Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 161755
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1255 PM EST Thu Nov 16 2017

LATEST UPDATE...
Aviation/Hydro

.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.

&&

.UPDATE...
Issued at 1158 AM EST Thu Nov 16 2017

Very light rain and snow showers will taper off through the course
of the afternoon as deep cyclonic flow pulls away and is replaced
by ridging. Holes in the overcast are already occurring over much
of the area and this trend should continue as we head into the
evening hours. Thinking we should see at least partial clearing as
we head through the evening hours, if not fairly widespread
clearing. The clearing is related to the ridging moving in as well
as warm air advection at 850mb and the flow becoming off shore.
Highs this afternoon will range from the mid 30s across Central
Lower Michigan to around 40 along I-94.

&&

.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 quiet weather (more or less) til Friday
night then 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 18Z TAFS through 18Z Friday afternoon)
Issued at 1255 PM EST Thu Nov 16 2017

The BKN-OVC MVFR cloud deck in place early this afternoon will
scatter out later in the day or this evening, leaving VFR/CLR
weather tonight. Some clouds above 12,000 ft will arrive later
tonight and on Friday.

Northwest winds of 15 to 25 knots currently will diminish to less
than 10 knots after 21Z, become light/clam tonight, then increase
out of the south-southeast on Friday to 10 to 20 knots by mid
morning. Some gusts of 25-30 knots will develop at MKG by 18Z
Friday.

&&

.MARINE...
Issued at 1158 AM EST Thu Nov 16 2017

Extended the small craft advisory through 1000pm this evening as
the waves will stay up into the evening. Additional marine
headlines are anticipated as we head into Friday and the weekend.

&&

.HYDROLOGY...
Issued at 1255 PM EST Thu Nov 16 2017

Wednesday`s rainfall totals were greatest through Central and
Northern Lower Michigan, while amount tapered off southeast toward
the Detroit area. Aside from Sycamore Creek near Holt, all sites
have experienced within bank rises or have show little impact.

Additional rises can be expected over the course of the weekend.
Primary concerns are the Sycamore Creek at Holt and the Looking
Glass River near Eagle. For this reason, Holt will remain under
an advisory, which was extended. The Looking Glass River is
forecast to rise above bankfull, pending realized precipitation
amounts. Precipitation totals could reach an inch in some places
late Saturday evening. Amounts will be greatest south of I-96.

Conditions become less active for the local area into the holiday
week, which should help mitigate flooding potential. Until then,
additional attention will be needed on area rivers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 10 PM EST this evening for LMZ844>849.

&&

$$

UPDATE...Duke
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Laurens
AVIATION...Meade
HYDROLOGY...JAM
MARINE...Duke



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