Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221300
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
900 AM EDT Tue Aug 22 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 303 AM EDT Tue Aug 22 2017

A cold front will be passing through the area today. Along and ahead
of this cold front, a few showers and storms will be possible this
morning before coming to an end this afternoon. Severe weather is
not expected. Clearing will take place this afternoon, and cooler
air will come in on gusty Northwest winds.

Most of the rest of this week and the weekend will be mostly dry and
cooler. There is a chance of a few showers on Thursday as a strong
upper wave drops down through the area.

&&

.UPDATE...
Issued at 900 AM EDT Tue Aug 22 2017

I added scattered showers and thunderstorms to our grids as there
is a secondary front or trough that has yet to come through. Most
of the high resolution models show a band of convection with that
trough this afternoon. The water vapor image loops show deep
moisture as far west as that trough and our lasted radar
observations show an band of showers now forming over Lake
Michigan near that trough. I also lowered the high temperature
into the mid 70s as there is enough cold air coming in from the
west to limit how warm it will get.

&&

.SHORT TERM...(Today through Thursday)
Issued at 303 AM EDT Tue Aug 22 2017

Rain amounts thus far with this event have been unimpressive in SW
Lower. The organized convection ongoing over IA, IL, and now IN
continue to limit the low level inflow ahead of the sfc cold front
that is now approaching Nrn Lake Michigan and extends down to the
Quad Cities area. SPC meso-analysis page indicates we are still
looking at 1000 j/kg of MU CAPE in place over the area ahead of the
front. A few showers have been forming, and these will continue to
be be possible until the front moves through today. The best chance
of rain will be across the far south where some of the better
convection could clip those areas.

We will clear out this afternoon as the dry slot moves over the
area. This also means we will see some gusty winds develop.

We will see upper troughing hold in over the area on Wed and
continue through Thu. Wed the flow is fairly laminar with a weak
short wave moving through just north of the area. We will see
diurnal cu develop inland, however it should be rather shallow with
the upper jet just north. The limited potential vertical development
will keep us from putting any rain chances in for Wed for now.

We are keeping rain chances in for Thu. The models are in fairly
decent agreement in dropping down a fairly significant short wave
through the area. This coming through around peak heating will allow
for better vertical development of the cu field, and allow for some
showers.

.LONG TERM...(Thursday night through Monday)
Issued at 303 AM EDT Tue Aug 22 2017

The latest runs of the ecmwf and gfs have thrown a huge wrench into
a generally straight forward forecast. Both models now develop a
tropical system in the northwest Gulf and move it inland and then
northeast toward either the Great Lakes (GFS) or the Ohio Valley
(ECMWF) late in the period.

Canadian high pressure will bring down chilly air Thursday night.
Most rural locations will see lows in the 40s and it`s possible the
colder locations over the northern cwa may see some 30s. As high
pressure drifts east, a slow warming trend will occur and temps will
climb into the lower to mid 70s, but lows will remain mainly in the
50s.

Chances for rain from Thursday night through Monday are fairly low,
A lot will depend on what, if anything, occurs with the potential
system in the Gulf, but even if it does develop, it`s probably not
going to impact southwest Lower until Tuesday at the earliest.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 711 AM EDT Tue Aug 22 2017

Widespread showers and embedded thunder is starting to work its
way out of the area. It may be another couple of hours before it
finally clears the KJXN area. As the back edge of the rain showers
progresses through, low cigs around 1500 ft are moving in. These
will overspread the terminals through this morning. The cigs will
then gradually lift through about 20-22z when conditions should
go back to VFR. Skies will then clear out soon after that.

Winds will remain gusty through the day, before decoupling toward
sunset tonight. Wind gusts of 25 to 30 knots will be common from
the W/NW.


&&

.MARINE...
Issued at 303 AM EDT Tue Aug 22 2017

We are still in line for a fairly decent wind/wave event for today,
that could last into Wednesday before subsiding. Good cold air
advection moving in over the relatively warm waters of Lake Michigan
will allow for waves to build efficiently today. Winds are expected
to come down slightly for Wed, but could still poise a hazard to
mariners and swimmers.


&&

.HYDROLOGY...
Issued at 305 PM EDT Mon Aug 21 2017

Area rivers are around normal levels for the time of the year and
well below bankfull. Though we are going to get localized heavy rain
of up to an inch tonight into Tuesday morning, most areas will not
see even minor river flooding. Some water covered roads are
possible. No significant precipitation is expected Wednesday through
Sunday, so any rises on rivers will have time to recover.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Wednesday afternoon for MIZ037-
     043-050-056-064-071.

LM...Small Craft Advisory until 6 PM EDT Wednesday for LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...04
AVIATION...NJJ
HYDROLOGY...63
MARINE...NJJ



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