Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220753
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
253 AM EST Wed Feb 22 2017

LATEST UPDATE...
Short Term/Long Term/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.

&&

.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 06Z TAFS through 06Z Wednesday night)
Issued at 100 AM EST Wed Feb 22 2017

Dense fog did develop as expected (from the 00z tafs). Also as
expected the dense fog was along and north of I-96. The I-94 taf
sites tried to clear this evening they we see the fog by 09z or
so. We actually have a weak warm front pushing through the area
this morning and that is what is causing the fog. So, once the
warm front gets north of here the fog should mix out quickly. Most
of our taf sites inland of MKG should clear by 16z or so. MKG may
have fog linger into the afternoon but I played that taf more
optimistically. So that will have to be watched. It will be
breezy in the afternoon to with winds gusting to 25 to 30 knots at
times. Mostly clear skies should prevail Wednesday night into
Thursday.


&&

.MARINE...
Issued at 254 AM EST Wed Feb 22 2017

I will keep the marine fog advisory going this morning. Likely we
will need a small craft advisory for Friday night into Saturday
but we have time for that.

&&

.HYDROLOGY...
Issued at 110 PM EST Tue Feb 21 2017

Rainfall amounts Tuesday morning have been light, in many areas
around a tenth of an inch. Rivers will not be impacted by this.
The Muskegon River is rising as the snowpack in the upper portion
of the basin melts. Rain from showers and thunderstorms is likely
Thursday night into Friday. Rainfall amounts are uncertain, but
they could be enough to cause some rivers to rise toward bankfull.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 9 AM EST this morning for MIZ037>040-
     043>046-050>052-056>059-064>067-071.

LM...Dense Fog Advisory until 1 PM EST this afternoon for LMZ844>849.

&&

$$

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



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