Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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418
FXUS63 KGRR 170520
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
120 AM EDT Thu Jun 17 2021

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 304 PM EDT Wed Jun 16 2021

- Fire danger risk for Thursday Afternoon

- Thunderstorms possible Thursday night into Friday

- Increased risk for strong/severe storms Sunday night through Monday

&&

.UPDATE...
Issued at 1010 PM EDT Wed Jun 16 2021

Our on-going forecast into Thursday looks fine. We currently have
dew points around 40 (sort of low for this time of year actually)
and the surface high is moving overhead tonight. We weak warm
advection starting at mid levels that will help us to decouple the
boundary layer and allow temperatures to get rather chilly. I
could see locations like Leota getting well down into the 30s
tonight. I did lower our low temperature forecast for tonight a
touch.

As our previous shift indicated, winds will increase during the
mid afternoon and dew points could still be in the 40s yet due to
mixing, so RH values could get close to 20 percent by mid to late
afternoon. My 1000/925 thickness tool (which works very nicely
and I still use over MOS forecasts) shows mid to upper 80s over
most of our CWA Thursday. So our risk for wild fires up north is
very much a concern. I kept our Fire Weather Watch as is.

&&

.DISCUSSION...(This evening through next Wednesday)
Issued at 304 PM EDT Wed Jun 16 2021

- Fire danger risk for Thursday Afternoon

The high temperatures on Thursday will end up in the low to mid 80s.
Afternoon humidity levels will once again fall off into the 20
percent range.  However the wind will be gusty...especially for the
Manistee National Forest area.  Thus conditions are expected to
approach Red Flag Warning Criteria.  We went ahead and issued a Fire
Weather Watch already for this possible event.

- Thunderstorms possible Thursday night into Saturday

A upper level wave tracks in from the west northwest during this
time.  Meanwhile a low level jet arrives and advects elevated
instability in for Thursday night.  Decent low level convergence is
noted. Usually we do see thunderstorms when this scenario occurs.
As for severe weather...while the risk is not zero...the diminishing
instability during the night would support weakening storms as they
try to move into the CWA from the west.  On Friday...with  a
strengthening west to northwest flow...the higher potential for
storms looks to be well inland perhaps toward Lansing and Battle
Creek.  Deep layer shear is over 40 knots so any storms that do form
during the day could become organized.

Models are not in good agreement on the setup for Saturday. From
the High Res Euro...daytime heating is shown for Saturday leading
to instability especially toward Battle Creek and Jackson. Deep
layer shear is shown to be elevated once again. Thus a risk for
storms may develop. The GFS however is showing little in the way
of instability and not much to focus any convection. We will
feature a low chance for mainly afternoon storms.

- Increased risk for strong/severe storms Sunday into Monday

Models generally show a an unseasonably deep mid level trough
digging into the Great Lakes Region Sunday into Monday. A strong
southwesterly low level jet advect abundant moisture into the
region with PWAT values shown to approach 2 inches. Deep layer
shear ramps up as well. Timing of the arrival of the system will
make a difference as far as how strong and how much coverage
there will be. However confidence is building that this system
will lead to convective impacts for the region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 117 AM EDT Thu Jun 17 2021

Mostly clear skies are expected today. Showers and thunderstorms
are possible very late in the period...after midnight. Many of the
models show storms developing over Wisconsin later this evening
and then moving SSE across southern Lake Michigan. However,
another model actually takes the storms farther east across Lower
MI. Even that though is after 06z. For the TAFs we kept things
dry. However, if things speed up, we could see a few storms close
to MKG after 04z.

&&

.MARINE...
Issued at 304 PM EDT Wed Jun 16 2021

Low winds and waves today will give way to strengthening winds
and building waves for Thursday. During the afternoon we should
see gusts topping 15 knots...especially north. The longer fetch
will also favor the highest waves up around Little and Big Sable
Points. Values are marginal for a headline at this time. Close
monitoring will be needed though.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Fire Weather Watch from 11 AM EDT this morning through this
     evening for MIZ037>040-043-044.

LM...None.
&&

$$

UPDATE...WDM
SYNOPSIS...MJS
DISCUSSION...MJS
AVIATION...04
MARINE...MJS



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