Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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454
FXUS63 KGRR 100809
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1257 AM EST Sat Dec 10 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 PM EST Fri Dec 9 2016

Wintry weather will continue to control the region`s weather through
the weekend and beyond.  The lake effect snows will slowly diminish
tonight into Saturday morning, however some favored areas could
still see up to another four inches of snow before it ends mid day
Saturday.  Then another storm will head our way late Saturday night
and continue into Sunday night.  Several more inches of snow appear
likely in this time frame too across all of Southern Lower Michigan.
If traveling over the weekend, keep abreast of the latest forecasts.

Periodic snows should continue into next week, but amounts should be
on the light side.  Daytime high temperatures will stay a few
degrees each side of 30 through Tuesday, then an arctic blast should
drop high temperatures to around 20 for Wednesday through Friday.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 327 PM EST Fri Dec 9 2016

Will allow the headlines to expire despite the continuation of
lighter lake effect snow.

Lake effect snows will continue, but with less intensity tonight
into Saturday.  Then a warm advection and possible FGen event ramps
up late Saturday night through Sunday night with the potential of
additional significant synoptic snow area-wide.

All indications show the lake effect will continue tonight into
Saturday.  Inversion heights slowly drop off, but the lighter snow
showers will still remain.  Hi-res models suggest a bit a
convergence area may set up between I-96 and I-94 where some areas
may pick up another 2-4 inches tonight through mid day Saturday.
This is certainly a lighter snowfall than over the past 24-36 hours.
Elsewhere the snow also continues, but accums will generally be
under an inch.

Attention then turns to the late weekend event.  At this point the
chances appear high that we will need more headlines for this event,
but we decided to hold off for now to let the current event wind
down.  It is possible we will issue headlines for this event later
tonight or by early Saturday.

The system currently offshore of Canada`s west coast will move
across the Central Rockies by Saturday night.  This will open up a
solid flow of Gulf moisture toward the Great Lakes the lingers into
Sunday.  Surface low pressure then moves from OK to MI Sunday night.

Several positives for snow exists with this system.  First off ample
moisture will be available, and along with lift within the DGZ, it
will snow.  The big question is how heavily.  Duration will be a
factor, with the deep moisture over the region throughout this
entire 36 hour period.

However the upper level pattern does not favor a rapidly
intensifying system with the lack of a deep upper trough.  The ECMWF
is leaning toward a weaker system at this point. As for solid
synoptic lift, the right entrance region of the upper jet should be
over us Sunday evening, but this looks fairly brief.  And depending
on if we see a more intense surface low, we may (or may not) see
enhancement from a low level jet Sunday afternoon.

So this system definitely has potential, but trends seem slightly
less favorable.  As stated above, will allow the current headlines
to expire prior to jumping into this next event.  Also forecaster
confidence is not high enough to issue headlines at this point
anyway. However, due to it`s long duration we can not rule out the
possibility of 6 to 10 inches with this system by Monday morning.
Again, the highest potential for steadier snows seems to come in
Sunday into Sunday evening and this leaves us some time to watch
further trends.

.LONG TERM...(Monday through Friday)
Issued at 327 PM EST Fri Dec 9 2016

Synoptic snows are tapering off Monday as sfc low pulls away and
area of mid level F-gen weakens and moves east along with trowal.
Then we watch an arctic front move through on Tuesday. QPF with this
feature has increased since yesterday and we could expect a quick
burst of snow with the fropa, especially across the northern half of
the forecast area where better moisture and low level convergence
will be.

Arctic cold then dominates the rest of the week with some lake
effect snows showers. The extreme cold will actually be a limiting
factor for snow amounts as the DGZ is near the surface Wednesday
through Friday, when high temperatures will be only in the teens. We
will have to watch for skies clearing on Thursday night as the 1040
mb sfc high builds over Michigan, which would lead to low
temperatures plunging below zero Friday morning.

A significant storm is taking shape over the Plains by the end of
the period but snow from it should hold off until after Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1257 AM EST Sat Dec 10 2016

Primarily MVFR lake-effect snow showers will continue between now
and 12z Sat, with occasional dips to IFR vsbys and AZO and BTL. A
shortwave trough will swing through and provide a boost to lake-
effect snow mainly between 12-18z. The shortwave will raise
inversion heights and increase moisture depth.

DGZ RH/Omega and 925-850 mb Omega would both support an I-96
dominant band of moderate snow showers, so have included a period
of IFR for GRR and LAN. Lighter snow showers are still expected
through early afternoon at the other TAF sites. Widespread
synoptic-scale snow moves in late Saturday night and will result
in aviation impacts mainly after 03-06z.

&&

.MARINE...
Issued at 327 PM EST Fri Dec 9 2016

Extended the small craft advisory into Saturday afternoon.  West
winds are only expected to slowly diminish.  The calmer conditons
may be brief though as we may need another small craft advisory by
Sunday with the approach of the next system.


&&

.HYDROLOGY...
Issued at 203 PM EST Fri Dec 9 2016

The primary focus will be on river ice development into next week.
At this point it appears conditions will be very conducive to
frazil ice development, and it could occur quickly after the
Arctic front passes through. You need mean daily temperatures to
be 20 degrees or colder to promote an increase in thickness of
river ice. This will occur starting mid week. So, river ice could
form once temperatures plunge and the threat is there for rapid
growth after it initially forms. Near to above normal river flows
are favorable for increased frazil ice development coupled with
Arctic air.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 3 PM EST this afternoon for
     LMZ844>849.

&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Ostuno
AVIATION...EBW
HYDROLOGY...Hoving
MARINE...JK



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