Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220143 AAA
AFDGRR

Area Forecast Discussion...UPDATED
National Weather Service Grand Rapids MI
843 PM EST Tue Feb 21 2017

LATEST UPDATE...
Update/Marine

.SYNOPSIS...
Issued at 325 PM EST Tue Feb 21 2017

Low clouds and fog look to develop tonight into Wednesday morning.
The sun should make an appearance Wednesday afternoon with
southwest winds increasing and temperatures warming into the 60s
away from the lake. A 70 degree reading near I-94 is not out of
the question if the low clouds and fog lift earlier than expected.
An approaching storm system will spread rain into the region
starting Thursday evening. Areas of heavier rainfall are
possible. A round of thunderstorms may move through Friday
afternoon and evening...some of which could be severe with
damaging winds. Cold air filters in on Saturday bringing a period
of light snow to the area, and while the accumulations will be
light there could be some slick spots possible on roads.

&&

.UPDATE...
Issued at 844 PM EST Tue Feb 21 2017

I issued a dense fog advisory for all of the CWA north of I-94
till mid morning Wednesday. Locations like South Haven and
Muskegon already have the fog and inland locations in the advisory
area area mostly below 3 miles and many locations are less than a
mile. All of the hi-res models are forecasting dense fog north of
I-94 by midnight and show it lasting into the mid morning hours.
Also most of the models suggest the southern edge will lift north
with the "WARM FRONT" overnight. For now I will not get cute with
that in the grids. If the southern edge of the dense fog does
lift north with time overnight we can cancel the advisory for
those counties early. One other issue is winds are a touch high
for dense fog but since we now have 4 locations at or below 1/4
miles it seems better to go ahead than wait for it to get
widespread.


&&

.SHORT TERM...(This evening through Thursday night)
Issued at 325 PM EST Tue Feb 21 2017

Primary concerns center on low cloud and fog potential into early
Wednesday, along with prospects for record warmth Wednesday
afternoon. Models are in pretty good alignment bringing abundant
975mb-925mb RH into the region overnight, and with light surface
winds in place this should set the stage for possibly extensive
stratus to form and also areas of fog as well. The GFS LAMP
guidance and to a lesser extent the NAM MOS are showing the
possibility of many locations being socked in by stratus and fog.
This seems plausible through at least 14z or 15z, when it may
eventually lose out the battle to diurnal mixing as SW winds
increase.

Tough call on whether our record-threatening warmth will
materialize Wednesday given it largely hinges on how fast we
clear out after a grey morning. If skies thin out by 15z or 16z,
we have a shot at getting well into the 60s and possibly near 70
closer to I-94. If the stratus is more stubborn than our chances
will be significantly hindered.

Low risk for a shower Wednesday night into Thursday morning as a
weak cold front slips through the region. The precipitation is
largely shown to be confined to northern Lower Michigan based on
the latest GFS/ECMWF. The GEM is further south and stronger with
this surface boundary and has more precip, but it is an outlier.

.LONG TERM...(Friday through Tuesday)
Issued at 325 PM EST Tue Feb 21 2017

The main issue in the long term deals with the potential impacts
from the storm for the end of the week.

Overall the models have trended a little warmer with this system.
Based on this the risk for freezing rain is lower for the onset of
the precipitation across my northern zones Thursday Night.  Thus I
have removed the mention of freezing rain from the forecast.  The
arrival of a low level jet Thursday Night will draw up abundant Gulf
moisture which will lead to some elevated instability. Will keep the
high POPs going with an area of rain and embedded thunderstorms
arriving from the south.

The region is still on track for possible severe weather on Friday.
There are certainly some ingredients showing up.  A powerful mid
level jet up around 100 knots tracks in from the southwest Friday
afternoon and evening.  At the same time instability is shown in the
models in the afternoon...when the low level jet restrengthens. With
a cold front forecasted to track through later in the day...it looks
possible for a narrow line of convection to form along or ahead of
this front. Based on the forecasted wind fields...any stronger
convection could lead to an increased risk for damaging winds.

The region becomes dry slotted for Friday night...so a lull looks
likely in the precipitation.  Wrap around moisture pivots through
the CWA on Saturday. This is when the colder airmass will be in
place.  So it looks like mainly snow showers on Saturday...but
eastern zones could see a r/s mix.

Another storm system may arrive on Tuesday.  This one has a similar
look to it...but somewhat colder.  The track could vary considerably
in the coming days. With a tap to the Gulf...heavy precipitation may
occur. For now will feature a wintry mix at the onset which then
transitions to rain.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 659 PM EST Tue Feb 21 2017

The cold front brought enough dry air to clear the low clouds from
the GRR,MKG and AZO, but the other taf sites have MVFR conditions
remaining. Since there is another quick moving shortwave (seen
over WI in IR and water vapor loops) this will bring winds quickly
back to the south and that will bring the moisture back in. All of
our high resolution models show dense fog developing near South
Haven (it already has) then quickly spreading north and east so
most of our area would have dense fog by 06z. As the "warm front"
lifts north early Wednesday morning the area of dense fog also
lifts with it so by 12z it is north of I-96. I have seen this
happen more than once. So my TAFs show this sort of trend, that is
fog by around midnight then that lifting to a stratus deck by
morning only to have it all clear by midday.


&&

.MARINE...
Issued at 844 PM EST Tue Feb 21 2017

Dense fog has already developed over southern Lake Michigan and
will spread quickly north over the rest of the near shore by
midnight or so. As a result I have issued a Marine Dense Fog
Advisory till 18z and will for now call that good. It should last
into the early afternoon Wednesday so I will keep it till then.

&&

.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.

&&

.CLIMATE...
Issued at 325 PM EST Tue Feb 21 2017

The records for our official sites on Wednesday are as follows:

Wed 2/22

Grand Rapids 67 - 1930

Lansing66 - 1930

Muskegon 55 - 1930

These records still could be broken depending on how quickly skies
clear out on Wednesday. Only a handful of sites in Lower Michigan
have ever reached 70 degrees in February. Grand Rapids, Lansing,
and Muskegon have not yet achieved this.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 9 AM EST Wednesday for MIZ037>040-
     043>046-050>052-056>059-064>066.

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

&&

$$

UPDATE...WDM
SYNOPSIS...Hoving
SHORT TERM...Hoving
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...CAS
CLIMATE...Hoving
MARINE...WDM



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