Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 211137
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
737 AM EDT Thu Sep 21 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 254 AM EDT Thu Sep 21 2017

A weakening cold front will drop down into the region this morning
and dissipate by the afternoon. Another unseasonably warm and
humid day is forecasted. There is a low chance of a thunderstorm
to develop...mainly inland...however most locations will remain
dry. The heat continues into Friday and Saturday as southwest
winds maintain the supply of very warm air. Less of a chance for a
storm to form exists Friday and Saturday as the moisture decreases
somewhat.

&&

.SHORT TERM...(Today through Saturday)
Issued at 254 AM EDT Thu Sep 21 2017

The weakening cold front was pushing into northwest parts of the
CWA early this morning. The thunderstorms associated with this
front were weakening as expected. Moisture was on the increase
here in MI. PWAT values from the 00z GRB sounding were up to 1.73
inches ahead of the front. So today will be on the humid side...in
addition to very warm temperatures. The Ludington to Baldwin area
may not be quite as warm as yesterday due to the impacts of the
front. As for the chances for thunderstorms...that risk has
lowered somewhat. The atmosphere will become quite unstable this
afternoon...but not much forcing will be around. Some high res
models do develop an inland thunderstorm or two...mostly after
21z. Will keep a low risk going for this to happen.

PWAT values drop off Friday and Saturday as a deepening southwest
flow moves in. Thus while it will become rather unstable these two
days...there will be less moisture for storms to form. In
addition...the mid levels will be dominated by
subsidence...limiting the potential for storms. Will keep Friday
and Saturday dry. The low level thermal structure does support
some 90s around the region.

.LONG TERM...(Saturday night through Wednesday)
Issued at 254 AM EDT Thu Sep 21 2017

High pressure will control our weather for much of the long term
period. The upper ridge will result in much above normal
temperatures and very humid conditions. We expect highs in the mid
to upper 80s Sunday through Tuesday before a cold front finally
moves through late Tuesday/Wednesday and pushes through
significantly cooler air. The best chance at seeing showers/storms
is Tuesday night and Wednesday ahead of the front. Temperatures
behind the front will be mostly in the 70s Wednesday. Even
cooler...but still near normal...temperatures are expected Thursday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 733 AM EDT Thu Sep 21 2017

The risk for impacts looks limited through this evening. Local
MVFR fog exists around KJXN and KAZO to start the day. That should
last only another hour or two. The atmosphere destabilizes this
afternoon. A local thunderstorm could develop. The potential for
one to impact a TAF site is too low to include it in the forecast
at this time.

We may see more in the way of fog later tonight as compared to
this morning. This potential is something we will need to monitor
through the day.

&&

.MARINE...
Issued at 254 AM EDT Thu Sep 21 2017

Outflow from thunderstorms resulted in some shifting winds early
this morning. A southwest flow will redevelop today into Friday.
Overall the pressure gradient looks relatively weak. That coupled
with warm air advection should keep the wave heights low. This
pattern favors much warmer than normal water temperatures.


&&

.HYDROLOGY...
Issued at 330 PM EDT Wed Sep 20 2017

Abnormally dry conditions are expected to continue into next week
aside from isolated pockets of heavy downpours. The most favored
locations for isolated showers and storms Wed night will be near
Lake Michigan, then on Thu in Central Michigan. Thereafter, warm and
dry weather is expected to dominate into early next week.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...MJS
HYDROLOGY...CAS
MARINE...MJS


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