Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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614
FXUS63 KGRR 102031
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EST Sat Dec 10 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 PM EST Sat Dec 10 2016

A cold and snowy weather pattern will continue through the
upcoming week. Lake effect snow showers will continue in progress
late this afternoon and evening and a low pressure system moving
northeast into the Great Lakes region will bring 5 to 9 inches of
snow Sunday. An arctic airmass will move in beginning Tuesday and
high temperatures by midweek will only reach the teens.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EST Sat Dec 10 2016

Primary short term fcst concerns involve determining how much snow
the low pressure system will bring Sunday.

Westerly flow lake effect snow showers will continue late this
afternoon and evening with deep low level moisture still in place
through the dgz and with h8 temps still down around -15 C yielding
high delta t/s.

The heavier les bands will continue to develop near to south of a
line from Muskegon to Rockford and Grand Rapids. An additional inch
or two of snow accumulation is possible late this afternoon and
evening where the les bands are most persistent.

The lake effect will morph into a hybrid lake effect/synoptic
event late this evening as flow becomes southwesterly and
isentropic upglide develops well out ahead of the Plains states
low pressure system.

Short range guidance has been persistent in showing potential for
significant synoptic snow with this system from late tonight through
Sunday evening. However some important trends have been noted in the
past 24-48 hrs. Overall thermal profiles tomorrow now look a little
milder which suggests it will be a heavier wetter snow but with a
bit less in terms of storm total snowfall given lower snow/liquid
ratios. It is also noted that overall guidance trends with snowfall
totals have been a little lower.

So we expect 5 to 9 inches of snow from late tonight through Sunday
evening. We cannot rule out a couple of locally higher amounts
approaching 10 inches but that would be the exception rather than
the rule.

Our current winter wx advisory headline that goes into effect at
10 pm this evening through early Monday morning looks excellent
and will remain unchanged given guidance trends the past 24-48
hours and that this will be a long duration event. Thx for coord
on headline decisions surrounding offices. Road treatments Sunday
should be effective given rising sfc temperatures into the upper
20`s to perhaps lower 30`s through the day. Nevertheless hazardous
travel conditions are still likely to develop given the amount of
snow expected and antecedent cold temps/road conditions prior to the
event.

We expect dry wx to return Monday as the synoptic system will be
long gone by then and h8 temps by Monday will have moderated
sufficiently enough to take lake effect potential out of the
equation. Tranquil wx will then continue through Monday evening
before the arctic cold front brings a potential burst of snow
early Tuesday morning with the coldest air of the season thus far
to follow.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EST Sat Dec 10 2016

The two big stories in the extended will be bitter arctic cold
Wednesday through Friday and another snowstorm next weekend.

Arctic front pushes through early Tuesday with potential for a quick
burst of snow along the front. Then lake effect snow showers will
begin and last into Thursday. The extreme cold will actually be a
limiting factor for snow amounts as the DGZ is near the surface.

High temperatures will only be in the teens Wednesday through Friday
with wind chills near or below zero each day. West flow and clouds
should moderate temperatures near Lake Michigan but inland areas
could plunge well below zero if skies are able to clear at night.
The best chance of this happening would be Thursday night under sfc
ridging and subsidence.

A significant storm is taking shape over the Plains by Friday and
the low track looks similar to the storm we are facing tomorrow with
strong isentropic ascent in an overrunning pattern. Several inches
of snow are possible Saturday. Some warmer ensemble members show a
mix but we have kept the blended forecast which is all snow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 102 PM EST Sat Dec 10 2016

Lake effect snow will bring variable conditions this afternoon
with IFR and some LIFR, mostly near GRR and AZO. A steady snow
will move in this evening with all of southern Lower Michigan
seeing steady snow by midnight and continuing into Sunday
afternoon with widespread IFR. Winds will go from west today
around 10 knots to southeast overnight and on Sunday.


&&

.MARINE...
Issued at 330 PM EST Sat Dec 10 2016

A small craft advisory remains in effect through early Monday
morning for wave heights that will average at least 3 to 5 feet
through then.

&&

.HYDROLOGY...
Issued at 129 PM EST Sat Dec 10 2016

The latest water temps on area rivers include the following
samples: 33 on the Muskegon River at Big Rapids, 34 on the
Kalamazoo River, and 35 on the Grand River at Eastmanville. Expect
rapid ice formation on these rivers starting the middle of this
upcoming week as air temps retreat into the teens and single
digits. Frazil ice development can occur quickly with these temps
combined with higher than normal flows. Snow also contributes to
ice development. In terms of ice jam potential, there is some risk
after ice develops given flows running on the higher side of
normal mainly for the Grand River basin. However, it is too early
to tell how much of a risk there is since the Grand River is
currently ice free. Residents in jam-prone areas should monitor
ice development over the course of the next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 10 PM this evening to 4 AM EST
     Monday for MIZ037>040-043>046-050>052-056>059-064>067-
     071>074.

LM...Small Craft Advisory until 7 AM EST Monday for LMZ844>849.

&&

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Ostuno
AVIATION...Ostuno
HYDROLOGY...Hoving
MARINE...Laurens



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