FXUS63 KGRR 221949
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
249 PM EST Sun Dec 22 2024
.KEY MESSAGES...
- Wintry mix focused on Monday
- Milder with small precipitation chances Tuesday-Friday
- Much warmer with rain next weekend
&&
.DISCUSSION...
Issued at 249 PM EST Sun Dec 22 2024
- Wintry mix focused on Monday
We will be issuing a Winter Weather Advisory for the entire area
starting early Monday morning, and lingering into Monday evening.
The northern portion will be for 2-5 inches of snow, the middle
section will be for a wintry mix of sleet, snow, and a little
possible freezing rain, and the southern portion will be for mainly
freezing rain.
A weak area of low pressure across the Central Plains this afternoon
will move toward the area through tomorrow. This system does not
look to be one that would cause impacts. However, with increasing
moisture and warmth ahead of it, a mixed bag of precipitation types
will bring some impacts to the area, especially given the holiday
time frame.
We will see a wing of warm air advection snow develop after midnight
across almost the northern half of the forecast area. This looks to
be a 3 to 5 hour period of a band of light snow moving from West to
East. This will bring no more than a few tenths of an inch of snow
by 12z. Then, we will see additional precipitation develop between
10-12z Monday as the frontal system approaches, and better moisture
makes its way up over the area by then.
This will bring another batch of snow to the northern third to half
of the forecast area. Further south toward I-96, the snow will then
mix likely with some sleet and possibly freezing rain. This occurs
as temps aloft approach freezing, before those temps wet bulb down
some to change things back over to snow in the afternoon. This
mixture will cut down on snow amounts, but have the travel impacts
from sleet and freezing rain. Further south for the southern two
rows of counties, the melting layer will be warm enough, and the sfc
below freezing into early afternoon that the predominate p-type will
be freezing rain.
Once the moves through, the heavier precipitation will stop, but we
get into the dry slot for the southern two thirds of the forecast
area. The northern section will see snow continue expected to be
just north of the dry slot. The rest of the counties may go to more
drizzle or freezing drizzle for the afternoon, depending on where
the 32-33F isotherm ends up. The most likely scenario is that it
comes close to the I-96 corridor, and southern two rows warm enough
above freezing to end the threat. This is uncertain however, as it
is something very tricky to pinpoint. Some places will see impacts
continue most of the day.
Finally everything will move out by late Monday evening with the
system, allowing everyone to dry out.
- Milder with small precipitation chances Tuesday-Friday
The period from Tuesday through Friday has trended a bit drier, but
there will still be small chances for precipitation in this period.
The changes are a result of one more northern stream short wave that
will move by, just to the NE of the area. This wave does not look
close enough to bring precipitation to the area late Tuesday and
Wednesday. It will slow up the pattern change that will take place
to go to more of the SW flow aloft. Moisture return will be delayed,
as will organized short wave activity.
A short wave ridge moving through on Thursday should bring just dry
weather with somewhat milder temperatures starting to move in.
- Much warmer with rain next weekend
The expected pattern change that will bring the much warmer and wet
conditions to the area now looks like it will be centered over next
weekend.
The ridge on Thursday moves by, and the long wave pattern then
becomes from the SW at that time. We actually may miss out on the
leading wave as it looks to get shunted to the SE of the area with
the next long wave trough pushing in quickly.
It is at that time that we see the deep moisture and warmth from the
Gulf arrive ahead of the short waves lifting NE toward the area.
There is a potential that we see 50 degrees once again with the
amount of warmth coming this way.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1235 PM EST Sun Dec 22 2024
Dry conditions with VFR cigs prevail through 12z Monday with
little in the way of aviation impacts expected. Winds of 7-12
knots expected today with gusts to 20 knots at the lakeshore.
More impactful aviation weather arrives after 12z as precipitation
spreads across the area. Current thinking is MKG likely stays cold
enough to stay as snow initially, mixing with rain near the end of
the TAF period. GRR and LAN will be right on the mixed
precipitation line, so snow and sleet mix is favored with a chance
that a little freezing rain mixes in. Further south at
AZO/BTL/JXN, conditions will favor freezing rain through the end
of the TAF period. Conditions will begin as VFR with cigs falling
to MVFR by the end of the TAF period at all sites except JXN.
Strong winds at 2kft, to 45 knots, will create a period of LLWS
after 12z at all terminals except MKG. Southerly winds of 10-15
knots are expected Monday with gusts to 25 knots inland and 30
knots near the lakeshore.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 1 AM to 11 PM EST Monday for
MIZ037>040-043>046-051-052.
Winter Weather Advisory from 6 AM to 11 PM EST Monday for MIZ050-
056>059.
Winter Weather Advisory from 6 AM to 7 PM EST Monday for
MIZ064>067-071>074.
MARINE...Small Craft Advisory until 10 PM EST Monday for LMZ846>849.
&&
$$
DISCUSSION...NJJ
AVIATION...Thomas