599
FXUS63 KGRR 121656
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
1156 AM EST Thu Dec 12 2019
LATEST UPDATE...
Synopsis/Update/Marine
.SYNOPSIS...
Issued at 1155 AM EST Thu Dec 12 2019
- Warm advection light precipitation this afternoon into tonight
(light snow to drizzle) over northern CWA
- Some freezing drizzle may mix in across Central Lower Tonight
- Cold front brings lake effect snow Saturday night into Sunday
morning. Expect some light accumulations west of US-131
- Some snow possible into Southern Lower Michigan early next week.
Indications are the main system impacts will miss our area to
the south and east. Colder with lake effect into Wednesday.
&&
.UPDATE...
Issued at 1155 AM EST Thu Dec 12 2019
No significant changes will be made at this time to the going
forecast. A mid level shortwave is moving our direction from the
upper midwest out of MN/WI. The wave will spread warm air
advection precipitation into Central Lower Michigan this afternoon
and evening. At this time, the dominant precipitation types looks
to be rain and snow transitioning over to some drizzle overnight.
Surface temperatures will be somewhat marginal however across
interior Central Lower Michigan, around 32F. Not out of the realm
of possibilities that we see a bit of freezing drizzle, but
confidence at this time is low. We could see some light
accumulation of snow centered from Scottville to Reed City on the
order of 1-3 inches in spots by Friday morning. At this time
though we are not thinking of issuing a Winter Weather Advisory,
but we will be taking another look through the course of the
afternoon.
&&
.DISCUSSION...(Today through next Wednesday)
Issued at 258 AM EST Thu Dec 12 2019
There are three major systems heading our way in the next week.
First is a weak system that should bring us mostly light snow to
drizzle northwest today and freezing drizzle tonight. Then a major
east coast storm will pull cold air into this area late Saturday
into midday Sunday, that will bring a 1 to 3 inch lake effect
snow event with it. Finally there is still the potential for a
major snow storm later Monday into Tuesday morning.
Afternoon and overnight system...
We have a weak shortwave tracking through the Great Lakes today
but the problem is there is a much stronger system upstream, on
the southern branch of the polar jet, coming on shore as I write
this. That will cause our system today to minor out as it moves
through the area. Which means the front stalls near us tonight as
the next upstream system pushes warm air back toward us due to the
digging trough, which by sunrise Friday will be over the midwest.
The warm advection lift precipitation will mostly be north of our
CWA today into early tonight. However as the front stalls we have
a persistent southwest winds (50 to 60 knots between 900 and 800
mb) which brings warm air into our area. Our surface temperatures
will rise above freezing south of Route 10 by midday. The freezing
level rises to near 2000 ft by evening. So any light snow with the
warm advection push (near route 10 this afternoon) will change to
light rain or drizzle by late in the day.
Tonight the deep moisture moves out so the DGZ will not be
saturated but the speed convergence and stalled front will trap
low level moisture and cause some drizzle tonight, mostly from the
lake shore to US-131. The question is will the surface temp fall
below freezing? Inland north of GRR has the best chance but that
area may be to far inland to see much drizzle. So for now no
weather advisory but we may need one if the next shift believes
there is a greater risk of accumulating freezing drizzle.
Saturday evening lake snow event....
This is the big east coast storm that will bring the cold air back
into our area. However the cold air push will be shortlived as an
even strong system comes onshore over the western CONUS Saturday.
That will force the shortwave trough brining the cold air in east.
Even so we get about 18 hours of cold enough air and deep enough
moisture for lake effect snow. This seems like a 1 to 3 inch sort
of event.
The Monday system...
The GFS has been forecasting this for nearly a week now and the
ECMWF has since the 10th /00z run been bringing the storm closer
to us on the operational runs. The 12/00z run brings snow to GRR
from the ECMWF. Since this is polar closed upper low dropping
south into and southern stream system, this will be watched
closely to monitor evolution.
&&
.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 632 AM EST Thu Dec 12 2019
A weak area of low pressure will track towards the Western Great
Lakes today. The most likely impact at TAF sites will be
southerly winds gusting between 20 and 30 knots, potentially
higher at MKG. Low-level jet will bring a core of higher winds
aloft, with 40-50 knots at 2000 feet causing low-level wind shear
from late morning into tonight. Precipitation will be limited at
TAF sites with this system and mostly affect central and northern
Michigan. Temperatures look warm when precipitation arrives into
MKG, and will carry only a rain mention. As we cool overnight,
there is some potential for light snow or freezing drizzle there,
but by then much of the precipitation will have ended. Watching
potential for drizzle or freezing drizzle overnight not just at
MKG, but also GRR.
&&
.MARINE...
Issued at 1155 AM EST Thu Dec 12 2019
6 to 10 foot waves are still expected this afternoon and evening
from Holland north up the lakeshore. The hardest hit areas will be
on the south sides of the points, from Ludington State Park down
to Ludington and from Little Sable Point down to Whitehall. The
waves in these locations will be more directly onshore given the
southwest trajectory. Winds and waves steadily decrease tonight
with a relatively calm period from Friday into Saturday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory until 7 AM EST Friday for MIZ037-043-
050-056.
LM...Small Craft Advisory until 7 AM EST Friday for LMZ844>849.
&&
$$
UPDATE...Duke
SYNOPSIS...WDM
DISCUSSION...WDM
AVIATION...HLO
MARINE...Duke
NWS GRR Office Area Forecast Discussion
