Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 151131
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
731 AM EDT Sat Jul 15 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 AM EDT Sat Jul 15 2017

It will remain slightly cooler than normal today as the Canadian
origin High pressure system passes through the area. This will
result in mostly sunny skies too. Another Canadian cold front will
head our way and be through most of the area by sunrise. Expect a
line of thunderstorms just ahead of the cold front. Any storms
will be brief and not all areas will have rain from these storms.
Another Canadian origin high pressure system will move into the
area Sunday and move east of the area Monday. This will provide
tow more days with near to below normal temperatures. Expect some
significant warming by mid week.

&&

.SHORT TERM...(Today through Monday)
Issued at 327 AM EDT Sat Jul 15 2017

The primary issue for this forecast is will there be thunderstorms
just ahead of the cold front tonight? If so, how strong will they
be? Otherwise we remain in general northwest flow at mid to upper
levels so temperatures will remain near to below normal through
Monday.

Tonight does not look as strong of a case as Friday morning did as
mid levels are not as moist. This past Friday morning we had the
effect bulk shear reach 45 knots near route 10 and the Craven-
Brooks severe index reached 40,000. We had most unstable capes
near 1500 j/kg and the Precipitable water reached near 2 inches.
Tonight the Craven-Brooks is forecast to stay no higher than
10,000, the bulk effective shear is forecast to stay under 30
knots. The Calibrated Prob severe, which got to 13 Friday morning
does not get over 2 tonight! Still there is a nice Thea-E ridge,
we are on the nose of the 1000/850 moisture transport vectors
(western CWA only), and the low level jet, there is an area of
1500 j/kg of most unstable cape to work with too. Plus we have the
300 mb jet exit region coming over our CWA. This is supported by
the latest hi-res models. I believe there will be a line of
thunderstorms but they will not be severe. We shall see!

Once that is all through the CWA (by sunrise Sunday) skies should
for the most part clear or at least no more than partly cloudy.
Could be lingering storms over the SE CWA till mid morning
through.

High pressure with Canadian polar air assures us of cooler than
normal temperatures with mostly clear skies Sunday night and
Monday.

.LONG TERM...(Monday night through Friday)
Issued at 327 AM EDT Sat Jul 15 2017

Mainly zonal flow will become a little more nw-se oriented by the
end of next week.  Most of the week looks dry, however, except for
Wednesday when both the ecmwf and gfs show a cold front moving
through the state. Scattered showers and storms are possible when
the front moves through and a strong to severe storm isn`t out of
the question. Shear values increase to 45 knots Wednesday afternoon
concurrent with a 30 kt llj. Both models also suggest that the front
will stall out near the MI/IN border and then move north as a warm
front, so Thursday could see showers/storms as well. Confidence
toward the end of the week wanes a bit as the models diverge on
solutions. The gfs shows a cold front moving through the cwa again
Friday, but the gfs is a day later. We may need to increase pops
Friday if the ecmwf is correct.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 732 AM EDT Sat Jul 15 2017

There is some low ceilings and fog in the area but for the most
part it is not impacting our TAF sites, expect GRR is BKN003 at
11z but the low clouds are patchy and thin and I believe should be
mixed out totally by 15z. Skies should be clear or nearly so till
after 00z. Given the nose of the low level jet is aimed at western
lower Michigan as it slowly sinks south overnight, I do believe
there is a good chance GRR and MKG will see convection from these
storms. For now I have VCTS and will call that good. After the
cold front expect MVFR going to IFR cigs (in the 09z to 12z time
frame Sunday).

&&

.MARINE...
Issued at 327 AM EDT Sat Jul 15 2017

Winds will increase some this afternoon but should remain below
small craft criteria. On Sunday, behind the cold front, just like
Friday, we may end up issuing a small craft advisory but it seems
premature to do that now.


&&

.HYDROLOGY...
Issued at 1054 AM EDT Thu Jul 13 2017

Rivers and streams have reached their crests or are nearing crest
levels following recent rainfall. Most sites continue to run above
to well above normal through the region with all site remaining well
within banks.

Rain returns to the area on Sunday. However, this moisture will be
of a scattered nature. Soaking rainfall will likely be confined to
locations directly affected by thunderstorms. Therefore, streams and
rivers should continue to see falls through at least Sunday with
little concern for flooding.

&&

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

$$

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



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