Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KGRR 171800

Area Forecast Discussion
National Weather Service Grand Rapids MI
100 PM EST Fri Nov 17 2017


Issued at 314 AM EST Fri Nov 17 2017

Our next storm system will bring rain to the area tonight into
Saturday. Isolated thunderstorms are possible near and south of
I-94 Saturday morning as the surface low tracks just south I-94.
The track of the storm will keep southwest Michigan out of the
truly warm air so most locations will have highs in 40s.

Once the storm passes to our east the cold air comes Saturday
night. During that time some lingering light rain showers will
change to flurries. Flurries are possible near and west of US-131
on Sunday.

A system passing well north of Michigan Monday into Tuesday will
put Southwest Michigan back not the warm air so highs will be back
in the 40s once again. The cold front comes through during Tuesday
which will put southwest Michigan back in the cold air that will
remain around through Thanksgiving. No significant precipitation
is expected most of next week (Monday through Friday).


.SHORT TERM...(Today through Sunday)
Issued at 314 AM EST Fri Nov 17 2017

The main issue with this forecast is the system that moves through
the area tonight into Saturday. We are looking at a period of
moderate to heavy rainfall (1/2" to 1" ) with the heaviest
rainfall near and south of I-94. This storm will have a
considerable amount of wind with it Saturday afternoon into Sunday
morning. We may need winds advisory headlines during that time.
With the cold air coming in lake effect rain showers should change
to snow showers Saturday night but the moisture depth is very
shallow so any snowfall will be mostly less than a half inch if
that. The snow showers/flurries will continue through Sunday.

For the most part the models have come into agreement on what
this system will do to Southwest Michigan. Having said that I want
to point out that the 00z NAM was an outlier so it was not used
in this forecast package.

What is driving this storm is a coupled jet feature with a left
exit region of a 140 knot southern stream jet passing south of
Michigan interacting with the right entrance region of the
departing northern stream jet (over Ontario). This creates a good
low level inflow from the Gulf of Mexico bringing precipitable
water values near an inch into our southern CWA. That is in the
top 10 percent for highest values at this time of year. Thus heavy
rainfall is possible with this system.  With the southern stream
jet so far south the surface low will likely track near I-80. That
will keep any stronger thunderstorms south of the state. Still a
few elevated storms will be possible Saturday morning (mostly
midnight till around 10 am). The heaviest rain will be near the
warm front so that too will be mostly near and south of I-94.
However due to the jet exit region of the northern stream jet
being over Ontario, the area of rain will cover nearly all of
Lower Michigan Saturday morning.

Once the storms move to our northeast as an occluded low Saturday
night into Sunday the cold air comes back in, but like with the
system we just had we do not get into the arctic air so
temperatures will struggle to fall below freezing. That will limit
any snowfall accumulations Saturday night into Sunday as the
moisture depth for lake enhances snowfall is limited.

So the bottom line is this will be a rain and wind event more than
anything else.

.LONG TERM...(Sunday night through Thursday)
Issued at 314 AM EST Fri Nov 17 2017

We continue to have a very progressive upper wave pattern over the
Northern Hemisphere and that will continue through this coming
week. Even so there is a continued preference for an east coast
trough and western ridge. So while the system move trough and do
not stall, we do get significant swings in the air temperature.

On Monday we see system on the northern stream pull a warm front
through the area with with limited moisture we will likely not
see any precipitation from that. It will just warm up into the 40s
on Monday. However progression of the upper waves continues so a
cold front comes through Tuesday. This will bring more cold air
back into the area, but once again not arctic air, so highs will
fall back into the 30s for Wed and Thursday. Then the next system
brings a warm front into the area and we should be back into the
40s on Friday.

None of these system have much moisture with them at this point so
I expect little if any significant precipitation this entire
week. Which of true will make Thanksgiving travel move easier.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 100 PM EST Fri Nov 17 2017

VFR conditions this afternoon will lower to MVFR by this evening
and then IFR overnight. A period of LIFR is possible this evening
as a line of heavier rain moves through southern Lower Michigan
with some thunderstorms possible from JXN to LAN around 03Z. The
chances of this are low enough to leave out of the forecast for
now but this will have to be watched. We do expect some LIFR
conditions on Saturday morning in heavy rain and fog.

Winds will be southeast to south this afternoon and evening with
gusts to 20 knots.


Issued at 314 AM EST Fri Nov 17 2017

I expanded the Small Craft Advisory into Saturday afternoon. More
than likely we will need a gale warning Saturday afternoon into
Sunday morning so to avoid double headlines I ended the Small
Craft Advisory early Saturday afternoon.


Issued at 1042 AM EST Fri Nov 17 2017

Better confidence in precipitation forecasts has resulted in
additional river advisories this morning. Widespread rainfall will
affect Lower Michigan tonight into Saturday with precipitation
totals of 0.75+ inches by early Sunday morning. Amounts will
increase from north to south with the greatest totals expected
south of I-96.

River rises are forecast through the weekend and should stabilize
into next week as precipitation vacates the area. Though current
forecasts anticipate drier conditions, rivers will remain elevated
and responsive. Any changes to include additional precipitation
may need to be closely monitored.


LM...Small Craft Advisory until 1 PM EST Saturday for LMZ844>849.



MARINE...WDM is the U.S. government's official web portal to all federal, state and local government web resources and services.