Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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496
FXUS63 KGRR 251753
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
153 PM EDT Mon Sep 25 2017

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 328 AM EDT Mon Sep 25 2017

Two more days of record high temperatures across most of Southwest
Michigan then the first cold front comes through early Wednesday
lowering high temperatures from near 90 to near 70 (which is close
to normal now). A second cold front comes through on Friday
bringing more fall like temperatures and some lake enhanced rain
showers with it. Any showers with the cold front early Wednesday
will be widely scattered and not produce much rainfall, even were
it does rain. The rainfall on Friday will be more widespread but
being lake enhanced will mostly be near the Lake Michigan shore.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 328 AM EDT Mon Sep 25 2017

We get today and Tuesday in the current record warm weather
pattern, then a significant change will occur and we will have a
rather progressive upper air pattern into next week.

This is one of those Henry RULE events. We have a closed upper
low over the Southwest CONUS and until we get a system strong
enough and close enough in wavelength it will stay there. We in
fact do have such a system currently near the dateline. By
tomorrow the wave lenght gets short enough to push the low
currently over the Southwest CONUS northeast over the top of the
longwave ridge, which is over the eastern CONUS.

However this is why we have only a very low chance for showers
with the front. The longwave ridge is still there as the front
comes through so all the good deep forcing is over Northern
Michigan and into Ontario Canada. It is over upper Michigan and
Ontario, north of Lake Superior where the best 1000/850 moisture
transport is Wednesday morning ahead of the front. In fact there
is not even all that much instability, down here, the most
unstable cape is mostly less than 500 j/kg early Wednesday morning
as the front comes through. So I am thinking only widely scattered
shower with the outside chance of a thunderstorm.

Meanwhile we are still in the warm stream of air so expect highs
both today and Tuesday to be from around 90 to the lower 90s.
There will be some cirrus clouds today which is partly from the
upper level outflow from Hurricane Maria. This should not be
enough to keep us from braking more record highs however for today
and Tuesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 328 AM EDT Mon Sep 25 2017

The transition to more fall-like weather will continue for the
latter part of the week and into the weekend.  There will be the
chance for scattered showers Thursday night and Friday.

The pattern should be fairly zonal on Thursday, bringing us
seasonally cool temps.  But then an upper trough deepens over the
Great Lakes by Friday and this should actually bring temps to below
normal values that should persist into the weekend.  The models have
trended deeper with this trough which also increases the chance for
rain in the Thursday night and Friday time frame.  This doesn`t look
like a drought-buster, but it would seem to be enough to settle the
dust. There could be some lake effect showers into Friday afternoon
and evening, but these look minimal as the air mass that follows the
short wave appears quite dry.

A large Canadian high pressure pushes in for the weekend.  Dry
weather should return, but it does not look like we warm until next
week.  So expect a pleasantly cool and dry weekend.  There could be
some patchy frost Friday and Saturday nights toward U.S. 10.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 153 PM EDT Mon Sep 25 2017

VFR prevailing with light south winds the rest of today, with some
areas seeing cumulus bases develop around 5 kft. MVFR to patchy
IFR visibility possible again tonight after 09Z mainly around
JXN but possibly extending to LAN, BTL, and AZO. Should become
fully VFR again after 13 or 14Z.


&&

.MARINE...
Issued at 328 AM EDT Mon Sep 25 2017

Likely we will need a Small Craft Advisory Wednesday once we get
into the cold air.


&&

.HYDROLOGY...
Issued at 153 PM EDT Mon Sep 25 2017

Rivers are running around normal to much below normal for the time
of year. Meanwhile, the US Drought Monitor is indicating dry
conditions across Southern Lower Michigan. Rainfall is possible
Tuesday night and Thursday night into Friday but, less than a
quarter of an inch is expected. No river issues are expected into
the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...CAS
HYDROLOGY...63
MARINE...WDM



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