Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251154

Area Forecast Discussion
National Weather Service Grand Rapids MI
754 AM EDT WED MAY 25 2016


Issued at 330 AM EDT Wed May 25 2016

Very warm and humid weather can be expected through Memorial Day
weekend. Unstable conditions will lead to periodic showers and
thunderstorms but the rest of this week and the holiday weekend will
not be a total washout.


.SHORT TERM...(Today through Friday)
Issued at 330 AM EDT Wed May 25 2016

Showers along/ahead of weakening sfc frontal boundary over
central lwr mi have dissipated so will start with a dry fcst this
morning. The front continues to wash out today but weak sfc
convergence may be just enough to support diurnal development around
Mt Pleasant/Clare/Big Rapids/Evart areas this afternoon. Also some
isolated cells possible along lake breeze front later today.

Fcst soundings after 18z from the RAP indicate that any convection
which develops should have high bases around 5000-7000 ft AGL with
inverted V/dry sub cloud layer likely. This could support some
locally high wind gusts. Guidance dew points today look too high
since deep mixing shown in the fcst soundings should mix down drier
air. Afternoon dew points of 50-55 seem more reasonable than the 60s
shown in much of the guidance. Believe that cape progs from GFS/NAM
are accordingly way too high and sbcapes should struggle to exceed
1000 J/KG. Also the mixing down of drier air could lead to another
day of highs exceeding guidance.

Likely pops are still very much in order for tonight as water vapor
imagery clearly shows a shortwave upstream that`s headed our way.
Passage of this feature, and the sfc warm front, Thursday morning
will bring in the more humid/unstable condition. Trigger for
scattered convection on Thursday and Friday afternoons is
questionable but storms should favor areas of enhanced sfc
convergence such as the lake breeze front. The svr threat is marginal
with deep layer shear generally below 30 kts.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EDT Wed May 25 2016

We expect that the unsettled weather pattern expected to be in place
for the short term will linger into the long term portion of the
forecast. Deep sw flow will remain in place through the weekend as
the upper low across the sw portion of the country lifts NNE through
the weekend. This will also keep better moisture moving in from the
Gulf of Mexico with a s/sw flow at the surface. These factors will
lead to instability remaining present that could be used with any
short wave that rides through.

The upper low is expected to move by the area Sunday night. This
should tend to diminish the rain chances a bit for Mon and Tue next
week. The upper flow will become zonal for a short time, and the low
level flow will not be tapping Gulf moisture for a short period.
There is not really any cooler air coming into the area in the wake
of this system with it remaining well north, so temperatures will
likely remain in the 80s for highs.

The trend for early next week is for the chances of rain to be a
little less than previously thought. We have kept the low chc in for
now. Ridging will build over the area in response to another digging
trough across the wrn portion of the country. The low level flow
will not be conducive for strong moisture advection. Temps should
end up well in the 80s with the building heights, and a lack of
cooler air behind the system moving through on the weekend.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 755 AM EDT Wed May 25 2016

VFR weather is expected to continue today into this evening. Any
cumulus that develops this afternoon should have bases above 5000
ft. Isolated tstms cannot be ruled out but the primary risk is
north of the srn lwr mi terminals. Did keep a mention of CBs in
the GRR TAF with expected convergence along the lake breeze front
otherwise kept the mention of afternoon CBs out of the other TAFS.

A more concentrated area of showers and thunderstorms is expected
to approach from the southwest after 00Z tonight... with coverage
increasing toward 06Z. While convection is more likely tonight,
conditions will probably still stay predominately vfr. However
some fog/stratus could develop toward 12z Thursday as a warm front
approaches and dew points rise.


Issued at 330 AM EDT Wed May 25 2016

Areas of dense fog will become a concern over Lk MI tonight and
beyond as dew points above 60 arrive.


Issued at 152 PM EDT Tue May 24 2016

Periodic showers and thunderstorms will move through the region
especially Wednesday night, Friday and Saturday. However, overall
rainfall amounts will likely be variable across the area. Some
locations may pick up well over an inch of rain through the
weekend, while other places much less. A good portion of the more
widespread rainfall could occur Wednesday night as a warm front
lifts through. Thursday and beyond will feature some diurnally
driven convection that could produce locally heavy rainfall...but
basin average rainfall is not expected to be excessive. Smaller
creeks and rivers could be susceptible to quick rises given this
setup. Main stem river flooding does not look likely.


.GRR Watches/Warnings/Advisories...


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