Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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530
FXUS63 KGRR 221735
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1235 PM EST Wed Feb 22 2017

LATEST UPDATE...
Marine

.SYNOPSIS...
Issued at 100 AM EST Wed Feb 22 2017

Fog will prevail early this morning but will lift by midday. It
will be unseasonably warm today, with highs well into the 60s.
Some record highs are possible this afternoon if we get enough
sunshine. A cold front will come through the area tonight but will
only serve to dry the air out and cool Thursday highs temperatures
by about 10 degrees but that is still well above normal.

A Storm from Colorado will bring showers and the threat of
thunderstorms to the area Thursday night and Friday. Some of the
storms Friday afternoon could be strong. It will also be windy.
The cold front trailing the storm will bring the chance for a
little snow Saturday but accumulations will be light at best. Yet
another storm heads our way for Tuesday of the following week,
that would be mixed precipitation changing to rain. Strong storms
are possible with this system too.

&&

.UPDATE...
Issued at 1114 AM EST Wed Feb 22 2017

Added low POPs across the Highway 10 region for later this
afternoon. A few showers have been crossing Central WI within
deeper moisture and this progresses into Central Lower by late
afternoon.

Some fog remains across Central Lower late this morning. But we
continue to see winds increasing through the afternoon,so expect
the fog will gradually lift.

Temps will be tricky today depending on the extent of clearing
this afternoon. Breaks are seen around LAN and also toward the SW
corner of the state. Feel these two areas of clearing expands this
afternoon as the stratus erodes with the mixing and higher sun
angle. So expecting most areas along and south I-96 will become
mostly sunny into the afternoon, and will maintain the low and mid
60s there. Areas north of I-96 should remain cloudier and this
should keep max temps mainly in the 55 to 60 degree range.

UPDATE Issued at 639 AM EST Wed Feb 22 2017

We issued an update a little while ago to cancel the srn half of
the Dense Fog Advisory. Winds aloft are picking up across the
south, which is helping to mix the lowest portion of the
atmosphere enough to reduce the fog that was dense earlier. It
remains dense across the north, and we expect that will dissipate
by mid-morning.

&&

.SHORT TERM...(Today through Friday)
Issued at 254 AM EST Wed Feb 22 2017

There are three issues to deal with this forecast. The first is
the fog, how long does it last this morning? Next is just how warm
does it get today, and finally just how much of severe weather
threat is there for Friday?

As for the fog issue, at 2 am the fog covers all but the I-94 part
of CWA east of Kalamazoo. We have a warm front advection type fog
early this morning as dew points south of Michigan are higher
than the surface air temperatures. So, as that next system tracks
over the northern Great Lakes this evening we have the southerly
surge ahead of the storm which of course brings the higher dew
point air north over the cooler air over Michigan and hence we get
fog. The good news is the air above the fog layer is rather dry
so with some mixing today we should be able to mix out the fog.
Helping the cause for this is that storm passing north of us this
evening. That will bring an increasing southerly wind field with
it that will help increase the mixing. So I do believe the fog
should lift by mid to late morning. I will leave the fog advisory
as it is.

The other issue with this is just how warm will it get today. The
1000/925 mb thickness forecast is the warmest of the week. So that
would suggest mid to upper 60s for highs, that would break or tie
most of the daily record highs for today if it happens. With the
fog this morning, that may hurt the cause. So due to that I was a
little conservative on the highs to today.

Tonight we have that system passing north of our area. It would
not be out of the question to get a shower from it, but if that
does happen it would more likely be over our northern areas,
closer to the mid level jet. It should be noted we do have a 40 to
50 knot low level jet tonight, but we do not have much mid level
moisture being so far south of the surface low track. So I have
the highest pop near and north of Route 10 but even there it is
only low chance type pops.

Thursday should be quite day weather wise as the southern edge of
very large Canadian high builds into our area. That will cool our
highs down about 10 degrees tomorrow from today but that will
still be around 20 degrees above normal even so.

