Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 302234
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
634 PM EDT Fri Oct 30 2020

LATEST UPDATE...
Update/Aviation

.SYNOPSIS...
Issued at 305 PM EDT Fri Oct 30 2020

- High winds and falling temperatures on Sunday

- Lake enhanced snow showers late Sunday

- Cold early week, moderating by mid-week

&&

.UPDATE...
Issued at 633 PM EDT Fri Oct 30 2020

I have updated our zone forecast to keep the clouds in through
early tonight. Satellite loops show no clearing trend that is
obvious to me.

Normally when we get on the anticyclonic side of the upper jet,
the skies typically clear here, even at this time of year. However
we still have a north wind in the boundary layer and that means
our cloudy layer is trapped. Toward midnight the boundary layer
wind turns to the south as the surface high moves east of this
area. That should bring up drier air from the south and finally
clear the clouds. This could mean warmer low temperatures but that
would depend on just when the clouds actually clear. So for now I
have left the low temperatures alone. If the clouds still show no
sign of clearing by 10 pm, I will likely increase our forecast low
temperatures significantly.

&&

.DISCUSSION...(This evening through next Friday)
Issued at 305 PM EDT Fri Oct 30 2020

-High winds and falling temperatures on Sunday

Forecast wind profiles continue to show 40 to 45 knots in the
mixing layer for Sunday afternoon and evening so we expect the
potential for wind gusts over 40 mph along Lake Michigan coastal
counties. Strong winds over the lake could also generate waves
large enough to cause some beach erosion and coastal flooding. The
best chance of that happening will be from late Sunday afternoon
through Sunday night.

- Brief shot of lake enhanced snow showers late Sunday

Sharp thermal trough with 850 mb temps plunging to minus 10C or
lower Sunday afternoon and evening. Strong CAA will mean
temperatures actually falling through the 30s during the day and
surfaces should be cold enough for any snow to stick, although
accumulations are expected to be an inch or less most places.

Model soundings show inversion heights generally in or above the
DGZ and cyclonic flow and lake generated instability helping
create some decent updrafts, although strong winds will tend to
prevent disrupt stronger bands. SOme rain will mlx in near the
shore because of the warmer lake temps near the surface. The
trough axis moves east with drying early Monday. Expect little to
no impact to travel at this time.

- Cold early week, moderating by mid-week

Trough moves out early next week with rising heights and moderating
temperatures by mid-week. 850 mb temps go from about 0C on Monday
to about 14C on Wednesday. No precip expected through the end of
the week as western CONUS trough amplifies keeping ridging across
the east.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 633 PM EDT Fri Oct 30 2020

Currently VFR cigs remain over our TAF sites. I am thinking the
clouds should start to clear toward midnight as winds in the
boundary layer turn to the south and that in turn brings up drier
air from Indiana and Illinois. Skies should for the most part stay
mostly clear into Saturday afternoon. By early evening the mid
clouds from the approaching system should start moving in.

Winds will light this evening then turn to the south and increase
toward sunrise. Gusty winds from the south are expected on
Saturday.



&&

.MARINE...
Issued at 305 PM EDT Fri Oct 30 2020

We have issued a Gale Warning and Lakeshore Flood Warning for the
entire nearshore for Sunday afternoon into early Monday. The
highest winds will be across the northern zones where gusts could
top Storm force at times on Sunday afternoon and evening. Erosion
of dunes and some coastal flooding also expected as waves build
over 10 feet in west and northwest flow.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Warning from 1 AM Sunday to 1 AM EST Monday for
     MIZ037-043-050-056-064-071.

LM...Gale Warning from 2 PM EDT Saturday to 1 AM EST Monday for
     LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...Ostuno
DISCUSSION...Ostuno
AVIATION...WDM
MARINE...Ostuno



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