Georgetown, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

528
FXUS63 KGRR 180157
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
857 PM EST Fri Jan 17 2025

.KEY MESSAGES...

- Transition from mild air to colder air tonight into Saturday

- Very cold temperatures and lake effect Sunday into Wednesday

- Moderating temperatures and unsettled Wednesday through Friday

&&

.UPDATE...
Issued at 857 PM EST Fri Jan 17 2025

Overall the forecast remains on track. Clearing has cause surface
temperatures to drop, but should see them rebound as the cloud
cover expands over the area with the warmer air temperatures in
place. Isolated cold spots mainly in shaded areas may cause icy
spots as rain begins mainly after midnight.

The transition to snow will be dependent on how fast the cold air
advects into the region. There are some varying solutions with
the CAMS being a little slower. Precipitation will be mainly
focused along and south of a South Haven to Lansing line. The
transition to all snow occurs around 3am to 7am from west to east.
Snowfall amounts will be dependent on this transition.
Probabilities of greater than a trace of snow are 50 to 70 percent
with probabilities of greater than an inch or more at 20 percent
or less through 7am Saturday.

&&

.DISCUSSION...
Issued at 334 PM EST Fri Jan 17 2025

- Transition from mild air to colder air tonight into Saturday

We are seeing a rare sunny January day today after clouds moved out
earlier this morning. This quiet weather is the result of a fairly
robust upper ridge axis that is passing through the state this
afternoon, in between the departing system from yesterday and the
strong trough coming in beginning tomorrow. Winds are just ramping
up this afternoon as the sfc high has moved east of the area, and
with a strong pressure gradient due to a 985 mb low over western
Ontario.

The leading edge of the major change in air masses at the edge of
the large upper trough and sfc cold front is across Western WI, SE
MN and Eastern IA as of early this afternoon. Also at this moment,
the front over SE MN and Eastern IA is associated with clear skies
as there is no appreciable moisture with it yet.

The models have been consistent in showing the front initially
arrives along the lakeshore still dry. Then after about midnight as
it starts pushing through the area, it will work in tandem with a
srn stream system near the Ark-La-Tex to draw moisture northward
from the Gulf fairly quickly.

The precipitation will be mainly focused on the SE third of the
forecast area based on the frontal and moisture timing. The
atmosphere will initially be warm enough for the precipitation to
start as rain, but will quickly transition over to snow as the
colder air moves in. There could be enough overlap across the SE
for some snow accumulations of an inch or so before the synoptic
precipitation moves out.

Lake effect snow showers will start up on Saturday, but do not
become very robust yet. We become under the influence of some upper
ridging behind the leading upper wave moving through tonight. This
keeps inversion heights down around 4-5k ft per lake modified
soundings. Over lake instability will be sufficient with 850 mb
temps down to the negative mid teens. The combination of these
parameters support only minor accumulations Saturday into Saturday
night. The locations that see those accumulations will be mainly
near the lakeshore with winds from the NNW.

- Very cold temperatures and lake effect Sunday into Wednesday

The lake effect will begin to get going better on Sunday, and will
affect areas further inland also. Reinforcing short wave energy with
the core of the upper cold pool will arrive on Sunday. Forecast
soundings show lake modified parcels having inversion heights rising
to between 10-15k ft. The winds will turn to be from NNW early in
the morning, to WNW by Sunday evening.

As has been messaged for days now, the DGZ will sink to be below the
cloud layer with the core of the cold air coming in. Snow showers
will be plentiful, but will not add up as quick as one might think
due to the small flake size. The flake size will reduce
visibilities, along with some blowing and drifting snow. This does
not look to be extraordinary with winds of 20-25 mph, but the snow
will be easily blown around being of a dry consistency.

Temperatures will be falling into the single digits by late Sunday
afternoon, and likely not warming above 10F until Wednesday. Temps
inland away from the influence of the lake will see the coldest
wind chills of -15 to -25F, with slightly "warmer" wind chills
closer to the lake. Cold Weather Advisories are likely going to be
needed as we get closer to the event.

- Moderating temperatures and unsettled Wednesday through Friday

The upper trough and the core of the low level cold air will shift
east by Wednesday. This will allow the temperatures to moderate back
into the 20s.

Even though the very cold air mass moves out, it will still be cold
enough for some lake effect/enhancement with 850 mb temperatures in
the negative mid teens C. That, combined with short waves coming
through on Wednesday and Thursday will provide for additional
chances of snow. The chances will be favored over the NW section of
the area as the flow will be from the SW.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 714 PM EST Fri Jan 17 2025

LLWS will continue for the next several hours, followed by a cold
front passing through during the late night which will shift the
winds. Light rain will develop just ahead of the cold front, which
will change to snow from northwest to southeast as temperatures
fall. Also tonight between about 04 and 07 Z, VFR ceilings will
quickly drop deep into MVFR. A few hours of IFR ceilings and/or
visibility may also develop near and south of AZO-LAN. During the
day Saturday, things will transition to broken MVFR ceilings with
scattered light lake effect snow showers. The snow showers
shouldn`t limit prevailing visibility much except for close to
Lake Michigan.

&&

.MARINE...
Issued at 334 PM EST Fri Jan 17 2025

We extended the Gale Warning through 10 pm this evening. Winds at
the limited marine sites still available are showing winds
near Gale criteria. Big Sable Pt is at 33 knots and the Muskegon
Airport was 41 knots. These winds will come down this evening as
the core of the wind moves out. Winds will surge once again with
the arrival of the cold front and behind it on Saturday. At this
time, it looks like winds will stay at 30 knots or below.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Gale Warning until 10 PM EST this evening for LMZ844>849.

&&

$$

UPDATE...RAH
DISCUSSION...NJJ
AVIATION...CAS
MARINE...NJJ