Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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030
FXUS63 KGRR 252358
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
758 PM EDT Tue Jul 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 303 PM EDT Tue Jul 25 2017
An area of high pressure will continue to push east of the region
into Wednesday. South to southwest winds around this system will
draw up an unseasonably moist airmass into Michigan. A cold front
will drop southeastward through the region later Wednesday into
Thursday morning. This will result in some showers and perhaps a
few thunderstorms. The pattern then dries out for the end of the
week.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 303 PM EDT Tue Jul 25 2017

The south to southwesterly flow tonight draws up an increasingly
moist airmass. The warm air advection may lead to a few showers
especially towards Ludington. Some of the high res models are
showing that the showers could actually build further southeast
than Ludington later tonight...perhaps into Grand Rapids toward
daybreak. The atmosphere is shown to remain stable tonight...thus
no thunderstorms will be in the forecast.

Looking at Wednesday into Thursday. Overall the trend supports
less in the way of rainfall...but that could still change.
A slow moving surface frontal zone slips southeastward through the
CWA. The lift is forecasted to be weaker and less instability
present. However....PWAT values are shown to climb up over 1.75
inches. The latest GFS does show decent upper level divergence at
the jet level over MI. Thus we still need to monitor the trends on
this approaching system. Will have somewhat lower POPs for the
passage of this front.

Models are in decent agreement in showing the atmosphere drying
out as high pressure settles in from the north for Thursday night.

.LONG TERM...(Friday through Wednesday)
Issued at 303 PM EDT Tue Jul 25 2017

The overall trend is for little real change in our current weather
pattern. Temperatures should, for the most part be near normal and
precipitation will continue to be sporadic.

The upper air pattern for July likely will continue into at least
early August. That pattern is general northwest flow aloft, which is
the result of an overall large scale ridge over the western CONUS
into western Canada and weak trough over the eastern Canada and the
CONUS.

Over this coming weekend a shortwave upper ridge will be located
just west of Lower Michigan and it will crest over this area Sunday.
It will be accompanied by a large Canadian origin surface high. That
will mean dry air which means cool nights and warm days. Expect
temperatures to be near normal during the afternoon (80 to 85) but
cooler than normal at night, mostly lows in the 50s with 40s
possible in the normally cooler locations.

By early next week the next upstream Pacific origin shortwave will
crest the longwave ridge (near 110W) and start to dig southeast into
the eastern CONUS.  That will bring a cold front through this area
early next week. Normally that would have thunderstorms with it but
since this is Canadian air displacing Canadian air and there will
not be much inflow from the Gulf to recharge it, I would think we
will see more of the same, a dry cold front and temperatures remain
about the same, lows from the mid 50s to lower 60s and highs from
around 80 to the mid 80s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 758 PM EDT Tue Jul 25 2017

VFR weather is forecast the next 24 hours. Mid and high clouds
will spill in from the north and west tonight with bases above
8,000ft. Winds will be essentially light and variable tonight with
the exception being KMKG where some light southerly winds will
occur at 5-10 knots.

On Wednesday, winds will pick up a bit from the south-southwest at
8-13 knots. A front will approach from the west on Wednesday, but
we feel VFR weather will continue through 00z. Cloud bases on
Wednesday will likely be between 5,000 and 10,000ft. Showers will
likely primarily stay off to the north and west of the TAF sites
through 00z. Considered including a VCSH after 18z, but thought
the threat was minimal enough to keep it out of the forecast.

&&

.MARINE...
Issued at 303 PM EDT Tue Jul 25 2017

The pressure gradient increases tonight into Wednesday. This will
support building waves as the southerly flow increases. It looks
like a close call for marine headlines later Wednesday into
Wednesday night for the northern zones. At this time the potential
is too low to go with headlines. Perhaps a greater risk for
hazardous waves exists for Thursday as a northerly flow and cold
air advection develops.


&&

.HYDROLOGY...
Issued at 1055 AM EDT Tue Jul 25 2017

With near- to drier-than-normal conditions lately and a dry pattern
setting up for the next week, scattered showers and thunderstorms
Wed and Thu will be a welcomed sight to those looking for rain.
This does not look like a guarantee for everyone to get appreciable
rainfall amounts. But with 1.5 to 2.0 PW values nosing in and
relatively slow storm cell movement, it`s possible for some
locations to receive over an inch or two of rain in a couple hours.
Excessive rainfall to the point of flooding does not appear likely
due to a questionable storm coverage extent over the area.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...WDM
AVIATION...Duke
HYDROLOGY...CAS
MARINE...MJS



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