Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 231137
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
737 AM EDT Sat Sep 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 329 AM EDT Sat Sep 23 2017

Hot and humid weather will continue into Tuesday before
a cold front comes through the area on Wednesday bringing
in cooler air. A stronger cold front will bring showers
and thunderstorms with much cooler air in Thursday into
Friday.

&&

.SHORT TERM...(Today through Monday)
Issued at 329 AM EDT Sat Sep 23 2017

The primary issue will be the heat and humidity into Monday.
With a building upper level high over the area, I expect little
in the way of cloud cover and no change in airmass through Monday
so what we had the past two days should continue into Monday. The
models continue to show the 1000/925 and 1000/850 thickness just
as warm this afternoon as the past two afternoons so no reason to
believe it will be any cooler. Thus expect highs in the lower to
mid 90s and heat index values between 95 and 100 degrees this
afternoon.

The models do show a slow cooling trend starting Sunday but with
the upper high holding as it does the cooling seems questionable.
As a result I kept highs significantly warmer than any of our MOS
output would suggest. Highs will stay in the lower to mid 90s
Sunday and Monday.

The upper level high will result in enough subsidence at mid
levels so that convection in the afternoon should be suppressed.
Even so I have 5 to 10 pct pop inland of US-131 just in case.

.LONG TERM...(Monday night through Friday)
Issued at 329 AM EDT Sat Sep 23 2017

The upper high will slowly drift to the east by Tuesday.  This will
let a weak front to move into SW MI.  Not much moisture with the
front as the upper high will still prevent any Gulf moisture to be
entrained.  It seems that we will only see very hit and miss
showers/storms with the front given this lack of moisture.  One more
hot day on Tuesday, then we chill down.

A more zonal flow develops by Wed/Wed night, while we see northerly
low level flow develop in the wake of the weak front.  Some timing
differences with the front, but temps should turn some 10 to 15
degrees cooler in this period.

We should continue to see progressively cooler temps into the latter
portion of the week.  By Thu/Fri an upper trough deepens over the
Great Lakes.  And along with a persistent northerly flow in the low
levels, H8 temps fall to around +2C by Friday.  Highs by Friday
should only be in the lower 60s.  The upper trough will also bring
the best chance of rain in the extended period, with showers
arriving Thu night and lasting into Friday morning.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 737 AM EDT Sat Sep 23 2017

Any fog will burn off quickly this morning then it will be VFR all
day. Some patchy fog is possible toward sunrise again Sunday
morning.

&&

.MARINE...
Issued at 329 AM EDT Sat Sep 23 2017

High pressure will result in light winds and mostly clear skies so
I see no marine issues till the cold front gets closer to the area
the middle of next week.


&&

.HYDROLOGY...
Issued at 1054 AM EDT Fri Sep 22 2017

Rivers are running around normal to below normal for the time of
year. Meanwhile, the US Drought Monitor is indicating dry conditions
across Southern Lower Michigan. Isolated thunderstorms may develop
during the afternoon and early evening near I-69. Near-record warmth
is expected today through the weekend. The next chance for rain is
Wednesday. No river issues are expected through next week.

&&

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

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...WDM
HYDROLOGY...63
MARINE...WDM


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