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Area forecast discussion 
National Weather Service Grand Rapids Michigan
321 am EDT Thursday Aug 28 2014

Latest update...
synopsis/short term/long term/marine

issued at 321 am EDT Thursday Aug 28 2014

High pressure will make today quite pleasant with highs in the 70s. A
warm front will move in tonight bringing showers and thunderstorms.
There is a decent chance for showers and storms Friday and Saturday.
Sunday should be relatively quiet before more showers and
thunderstorms roll through on Monday. Severe weather appears
possible with the storms on Monday.


Short term...(today through saturday)
issued at 321 am EDT Thursday Aug 28 2014

Surface high pressure will drift east over Lake Huron today as a
deep upper trough slowly progresses east over the Great Plains.
Fair weather is expected today...with rain chances holding off
until late tonight. Showers and storms are expected to move in
north of a warm front tonight into Friday. Based on latest low
level jet placement and moisture transport...the best chance for
rain overnight will be north and west of Grand Rapids. There is a
chance for showers and storms Friday...but the better chance for
heavy rain would be Saturday.

Conditions are not favorable for severe weather Friday and Saturday.
Instability will largely remain limited due to widespread cloud
cover. 0-6 km bulk shear values of 25 kts Friday evening is on the
low end and only marginally supportive of strong to severe storms.
Shear profiles are more favorable at around 35 kts up toward
Ludington on Friday afternoon.

High temperatures will gradually warm through the short term given
the establishment of southerly flow and warm air advection by tonight. Highs in
the 70s today will give way to upper 70s to around 80 on Friday
and lower 80s on Saturday.

Long term...(saturday night through wednesday)
issued at 321 am EDT Thursday Aug 28 2014

Overall the Labor Day weekend will feature seasonably warm and humid
conditions with thunderstorm activity Saturday night and then a more
significant thunderstorm event on Labor Day as a cold front with
a strong upper wave moves through the area.

The models are largely in good agreement on the overall pattern
through Wednesday. We currently have near zonal flow near the
Canadian boarder with a opening up southern stream upper low moving
into Colorado. The Colorado system moves through the Great Lakes
Saturday. As I suggested yesterday the models tend to under-forecast
the strength of these types of systems... so I favor the 00z European model (ecmwf)
having a slower and stronger upper wave as it moves through Michigan
Saturday into early Sunday. This increases the threat for
thunderstorms over southwest lower Michigan Saturday night as the
upper level system will still be moving through the area.

Also significant to our weather is a system currently north of
western Alaska which has a strongly digging 100 knot jet core on
west side of it. That helps to cause the system moving through
southern Alaska to dig into the northwest Continental U.S. By Saturday. It is
that system that moves through the Great Lakes Monday with strong
upper dynamics. The more I look at this system the more I believe
there is a significant threat for strong to severe storms over
southwest lower Michigan Monday afternoon into Monday evening. There
is a coupled upper level jet that comes through the western Great
Lakes Monday afternoon into early Tuesday. The lower level response
to that is a strong low level jet... a decent Gulf moisture feed
with precipitable water values near 2 inches. The timing is just
right for strong thunderstorms to southwest lower Michigan late in
the day or early evening. We will have to watch this over time to
see of the severe weather threat continues.

A shortwave ridge moves through the area on Sunday between the
departing southern stream system and the much more dynamic system
that comes through the area Monday into early Tuesday. I would
imagine Sunday should feature mostly dry weather with afternoon
temperatures mostly in the lower to middle 80s.

Behind the cold front Tuesday into Wednesday should be quiet as the
upper level jet does not quiet dig this far south. I have to admit
through it would not be surprised to see later model runs show the
polar jet getting farther south Tuesday. So I have low chance probability of precipitation
just in case that does happen for Tuesday. It will be cooler Tuesday
into Wednesday.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1159 PM EDT Wednesday Aug 27 2014

High confidence in VFR conditions over the next 24 hours. A brief
period of MVFR ceilings/visibilities cannot be ruled out at jxn roughly 08z-
12z but was not confident enough to have MVFR in the taf there.
Expect any shower/thunderstorm threat to hold off until after 06z Friday.


issued at 321 am EDT Thursday Aug 28 2014

Winds and waves on Lake Michigan will remain light and around 1
foot today. Winds will pick up tonight into Friday. South winds in
the 15-20 knots range Friday are expected to build waves into the 2-4
foot range north of Whitehall. Waves in the 1-3 foot range are
expected south of Whitehall. Showers and thunderstorms are
possible late tonight through Saturday. Strong to severe storms
are possible on Monday.


issued at 400 PM EDT Wednesday Aug 27 2014

Heavy rain threat increases late Thursday night into Saturday as
moist airmass returns. Slow moving storms could bring some
localized flooding. A cold front could bring more heavy rain on


GRR watches/warnings/advisories...


short term...ebw
long term...wdm

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