Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 271803
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
203 PM EDT WED JUL 27 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 329 AM EDT Wed Jul 27 2016

A slow moving cold front will result in scattered thunderstorms
today, mostly north of I-96. It will be very warm with highs from
the mid 80s to near 90. A wave on the front will slow its push
south tonight and as the wave on the front moves across Lower
Michigan Thursday, it will result in more widespread showers and a
few thunderstorms. Due to the clouds and showers it will be cooler
with highs in the lower 80s. After the frontal wave moves south
and east of the area Friday skies will start to clear as Canadian
high pressure builds in behind the front. The weekend will be
partly cloudy with near normal temperatures thanks to that
Canadian high.

&&

.UPDATE...
Issued at 1217 PM EDT Wed Jul 27 2016

Instability continues to build across Central Lower Michigan at
16z ahead of a weak boundary sagging into the U.S. 10 area. Most
Unstable CAPE values are near 2000 J/KG already in the northwest
CWA with LI`s as low as -5C. So, plenty of instability will be in
place today as it builds further this afternoon. Focus for shower
and thunderstorm development will come from convergence along the
weak boundary dropping south or the lake breeze. In addition, a
weak low is forecast to develop over Central Lower Michigan this
afternoon which likely forms from mesoscale processes. The low will
aid in convergence as well. Late in the afternoon convection may
be aided by a shortwave upper trough coming in from the west this
afternoon.

We are expecting isolated to scattered convection forming this
afternoon. The convection will likely be of the pulse type, going
up and coming down in a hurry given our lack of shear. New cells
will form on the outflow boundaries. 0-6km shear values are only on
the order of 20 knots today. We are not expecting severe weather.
The strongest of cells today may produce winds to around 40 mph
and hail to a half inch or so.

Highs will top out in the mid to upper 80s at most locations.

&&

.SHORT TERM...(Today through Friday)
Issued at 329 AM EDT Wed Jul 27 2016

We are tracking a slow moving cold front and the associated
thunderstorms for today. the front will only reach near I-96 by
evening. Any thunderstorms will remain near and north of the
front. The front will then stall near I-96 tonight as a surface
wave tracks along the front, crossing Lower Michigan Thursday.
Areas near and north of I-94 could see a decent amount of rain
Thursday if the ECMWF 00z run is correct as it results in over
and inch of rain over a large area of our central and northern
CWA. Since the models have been back and forth on this idea I have
50 pct pops for tomorrow but this may have to increased if the
latest ECMWF is to be believed.

That system clears the area Friday bringing clearing skies and
near normal temperatures.

.LONG TERM...(Friday night through Tuesday)
Issued at 329 AM EDT Wed Jul 27 2016

Zonal flow will transition to more of an upper trough by late this
week. But that doesn`t necessarily mean that we`ll see rain. Indeed,
a sfc high over eastern Ontario and Quebec will produce a relatively
dry northeast flow Friday night through Monday which should keep
pcpn pushed south of the cwa. GFS and ECMWF show a few short waves
moving across Indiana and Ohio over the weekend, but almost all of
the pcpn is shown south of the cwa. We`ll keep a slight chance of
pcpn in south of I-94 Friday night and Saturday, but more than
likely we`re looking at dry wx through Tuesday.

Highs will mostly be above normal due to the lower dewpoints and the
ridge to the northeast. Highs in the lower 80s Saturday will climb
to the mid to upper 80s Sunday through Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 203 PM EDT Wed Jul 27 2016

The bulk of the tstm activity this afternoon/evening is expected
to be north of I-96 and east of Hwy 131... so left the thunder
threat out of the TAFs with the exception of LAN between 20Z and
00Z where decent sfc convergence will exist at pk heating. A few
isolated cells cannot be ruled out at the other terminals but feel
the chance is too low to include elsewhere. Any tstm could
produce brief IFR or lower conditions due to heavy rain.

A general decrease in coverage and intensity of convection is
expected after sunset although a few showers could linger through
the night mainly north of I-96. Some areas of fog could form late
tonight, especially where it rains today and at AZO/BTL/JXn where
dew pts are a bit higher and where skies should be clear enough to
form radiation fog with calm winds. Fog will mix out Thursday
morning by 13-14Z.

Scattered tstms are expected to redevelop area-wide after 16-18z
Thursday.

&&

.MARINE...
Issued at 329 AM EDT Wed Jul 27 2016

No major issues seen through Saturday.


&&

.HYDROLOGY...
Issued at 150 PM EDT Tue Jul 26 2016

No river flooding is expected into next week. There is a chance of
rain in the forecast Wednesday into Saturday night. Total rainfall
should be under an inch. River levels are around normal for this
time of year. Even with the precipitation, no rivers should approach
flood level.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

UPDATE...Duke
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...99
AVIATION...Meade
HYDROLOGY...63
MARINE...WDM


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