Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221928

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 PM EDT Sat Jul 22 2017

Synopsis/Short Term/Long Term/Marine

Issued at 328 PM EDT Sat Jul 22 2017

Generally fair weather will continue the next few days with the
exception of a few showers and thunderstorms tonight and Sunday
north and east of Grand Rapids. A cold front moving through Sunday
afternoon could drive some stronger thunderstorms towards Lansing
and Jackson.


.SHORT TERM...(This evening through Monday night)
Issued at 328 PM EDT Sat Jul 22 2017

Forecast challenge in the near term is for coverage of showers
tonight and potential for strong to severe storms Sunday mostly
east of Grand Rapids.

For tonight...expect showers and isolated thunderstorms after
midnight across the northern zones as vigorous short wave trough
with closed upper low approaches in fast northwest flow regime.
This trough will also be driving a cold front through Sunday
evening. Sfc convergence ahead of the front combined with
afternoon instability and about 30 to 35 knots of 0 too 6 km shear
should be enough to generate a line of thunderstorms during the

The strong west to northwest sfc flow in the afternoon indicates
that lake modified air will be driven well inland leading to the
convective lake shadow effect and this is also indicated by the
NCAR HiResW ARW which has a line of strong convection forming
across the eastern forecast area around 18Z to 20Z and quickly
moving east. So the severe weather threat does appear limited to
the eastern zones on Sunday afternoon.

Once the storms go past there will be a few instability showers
remaining through Sunday night in cyclonic flow which could be
diurnally enhanced on Monday before the upper trough axis moves
east and sfc ridging builds in for Monday night.

.LONG TERM...(Tuesday through Saturday)
Issued at 328 PM EDT Sat Jul 22 2017

Tuesday will start off with high pressure overhead.  This fair
weather system is predicted to track eastward through the day.
Near seasonable temperatures and dry weather are expected.

Southerly flow increases Tuesday night into Wednesday ahead of an
approaching cold front.  Warmer temperatures will make a return to
the region with highs approaching the mid 80s for many locations.
This will also lead to building instability during the day. Any
morning showers could turn into thunderstorms for the afternoon.
Models do vary on the amount of instability that develops with the
High Res Euro showing much less than the GFS.  Either way...the
combination of synoptic lift...instability and a surface cold front
approaching will feature a risk for storms in the forecast until the
cold front pushes through.

A positively tilted mid to upper level ridge is shown to move in for
the beginning of the weekend.  Will go with dry weather and close to
seasonable temperatures.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 124 PM EDT Sat Jul 22 2017

The atmosphere has become unstable...especially near KJXN. A few
showers and thunderstorms could develop over the next hour or two.
I have included in the KJXN TAF vicinity TS this afternoon. MVFR
clouds were slowly mixing out...with local IFR. The overall trend
does support ceilings climbing some more this afternoon. Thus many
of the TAF sites are expected to go to VFR.

The low level RH remains relatively high going into the evening.
With some clearing expected...fog and low clouds could
develop...especially after midnight.

A small risk exists for a morning shower or thunderstorm tomorrow.
Somewhat of a better risk exists in the afternoon after 18z
mainly towards KLAN and KJXN.


Issued at 328 PM EDT Sat Jul 22 2017

Winds and waves will remain relatively light through the weekend.
There could be areas of fog tonight and a low chance of
thunderstorms late tonight and through SUnday afternoon.


Issued at 1123 AM EDT Sat Jul 22 2017

We again escaped the heavy to excessive rain that fell in
southern Wisconsin and northern Illinois. While that area floods,
most of our area continues to run drier than normal these past 1
to 2 weeks. With high atmospheric water vapor content, the showers
Saturday morning efficiently put down over a half inch of rain but
only in a few isolated spots. Scattered showers or storms Sunday
will provide only spotty relief to the dry weather. After that, the
next potential for a storm will be Wednesday.




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