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FXUS63 KGRR 191756
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
156 PM EDT Tue Jun 19 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EDT Tue Jun 19 2018

Showers and a few thunderstorms will continue today as a
cold front slowly settles south through Lower Michigan. It
will be cooler and less humid for the rest of the week.

&&

.UPDATE...
Issued at 1126 AM EDT Tue Jun 19 2018

Main item of concern is tied to the showers and thunderstorms
moving across Lake Michigan as of 1115 AM. Satellite imagery shows
some cooling tops and there is lightning even at mid lake with
limited instability. The impetus for the area of precipitation was
a line of storms that developed out toward Des Moines Iowa around
06z. So, expecting at the very least rain/rain showers to spread
in this afternoon. Instability is not forecast to be great, on the
order of 500-1000 j/kg this afternoon across the southern half of
the forecast area. Not expecting much in the way of convection
across Central Lower Michigan with positive 850mb LI's up there.

Two items that may need further attention this afternoon are a
lowering of the high temps given the clouds and rain and the
possibility for increasing pops across the south. Have already
bumped pops up to likely across the south and may need to go
further yet.

&&

.SHORT TERM...(Today through Thursday)
Issued at 328 AM EDT Tue Jun 19 2018

Surface dew points are dropping in northerly flow at this moment
and this will continue through Wednesday and beyond. Despite the
advection of drier air at low levels, rain showers and the chance
for an isolated thunderstorm exists as warm advection pattern at
mid levels continues.

Eventually the upper ridge is flattened and replaced with central
Canadian trough as sfc ridging builds in with fair and much cooler
weather. Sfc ridging will bring dry weather Wednesday and
Thursday.

.LONG TERM...(Thursday night through Monday)
Issued at 328 AM EDT Tue Jun 19 2018

This morning, the upper-level pattern is somewhat benign with
ridging extending up the Atlantic coast of British Columbia,
troughing across northeastern U.S. coast, and a "cut-off" low over
the northern (U.S.) Rockies. As troughing re-intensifies across the
northeast and a deep summertime high pressure system builds in the
desert southwest, the upper-level low will ever so slowly meander
through the central U.S. through much of the workweek.

A quick look at the previous 7-day rainfall across the Midwest is
rather eye opening with a large area of 2-5+ inches observed across
much of the western Great Lakes and generally an inch or less across
the majority of lower Michigan. In fact, one might think Lake
Michigan has a rain shadow given just how little precipitation has
fallen across lower Michigan over the past week! However, we are
thankful not to be dealing with the flash flooding and spotty severe
weather that has been bothering our neighbors to the north and west
the past week.

Locally, our next best chance of precipitation will come this
weekend with the aforementioned slowly-moving low as it visits the
Great Lakes. The exact timing, location, and magnitude of the rain
will get ironed out in the coming days, but at this point it looks
like some areas in lower Michigan may pick up a healthy amount (>
0.5 inch). Given modest forecast instability, I feet comfortable
maintaining thunder in the forecast at least through Saturday
evening.

A high pressure system will then build into the region early next
week bringing seasonable temperatures (and comparatively more
"comfortable" humidity levels).

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 155 PM EDT Tue Jun 19 2018

An area of showers and embedded thunderstorms are moving through
the TAF sites at 18z. We are thinking the thunderstorms will be
confined to the I-94 sites. Some MVFR conditions are possible for
a time this afternoon at the I-96 TAF sites with IFR possible
along I-94 due to the heavy rain as they move through. The showers
and storms will likely taper off after 20z-21z.

We will likely trend VFR once again in most areas late this
afternoon in the wake of the rain. All sites will move into MVFR
after dark (after 02z). Another batch of rain will likely move
through the TAF sites between 03z and 12z. There is the
possibility for some embedded thunderstorms once again.

The rain should end Wednesday morning after 14z, with conditions
improving from north to south during the midday and afternoon
hours to VFR.

&&

.MARINE...
Issued at 328 AM EDT Tue Jun 19 2018

Winds and waves will continue to be relatively light as high
pressure begins to build into the central Great Lakes with
primarily offshore winds.


&&

.HYDROLOGY...
Issued at 1234 PM EDT Tue Jun 19 2018

Recent rainfall has resulted in a slight rise on a few area rivers.
With river levels running near normal, no flooding is expected.

More rain is possible today through Wednesday night and again Friday
through Saturday night. Scattered to numerous showers and
thunderstorms may develop. Generally expect less than an inch of
rain, with locally heavy rainfall possible with the storms. This may
result in localized flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

UPDATE...Duke
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Borchardt
AVIATION...Duke
HYDROLOGY...63
MARINE...Ostuno
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