Special Marine Warning 21, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
323 AM EDT Thu Aug 9 2018

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 323 AM EDT Thu Aug 9 2018

A line of showers and a few storms will be possible mainly this
morning. Skies will then clear out this afternoon with near average
temperatures.

A chance of afternoon/early evening showers and storms will be
possible each day through the weekend. Most of the time it will be
dry, but a few showers/storms will pop up each afternoon.
Temperatures will max out in the low to mid 80s each day.

The threat of rain looks to diminish a bit Monday into Tuesday as
the system providing the rain chances over the weekend should rotate
east of the area. This will be temporary as another system could
move in on Wednesday, bringing more chances of showers and storms.

&&

.SHORT TERM...(Today through Saturday)
Issued at 323 AM EDT Thu Aug 9 2018

Our initial concern in the short term is the line of showers and
scattered thunderstorms dropping SE toward the area. The focus will
then shift to diurnal convection as upper troughing eventually
closes off, and keeps pcpn chances in here.

The line of showers and storms moving SE across NE Wisconsin this
morning has maintained itself, and even filled in a bit more through
time. The models, especially the convection allowing models (CAMs)
have kept this line intact longer, reaching most of the area before
diminishing. This seems to be fueled by a 25 knot low level jet
ahead of the sfc front that is keeping MU CAPEs over 2000 J/kg
immediately ahead of the line. We are thinking this will affect much
of the area with a quick burst of rain, but it will diminish further
south as the low level jet undergoes its typical weakening
toward/after sunrise.

We do expect that with this line driving through and any associated
outflow, that additional development of convection should take place
south and east of the area not affected by the line.

We are expecting a few more diurnal showers/storms to fire Fri
afternoon. This will be supported by a short wave that will be
dropping in from the NW. The better coverage may be across the SW
corner of the area where lake breeze convergence may be maximized
with a Erly component of the synoptic wind converging with the Wrly
lake breeze component. Shear will be relatively weak with values up
to 25 knots or so.

Diurnal convection will once again be possible on Saturday
afternoon/evening. The short wave diving in from the NW on Friday
will be closed off as another short wave dives into the trough
already in place. Diurnal instability will develop with the cooler
mid levels and sfc heating taking place.

.LONG TERM...(Saturday night through Wednesday)
Issued at 323 AM EDT Thu Aug 9 2018

Sunday looks like somewhat of a repeat of Saturday, before we
diminish the rain trends a bit for Monday, and more so on Tuesday.
The upper low should be centered just south of the area on Sunday,
allowing for more pop up showers and storms to form in the
afternoon/evening hours.

Models have been somewhat consistent with rotating the upper low a
little more east by Monday, and out of the area on Tuesday. This
will allow for drier conditions to be found as upper ridging builds
over the area.

We continue to watch a potentially interesting system that could
affect the area on Wednesday and/or Wednesday night. This is
especially true of the Euro which has shown some sort of deepening
meso-scale low and heavy band of rain somewhere near the state for
multiple runs. The features that appear to be driving this are an
upper low that will be lifting to the NE toward the area, and a nrn
stream short wave digging in across the region that will try to
phase with it. We can't put much detail in for heavy rain for now.
However, the Euro has a good track record recently at least
acknowledging these kinds of systems will occur in some general
vicinity.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 144 AM EDT Thu Aug 9 2018

Our main concern for the 06z fcsts is the broken line of showers
and storms over NE Wisconsin as of 0545z. The trend in the model
data has been for a better chance of this line holding together
and making it through the terminals. We have allowed for a three
hour period of bkn skies with VCSH for the time being. Thunder
remains possible, however we are not confident at this time that
thunder will persist long enough to reach the terminals in SW
Lower. A brief bout of MVFR/IFR will accompany the pcpn if it hits
any terminal.

Once the line pushes through, mainly sct cumulus development will
persist for the afternoon before diminishing this evening as we
lose the heating of the day. Any additional shower/storm
development this afternoon should end up south and east of the
terminals.

&&

.MARINE...
Issued at 323 AM EDT Thu Aug 9 2018

A little bit of a wind max is moving over the marine areas this
morning. It is bringing winds of 15 to 20 knots to most observations
as of 07z. This wind max will be moving out today, allowing for
winds to settle a bit and not require any headlines.

The weekend looks like winds and waves should behave for people
wanting to go out on the lake. The gradient is expected to stay
relatively light, and should not cause issues.

&&

.HYDROLOGY...
Issued at 310 PM EDT Wed Aug 8 2018

Rain Tuesday night was heavy in spots along the Grand and Kalamazoo
River basins. The area southeast of Lansing saw particularly heavy
rainfall, with measured amounts between 3 and 5 inches. The rivers
did rise, but were able to stay well within their banks due to
recent dry conditions.

Showers and thunderstorms are possible this afternoon in a warm and
humid airmass. Coverage will not be very high however, and most
locations will stay dry. A weak cold front will drop through the
region late tonight and Thursday. This will provide additional
showers and thunderstorms, but again coverage will be limited. Rain
may be briefly heavy in storms that develop both today and Thursday,
but widespread flooding is not expected.

Occasional, but low, chances for showers and storms will exist
Friday through Sunday, but areas of organized areas of rainfall are
not forecast.

&&

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

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...NJJ
AVIATION...NJJ
HYDROLOGY...HLO
MARINE...NJJ

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>