Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 180723

Area Forecast Discussion
National Weather Service Grand Rapids MI
323 AM EDT Sun Mar 18 2018

Synopsis/Short Term/Long Term/Marine

Issued at 322 AM EDT Sun Mar 18 2018

Mostly clear skies and even warmer afternoon temperatures are
expect today thanks to a Pacific origin high pressure system moves
into Lower Michigan from the west. Highs should be well up into
the 50s inland of the Lake Michigan shore. Today is likely to be
the warmest day of this entire week (through Sat the 24th).

A back door cold front will come through the area this evening
bringing the southern edge of a large polar origin high pressure
system into the area. The polar high pressure system gets blocked
by an east coast storm in the Tuesday to Wednesday time frame,
that will in turn result in those cooler than normal temperatures
and dry weather to persist most of this coming week.

There is a hint of a significant precipitation producing system
moving into Southwest Michigan toward next weekend but it is to
early to say just how that system will impact this area if in fact
it does not end up going south Michigan like several storms
already have.


.SHORT TERM...(Today through Tuesday)
Issued at 322 AM EDT Sun Mar 18 2018

Enjoy the sunny and warmer than normal afternoon temperatures
today since colder air returns tonight and will persist most of
this coming week. That cooler is thanks to a weak surface cold
front that comes through the area dry this evening. I expect
little in the way of clouds with the front coming through tonight.

The "Big Picture" features a split polar jet stream. The northern
branch is for the most part over northern and central Canada and
the southern branch is along the Gulf states. There is a large
storm system over the western CONUS and another storm just off
shore over the eastern Pacific, that are helping to keep the polar
jet split. That is expected to remain true through this coming
week (split polar jet). That means all the storm systems coming
across the CONUS from the Pacific will track south of Michigan and
all the really cold air and really warm air will also stay out of
this area.

Even so a strongly developing storm north of Japan early this
week amplifies the upper wave pattern across the north Pacific
(think Rossby waves) into North America by mid week. Even with the
amplified pattern the northern branch of the polar jet stays
north and the southern branch stays south. That helps to keep the
next system on the southern stream south of Michigan Monday and
Tuesday. By Tuesday that system becomes a significant east coast
storm. Which helps to bring some of the polar air just to our
north south into this area. However the true polar air stays north
since the polar jet remains north through the week. The result of
all this is cooler temperatures but little or no precipitation
through at least Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 322 AM EDT Sun Mar 18 2018

The region will stay quite chilly through the middle portion of the
week, with a slight warming trend late.  The next chance of pcpn
won`t occur until late Friday or Friday night and lasting into

Canadian high pressure remains in control early in the extended
period.  However there will be an upper trough over the Western
Great Lakes at the same time.  This will act to keep the cold air
mass in place.  With H8 temps in the -8C to -10C range.  We may even
see a few lake effect flurries from time to time through the middle
of the week.

Low pressure is expected to develop over the Central Plains by early
Friday and this system tracks along a baroclinic zone that should be
just to our south.  The guidance suggests the low moves across
Central or Southern Indiana on Saturday.  This keeps SW MI over the
colder portion of the system.  Rain or a rain/snow mix should start
over the southern CWA Friday afternoon, with the mix spread north
with some FGEN coming into play.  On it`s current path we should
gradually turn toward more of a snowy scenario as we wet bulb down
and the low to our south drags in colder air by late Friday night
into Saturday.

We will need to continue to monitor trends as the path of this
system will be critical to how much pcpn we get and it`s type.
Suffice it to say at this point, there is potential for accumulating
snow late Friday night into Saturday, especially along and south of
I-96 given the current solutions.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 120 AM EDT Sun Mar 18 2018

A continuation of VFR conditions is expected for the next 24
hours. A bit more wind is expected by afternoon. It will be from
the west to around 10 knots. These winds will drop off again into
the early evening.


Issued at 322 AM EDT Sun Mar 18 2018

Winds will increase Monday as the polar air is brought in from the
north and northeast on the southern edge of that large polar high.
This may increase winds into the Small Craft Advisory range by
Monday but due to the northeast surface winds the larger waves
will stay off shore. So at this point I see no need for Small
Craft Advisory.


Issued at 322 PM EDT Sat Mar 17 2018

The Portage River near Vicksburg will remain just above flood stage
through Tuesday and then remain near flood stage through the end of
next week. Otherwise, dry weather is expected through next week.




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