Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 200730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT TUE SEP 20 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EDT Tue Sep 20 2016

A mild September weather pattern is forecast to continue the next
few days with high temperatures pushing into the upper 70s and lower
80s. The warmth is courtesy of a south and southwest flow of air
aloft ahead of a low pressure center that will be situated in the
plains states much of the work week. Chances for showers and storms
will exist Wednesday through Friday as a warm front will be situated
across the Great Lake State. Best chances for precipitation will be
over Central and Northern Lower Michigan.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue Sep 20 2016

Main focus through the short term is on shower and thunderstorm
chances through the period.

We look to stay dry for the most part today and tonight as high
pressure drifts through the region. That being said, cannot rule out
a few lingering showers this morning in the south as the cold
frontal boundary sags south/weakens further. Best instability
remains southwest of the forecast area so not expecting any thunder
in the precip that lingers. Tonight, a weak low level jet on the
order of 20 knots moves across Lake Michigan and into western
portions of the forecast area towards daybreak. The low level jet is
associated with the warm front lifting back into the area from the
south tonight. Have 20-30 pops in the forecast for late tonight
after 5AM for an isolated to scattered shower or thunderstorm. PWATs
ramp up considerably between 8pm and 8pm and usually we see some
precip with such a surge. Values are back to near 1.60 inches by
daybreak.

Wednesday through Thursday a warm front will be situated across
Central Lower Michigan which will likely be a focus for shower and
thunderstorm development. The low level jet is quite weak though
through this time and there is very little upper level support in
terms of a notable shortwave. Thinking we are looking at some
diurnally driven showers/storms both Wed and Thurs
afternoon/evening. 30-50 pct chances should cover things for the
most part, but we do have some 60 pops in the far northwest at
times to match up with neighboring offices.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue Sep 20 2016

Forecast concerns during the long term mainly deal with pcpn chances
Friday night and Monday.

The medium range models have been showing a weak cold front pushing
south into the southern Lower Michigan and washing out for several
runs, including the 00z iteration. Convergence along the boundary
appears just sufficient to squeeze out a shower Friday night, but
not much more before drier air from the northeast advects into the
cwa. Highs will cool off from the lower 80s Thursday to the lower
70s Saturday through Monday.

Saturday and Sunday look mainly dry as high pressure builds south
from Ontario. The next cold front is progd through the cwa Sunday
night/Monday by the GFS and Monday night by the ECMWF.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 112 AM EDT Tue Sep 20 2016

A brief shower is possible for the next couple of hours at GRR and
MKG, otherwise sct-bkn clouds around 10k feet are expected through
the period.

&&

.MARINE...
Issued at 330 AM EDT Tue Sep 20 2016

In general a light wind regime through Thursday is expected.
Therefore, waves will remain at or below 2 feet through that time.
Late tonight a weak low level jet picks up which may boost wave
heights for a time late tonight into Wednesday morning to around 2
feet. Winds may increase during that time to 10-15 knots out of the
south, otherwise winds look to be 10 knots or less Today through
Thursday.

&&

.HYDROLOGY...
Issued at 329 PM EDT Mon Sep 19 2016

The hydro concerns with tonight`s cold front are limited. Any
heavier rainfall this afternoon and evening is expected to be
localized, and widespread rainfall amounts should remain less than
0.50 inches. Most of this rain will fall north of Interstate 96,
with the Ludington area seeing the most. A few smaller streams could
see brief rises, but widespread river rises are not likely.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...04
HYDROLOGY...JAM
MARINE...Duke



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