Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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021
FXUS63 KGRR 190019
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
719 PM EST Thu Jan 18 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 302 PM EST Thu Jan 18 2018

Quiet weather will persist for the area through Saturday as systems
will remain far enough away through then. Temperatures will
gradually warm through Saturday with highs approaching 40 on
Friday, and into the lower 40s on Saturday.

Some drizzle/freezing drizzle will become possible late Saturday
night into Sunday. The chance of precipitation will continue through
Sunday, with the best chance of rain and the warmest temperatures
coming on Monday.

Colder air will move back in behind the front late Monday into
Tuesday. Some lake effect snow showers will be possible into mid-
week before temperatures moderate once again.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 302 PM EST Thu Jan 18 2018

Our main items of interest in the short term are cloud trends
through the period, and chances of drizzle/freezing drizzle for
Saturday night.

Low clouds have been slowly eroding from South to North today as the
low level flow has become more SW, and the thin cloud deck has been
mixing out some inland. The colder air that has been present around
1-3k ft up is slowly moderating. This is making it more difficult
for the lake effect clouds to develop and survive, and is not
trapping in the moisture as much.

We are siding with the more optimistic Euro solution with regards to
cloud cover for tonight through Sat. It does not have as much low
cloud cover as the NAM and GFS. This seems plausible with the temps
just above the sfc warming and not supporting lake effect as much.

With lake effect then out of the picture, we will have to wait for
the low level moisture from the Gulf of Mexico to arrive ahead of
the incoming system late in the weekend. When that moisture arrives,
it will not be deep (unsaturated DGZ), but plenty of moisture and
warm advection could develop some drizzle/freezing drizzle. Temps
will be close to freezing, and any freezing drizzle would be brief
as temps will warm.

.LONG TERM...(Sunday through Thursday)
Issued at 302 PM EST Thu Jan 18 2018

There is little question (can`t be 100% this far out) we will get a
classic, warm side of the system, winter storm event Sunday night
into Monday. Then a lake enhanced snow event which has similar high
odds of occurring, happens Tuesday into Wednesday.

It will be significantly warmer than normal Sunday into Monday but
then as has happened last week, the cold air surges back in bringing
us once again below freezing with some snow on the ground. I still
believe the period from Thursday through Monday will be the warmest
7 days of the month of January 2018 in Southwest Lower Michigan. The

This is one of those southern stream Pacific waves that phases with
the northern stream and goes negative tilt as it comes into our
area. It has great dynamics, the precipitable water nearly 3 times
normal Monday morning during the time of the best inflow and will be
close to the all time record (.93") for the date.  We are in the
sweet spot for the 1000/850 moisture transport vectors (at the north
edge of the strongest advection).

There is excellent agreement between the GFS and ECMWF ensembles and
their operational runs now for both the timing and track of the
system as well as with the Canadian model. The surface low tracks
from just east of DSM Iowa 7 am Monday to near CIU Michigan by
midnight Monday night. The triple point should track from near RFD
Illinois at 7 am Monday to near HTL Michigan by evening. That brings
the primary rain band through during the morning hours of Monday. It
still looks like between .50 and 1.0 inches of rain in most
locations. Being in the warm air I would expect temperatures to
reach into the 50s (not in our forecast grids yet but likely will be
before to long).

Being so wrapped up of a system and given the omega block over the
north Pacific Ocean, we will get several days in the cold air behind
this system so expect a west than northwest wind lake effect event
into Wednesday.  I could see this being a 3 to 6 inch sort of
snowfall event, thus putting back what got melted off.

I should mention on Sunday with the warm advection over the shallow
cold air layer, it would not be out of the question there could be
some freezing drizzle north of GRR.  That will have to be watched.

Bottom line we get a storm that will bring enough precipitation to
get GRR`s monthly rainfall total to near the normal for the entire
month of January (2.09"). MKG will more than likely go above their
normal of 2.03" and LAN will likely get to or exceed there 1.65"
normal for January by the time the storm ends.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 719 PM EST Thu Jan 18 2018

Low level wind shear is a concern this evening through 06z, as a
core of wind moves through at 2,000ft. WSW winds (250 degrees)
near 50 knots will provide shear given surface winds will run
between 8-14 knots sustained.

Otherwise, low clouds are a possibility tonight, but a lower
probability than last night. For this reason only included
scattered 3,500ft clouds at the northern 3 TAF sites of KMKG, KGRR
and KLAN. We will be monitoring satellite imagery closely, but
overall feel the clouds will remain north of the TAF sites
tonight.

A mid cloud deck will move through the area on Friday with bases
between 10,000ft and 20,000ft. Essentially VFR weather is expected
through the TAF period. Winds will become gusty again from the
southwest (220 degrees) on Friday after 15z or so.

&&

.HYDROLOGY...
Issued at 302 PM EST Thu Jan 18 2018

The latest update from the Muskegon River ice jam in Mecosta County
is that slow improvement continues. Chunks of ice remain in the
river, but are stable at this point with slowly falling river
levels. Minor flooding is ongoing immediately along the river bank
in low lying areas.

A warming trend through the weekend will result in snowmelt.
Existing snow depths generally contain 0.2" to 0.5" of liquid.
Precipitation amounts of 0.5" to 1.00" are possible through early
Tuesday. This will most certainly lead to some rising rivers with
minor flooding possible next week, especially on smaller streams.

Highs in the 40s and lows in the mid-20s to around 30 degrees may
not be quite warm enough to drastically weak ice on all rivers. This
may mitigate some of the impact. However, ice jams are nearly
unpredictable. Residents living near rivers in flood prone areas
should remain vigilant late this weekend and next week should ice
jams develop.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...WDM
AVIATION...Duke
HYDROLOGY...JAM



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