Most areas will likely see gusts between 45-55
mph. The immediate lakeshore however may see gusts to around 60
mph. Scattered power outages will be likely late Saturday night
through Sunday evening.

Snow is in the forecast for Sunday, at least mixing in at times
through the course of the day as temperatures plunge through the
profile behind the cold frontal passage. Wet bulb zero heights
drop below 1500ft in all areas Sunday morning. So rain will mix
with snow at the very least. In terms of any accumulation, that
seems to be confined to the northern CWA up across Central Lower
Michigan near U.S. 10. We could see an inch or two in spots across
Lake and Osceola counties especially. The northern portions of
those counties towards Cadillac could see a touch more than that
given a lake effect punch that occurs in strong cold air advection
and upslow flow onto the high ground just south of Cadillac.

-- Mainly dry work week with moderating temperatures --

Beyond our weekend system (precip tries to end Sunday night) we
should see a mainly dry week. There are a few chances for a bit of
precipitation though... 1) a weak trough moving through on
Monday, 2) possible warm front in the area Wednesday night and 3)
a frontal boundary in the area Thursday night into Friday. The
highest chance looks to be out in the far reaches of the forecast
with the Thursday night and Friday front. Given the range in the
forecast not overly confident we will see precipitation then
however.

Temperatures start the week on the cool side of normal and
moderate to the warm side of normal by weeks end.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1255 PM EST Fri Nov 13 2020

MVFR ceilings persist into this afternoon and are expected to
persist into the evening. Clearing can then be expected later this
evening into overnight as winds shift southerly after 06z
Saturday.

&&

.MARINE...
Issued at 330 PM EST Fri Nov 13 2020

A significant marine event is expected this weekend. A strong fall
storm system will work northeast through the Great Lakes Saturday
night and Sunday. Gale force winds at least are expected late
Saturday night and Sunday. At this point we are issuing a Gale
Warning for Saturday night through Sunday and Sunday evening. 40
to 45 knot gales are likely. Recent events have not had 50 knots
in the profile to tap into. This event is trending up in terms of
wind and we are now seeing 50 knots in the mixed layer on Sunday.
50-55 knots are seen in BUFKIT overviews at Holland on Sunday.
Worst of the conditions should be Sunday morning. Waves of 10-15
feet are likely with the potential for have peak waves above 15
feet. At this point going to roll with a Gale Warning, but the
potential exists for a possible upgrade to a Storm Warning.

Beach and dune erosion will be a certainty. Lakeshore flooding is
a bit more complicated. Water levels have fallen about a foot in
Western Lower Michigan from mid summer, from about 582.4 feet down
to 581.4 feet at the Holland NOS station. So, we will need a
bigger surge to produce flooding and this event may just be that.
The most prolific flooding is produced when strong easterly flow
occurs in the Straits of Mackinac pushing large amounts of water
temporarily from Huron into Michigan. This happens for a time
Saturday night in southeasterly flow. If the low trends further
south and moves across Northern Lower MI, we could have bigger
issues (with more flow working through the Straits). At this
point that does not appear to be likely, but we are watching
trends, which currently are to bring the low a bit further south.

Bottom line to all of this is we are looking at a significant
wind/wave event on the lakeshore Saturday night and Sunday.
Significant erosion is expected, and a lakeshore flood threat
may be on the increase. Lakeshore Flood headlines will not be
issued yet, but they will be needed at least for the erosion
angle.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EST this evening for LMZ844>849.

     Gale Warning from 7 PM Saturday to 1 AM EST Monday for
     LMZ844>849.

&&

SYNOPSIS...Duke
DISCUSSION...Duke
AVIATION...Thielke
MARINE...Duke

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