Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 120448

Area Forecast Discussion
National Weather Service Grand Rapids MI
1248 AM EDT Mon Mar 12 2018


Issued at 330 PM EDT Sun Mar 11 2018

Winter weather is back in the forecast late tonight into
Wednesday. A cold front trailing a surface low tracking south
southeast through Lower Michigan Monday will bring a period of
snow to just about the entire area but amounts will be mostly
around an inch. Even so the snow showers will impact the morning
commute. Once the front comes through, there will only be
scattered snow showers (maybe mixed rain in the mid afternoon).
Then a secondary cold front comes through with the truly cold air
Monday evening. That will bring lake effect snow showers to
locations near the Lake Michigan shore into Wednesday morning.

High pressure will bring warming temperature and dry weather
Thursday into Friday. A complex storm system would bring a mix of
precipitation to the area next weekend.


.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EDT Sun Mar 11 2018

Snow showers late tonight into mid morning Monday are our primary
concern. Behind that there will be a north wind lake effect event
Monday night into Tuesday night.

Tonight we are focused on the exit region of a 100 polar jet core
that is diving southeast toward Lake Michigan even as I write
this. That jet core is what will help power the next east coast
Nor- Easter Monday into Tuesday. For southwest Michigan through it
just means a band of snow showers tracking north to south across
the area between midnight and noon Monday. The best dynamics and
lift will be over areas north US-131. There is good lift in the
DGZ with this event and just about all of the HI-RES models give
our area around an inch of snow between midnight and 10 am or so.

The really cold air does not come into the area until late
afternoon or evening so we may see temperatures approach 40
degrees inland of Lake Michigan in the afternoon. That would mean
any instability showers in the afternoon may mix with rain.

As is very typical of powerful east coast storms over Michigan we
get mostly north winds as the storm tracks northward near our
latitude. This will be the case Monday night into Tuesday night.
With 850 temps falling to around -15c by Tuesday evening, there
will surely be lake effect snow showers. Inversion heights near
the snow band increase to near 10000 ft, which is more than deep
enough of significant lake effect snow showers. However with
north winds, the snow bands will be near the lake shore if not off

At this point I see no point in issuing any headlines for either
the event Monday morning (snowfall amounts are to low) or for the
Lake Effect event Monday night into Tuesday but that may need a
headline if the snow bands move on shore.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EDT Sun Mar 11 2018

The models are in good agreement Wednesday and Thursday, but then
disagree with how quickly we warm up for the latter half of the week.

We remain chilly Wed/Thu as the upper flow remains northwesterly and
surface high pressure over Central Canada continues to pump in
chilly northerly winds.  Minor lake effect and/or diurnal
instability may cause a few snow showers into Wednesday evening,
then Thursday should be mainly dry.

But then big differences arise.  The ECMWF holds on to the northwest
flow pattern, while the GFS and it`s ensembles develop more of a
zonal flow.  Will delay the warming trend until Friday night and
into the weekend based on these trends.  Given the thermodynamic
differences, the confidence is below above in how/when low pressure
over the Central Plains develops/tracks.  But will delay the onset
to pcpn until Friday night as the trends appears slower.  This
appears to move in as mainly rain, with a rain/snow mix across
Central Lower.

The models finally agree on a zonal flow by the weekend when the
warm up appears more likely.  Will hold off on the next chance of
rain until Sunday afternoon.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1246 AM EDT Mon Mar 12 2018

A short period of light snow will develop around 10z at MKG and a
few hours later than that at JXN. Cigs and vsbys will fall to MVFR
and perhaps briefly IFR conditions before the light snow moves
out. Cigs/vsbys will improve during the afternoon.


Issued at 1052 AM EDT Sun Mar 11 2018

Expected precipitation Monday into Tuesday will be light and
should not impact rivers. This will allow river levels to
continue falling.




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