Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 181106
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
706 AM EDT Thu May 18 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 240 AM EDT Thu May 18 2017

A low pressure system will track from Wisconsin through Northern
Lower Michigan today. A cold front associated with this system
will track through the region today. A few showers or
thunderstorms may accompany the passage of this feature. Strong
gusty winds today may occasionally top 40 mph. A large area of
high pressure then settles into Ontario for Friday. This fair
weather system will lead to dry conditions for much of the Great
Lakes region on Friday. Another low pressure system moves in for
the weekend leading to unsettled weather.

&&

.SHORT TERM...(Today through Saturday)
Issued at 240 AM EDT Thu May 18 2017

The main challenge in the short term deals with how strong the
wind gusts will be today. It appears they will end up stronger
than currently forecasted.

Models are showing stronger winds at around 850 mb today...up over
40 knots. Combining this with the deeper mixing(to 850 mb) that
is forecasted...it looks like many locations will see surface
gusts over 45 mph later this morning and into the afternoon. Based
on this...will go with a wind advisory today for most of the CWA.

As for the thunder risk...models really do not generate much
convection today. We do destabilize through the morning...and the
axis of deeper instability persist along the I94 corridor through
the afternoon. Will keep a risk for thunderstorms going...but
overall POPs will remain low for the day. Given the strong wind
fields that will be in place...any stronger downpour could lead to
strong gusty winds at the surface.

Tonight through Friday....it looks mainly dry. Around Jackson
there could still be a storm through 01z to 02z...but overall the
focus for that looks further south.

A slow moving low pressure system approaches the Western Great
Lakes region from the southwest Friday night into Saturday. The
axis of instability and deeper moisture pivots into the CWA as we
go through the period. This supports increasing POPs and a rising risk
for thunderstorms.

.LONG TERM...(Saturday night through Wednesday)
Issued at 240 AM EDT Thu May 18 2017

The cold front associated with the low pressure system that will
be tracking through the Western Great Lakes region Saturday night
into Sunday will push through the CWA. Showers and thunderstorms
may result. The axis of instability tracks east of the CWA Sunday
afternoon. As a result I will diminish the risk for thunderstorms
then from west to east.

A cooler Canadian airmass arrives for Sunday night into Monday as
the low tracks eastward through Ontario. Will feature well below
normal temperatures.

Models are trying to develop a wave of low pressure on the surface
front Monday night into Tuesday. Then then track this system into
Michigan. If this happens...we could end up with a cool wet period
then. This is associated with the passage of a deep upper
trough...would support higher POPs.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 702 AM EDT Thu May 18 2017

Impacts from the wind today is expected at the TAF sites. The wind
will increase this morning as the temperature climbs. Gusts over
35 knots are expected for a period during the day...roughly 14z to
22z. The wind will be shifting as well...with southwest winds
becoming northwest tonight.

Little in the way of showers are expected today...so I did not
include them in the TAFs. MVFR clouds may move in later today and
more so tonight.

&&

.MARINE...
Issued at 240 AM EDT Thu May 18 2017

No changes to the marine headlines. Strong gusty winds will
continue as the cold front pushes through...supporting the SCA.


&&

.HYDROLOGY...
Issued at 1241 PM EDT Wed May 17 2017

Streamflow is currently normal for most sites. Although a few
storms may move through the region through Thursday, they won`t be
widespread enough to impact the main basins. Still looking at
basin average rainfall amounts this weekend of 0.50"-1.00". Can`t
rule out some locally higher amounts. That shouldn`t be enough
rain to cause more than some within bank rises, though above bank
rises can`t be ruled out. Additional rainfall is possible by the
early and middle portions of next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory from 11 AM this morning to 8 PM EDT this evening
     for MIZ040-044>046-050>052-056>059-064>067-071>074.

LM...Small Craft Advisory until 6 AM EDT Friday for LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...Hoving
MARINE...MJS



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