National Weather Service Raw Text Product

Displaying AFOS PIL: AFDGRR Received: 2017-12-07 05:01 UTC


888 
FXUS63 KGRR 070501
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1201 AM EST Thu Dec 7 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 329 PM EST Wed Dec 6 2017

A period of lake effect snow will continue through tonight and 
Thursday. Areas along and west of U.S. 131 will see 2 to 4 inches 
with locally higher amounts.  Meanwhile areas east of U.S. 131 will 
see two inches or less.  We will see a brief lull in the snow 
Thursday night.  Then more lake effect snow kicks back up on Friday, 
mainly from Holland north and west of U.S. 131.  All areas will see 
snow by late Friday night as a clipper system moves in.  Once again 
the heaviest snows can be expected from U.S. 131 westward, while a 
more widespread snow can be expected to the east too.  The snow will 
wind down on Saturday, then more solid snow chances return Monday 
night through Tuesday night.

Temperatures will remain chilly with daytime highs mainly in the 
upper 20s to mid 30s.  Lows will mainly be in the 20s into the 
middle of next week.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 329 PM EST Wed Dec 6 2017

A WNW flow lake effect will impact the CWA tonight and Thursday. 
Then more lake effect, with a WSW flow, is expected Friday into 
Friday night.  This will occur ahead of a strong clipper system that 
will increase the snow across all of the CWA late Friday night.

Will not change any of the winter headlines at this time.  We will 
need watch how the bands set up over the SW CWA as it is possible we 
will need to add Barry and Calhoun Counties to the advisory.  With a 
285-310 flow through the event the more intense bands crossing the 
widest part of the lake could also spill into these two counties.

Inversion heights continue to lift tonight and the lake effect will 
continue to increase.  The peak snowfall intensity will probably be 
occurring during the morning rush on Thursday.  The first 
significant snow during a rush hour certainly raises concerns. After 
a morning peak in the moisture, it begins to lessen through 
Thursday, likely resulting in diminishing snows through the 
afternoon.  All in all, expect 2 to 4 inches across much of the 
lakeshore counties and localized more.  A bulge inland is expected 
across Lake and Kalamazoo Counties, and as mentioned above, perhaps 
Barry and Calhoun Counties.  Away from these counties accums are 
expected to be 2 inches or less.  Breezy winds will cause some 
drifting snow.

The short wave crosses the region mid day Thursday which will lead 
to a lull in the snow Thu night.  But then the moisture depth 
increases again on Friday when inversion heights of 6-7k feet move 
in.  The flow in this time frame is more WSW ahead of an approaching 
clipper.  1 to 2 inches seems the likely snow accums range, with 
locally higher amounts.  This mainly falls north of Holland and west 
of U.S. 131.  Once again it will be breezy, so some drifting is 
expected.

The clipper system continues to look impressive and will likely need 
winter headlines.  It moves in late Friday night.  Lake enhanced 
snow will continue and could become quite heavy.  Given a synoptic 
system, inland areas will also see a more widespread snow too.  At 
this point an additional 2 to 5 inch snowfall appears likely, 
heaviest toward the lakeshore.  However these types of systems will 
over perform at times.  Winds lighten up overnight so drifting is 
not expected.

.LONG TERM...(Saturday through Wednesday)
Issued at 329 PM EST Wed Dec 6 2017

Bouts of lake effect snow are expected through the long term period 
as the deep upper trough remains across the eastern half of the 
country. Lake effect will be boosted on Saturday via a low pressure 
system diving southeast through the Great Lakes region. Most areas 
on Saturday will see an inch or two of snow via the low. Lakeshore 
counties will see even more given a lake enhanced snow regime. 
Southwest flow will turn northwest through the course of Saturday 
making accumulations likely in all areas towards the lake. Lake 
effect snow events that are enhanced via synoptic systems can be 
some of the more impactful snow we see, so traveling on Saturday 
will need to be monitored. 

A lull in the snow activity will occur on Sunday as ridging moves 
through the area. A nose of warm air on Sunday and Sunday night may 
actually take lake effect snow out of the equation for a time as 
delta t's dwindle near or below critical values.

A cold front will drop through the area on Monday ushering in cold 
air and another round of northwest flow lake effect. The lake effect 
will last into Tuesday and Wednesday. 

After a delayed start to this wintry pattern at least in the 
Southern Great Lakes, we should see most areas covered in snow by 
early next week. Temperatures much of the long term will be below 
normal, the exception being Sunday into Monday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1157 PM EST Wed Dec 6 2017

A cold front moving through the state will create in increase in
snow showers as colder air moves south over the lake. That in turn
will result in some MVFR conditions through mid afternoon. Snow
showers will diminsh by late in the day and VFR conditions will
return. 

&&

.MARINE...
Issued at 329 PM EST Wed Dec 6 2017

Small craft advisory will be in affect at least through Friday given 
the brisk westerly winds.


&&

.HYDROLOGY...
Issued at 329 PM EST Wed Dec 6 2017

Several rounds of snow are expected over the next week due to a 
combination of lake effect processes and passing low pressure 
systems. The first round of more widespread snow will occur late 
today through Thursday afternoon, bringing several inches of snow to 
counties near the lakeshore. Total liquid equivalent (melted snow) 
through Thursday evening will be below one-quarter of an inch for 
most locations, but locations in Allegan, Van Buren, and Kalamazoo 
counties could see locally higher totals up to one-half inch. No 
issues with flooding or rivers are expected. Another round of more 
widespread snow is expected to start mid-day Friday and last through 
Saturday afternoon. This looks to bring another tenth to one-quarter 
of an inch of liquid equivalent, and again not cause any issues 
aside from accumulating snowfall.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 4 PM EST Thursday for MIZ037-038-
     043-050-056-064-071-072.

LM...Small Craft Advisory until 7 PM EST Friday for LMZ844>849.

&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Duke
AVIATION...04
HYDROLOGY...HLO
MARINE...JK