Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 151736
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
136 PM 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.

&&

.UPDATE...
Issued at 1052 AM EDT Sat Jul 15 2017

Raised max temps a few degrees. Now that the morning stratus has
burned off, much of the remainder of the day will be mostly sunny
with temps reaching around 80 for inland areas.

&&

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 137 PM EDT Sat Jul 15 2017

VFR conditions will continue through this evening. A few
thunderstorms are possible after midnight across western Lower
Michigan. Low clouds will move in Sunday morning with MVFR and IFR
conditions developing after 12Z.

Winds will be from the west to southwest less than 10 knots
through Sunday.

&&

.MARINE...
Issued at 1052 AM EDT Sat Jul 15 2017

Will issue a small craft advisory and beach hazards statement for
Sunday. North winds will kick up to around 25 knots on Sunday, and
along with the cold advection, waves will build. Swimming risk
will become high. Being a mid summer weekend it is prudent to
issue this with about a 24 hour advanced notice.


&&

.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...Beach Hazards Statement from Sunday afternoon through late
     Sunday night for MIZ050-056-064-071.

     Beach Hazards Statement from Sunday morning through late Sunday
     night for MIZ037-043.

LM...Small Craft Advisory from 8 AM Sunday to 4 AM EDT Monday for
     LMZ848-849.

     Small Craft Advisory from 1 PM Sunday to 4 AM EDT Monday for
     LMZ844>847.

&&

$$

UPDATE...JK
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...04
AVIATION...Ostuno
HYDROLOGY...JAM
MARINE...JK



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