000
FXUS63 KGRR 012352
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
652 PM EST Tue Dec 1 2020

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 1235 PM EST Tue Dec 1 2020

- Peaceful weather through Thursday

- A few weak cold front Fri through Tuesday

&&

.DISCUSSION...(This evening through next Tuesday)
Issued at 248 PM EST Tue Dec 1 2020

-- Peaceful weather through Thursday--

Expect all areas to see skies becoming clear or nearly so by mid
evening. This clearing is helped along by the polar jet crossing
our area this afternoon, putting SW MI on the anticyclonic side
of it. That nearly always will clear out the low clouds, even at
this time of year. Of course with clear skies temperatures will
fall into the 20s. There will still be enough wind in the boundary
layer though to keep the air mixed so temperatures will likely
not fall into the teens expect in the more protected area from the
prevailing wind.

High pressure at the surface and upper ridging overhead will
provide for a mostly sunny Wednesday with temperatures rising into
the lower to mid 40s by afternoon. The skies should remain mostly
clear into Thursday morning, so lows will fall into the 20s during
the early morning hours but rise once again into the 40s by
Thursday afternoon.

-- A few weak cold front Fri through Tuesday--

Overall, through a good part of next week we remain in split upper
level flow. The northern stream polar jet will largely stay north
of the CONUS into late next week. Even so, there is longwave
ridge over the western Canada and United States and trough over
eastern Canada and the United States. So Pacific shortwaves will
climb the western ridge and try to dig southward into eastern
Canada over the next 14 days. However, due to the split flow, a
fairly strong southern stream jet will block the northern stream
shortwaves from digging far enough south to really bring enough
cold air into the area of meaningful lake effect snow and below
normal temperatures.

The 12z ECMWF is stronger on the cold front that comes through
Friday. It would bring an area of 1 to 3 inches of snow north of
I-96 during the day time on Friday. The GFS is much weaker and
we`d get nothing. So that will have to be watched.

The next system comes through later Sunday into Monday. Once again
the ECMWF is stronger and digs the system farther south than does
the GFS so we would again see some light snow if the ECMWF were to
be correct on that system.

The southern stream system we have been forecasting to maybe
bring some precipitation this far north toward the weekend will
remain south of the Great Lakes. That is due to the large scale
pattern forcing the system to track well south of here before it
can turn toward the northward.

The bottom line is partly cloudy skies (for the most part) with
highs between 35 and 45 and lows from 20 to 30 for the next week
or so.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 652 PM EST Tue Dec 1 2020

VFR weather is expected the next 24 hours. There are some lower
clouds (MVFR) over Southern Lake Michigan at 00z. We expect these
clouds to scatter out tonight as temperatures rise aloft
eliminating the process that is creating them. Bottom line, mainly
clear skies are expected through Wednesday evening. Winds will
remain a bit gusty tonight from the north-northwest at 10-20
knots. On Wednesday, the winds will gradually shift to the west.
Wind speeds on Wednesday should run between 10 and 15 knots the
bulk of the day.

&&

.MARINE...
Issued at 248 PM EST Tue Dec 1 2020

I made no changes to our Marine headlines. Winds will slowly
decrease over the next 24 hours as the system that brought the
gales to the Great Lakes continues to lift northeast into the
Canadian Maritimes.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 1 PM EST Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
DISCUSSION...WDM
AVIATION...Duke
MARINE...WDM

NWS GRR Office Area Forecast Discussion