National Weather Service Raw Text Product

894 
FXUS63 KGRR 210347
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1147 PM EDT Tue Aug 20 2019

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 PM EDT Tue Aug 20 2019

- Threat for strong to severe storms this afternoon and evening.

- Isolated showers/storms both tonight into Wednesday.

- Dry weather Wednesday night through at least Sunday.

- Cooler weather forecast Thursday through Saturday.

&&

.DISCUSSION...(This evening through next Tuesday)
Issued at 327 PM EDT Tue Aug 20 2019

First concern in the 7 day forecast is the threat of thunderstorms
this afternoon and evening. Severe weather remains possible given
the amount of instability in place. MUCAPE values over the
southern 2/3rds of the forecast area remain in excess of 3000 j/kg
with LI's of -10C. So, plenty of instability is in place. Shear
remains lacking with 0-6km values less than 30 knots. So far the
warm sector cores have gone up modestly across the area but have 
not reached severe levels. We are interested to see what happens
when the gust front associated with the MCV/earlier convection
over Illinois moves into an unstable air mass over the southwest
CWA. We should see convection grow upscale as this broken line of
showers and storms comes off the lake an into areas southwest of
GRR. Showers and storms are likely late this afternoon and evening
as the MCV/gust front moves east across our area. Cannot rule out
some severe weather with damaging winds and large hail being the
main threats.

Isolated to scattered showers and storms will remain possible
tonight and into much of Wednesday as it takes until late in the 
day before the front progresses south of the forecast area. A
stronger storm or two will be possible from GRR to the south and
east from the midday hours of Wednesday through the afternoon.

Wednesday night through Sunday looks to be dry with a slow moving
surface high pressure system moving through the area. Highs
Thursday through Saturday only look to top out in the 70s with
850mb temperatures in the +5C to +10C range.

Next chances for rain come out in the Monday/Tuesday time frame of
next week when a cold front presses in from the west. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday) 
Issued at 1140 PM EDT Tue Aug 20 2019

Conditions will deteriorate to MVFR/IFR overnight due to
development of low clouds and patchy fog. Conditions will improve
to VFR by late morning and a cold front will bring scattered
showers.

A thunderstorm is also possible late in the morning to early 
afternoon mainly at KJXN where greater instability will develop. 
This could cause brief reductions to MVFR/IFR there. Northwest 
winds will gust to around 20 kts at times in the afternoon with 
subsiding winds and VFR conditions Wednesday night. 

&&

.MARINE...
Issued at 327 PM EDT Tue Aug 20 2019

Holding off on headlines for now, but am concerned about a period
of higher waves Wednesday starting up north near Ludington at 11am
and working south through the course of the day. 3-5 footers look
quite possible with our local GLERL model run off of the NAMnest
winds showing a few 6 footers. The waves drop below 4 feet via
this model run near South Haven around midnight tomorrow night.
So, the time frame of concern is roughly noon on Wednesday to
midnight. 

Winds will generally be on the light side through Wednesday
morning with waves remaining low as well through that time.


&&

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

$$

SYNOPSIS...Duke
DISCUSSION...Duke
AVIATION...Laurens
MARINE...Duke