Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 161245
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
745 AM EST Thu Nov 16 2017

LATEST UPDATE...
Marine

.SYNOPSIS...
Issued at 322 AM EST Thu Nov 16 2017

The system that resulted in all the rain on Wednesday is now
pulling away from the area and surface high pressure will cross
Michigan tonight. This will end the showers of rain and snow early
this morning and during the afternoon skies should start clearing.
Tonight should be mostly clear and cold with lows in the 20s. The
next storm system will track through the Great Lakes Friday night
into Saturday. The surface low will likely track between I-94 and
I-80 during the mid morning hours of Saturday. This storm will
bring a surge of very warm air north with it and that will mean
heavy rain Friday night with thunderstorms (not severe) possible.
Once the system moves east of the area it will deepen rapidly and
that will bring in much colder air, gusty winds and rain showers
changing to snow showers Saturday night. Snow showers should come
to an end Sunday as yet another surface high moves into the area
by Monday.

&&

.SHORT TERM...(Today through Saturday)
Issued at 322 AM EST Thu Nov 16 2017

The main issues this morning are just how quickly to end the
threat of showers (rain and snow) this morning and how quickly to
bring in the clearing this afternoon. The other issue is the storm
Friday night into Saturday but there is little question now on
the timing and that we will see heavy rain and gusty winds with
this system.

First through we have occluded low pulling out of the area this
morning. It has brought down just enough cold air that there are
lingering flurries and sprinkles around These will come to an end
shortly after sunrise the trailing shortwave moves east of the
area. Also by midday the polar jet core will be moving overhead.
Typically once that polar jet is just east of the area any lake
enhanced showers end (moisture depth becomes to shallow). Once it
gets well east of the area this evening the combination of surface
high pressure and a shortwave ridge should allow skies to clear.
So all areas should have lows below freezing by Friday morning.

Next up is that storm we have been writing about for nearly 2
weeks now. As it turned out the ECMWF at the longer ranges was to
slow and the GFS was way to fast. Now however they are in much
better agreement and show the center of the storm tracking near of
just south of I-94. The ECMWF 51 member ensemble mean low
positions show much less spread than even 24 hours ago the track
of this storm. Only the NAM has it tracking across central lower
Michigan. The Canadian has it tracking along I-80.

In any event this system has good upper air dynamics with it and
strong gulf inflow thanks to the 140 to 150 knot polar jet core
driving the system. That jet core tracks across MO to southern
Ohio Saturday night. That puts southwest Michigan in the coupled
jet lift area Saturday morning (the northern stream jet core of
120 to 130 knots is just north of Lake Superior Saturday morning).
With that coupled jet we get a strong low level response so
precipitable waters reach to over an inch, with is nearly 2
standard deviations from normal and near the all time record for
mid November over Michigan. The 850 li falls to -2c, the most
unstable cape rises to near 500 j/kg south of I-96 (all of this is
between midnight and 7 am Saturday). So we have good chance of
elevated thunderstorms (non severe due to the deep stable layer
below below the frontal inversion).

This storm rapidly occludes and brings in cold air behind it. I
expect 30 to 40 mph wind gusts by late Saturday afternoon as the
cold air comes in. It will not get cold enough for snow till after
sunset. Even so expect afternoon rain showers as the cold air
starts to move back in.

So, the bottom line is quite weather (more or less) till Friday
night that, rain, possible thunderstorms and breezy. High
temperatures Saturday will be around sunrise. Then we will see
falling temperatures and windy Saturday afternoon with rain
showers.

.LONG TERM...(Saturday night through Wednesday)
Issued at 322 AM EST Thu Nov 16 2017

Windy and colder conditions will continue Saturday night in a brisk
nw flow caa pattern with a strong pressure gradient between the very
strong low pressure system north of Lake Ontario and the ridge over
the central Plains states.

Any mixed rain/snow showers Saturday evening will quickly change
over to light snow showers as colder air moves in. Light snow
showers and flurries will linger on Sunday before ending.

A weak high pressure ridge will bring fair wx Sunday night through
Monday night with seasonable temps. Tranquil wx with seasonable
temps will continue Tuesday and Wednesday.

Light pcpn associated with a low pressure system moving across the
Lake Superior region should stay north of our area with a dry cold
frontal passage expected for our area Tuesday. A slightly colder
airmass will advect in behind that front for midweek with high temps
Wednesday only expected to reach the 30`s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 644 AM EST Thu Nov 16 2017

Currently MVFR cigs prevail over most of Lower Michigan. There are
still a few flurries or sprinkles from the lake enhanced
precipitation event that will end shortly. Over time as the
surface low pulls out of the area, ceiling should slowly increase
to VFR by early afternoon. As winds turn more to the north later
this afternoon skies will start to clear. By 00z most if not all
of the low clouds will be gone. However high clouds from the next
system will already be moving in. So skies will not stay clear
long. For VFR flight operations through after 21z it should be all
clear till later Friday night when the rain moves back in.


&&

.MARINE...
Issued at 745 AM EST Thu Nov 16 2017

I have replaced the gale warning with a small craft advisory
through 6 pm. While it is true that Manistee and Big Sable Point
have recently had gusts to 36 knots all of my marine observation
sites continue to show a steady decrease in wind speeds and gusts.
It would seem to me by 8 to 9 AM all area will have wind gusts
under staying under gale force.

&&

.HYDROLOGY...
Issued at 330 PM EST Wed Nov 15 2017

So far Wednesday rainfall totals have reached a quarter to half inch
in the Kalamazoo and Grand river basins, and a half to one inch in
the Muskegon and upper Saginaw basins. Minor river level rises will
occur due to the already saturated soil, but above-bankfull rises
are unlikely (except for the Sycamore Creek at Holt). Another half
to one inch of rain is likely Friday night into Saturday, and this
may push some flood-prone rivers above bankfull.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 6 PM EST this evening for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Laurens
AVIATION...WDM
HYDROLOGY...CAS
MARINE...WDM



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