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fxus63 kgrr 271805 

Area forecast discussion
National Weather Service Grand Rapids Michigan
205 PM EDT Tue Jun 27 2017

Latest update...

issued at 330 am EDT Tue Jun 27 2017

High pressure will provide plenty of sunshine today although
temperatures will remain below normal. It will not be as windy as

On Wednesday and Wednesday night a warm front will push in from
the southwest, resulting in showers and thunderstorms. The best
coverage of storms will be north and west of Grand Rapids.

The main thunderstorm risk on Thursday is expected to be south of
Michigan, but that risk will expand north again on Friday and
Friday night.


Short term...(today through thursday)
issued at 330 am EDT Tue Jun 27 2017

Main focus is on convective potential Wednesday through Thursday.

Models have been consistent in showing a 50 to 60 knot swly low
level jet developing on Wednesday over Wisconsin as a shortwave
tracks across the Dakotas and Minnesota. This setup is expected to
fuel widespread showers and storms over central and northern Wisconsin,
which should work into western and northern lower Michigan in the
afternoon and evening.

Current model quantitative precipitation forecast solutions indicate the heaviest rain, on the
nose of the low level jet, should pass to our north. However the
NNW-SSE orientation of the thickness pattern may cause the WI
storms to curve/propagate more southeastward, at least initially,
which could lead to a heavy rain threat for a time Wednesday night
north of a line from roughly Holland to Alma. The main axis of
heavy rain lifts toward Northern Lake Huron later Wed night as
the shortwave moves toward Lake Superior.

It would appear that Thursday may end up being relatively quiet
since the low level jet peels away and we end up with a divergent
low level westerly flow over the area. This pattern usually keeps
most of the area dry, although some diurnal sfc based storms
could pop along and south of I-94 where sfc convergence will exist
along the sfc cold front which slips south through our area in
the morning.

In the near term, today looks rather quiet as the upper trough
begins to slowly lift out and sfc ridging impacts the area. Can't
rule out an isolated shower or two in far eastern sections.

Long term...(thursday night through monday)
issued at 330 am EDT Tue Jun 27 2017

Active wx is anticipated during the early portion of the long range
fcst period with potential for several rounds of convection. There
is potential for showers and storms Thursday night with a lingering
frontal boundary over the lower Great Lakes region.

Initially Thursday evening the better chance for convection should
be just south of our area across northern Illinois/in/OH, but the boundary
will likely move north Thursday night. An increasing nocturnal llj
will also focus some convective development.

A better chance for more widespread convection will come Friday as a
low pressure system and cold front move through. Some strong to
severe storms are possible given lift from the approaching front in
conjunction with ample low level moisture and potential for moderate
instability to develop. Deep layer shear values of 35 to 45 kts are
also favorable for some strong to potentially severe storms.

Larger medium range guidance discrepancies arise for the weekend
into early next week leading to lower confidence in that portion of
the fcst. Initially a somewhat cooler and drier airmass will move in
behind the cold front for the weekend. However there are some
signals in longer range guidance that the wx pattern could turn more
active again early next week as another system potentially moves in
from the west late Monday or Tuesday.


Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 157 PM EDT Tue Jun 27 2017

An area of high pressure will become situated over the central
Appalachians on Wednesday. This fair weather system will act to
keep aviation impacts to a minimum. Showers and thunderstorms
associated with an area of moisture will approach the taf sites
from the west on Wednesday...but are not expected to arrive until
after 18z. Southerly flow will be strengthening toward 18z.


issued at 330 am EDT Tue Jun 27 2017

Still some 4 foot waves from South Haven south early this morning,
but the trend should be for subsiding waves as high pressure
impacts the region. Small craft advisories and beach hazard
statements will likely be needed again Wednesday as winds increase
considerably from the south.


issued at 1119 am EDT Mon Jun 26 2017

River levels are trying to return to normal across the region...with
the Chippewa river at Mt. Pleasant and Pine River at Alma above flood
stage. Scattered showers and thunderstorms...which will develop as
an upper low moves over the state this afternoon...are not expected
to produce the areal coverage or intensity of precipitation needed
to slow the falling of the stages. Therefore...expect river levels
to continue to fall steadily over the next 24 hours.

Another round of potentially heavy rainfall will occur later
Wednesday into Wednesday night. Deep moisture returns to the
region...and bands of heavy rainfall may occur across central
portions of lower Michigan. Rivers in Isabella and Gratiot
counties are especially vulnerable to excessive rainfall...and
significant rises would likely develop on the Pine and Chippewa
rivers should the heavy rainfall occur in these basins.


GRR watches/warnings/advisories...



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