Our system for Friday is the energy from one of those strong East
Asia Jet features that has helped the past week or so be so warm
in this area. So, when this systems comes out of the Rockies it
will be rather potent with a lot of dynamical energy. We end up
getting one of those coupled jet features as the departing
northern stream Canadian Jet heads off into Ontario while the
southern stream jet core heads toward Chicago. This results in an
upper trough that goes slightly negative tilt. It also results in
a 50 to 60 knot low level jet and that brings precipitable water
values to near an inch which is close to all time record values
for February. When you add in the 50 to 70 knots of deep layer
shear one has a case for strong storms. The biggest negative is
the capes are not that high, around 500 j/kg for the most unstable
cape. Also the cape is very thin, so that is not great for severe
storms. It would seem to me wind would be the biggest threat with
these storms. Of course with all that Gulf moisture locally heavy
rain is possible but the system moves through quickly so I do not
see that as a serous heavy rain, or river flooding type event.

.LONG TERM...(Friday night through Tuesday)
Issued at 254 AM EST Wed Feb 22 2017

The threat of severe weather will remain for a few hours into Friday
evening, before it ends as the cold front presses through the area.
We are expecting that most of the area will see the dry slot move
overhead then late Fri evening and overnight Fri night.

The wrap around pcpn will then rotate through the area from west to
east late Fri night and Saturday morning. This will transition over
to snow fairly quickly once it starts. This snow does not look to
accumulate much as it will progress through the area fairly quickly,
and ground temps will be fairly warm from the recent warm spell.
Some light lake effect will follow on Sat night as H850 temps drop
to around -15C. Ridging will move in fairly quickly Sun morning
diminishing the lake effect.

We will see a couple of weaker waves move through Sun afternoon
through Mon morning that would bring some light snow to the area.
One will move overhead, while a stronger wave will move by to our
south, and clip the southern counties.

We then will be watching another intense system take shape to our SW
early next week. Another strong upper trough will dive in across the
Wrn U.S. and amplify as it moves east of the Rockies. This will
develop a strong sfc low SW of the area that will tap an abundance
of warmth and moisture from the Gulf. This pcpn looks to move in on
Tue. We can not rule out a brief mix of pcpn if it comes in early
enough. All pcpn should then change to liquid quickly with a srly
flow pushing the cooler air mass out easily. Thunder looks possible
with the strength of the system and the very warm and moist air
mass.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 650 AM EST Wed Feb 22 2017

A difficult forecast to say the least, with low cloud trends quite
uncertain this morning. The VLIFR has shifted mostly north of the
terminals, although KMKG has seen it come back in this morning. We
expect these very low conditions will shift north through the day
as winds aloft increase. We have trended the fcsts toward a
thought that moisture will lift toward afternoon and mix out. Much
of the data is indicating lots of low level moisture getting
trapped near the sfc and remaining through the day. We believe
that the winds and shallow moisture will mix drier air down for a
decent amount of sunshine this afternoon.

We expect that some of the light fog/haze will redevelop tonight
as winds diminish some inland. We have started it around 06z
tonight, and lowered cigs and vsbys further around 10z or so.

&&

.MARINE...
Issued at 1234 PM EST Wed Feb 22 2017

Will extend the dense fog advisory over the lake until 5 PM. This
is when winds will be increasing and eroding the fog.

&&

.HYDROLOGY...
Issued at 1201 PM EST Wed Feb 22 2017

Snowmelt in the headwaters of the Muskegon River basin has caused
the river to rise to above normal for late February. The Grand and
Kalamazoo rivers are running near normal. Showers and storms on
Friday may put down swaths of rainfall in excess of a half or
perhaps 1 inch. Some rivers would be susceptible to rising above
bankfull if that amount of rain falls in their respective basins.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Dense Fog Advisory until 5 PM EST this afternoon for LMZ845>849.

&&

$$

UPDATE...JK
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...NJJ
HYDROLOGY...CAS
MARINE...JK



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