Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 190730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT FRI AUG 19 2016

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

.SYNOPSIS...
Issued at 330 AM EDT Fri Aug 19 2016

We are entering an active weather period Today across the Great
Lakes region, which will stretch into Sunday. Today we look for
scattered showers and thunderstorms to develop in a warm and moist
southerly flow of air. Tonight into Saturday low pressure will form
off to our southwest and gradually move into the northern Great
Lakes. The low will stengthen Saturday night and into Sunday driving
a cold front through our area Saturday evening. Showers and
thunderstorms are likely Saturday afternoon and evening along and
ahead of the cold front. Some of these storms may become strong to
severe. Strong westerly winds behind the low on Sunday will bring
cooler and showery weather to the area. Highs will push into the 80s
today, hold near 80 on Saturday beneath cloud cover and hold in the
70s on Sunday.


&&

.SHORT TERM...(Today through Sunday)
Issued at 330 AM EDT Fri Aug 19 2016

Shower and thunderstorm chances remain the focus right through the
short term. Ascertaining the threat of severe weather Saturday
afternoon and evening is also a focus.

Chances for showers and storms Today and Tonight look rather
scattered in nature with not much of a low level jet to speak of. In
general the low level jet through 12z Saturday is on the order of 20
knots or less. Our chances for showers and storms will likely be
tied to upstream convective vorticity maximums that move our
direction from Wisconsin. One such vort can be seen spinning across
far southwest Wisconsin at 0730z. Essentially have chance pops (30-
50 pct) both today and tonight. Hard not to think our chances will
be somewhat diurnally focused with CAPE values peaking this
afternoon in the 2000-3000 j/kg range. Given weaker wind fields any
threat for severe will come towards max heating in the strongest
cells.

Main time frame of concern will come Saturday afternoon and evening
with strong wind fields are forecast to come together late in the
day. The extent of convection tonight into Saturday morning will
likely determin our chances for severe later Saturday afternoon and
evening. Depth of the low is still in question as the NAM and
Canadian are stronger and slower. Bottom line is a broken line of
storms will work through the area between 18z and 03z. Severe
weather cannot be ruled out and agree with the marginal threat for
now.



.LONG TERM...(Sunday night through Thursday)
Issued at 330 AM EDT Fri Aug 19 2016

High pressure will produce fair wx with seasonably cool temperatures
Sunday night through Monday.  Temperatures will fall into the 40`s
Sunday night over our northern fcst area and high temps Monday will
only reach the lower to middle 70`s.

Fair weather will continue Tuesday and Wednesday and temperatures
will undergo a slow moderating trend in a south to southwest flow
waa pattern on the back side of the departing ridge. The next system
approaching from the west will bring the next chance for showers and
thunderstorms late Wednesday through Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1218 AM EDT Fri Aug 19 2016

Vfr conditions will continue overnight through Friday morning.
Scattered showers and thunderstorms will develop Friday afternoon
and linger through Friday evening. Conditions will remain
primarily vfr at all the terminals but could briefly dip into the
mvfr/ifr flight categories in heavier showers and storms Friday
afternoon and evening. Some patchy fog may develop after 06Z early
Saturday morning.

&&

.MARINE...
Issued at 330 AM EDT Fri Aug 19 2016

Southerly winds today may push waves into the 2-4 foot range at
times, but overall expecting sub advisory conditions. The weekend
looks to be rough on Lake Michigan and that may start as early as
Saturday afternoon. Southerly flow begins to strengthen in earnest
then and winds by evening could be pushing into the 20-30 knot
range. Waves may reach Small Craft Adv criteria by evening. The main
time frame of concern however is Saturday night into Sunday. Models
have yet to come into full agreement on the depth and position of a
strong low moving through the western Great Lakes. We are at least
looking at Small Craft Adv criteria these two periods as well as
Beach Hazard Statement worthy conditions. If the deeper NAM/Canadian
solutions verify we could be talking a rather rare August gale
event. Bottom line, later in the weekend will be very atypical for
summer time in the Great Lakes. Waves of 4 to 7 feet look likely
later in the weekend with 6 to 10 footers in the realm of
possibilities.

&&

.HYDROLOGY...
Issued at 201 PM EDT Thu Aug 18 2016

A flood warning continues for the Portage River near Vicksburg in
Kalamazoo County, however this river has already crested and should
continue a slow fall. This is generally the case elsewhere,
including the Sycamore Creek near Holt. One exception is the
Kalamazoo River near New Richmond, which is expected to crest Friday
around 15.1 feet, but this will result in minimal impacts.

Significant rain is not expected again over the Grand and Kalamazoo
River basins until Saturday night, when confidence is fairly high
for widespread precipitation in the neighborhood of 0.50-1.00".
Although this provides extra time for the most at-risk areas to
recover, soils will still remain moist and the smaller streams and
creeks especially could respond quickly to localized heavier
rainfall. Additional precipitation for the weekend will certainly
need to be monitored.

&&

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

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...TJT
MARINE...Duke



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