Severe Thunderstorm Warning 70, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
646 PM EDT Fri Aug 11 2023

LATEST UPDATE...
Aviation

.SHORT TERM...(This evening through Saturday night)
Issued at 347 PM EDT Fri Aug 11 2023

Our busy part of the short term will be the first 18 hours or so
with multiple chances of convection, some of which could become
locally strong to severe.

As of 3 pm this afternoon, and band of showers and general
embedded storms exists in an arc from Ludington to Howell and then
near Jackson. This round of convection is associated with the
leading edge of a 30+ knot low level jet moving through the area
this afternoon. This is helping to bring a period of more unstable
conditions to the area. The SPC Mesoanalysis page is indicating
MU CAPEs of 2500 J/kg over the far SW corner of the area, of which
this is based mostly in the low levels.

That said, the highest threat of severe weather for our area looks
to be this afternoon and early evening for the SE corner of our
area. That area saw a bit more sunshine earlier, has not seen much
in the way of rain so far, and will see additional instability build
over the next few hours with the warm sector moving in and some
additional diurnal heating. To serve as triggers are a lake breeze
and upper short wave moving in. The CAMs are indicating that a line
will likely form in the next couple of hours near U.S.-131, and push
eastward.

Deep layer shear on the order of 30-35 knots will be sufficient to
help organize the storms. Some mid level dry air and fairly
unidirectional shear profiles will likely support wind as being the
main threat. Mid level lapse rates in the mid 6's C/km and some
decent CAPE in the hail growth layer will support some large hail
chances. As mentioned earlier too, with the low level jet overhead,
low level shear values and some slight directional shear down low
will present a slight chance of a tornado.

We should see a break from mid-evening through about 2 am or so
overnight in the wake of the short wave moving through in the next
few hours. Then another wave and cold front will approach later in
the night, bringing another chance of storms. Low level instability
will be a bit capped overnight, but there will be plenty of elevated
CAPE that remains ahead of the next wave and front. Depending on the
model, we could hold on to over 2,000 J/kg through the frontal
passage. The elevated nature of the instability will limit the
severe threat here a bit. Can not rule out some hail or wind
however, so we will continue to monitor.

After this convection moves out just prior to daybreak on Saturday,
only a few light lingering rain showers will remain possible
Saturday morning toward I-94. That should clear out Saturday
afternoon, and the area should remain mostly dry through Saturday
night.

.LONG TERM...(Sunday through Friday)
Issued at 347 PM EDT Fri Aug 11 2023

An upper low will remain nearly anchored over central portions of
Canada through the long term period off to the north of Manitoba
and Saskatchewan. A general northwest flow is in place across the
Great Lakes into the Northern Plains a fair amount of the time.

Two main troughs swing through the area during the long term the
first is Sunday night through Monday night. The second is
Wednesday night through Thursday night. During both of the
aforementioned time frames we will see good chances for
precipitation as both upper waves are strong. They almost have a
fall look to them given the depth of the troughs swinging through.
Higher pops are in the forecast with the first system given much
higher dew points and more depth of moisture. We currently have 90
pops in the forecast on Monday. The later in the week system pops
are below 50 pct given the moisture being shunted to the south and
east with the first system.

High temperatures through the week will be a bit below normal in
the 70s on most days.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 646 PM EDT Fri Aug 11 2023

For the 00z forecasts, we will be looking at one more possible
round of storms. The first couple of rounds will be east of the
area by 00z. We should see VFR conditions rule through about
06-07z. Just some residual cloud cover from the storms here, and
blowoff from storms to our west.

There continues to be a potential for one more round of
showers/storms overnight. There is some decent agreement that the
line will be approaching the lakeshore after 06z, and progress to
the ESE thereafter. We will hold with the VCSH/VCTS wording for
now given that this is still somewhat uncertain. This can be fine
tuned with the next forecast. MVFR will be likely if the
showers/storms affect any site, with some isolated and brief IFR
possible.

Some showers may linger along the I-94 corridor in the morning.
Those should clear out by noon/16z Sat, then clouds will gradually
clear out in the afternoon. Some wind gusts from the W/NW may gust
up to around 20 knots Sat afternoon.

&&

.MARINE...
Issued at 347 PM EDT Fri Aug 11 2023

We continue to monitor a need for a possible Small Craft/Beach
Hazards statement this afternoon for a marginal event. The general
flow has increased ahead of the waves of low pressure coming in
through tonight. So far, winds have remained below 20 knots and have
been offshore. They are starting to turn onshore, and waves are
approaching 3 ft. The various waves of convection will complicate
this, but will hold off for the time being. Winds and waves will
come down Saturday morning.

We will have some down time from Sat afternoon through most of Sun
where winds and waves should not be a problem with high pressure and
a light gradient moving in. The next period of concern with possible
headlines needed will be Sun night through Mon with the next system
moving through.

&&

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

SHORT TERM...NJJ
LONG TERM...Duke
AVIATION...NJJ
MARINE...NJJ

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Special Weather Statement
National Weather Service Grand Rapids MI
541 PM EDT Fri Aug 11 2023

MIZ052-112315-
Gratiot MI-
541 PM EDT Fri Aug 11 2023

...A strong thunderstorm will impact portions of Gratiot County
through 715 PM EDT...

At 541 PM EDT, Doppler radar was tracking a strong thunderstorm near
Carson City, or 11 miles west of Ithaca, moving east at 20 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Alma...                Ithaca...              St. Louis...
Breckenridge...        Wheeler...             Sumner...
North Star...          Ashley...              Perrinton...
Elm Hall...            Gratiot Community Ai...
Bannister...
Pompeii...             Middleton...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4312 8484 4329 8484 4329 8485 4337 8485
      4342 8465 4347 8448 4346 8437 4312 8437
TIME...MOT...LOC 2141Z 252DEG 15KT 4326 8482

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

LAURENS

Special Weather Statement
National Weather Service Grand Rapids MI
643 PM EDT Fri Aug 11 2023

MIZ067-074-120015-
Ingham MI-Jackson MI-
643 PM EDT Fri Aug 11 2023

...A strong thunderstorm will impact portions of northern Jackson and
southern Ingham Counties through 815 PM EDT...

At 643 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles southwest of Leslie, or 10 miles south of Eaton Rapids, moving
east northeast at 25 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Mason...               Leslie...              Stockbridge...
Aurelius...            Onondaga...            Bunker Hill...
Springport...          Parma...               Dansville...
Eden...                Fitchburg...           Tompkins...
Rives Junction...      Mason Jewett Airport...
Munith...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4231 8413 4226 8463 4238 8471 4241 8465
      4242 8460 4258 8460 4265 8415
TIME...MOT...LOC 2243Z 245DEG 21KT 4236 8459

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

LAURENS

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