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Area forecast discussion 
National Weather Service Grand Rapids Michigan
724 am EDT sun Aug 31 2014

Latest update...

issued at 328 am EDT sun Aug 31 2014

High pressure will move across lower Michigan today. This should
result in at least partial sunshine across the area this afternoon.
An isolated thunderstorms is possible east of US-131 and south of
I-96 during the early to middle afternoon. Expect mostly clear skies
tonight with lows mostly in the 60s. A cold front moving into the
area by late Monday night will result in thunderstorms Monday
afternoon into Monday evening. Some of these storms could be
strong to severe. Temperatures will warm with highs in the 80s.
Cooler and drier weather follows the cold front for Tuesday into


Short term...(today through tuesday)
issued at 328 am EDT sun Aug 31 2014

We continue to track the potential for severe storms Monday
afternoon into Monday evening. Otherwise tranquil weather is
expected today into tonight.

An unseasonably strong Pacific system will bring the polar jet
stream unusually far south for early September (1 in 10 year return
period for early september) on Monday. A couple jet feature will
help focus thunderstorms Sunday night into early Monday over
Minnesota and Wisconsin. This strong upper level jet will result
in a 35 to 45 knot low level jet that will track across southern
Wisconsin early Monday morning then lift northeast will the
coupled jet core into Upper Michigan Monday afternoon. The 1000 to
850 moisture transport vectors converge over eastern Wisconsin
during the early to middle morning hours of Monday but that
feature... like the low level jet also lifts northeast into Upper
Michigan and Eastern Lake Superior by early Monday afternoon.
Meanwhile there should be at least 1500 j/kg of mixed layer cape
over central and eastern lower mich gain by early Monday
afternoon and there will be 30 to 40 knots of deep layer shear
Monday afternoon over all of lower Michigan. All of this would
suggest at least some potential for a line of thunderstorms
crossing lower Michigan during the late morning into middle afternoon.
Soundings from the GFS suggest the equilibrium level will be near
the tropopause and there is a significant amount of cape in the -10 to
-30 range so hail would be possible as well as gusty winds.

So...will there be severe storms over southwest lower Michigan on
labor day? All of this suggest severe storms are surely possible.
We are in slight risk from the Storm Prediction Center day 2 outlook. However there
are some questions. First southwest Michigan is in the speed
divergence area of the low level jet Monday afternoon. That is not
the place you would want to be to get concentrated severe storm
activity. Also southwest Michigan is in the right front exit
region of the jet which is actually over Wisconsin yet Monday
afternoon. This is also not conducive to severe storms. Anther
negative is the line of storms coming out of Wisconsin during the
middle morning hours of Monday. That will bring layered clouds across
the area cutting back on surface heating. Yet given all of the
above there still at least a slight risk as Storm Prediction Center indicates. We will
have to watch how the convection actually plays out Monday morning
before we have a better idea of how great the severe risk here is
on Labor Day.

The entrance region of that same polar jet core comes across
Michigan early Tuesday. That will educe a wave on the front and
may bring convection back north into Southern Lower Michigan
during the early morning hours of Tuesday. We will have to watch
this closely. These could be strong storms too if the get this far
north. Once that is through quiet weather returns by Tuesday

Long term...(tuesday night through saturday)
issued at 328 am EDT sun Aug 31 2014

The long term portion of the forecast will feature quiet weather for a
good majority of the period. A flat upper ridge will build in by Tuesday
night in the wake of the early week system. We will see surface ridging
take control of the weather for Wednesday and mostly Thursday keeping most of
the area dry. As srly flow increases on Thursday...we will see quite warm
temperatures move in. The area should be well into the 80s by Thursday with h850
temperatures increasing to the upper teens c. This could be a bit
conservative for maximum temperatures.

The only unsettled period looks to be during the late Thursday through
early Sat time frame. We will see our flat upper ridge be pushed out
by an upper trough expected to extend from central Canada to the northern
rockies on Thursday. This upper trough will push a cold front into the
area centered on the day on Friday right now. This front should move
into a fair amount of instability...helping to produce showers and

This front should clear the area by Sat morning....allowing cooler
and drier air to filter back into the area from the north.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 724 am EDT sun Aug 31 2014

Currently (11z) there is a band of IFR ceilings with MVFR visibilities
through kgrr and klan while kmkg...kazo and kbtl are VFR. However
infrared satellite loops the clouds are not far away from those other
sites. I believe all of the taf sites will have IFR ceilings for
several hours this morning before this all mixes out by early

There is enough instability for showers to redevelop this
afternoon. However... the only locations where there is enough
surface convergence for those showers to be forced is for the
I-94 taf sites. That is where the front will be stalled this
afternoon. So I continued the idea of vcsh for those taf sites.
Actually a thunderstorm would not be out of the question for those
taf sites.

Skies should clear across the area tonight. There should be enough
wind in the boundary layer to keep VFR going through the night.


issued at 328 am EDT sun Aug 31 2014

No concerns in the first 18 hours or so for the nearshore waters with
light winds expected. Conditions are looking likely for another
Small Craft
Advisory/beach hazards event for the day on Monday.

High pressure building in across the area today will keep the
gradient light and winds at or below 10 knots for the most part.
Winds will start increasing tonight and could be flirting with Small
Craft Advisory criteria just after daybreak on Monday ahead of the
next front. Winds and waves look like they could be a little
stronger/higher compared to the past event yesterday.


issued at 220 PM EDT Sat Aug 30 2014

Precipitable water values over 1.75 inches support locally heavy rain. Storms
have been moving quickly and thus the duration has been limited.
With several rounds of storms possible Monday into Monday
night...will need to monitor the heavy rain potential especially
with precipitable water values unseasonably high and stronger forcing moving in.
Elevated risk for locally excessive rain exists.


GRR watches/warnings/advisories...


short term...wdm
long term...njj

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