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892
FXUS63 KGRR 171909
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
308 PM EDT Mon Jul 17 2017

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

.SYNOPSIS...
Issued at 308 PM EDT Mon Jul 17 2017

It will be quiet tonight and Tuesday.  Then a cold front will bring
scattered showers and storms to the region late Tuesday night into
Wednesday.  Another round of showers and storms will be possible
again by late Wednesday night into Thursday.  It appears we will
have a chance of storms again Saturday and Monday, but that timing
could change.

Daily high temperatures will mainly be in the 80s each day, but an
isolated report of 90 will be possible Friday.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 308 PM EDT Mon Jul 17 2017

Showers and storms will return in the Tuesday night through
Wednesday period, but these will remain scattered, with some areas
possibly staying dry.

Surface and upper ridging will keep the region dry through Tuesday.
We may see pockets of stratus develop again overnight, mainly south
of I-96, otherwise expect partly cloudy skies.  It looks like we
finally erode the low level moisture to expect a mostly sunny
Tuesday from mid morning onward.  A bit warmer Tuesday with low to
mid 80s for highs, which is about normal.

A cold front will move our way by Tuesday night and cross the CWA on
Wednesday.  Given the timing, it appears the instability will be
lacking to expect severe storms.  Also not expecting we will see
large aerial coverage since the jet dynamics does not appear to be
in the best location for SW MI.  Perhaps the best coverage will
occur when the right exit region of the upper jet crosses the U.P.
and Northern Lower Tuesday night.  Will have high chance POPs over
the far NW CWA and taper them to the south.  Then as the front moves
through on Wednesday only expect widely scattered convection along
the front, largely in the first half of the day.

A brief lull in the action much of Wednesday afternoon and evening,
then indications are that an MCS should develop over MN/IA Wednesday
evening and may reach SW MI in a weakening state late Wednesday
night.

.LONG TERM...(Thursday through Monday)
Issued at 308 PM EDT Mon Jul 17 2017

A weak low pressure system and cold front in conjunction with an
upper level disturbance will combine to bring scattered showers and
thunderstorms Thursday. The cold front should advance just far
enough south by Thursday night for dry wx to briefly return to most
of our area through Friday afternoon as a weak high pressure ridge
builds in to the north. However a few showers and storms may linger
over our far southern fcst area in closer proximity to the stalled
out boundary.

The boundary just off to our south will lift back to the north as a
warm front late Friday and Saturday and bring more showers and
thunderstorms. Some stronger to potentially severe convection is
possible Saturday as low pressure moves east along the front. This
type of synoptic setup is also conducive to potential for locally
heavy rainfall. Showers and storms may linger through Saturday night
into early Sunday before the system finally moves out of our region.

Low confidence in the fcst for early next week due to large medium
range guidance discrepancies. The 12Z operational gfs guidance now
suggests that a fairly active wx pattern may continue Sunday into
early next week with a nearly stationary frontal boundary over the
Ohio Valley region that would be close enough to our area to bring
more showers and storms.

However the ecmwf suggests that high pressure will build in from the
west Sunday and Monday. Rather warm and humid wx is anticipated
through most of the long range fcst period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1251 PM EDT Mon Jul 17 2017

VFR conditions are anticipated at all the terminals through early
Tuesday afternoon. Lingering MVFR at KAZO attm should quickly
improve to VFR during the next hour or so as the small area of
lingering low clouds dissipates. Fair wx cumulus will linger this
afternoon and early evening before skies become mostly clear
tonight. Fair wx cumulus will redevelop toward midday Tuesday.

&&

.MARINE...
Issued at 308 PM EDT Mon Jul 17 2017

Quiet conditions will remain on the lake through the short term.
However boaters and beach goers will have to monitor periods of
thunderstorms starting Tuesday night and lingering into Wednesday
night.

&&

.HYDROLOGY...
Issued at 145 PM EDT Mon Jul 17 2017

Current river flow across the region is running anywhere from near
to much above normal. The Kalamazoo River basin is largely near
normal, with the Grand, Muskegon, and Saginaw River basins near to
above normal. For some locations, the upcoming pattern may lead to
above normal flows with perhaps within or above bankfull rises.

Several opportunities for thunderstorms exist beginning late
Tuesday night/early Wednesday morning right on through the
weekend due to a frontal boundary hovering around the region.
While many portions of this time frame will be dry, when it does
rain it could be quite heavy. Precipitable water values will perk
up to around 1.75" early Wednesday morning with possible storms
propagating from Wisconsin to Lower Michigan, but they could be
weakening in the process. Additional chances exist for the second
half of the week and weekend as precipitable water values
occasionally soar to 2.00" or higher, mainly Thursday and then
again this weekend. Where storms train and persist, localized
flooding is a possibility especially toward the end of the week.

&&

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

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...Hoving
MARINE...JK