Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 261634

Area Forecast Discussion
National Weather Service Grand Rapids MI
1234 PM EDT THU MAY 26 2016

Mesoscale Discussion

Issued at 1234 PM EDT Thu May 26 2016

A warm, moisture-laden airmass is currently in place across Lower
Michigan. 16z MLCAPE was analyzed at greater than 1000 J/kg across
most of the forecast area. 12 pm surface dewpoints were in the mid
to upper 60s. Around 1500+ J/kg MLCAPE is forecast into early
evening. Moisture and instability are certainly sufficient for
storms this afternoon.

An area of 30 knots of deep layer shear has nosed into the
northwest forecast area. 0-6 km bulk shear change of +15 kts in
the past 3 hours was noted in portions of Wisconsin and Illinois.
A weakening shortwave is expected to provide modest mid-level
forcing into early evening. Any stronger convection will likely
have to rely on lake breeze convergence. Given the unstable
environment and marginal deep layer shear, scattered storms are
expected mainly in the 2-7 pm timeframe. A few could be stronger
with gusts over 30 mph and pea size hail.


Issued at 330 AM EDT Thu May 26 2016

Warm and humid weather with periodic showers and thunderstorms will
continue through at least Sunday. A cold front late in the holiday
weekend may bring dry and less humid weather for Memorial Day.


Issued at 754 AM EDT Thu May 26 2016

Based on upstream trends and latest HRRR runs have updated to
increase pops this afternoon, mainly near/east of a line from GRR
to AZO. Will also now need to monitor the risk for some stronger
storms as latest RUC update is more ambitious with deep layer
shear /35 kt 0-6 KM layer/ and low level jet /25-30 kt at H8/.
Capes in excess of 2000 J/KG could make for a few hours of active
weather for parts of the area between roughly 2PM and 6 PM. This
is all related to the shortwave/MCV feature drifting in from the
west later today, working in concert with the lake breeze front
near pk heating.


.SHORT TERM...(Today through Saturday)
Issued at 330 AM EDT Thu May 26 2016

Shortwave responsible for overnight rain will exit early this
morning leaving a window of predominately dry weather this morning.
However low chc pops are warranted for this afternoon as instability
builds and fuels scattered diurnal convection.

Sfc Dew pts near 65 will lead to SB Capes near 2500 J/KG inland from
Lk MI. Current water vapor imagery shows another shortwave/several
vorticity maxima upstream across MN/IA/MO. The arrival of this
shortwave should be a trigger for afternoon convection, in
additional to wk sfc convergence along the lk breeze front.
Coverage is expected to be scattered.

The next feature of interest is a shortwave which rounds the base of
the trough in the srn plains later friday, and heads slowly
northeast, reaching Wisconsin by 12Z Sunday. Models indicate a 30-40
kt low level jet developing ahead of this wave, which becomes aimed
at Sw Lwr MI for a prolonged period from Friday afternoon through
Saturday night. PWATs of 1.5 to 1.75 are progged during this time,
with deep unidirectional flow and continued MU Capes over 1000
J/KG - possibly leading to a heavy rain threat. The severe
weather threat remains quite low however since deep layer shear
values generally remain under 30 kts.

.LONG TERM...(Saturday night through Wednesday)
Issued at 330 AM EDT Thu May 26 2016

As we work through the holiday weekend the dominate ridge that has
been parked over the eastern seaboard should gradually weaken.  This
will allow an upper trough and cold front to push across the Great
Lakes late Sunday or Sunday night.  This will not only bring more
risks of showers and storms, but it will also bring less humid air
into the region to end the holiday weekend.  Memorial Day and into
the mid portion of next week should be very pleasant, not as warm
and less humid.

The models rebuild the ridge in the east toward mid week, but
surface high pressure does not slide by until about Tuesday
afternoon, so the warmer southerly breezes won`t move in until
Wednesday at the earliest.

I tweaked the Sunday night min down a bit as we should be in the
cooler air mass by then.  Minimal rain chances finally move in by
Sunday night and linger until Tuesday night or Wednesday.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 750 AM EDT Thu May 26 2016

VFR weather this morning followed by scattered thunderstorms this
afternoon. Main threat of storms is roughly 18Z-23Z, east of HWY
131. Any storm potential at MKG should end earlier, by 20-21z, as
the stable lake breeze spreads inland.

Any lingering storms toward LAN/JXN ending early this evening
then some fog or stratus probably forming at night. We could see
IFR conditions developing after 06z tonight, especially after


Issued at 330 AM EDT Thu May 26 2016

Dew points over 60 have arrive which support a fog threat over lk
mi. However the flow is 10 to 20 kts out of the south which may help
keep things mixed just enough to limit the fog threat. Will maintain
areas of fog in the nearshore fcst for the next 48 hours, but
confidence too low for any fog advisories due to the wind speeds.


Issued at 314 PM EDT Wed May 25 2016

The rivers are certainly in a position to handle a half inch to an
inch of rain through the weekend with little impact other than
mainly within bank rises. Locally heavier rainfall could potentially
cause quicker rises on smaller creeks and streams, but the basin
average QPF should not be high enough to warrant flooding on main
stem rivers or even tributaries. Nevertheless, local trends will be
monitored as storms occasionally develop across the region for the
next several days.


.GRR Watches/Warnings/Advisories...


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