Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 052344
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
644 PM EST Mon Dec 5 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 254 PM EST Mon Dec 5 2016

Quiet and seasonable weather is expected for the area through
Tuesday. There will be a small chance of some light rain or snow on
Tuesday, but this is not expected to create any impacts to the
area.

We will start to see colder air filter into the area Tuesday night
and Wednesday. Some light lake effect will become likely at that
time across the western portion of the area. Lake effect will become
stronger Thursday and Friday as the coldest of the air moves in
over the relatively warm Lake Michigan.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 254 PM EST Mon Dec 5 2016

Our biggest concern in the short term is with lake effect potential
late in the period. We will see a chance of light rain or snow on
Tuesday. This is not expected to be widespread, or create any
problems.

Fairly quiet weather can be expected for the first couple of periods
of the fcst with just a small chc of pcpn expected for most
locations. Some sunshine is out across Central Lower this afternoon,
with more low clouds spreading to the NNE from IL and IN. This
moisture is very shallow and does not have much forcing with it
with the sfc ridge overhead.

Most of the CWFA will be in between systems for Tue. There is a srn
stream system that will travel from the Gulf to the Mid-Atlantic
states, and another nrn stream system coming from the Central
Plains to the Upper Midwest. Most of the pcpn with each of these
systems should miss most of the area, except for clipping the NW and
SE corners. We have a slight chc everywhere as we can not rule out
pcpn anywhere with some phasing trying to take shape. P-type may
start off as a brief mix before it would change to rain.

Any lingering pcpn Tue evening will change over to snow quickly.
This occurs as colder air starts to move in the wake of the nrn
stream system. H850 temps will drop to around -10 to -12c Tue night,
which will be plenty sufficient for Lake Effect with lake temps
around 8-9C. Moisture depth is quite limited initially expected to
stay below 5k ft and only clipping the DGZ.

Lake effect will start to become a bit more robust late in the short
term on Wed night. This occurs as we become more established under
the cyclonic flow aloft and colder low level temps coming in. This
should just start ramping up as enter into the long term on Thu.

.LONG TERM...(Thursday through Monday)
Issued at 254 PM EST Mon Dec 5 2016

Forecast issues in the extended are mostly focused on coverage of
lake effect snow Thursday through Saturday. Expect several inches of
snow across the western zones in generally west to northwest flow
regime during that time frame.

Lake effect snow showers will be underway on Thursday with an arctic
front moving through and inversion heights above the DGZ. The
northwest flow regime looks favorable for an I-94 band to form and
drop several inches of snow across our southern zones as it persists
into Friday. It is still early to quantify, but snow totals could be
over a foot in some places in Allegan and Van Buren Counties by the
time the snow winds down early Saturday.

On Saturday, the lake effect snow showers will be decreasing but we
will have to watch a shortwave trough moving across the northern
Plains. This will have the potential for a sfc cyclone and some
synoptic snows by Saturday night into Sunday in warm air advection
pattern. 12Z operational ECWMF seems to be a warm outlier at this
point and would mean liquid p-type Sunday, with 12Z GFS and most
ensemble members colder and mostly snow. Will have a mix across the
south and snow elsewhere.

Arctic air returns on the back side of the storm for Monday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 642 PM EST Mon Dec 5 2016

A northward moving warm front will keep cigs aob 2k ft this
evening. Cigs should go vfr once the front moves north after 06z.
Tuesday, low pressure moving north from the Gulf will increase low
level moisture over southwest Lower MI and we could see some mvfr
fog at a few locations.

&&

.MARINE...
Issued at 358 PM EST Mon Dec 5 2016

We will be holding off on the Small Craft Advisory for tonight
north of Whitehall after all. Latest data indicates waves will
stay 2 to 4 feet or less with a SSE flow.

The next period of likely headlines looks like from late Tue through
most of the rest of the week. This will be as the colder air blasts
in across the area.


&&

.HYDROLOGY...
Issued at 1237 PM EST Mon Dec 5 2016

Liquid equivalent of last night`s snowfall generally ranges from
0.25" over south-central Michigan to 0.50" over southwest Michigan,
where the highest snowfall totals were reported.

The Maple River at Maple Rapids was previously being watched for
rising river levels, but never seemed to follow expected trends, nor
did the site every achieve bankfull. It continued to fall through
this morning and quarter inch amounts are not expected to bring it
anywhere near bankfull. As a result, the advisory has been dropped.
The current downward trend may stall and return to a slight rise
through mid-week. Rises are expected to remain within banks.

River levels through the area are running near and above normal.
Given the current status, moist soils and active pattern through the
next several days, river activity may need to be monitored.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Ostuno
AVIATION...04
HYDROLOGY...JAM
MARINE...NJJ



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