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FXUS63 KGRR 161915
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
215 PM EST Sun Dec 16 2018

LATEST UPDATE...
Synopsis/Discussion

.SYNOPSIS...
Issued at 215 PM EST Sun Dec 16 2018

No major changes were introduce to the forecast, with the highlights
as follows:

- Patchy fog may redevelop again tonight mainly east of US-131.

- A cold front will pass through Lower Michigan tonight with
minimal impacts expected.

- Tuesday will be noticeably colder and blustery thanks to gusty
northwest winds.

- Warmer temperatures are expected midweek, with a mixture of
light rain and snow possible Thursday night and into Friday.

&&

.DISCUSSION...(This evening through next Sunday)
Issued at 215 PM EST Sun Dec 16 2018

After a foggy morning, it's turning out to be a nice day out there
with mostly sunny skies and temperatures in the mid to upper 30s
being observed across portions of Lower Michigan except along the
lakeshore and portions of Gratiot and Clinton counties where
stubborn stratus (and even still patchy dense fog) continue. The
expectation is for the remaining stratus and fog to continue
eroding this afternoon giving most areas a chance of seeing the
sun before nightfall. As expected, winds have adopted a
southwesterly component which will veer westerly tonight in
advance of an approaching cold front.

Patchy dense fog may redevelop tonight mainly across eastern
portions of the area between 00Z/7PM to 05Z/12AM owing to residual
low-level moisture, though winds tonight should be stronger than
last likely limiting the intensity and areal extent of any fog
that develops. Broken clouds will make a return toward daybreak
as the aforementioned cold front sweeps across the Great lakes.
The coldest 850 mb temperatures appear that they will stay north
of our area and hence keep chance for lake effect precipitation
minimal. However, tomorrow will feel noticeably colder thanks to
blustery northwesterly winds gusting to 20 to 25 mph leading to
wind chills in the upper teens to lower twenties.

Much of the workweek looks quiet owing to a building upper-level
ridge and associated subsidence beneath. Surface temperatures will
return to above normal Tuesday through Thursday as 850 mb
temperatures warm to +4 to +6 C. Note that we'll have a great shot
of seeing the sun for several consecutive days this week, an
apparent rarity this season.

Forecast model guidance continues to advertise that a deep trough
will develop across the central United States toward the end of the
week with an associated deepening surface low pressure system off
the Gulf Coast. As has been the case with the past two synoptic
systems, it seems the most likely path of the low will be south and
east of Lower Michigan keeping the brunt of precipitation outside
of our area. However, there continues to be a signal for a brief
period of light precipitation Thursday night and into Friday
morning, which may end up being rain changing to snow based on
forecast thermal profiles (note that no snow accumulations are
currently in the forecast).

This weekend, we'll return to a more winter-like pattern as the
backside of the aforementioned trough elongates developing
northwest flow aloft (with us on the cold side), introducing
periodic chances for lake effect snow and perhaps a clipper system
or two. As always during the holidays, those planning to travel
this weekend and early next week are encouraged to stay up to date
on the forecast.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1213 AM EST Sun Dec 16 2018

Visible satellite trends (as well as looking out our window here
near KGRR) indicate that the fog is becoming increasingly thin.
The expectation is for all TAF sites to reach VFR (e.g. visibility
> 6 miles and cigs well above 3000 ft) by 20Z/3PM, with LAN being
last. The fly in the ointment is the potential for a narrow bank
of stratus currently located along the lakeshore to continue
pushing eastward across Lower Michigan this afternoon, under which
cigs of only a few hundred feet are occuring. Should the clouds
continue moving inland, they would approach GRR toward 20Z/3PM. For
now we will be optimistic and favor VFR conditions continuing
through the afternoon but trends will have to be closely
monitored.

Southwesterly winds this afternoon will veer westerly and
eventually northwesterly tonight as a cold front moves through
Lower Michigan. Winds may gust in excess of 20 kts toward the
end of the TAF period, as well as a return to MVFR cigs.

&&

.MARINE...
Issued at 1213 PM EST Sun Dec 16 2018

With the passage of a cold front tonight, winds are expected to
increase and peak at 20-25 kts while shifting northwesterly. Wave
heights in turn will ramp up exceeding 5-7 ft by Monday morning. A
Small Craft Advisory will therefore be issued tonight through
Monday.

&&

.HYDROLOGY...
Issued at 1213 PM EST Sat Dec 15 2018

River levels remain fairly steady now after peaking from rainfall
earlier this week. While Maple River and Sycamore Creek were
expected to peak above bankfull, they are now expected to remain
steadily below bankfull though the upcoming week. Meanwhile high
pressure through the majority of the week will allow for continued
dry conditions with no hydro concerns. Mild daytime temperatures in
the middle to upper 30s will also help limit any ice concerns
through the week. All-in-all, quiet conditions expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 8 PM this evening to 8 PM EST Monday
for LMZ844>849.

&&

$$

SYNOPSIS...Borchardt
DISCUSSION...Borchardt
AVIATION...Borchardt
HYDROLOGY...ANH
MARINE...ANH
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