Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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668
FXUS63 KGRR 152252
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
652 PM EDT Tue Aug 15 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 247 PM EDT Tue Aug 15 2017

High pressure will result in dry weather tonight into Wednesday
evening. Humid conditions with showers and thunderstorms are then
expected Wednesday night into Thursday night, as a low pressure
system passes to the north of the region and drags fronts through
the area. Some of the thunderstorms Thursday could be strong, but at
this time heavy rain seems to be the primary concern. A weak upper
level disturbance will then bring a chance of showers Saturday,
otherwise the weather should be dry into Tuesday. Temperatures
Friday will be below normal but the rest of the week will in
general be warmer than normal.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 247 PM EDT Tue Aug 15 2017

The main player in the short term remains the low pressure system
expected to pass to the north of the area while dragging a warm/cold
front pair through the region Wednesday night into Thursday night.
This system is trending slower and a little farther north, with
precipitation now expected late Wednesday night into Thursday
night. and the main forcing passing over Lake Superior.

Expectations are for showers and storms to move in from the
southwest late Wednesday night bringing extensive cloud cover and
moisture. Clouds, showers and a few thunderstorms will cover
Southwest Lower Michigan Thursday. Most of the forcing with this
system is expected to remain near Lake Superior, so severe storms
are not expected to develop. Precipitable water will approach 2
inches, so heavy rain seems to be the main hazard.

And then there is this from the previous forecaster/s discussion...
if any pockets of heating can occur, capes could reach over 1500
J/Kg and deep layer shear of 30-35 knots would support the
possibility of some stronger/organized convection developing.

.LONG TERM...(Friday through Tuesday)
Issued at 247 PM EDT Tue Aug 15 2017

A couple of minor systems will bring chances for precipitation
Saturday and again next Tuesday. Otherwise, a majority of the time
will be dry and fair with seasonal temperatures.

The midweek upper wave will be exiting to the northeast during the
day Friday. Leftover morning showers cannot be ruled out, especially
heading into Northern Lower MI, but this should quickly erode.
Surface ridging builds in to provide improving conditions with
comfortable temperatures funneling in behind the system. High temps
will span the 70s.

A quick moving shortwave dives southeast from Manitoba into the
Great Lakes by Saturday afternoon. This could result in some
precipitation Saturday, but does not look to be a widespread event.
There isn`t a lot going for it with just a few hundred J/kg of CAPE
and rather unimpressive lapse rates. Expect some afternoon showers
and a few thunderstorms with diurnal heating. This should all exit
by Sunday.

Low amplitude ridging takes shape from Sunday into early next week.
This should provide a couple of consecutive days of dry weather with
temperatures warming into the 80s. The next chance for rain may hold
off until late Tuesday, which would result from a slow moving cold
front on a NW to SE trajectory.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 652 PM EDT Tue Aug 15 2017

VFR ceilings prevail across SW MI this evening. The cumulus clouds and
stratocumulus clouds should be gone by 01-02z. Then I expect just
some high clouds from storms upstream. Winds will turn toward the
east by morning. I expect some cumulus clouds again tomorrow. MKG
will have a lake breeze turning the wind there to the west by
afternoon.

&&

.MARINE...
Issued at 247 PM EDT Tue Aug 15 2017

Winds will be on the decrease this evening, and should remain under
10 knots into Wednesday night, as high pressure blankets the region.
Waves should be under 3 feet this evening, and then under 2 foot
into Thursday.


&&

.HYDROLOGY...
Issued at 1137 AM EDT Tue Aug 15 2017

Observations reflect 24-hour rainfall amounts of 0.25-0.50 and
locally around 1.00 inch between I-96 and I-94, stretching from
Lake Michigan, east to the Detroit area. A couple of the rivers in
this swath (e.g. Jackson) show rises, but are expected to remain
well within banks. Another area of beneficial rain fell from
Ludington to Harrison and locations to the northeast.

The midweek system is beginning to look a bit more impressive with
each update in guidance. Precipitable water values are around and
above 2 inches, especially along and south of I-96, late
Wednesday night into Thursday afternoon. It is looking more
plausible that at least locally heavy rain could result as the
best lift moves in along the warm front Wednesday night into
Thursday morning. Another round of rain could develop with the
passage of the cold front during the day Thursday. Timing could
play a role in determining thunderstorm intensity, which could
affect overall rainfall amounts. Given the anomalous moisture
values and overall potential, this system may need monitored as
the forecast evolves through Wednesday.

&&

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

$$

SYNOPSIS...63
SHORT TERM...63
LONG TERM...JAM
AVIATION...WDM
HYDROLOGY...JAM
MARINE...63



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