Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KGRR 021747
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1247 PM EST Fri Dec 2 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 329 AM EST Fri Dec 2 2016

The lake enhanced light rain showers...mixed at time with wet snow
will change to all snow showers tonight before they come to an
end by mid afternoon Saturday as an area of surface high pressure
moves across western Great Lakes. Temperatures will for the most
part stay in the 30s into Saturday evening. Another system moves
through the area on Sunday bringing a period of snow during the
afternoon. Light accumulations of snow are expected as
temperatures should not get much above freezing on Sunday.

Early next week a complex storm system moves into the area
bringing warmer air and the likely hood of a significant rain
event Tuesday. The arctic front follows this on Thursday with lake
effect snow showers and temperatures likely falling during the
day into the 20s. Lake effect snow showers will likely continue
through Friday. Highs on Friday may struggle to reach 20 degrees.

&&

.SHORT TERM...(Today through Sunday)
Issued at 329 AM EST Fri Dec 2 2016

Two events of significance to watch. The first is the lake effect
rain shower event. Will this change to snow and if so will there
be any accumulations? The next event to watch is the snow event on
Sunday. It is more and more looking like this will be the first
measurable snow event over just about all of our CWA for the
season.

I expect the lake effect showers will continue into Saturday
before the winds from the surface through 850 mb becomes more
anticyclonic. All of the models continue to show a layer of
saturated air from around 2500 feet to around 6000 ft over the
area into mid afternoon Saturday before it lifts out of the area.
With the lake near 50 degrees, and 850 mb temps colder than -5c,
this will keep shallow convection going. For today the most
significant QPF will be southwest of Grand Rapids thanks to west
winds becoming northwest by early afternoon.

As for precipitation type, that is questionable. Now we are seeing
mostly rain falling. However all models bring the wet bulb zero
below 1000 ft agl by sunrise today. Even so air temperatures
remain in the mid to upper 30s so I have to believe we will mostly
be seeing rain today. Tonight surface temperatures should fall to
near freezing and the wet bulb zero should be in the ground. That
would mean all snow. However the DGZ is out of the clouds by then.
Even the -8c isotherm is out of the clouds by sunrise Saturday.
Even so, I have seen time and time and again with this sort of
thing we get snow pellets and not freezing drizzle (cloud temps
colder than -5c). So I changed the precipitation to all snow
tonight but it will be very light so I do not expect much
accumulation.

Saturday afternoon into Saturday night shortwave ridging and
surface ridging moves through the area. While that may not clear
the sky it should end the precipitation until midday Sunday.

On Sunday the next major Pacific storm system will have pushed far
enough east to bring an upper level shortwave wave through the
area. This is a jet lift and warm advection push sort of event.
Since we remain in the cold air through the event, there is no
warm layer aloft with this event. The moisture is deep and there
is good lift in the DGZ. I have seen this type of event more than
once too, the models try bring the surface temperatures into the
mid to upper 30s Sunday afternoon. However what typically happens
when you get significant snowfall falling into air just above
freezing the air temperature falls to the wet bulb temperature
which in this case is below freezing. So this will be an all snow
event and air temperatures during the snow event will be near
freezing. As such I would expect 1 to 2 inches on grassy surfaces
Sunday afternoon. This may become a problem after sunset since
roads surfaces and bridges may then freeze. We will have to watch
for this.

The bottom line is light lake effect showers (rain to snow by
evening if not sooner) then just mostly cloudy by Saturday
afternoon into Sunday morning. Then expect a period of snow during
the afternoon into the early evening that could bring us 1 to 2
inches.

.LONG TERM...(Sunday night through Thursday)
Issued at 329 AM EST Fri Dec 2 2016

After some lingering snow Sunday night, then we warm for Monday and
Tuesday.  Then a significant pattern change appears in the offering
by Wednesday night and Thursday with much colder temps and some snow.

The snow, possibly mixed with rain, will diminish fairly quickly
from SW to NE Sunday evening, with event totals generally 1-2
inches.

With the upper flow remaining fairly amplified and progressive, we
quickly should see surface and upper ridging build in by Monday.  H8
temps climb to around +2C, allowing temps to reach 40 to 45 for
Monday and Tuesday.  Monday should be dry, but then, as the ridge
moves east by late Monday night into Tuesday, we will get into deep
southwest flow and better moisture.  The models all show a Western
Gulf surface low moving NE into the Great Lakes by Tuesday/Tuesday
night. It appears a bit farther south and east, but it still appears
this system will bring all rain through Tuesday.  We do begin to
bring in cooler air behind the system by Tuesday night and
Wednesday, when some light rain should mix or change to snow.

Still some model differences with the pattern change for Wednesday
night and Thursday, but the general message is there - colder and
snowier. A deepening upper long wave develops over the middle of the
nation, wrapping in the colder air.  The models differ on how a
surface low forms and it`s timing, but in general expect cyclogensis
to our SE by Wednesday night.  This system should have plenty of
Gulf moisture influence, along with brisk NW winds coming across the
Great Lakes, and H8 temps plunging to around -10C.  All this points
to accumulating snows, especially over the favored areas west of
U.S. 131.  Thursday should see falling temps into the 20s with wind
chill readings perhaps as cold as 10F above zero.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1247 PM EST Fri Dec 2 2016

Ceilings will continue around 2500 to 3500 feet AGL through the
evening then lower a bit overnight. There will be a few snow
showers on Saturday morning but they should not be heavy enough
to bring IFR conditions for any length of time. Winds will be
northwest today with some gusts this afternoon to 20 knots and
then go west on Saturday around 10 knots.

&&

.MARINE...
Issued at 329 AM EST Fri Dec 2 2016

I plan on no changes to the Small Craft Advisory we currently
have in effect till this evening (7 pm). Winds will slowly
decrease today so that should allow for waves to subside too.
Since it likely will take a few hours for the waves to come into
balance with the lighter winds, we should be fine with our
headlines.


&&

.HYDROLOGY...
Issued at 330 PM EST Thu Dec 1 2016

Periodic light lake enhanced precipitation is expected into the
weekend, which will not have much affect on river levels. Maple
Rapids continues its slow climb toward bankfull while Sycamore Creek
has fallen below bankfull. A couple chances for more substantial
precipitation are possible next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 PM EST this evening for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...Ostuno
HYDROLOGY...CAS
MARINE...WDM


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.