Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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248
FXUS63 KGRR 310406
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1206 AM EDT WED AUG 31 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 324 PM EDT Tue Aug 30 2016

Scattered showers and a few storms will remain possible tonight,
before gradually shifting south of the area on Wednesday as a cold
front pushes through the area. Much cooler and drier air will then
filter in for the rest of the week.

Much of the upcoming holiday weekend looks dry for the area with
gradually warming temperatures. The threat for rain will increase
starting on Labor Day and continue into Tuesday.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 324 PM EDT Tue Aug 30 2016

Our main focus of the forecast is on precipitation trends through
Wed as the cold front to our NW will gradually push through the area.

Some scattered showers with isolated thunder has developed thus far
this afternoon. Colliding boundaries from the weakly sheared storms
could pop up a few additional showers/storm through the afternoon.
The showers/storms have been unimpressive thus far, and we do not
expect much of an uptick in intensity this afternoon. The only real
threat is locally heavy rainfall due to the slow movement and rich
moisture content of the air.

A few more showers and storm will remain possible tonight as the
front sinks south into the area. Instability will be on the wane as
we lose the diurnal component. Some instability will remain as the
front begins to encounter the richer moisture further south. A lack
of a low level jet and organized short wave tonight will limit the
coverage to the chc/sct category.

A few showers/storms will remain across the south on Wed, and then
clear out of the CWFA in the afternoon. The front looks to be
located toward I-94 around 12z Wed and will sink south. There will
not be an opportunity for any diurnal instability to build, so any
storms that would occur will stay well behaved.

The only other period to note in the short term is the Wed
night/early Thu time frame where a shower is not out of the realm of
possibilities. We will see a fairly strong short wave drop SSE
through the area at that time. It will be lacking moisture, and
should be 2/3rds through the CWFA by 12z Thu. Some lake enhancement
could be occurring, but with a NNE flow at that time, we will stay
dry inland. We will not have a real good opportunity to tap diurnal
instability either with the wave moving out early Thu.

.LONG TERM...(Friday through Tuesday)
Issued at 324 PM EDT Tue Aug 30 2016

Considerable mid level height rises occur Friday into Saturday as a
ridge replaces the trough.  This ridge remains in place as we go
through Sunday.  As a result...the region will be looking at a dry
period.  Temperatures will be moderating...especially in the
Saturday to Sunday timeframe.

The ridge pushes east of the area Sunday into Monday.  Deep
southwest flow develops.  This will support a continued warming
trend along with the arrival of higher precipitable water values.
This will result in an increasingly unstable airmass as we go from
Monday into Tuesday.  As a result...will feature a risk for showers
and thunderstorms early next week.  Well above normal temperatures
are expected.  Some uncertainty in how the east coast storm tracks
next week...which will play a factor when our next cold front
passage occurs. For now...will keep it warm through Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1203 AM EDT Wed Aug 31 2016

Primarily Vfr conditions will gradually deteriorate to mvfr
overnight due to low clouds and patchy fog. Pockets of ifr
are also possible particularly at KMKG where conditions have
just dipped to ifr due to fog. Isolated rain showers will continue
to develop overnight. The threat for a storm is now too low to
warrant inclusion in any of the terminal forecasts overnight.

Conditions will improve to vfr early to mid morning and then stay
vfr through Wednesday afternoon and evening as fair weather
returns and a drier airmass moves in.

&&

.MARINE...
Issued at 324 PM EDT Tue Aug 30 2016

Main impacts for marine interests will be the higher winds and waves
expected to develop on Wednesday, and last through Thursday. Good
cold air advection will take place behind the front, and interact
with lake water temperatures near their peak for the season. This
should build up the waves well. Thus, we have issued a beach hazards
statement and SCA. The only caveat to this is that there may be
times where the wind direction will temporarily shift to more NNE.

The other thing to watch for also will be waterspout potential,
especially Wed night and Thu. This is when the core of the coldest
air aloft will be overhead and will interact with the warmer lake
temps.


&&

.HYDROLOGY...
Issued at 105 PM EDT Tue Aug 30 2016

Scattered slow-moving thunderstorms Tue afternoon are capable of
producing local rainfall amounts over a half inch in a short
amount of time. Deeper atmospheric humidity and correspondingly
higher PW values are in southern Michigan but greater instability
and storm coverage will be in central Michigan Tue afternoon.
Small basins will likely be able to handle any locally heavy
rainfall, but minor ponding of water on roadways is possible.
After the cold front clears on Wed, the next chance for
appreciable rainfall will hold off until next week.

&&

.GRR Watches/Warnings/Advisories...
MI...Beach Hazards Statement from 10 AM EDT this morning through
     Thursday evening for MIZ037-043-050-056-064-071.

LM...Small Craft Advisory from 10 AM this morning to 11 PM EDT
     Thursday for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...Laurens
HYDROLOGY...CAS
MARINE...NJJ



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