Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 171150
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
750 AM EDT Sun Mar 17 2024

.KEY MESSAGES...

- Impactful lake effect event likely tonight and into Monday

- Chance of Snow/Mix Late Week

&&

.DISCUSSION...
Issued at 316 AM EDT Sun Mar 17 2024

- Impactful lake effect event likely tonight and into Monday

Confidence continues to increase that we will see a period of
accumulating snow that will likely impact the Monday morning commute
for the NW and SW sections of our forecast area. We will not issue a
headline quite yet, but believe one is likely going to be needed.

There are a few areas of light precipitation falling across the area
early this morning. Based on observations around the area, these are
only producing some light sprinkles or flurries, with maybe a light
shower under the strongest radar echoes. Cooler air continues to
filter in with upper troughing in place over the area. We will have
a couple of short waves move through, and keep the chances of light
precipitation going. The dominate p-type will likely become snow
this morning as freezing levels continue to fall with the colder air
moving in. We are not expecting any accumulation through most of the
day with sfc temps in the 30s and mid-March solar radiation.

We will see the snow showers increase in coverage and intensity,
especially for the NW and SW quadrants of the area later this
afternoon and especially tonight. The short waves moving through
today will allow the cyclonic flow and coldest air aloft to move
overhead tonight and much of Monday.

850 mb temps dropping down to around -12C will provide good
instability over the 3-4C Lake Michigan waters to get some good lake
effect bands going. In addition, the coldest air aloft will allow
for inversion heights to climb to around 10k ft. This will help to
produce some good NW to SE lake effect bands with the flow from the
NW. The favored areas will be areas west of a Grand Haven to
Kalamazoo line, and west of a Whitehall to Cadillac line.

Right now, we are expecting a 1-4 inch range for these areas, with
some locally higher amounts from late this afternoon through Monday
morning. It does look like that with accumulations overnight and
ongoing snow showers Monday morning, the Monday morning commute for
these areas will be impacted. Something that has been fairly rare
this winter. We expect that an advisory will likely be needed at
this point. By later Monday afternoon, the favorable ingredients for
lake effect will be diminishing as the upper trough and the
coldest of the air will be moving out.

- Chance of Snow/Mix Late Week

A clipper tracks southeast out of Canada late Tuesday/Tuesday night
in fast northwest flow but the low center remains to our north and
moisture is limited. Currently no POPs in the forecast but we will
have to watch Tuesday night across the northern zones where WPC does
have some light QPF.

Complex evolution of the flow regime across the CONUS middle and
late next week with a rex block across the West breaking down and
upper low moving east. The Euro has trended towards the GFS and GEM
showing a polar vortex across Hudson Bay bu Friday. The GFS still
has lower heights extending south into the Great Lakes, allowing
more shortwave troughing here and creating a baroclinic zone where
there is frontogenetic forcing.

An area of snow blossoms in this baroclinic zone across the NW
CONUS/SW Canada on Wednesday and moves southeast, arriving in Lower
Michigan by late Thursday into Friday. This could bring at least a
light accumulation of snow.

There is some uncertainty by the weekend with ensemble support for
continued unsettled weather along the baroclinic zone and a
potential inverted trough bringing snow and mixed precip into
Saturday. THere is also some support for a stronger shortwave trough
with the cold front pushing south and lake effect snow showers into
the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 750 AM EDT Sun Mar 17 2024

Scattered snow showers this morning with mostly VFR conditions
then snow showers will become more numerous by this afternoon and
evening with areas of MVFR conditions across western Lower
Michigan and some IFR this evening and overnight. Northwest winds
will gust over 20 knots through much of Sunday afternoon and
evening.

&&

.MARINE...
Issued at 316 AM EDT Sun Mar 17 2024

We went ahead and extended the Small Craft Advisory yet again, this
time through Monday night. This will likely have to continue to be
extended even further in subsequent forecasts.

We are looking at cold and gusty winds from the NW continuing
through Monday. They will let up very briefly late Monday, only to
see them return Monday night out ahead of the next system that will
be approaching the area.

We should finally see a better period of less wind and wave action
by Wednesday as high pressure and a weak pressure gradient move over
the area.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT Tuesday for LMZ844>849.

&&

$$

DISCUSSION...Ostuno/NJJ
AVIATION...Ostuno
MARINE...NJJ


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