Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 252348
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
748 PM EDT Sat Mar 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 307 PM EDT Sat Mar 25 2017

A slow moving system will gradually move toward the area through
Sunday, before it finally begins to exit Sunday night. This system
will bring multiple waves of rain showers with some embedded thunder
through Sunday afternoon. The rain chances will then diminish Sunday
night as the system pulls away.

Another system will likely clip the southeast portion of the area
late Monday and Monday night as a low slips by to our south and
southeast. Drier weather with seasonable temperatures can then be
expected much of the week.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 307 PM EDT Sat Mar 25 2017

Our main challenges in the short term have to do with rain trends
into Sunday night, and convection chances during that same time
frame. The general thought through Sunday afternoon is that we are
expecting multiple waves of rain showers with some embedded thunder
at times. The best chance for thunder will come on Sunday afternoon,
with some thunder possible tonight.

We are seeing the band of rain showers that was parked over the srn
section of the CWFA last night and this morning shift north through
the area this afternoon. This is the result of a sfc low across IL
that is rotating north around the main low over Missouri this
afternoon. The srly flow aloft ahead of it is shifting the fgen band
north, and likely out of the area over the next few hours.

There may be a brief break in the more widespread shower activity
late this afternoon and early this evening. This break will come to
an end as we will see another moisture transport max aloft move in
with a llj ahead of the MO low. This will bring more showers across
the area by late evening and overnight. Thunder will be possible
with this moisture surge as elevated LI/s drop a tad below zero
overnight.

Not sure if there will be a break between the elevated showers/
storms tonight, and additional showers for the first half of Sun.
These will be supported by the sfc front associated with MO sfc low.
It looks like the front will move through, and we will see some of
the warmer air move in across the SSE. This will result in some
instability with the cold pool aloft coming in. Fcst soundings show
thin CAPE profiles and relatively weak shear profiles. We could see
some wind gusts of 30-40 mph and small hail, but we are not
expecting anything that will cause any big issues.

The low will pull away on Sun night and be gone come Mon morning.
There could be a couple of lingering showers early Mon but, most of
the day should end up dry. We will see a wave move up toward the SE
portion of the state mainly Mon night that will ride up a lingering
sfc boundary that will extend to the SW. This will bring some rain
to the SE portion of the CWFA.

.LONG TERM...(Tuesday through Saturday)
Issued at 307 PM EDT Sat Mar 25 2017

Temperature will be near normal for most of this period.  It will
also be dry with little threat of rain or snow until Thursday or
more likely Friday.

We continue to see an extended East Asian Jet through this coming
week. That helps to keep the northern and southern stream flow split
across North America. That keeps the arctic air well north and the
really warm air south of Michigan. The northern stream jet is near
70N while the southern stream is more so in the 30N to 40N area as
it crosses the CONUS. The next system to impact Michigan late next
week is currently near 45N and 145W (south of the Gulf of Alaska and
just off shore of the CONUS west coast).

What causes the long break in the rain here (dry Tuesday through
most of Thursday) is the Canadian system that is currently over
Hudson Bay. It "bombs" out just south of Greenland Monday and that
builds a large upper high north of it. That in turn blocks the flow
over eastern Canada and the north Atlantic. Which then allows the
next upstream northern branch wave to dig a touch more southward.
That allows a Canadian arctic surface high, currently over
northwestern Canada, to build just far enough south so as to bring
us the southern edge of that arctic high pressure system later
Tuesday into Thursday. If that upper wave (from Canada) digs a touch
more south, we could get unseasonably cold mid week.

While all of that is happening the Pacific shortwave, currently just
off the west coast comes inland and closes off (on all the models)
at upper levels over the southwestern CONUS in the Mon/Tue time
frame. However, there are numerous Pacific systems heading east to
help boot that system east and shear it out of the southwest CONUS.
The question becomes how far north does it get when it gets this far
east? The ECMWF tries to merger the northern and southern stream
waves resulting in a much farther north track through the Great
Lakes. The GFS just shears the system out to our south. It should be
noted however that the ensembles of the GFS are farther north with
this system.  That suggesting the ECMWF track is more likely. In
either case we stay in the cool air but that cool air is not cold
enough for snow, just a chilly rain. If the ECMWF is correct next
weekend would cool and wet. Which for the most part is similar to
this current weekend. If the GFS were to be correct it will be cool
and partly cloudy.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 748 PM EDT Sat Mar 25 2017

The region was mostly IFR, but some MVFR was trying to develop as
the area gets back under the warm sector and mixing increases.
Wrote the TAFs in that manner, that the IFR lingers this evening
with some areas briefly improving to MVFR. Feel we will eventually
go back to mostly IFR late tonight or early Sunday morning. This
will most likely continue much of Sunday.

As far as the risk of some thunderstorms, the best chance will
occur over the I-94 TAF sites, with lesser chances north toward
I-96. Much of the instability arrives after midnight local time,
and gradually departs through the mid to late morning hours of
Sunday. Another round of storms will be possible again toward the
southwest corner of MI into Sunday evening.

&&

.MARINE...
Issued at 307 PM EDT Sat Mar 25 2017

Brisk East winds will continue through tonight, and could even last
into the early part of the day on Sunday. This will continue to
justify the Small Craft Advisory that is in effect.

It appears that we may not need marine headlines for a bit after the
current headline event ends. Winds look to remain at or below 20
knots through much of the upcoming week.


&&

.HYDROLOGY...
Issued at 307 PM EDT Sat Mar 25 2017

Locally over one inch of rain has fallen particularly over the
eastern reaches of the Grand River, as well as the Thornapple River,
Maple River, Looking Glass River, and Sycamore Creek. Additional
rainfall through Sunday will continue to aid in boosting river
levels for these areas. Above bankfull rises are anticipated over
the next few days for Ionia, Hastings, Maple Rapids, Eagle, and
Holt. Another round of rain toward the end of the week may ensure
that these rivers remain near or above bankfull. We will continue to
monitor the trends.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 11 AM EDT Sunday for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...WDM
AVIATION...JK
HYDROLOGY...Hoving
MARINE...NJJ


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