Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

614
FXUS63 KGRR 171750
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1250 PM EST Fri Jan 17 2020

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 300 AM EST Fri Jan 17 2020

- Wet and heavier snow to fall Friday night into Saturday for most
of the area

- Lake effect snow showers to affect the area Saturday night into
Monday

- Next system to bring some rain and snow next Thursday and beyond

&&

.UPDATE...
Issued at 1142 AM EST Fri Jan 17 2020

Will not be making any changes to the going forecast with this
morning update. The forecast looks the same to us with no major
changes needed. The Winter Weather Advisory runs through 700pm on
Saturday.

Warm air advection synoptic scale snow moves in this evening from
the southwest and will continue right through the night and into
Saturday morning. A warm air advection snow is about as slam dunk
as it gets and the insentropic lift is actually strong and pretty
lengthy on the order of 9 to 12 hours. We are thinking everyone
sees a 4 to 8 inch snowfall, with solid 6 inches amounts in many
areas especially from the 96 corridor northward. Given the high
DGZ, the flake size will be a little smaller and end up providing
a dense snow. Given temperatures rising towards freezing as the
snow moves in, it will also be heavy and on the wet side.

Temperatures will warm to above 32F on Saturday in most areas, so
the main roads will turn somewhat sloppy. Synoptic snow will
continue off and on through the day on Saturday with lulls
occurring as the dry slot will be moving through. Some drizzle or
freezing drizzle is possible on Saturday as the DGZ becomes
unsaturated. The other ptype item of note is the chance for a bit
of sleet along I-94 late tonight. The bulk of the snow with the
synoptic side of the system will be on the ground by about 1000am
on Saturday.

Winds will crank up Saturday afternoon and continue through the
night and into Sunday morning. Lake effect snow will begin
Saturday evening with considerable blowing and drifting snow
developing Saturday evening. We will eventually need to continue
headlines into Saturday night and Sunday given the strong winds
potentially through and maybe east of the 131 corridor.

Keep in mind the Arctic front comes through between 700pm and
1000pm on Saturday which will plunge temperatures from around or
above freezing to falling through the 20s. We could have some
quick freeze up issues on area roadways given the fairly quick
temp drop Saturday evening.

More details to come with the afternoon update, but the bottom
line... we are staying the course with the headlines with high
confidence.

&&

.DISCUSSION...(Today through next Thursday)
Issued at 300 AM EST Fri Jan 17 2020

-- Wet and heavier snow to fall Friday night into Saturday for most
of the area --

The area remains on track to see a impactful snowfall tonight and
Saturday morning. With this in mind, we will be holding on to the
Winter Weather Advisory as is for this forecast package.

After a quiet day in which we just see clouds thicken up, and winds
increase a bit, a fairly robust of snow is expected to move in after
dark, and persist into Saturday. This snow will be the result of a
very strong push of moisture coming in via a 70 knot low level jet
nosing up into the area. The peak snowfall rates should come after
06z tonight and last until around, or just after 12z Saturday. We
are looking at potential inch/hour snow rates of a more wet and
heavy snow with lower snow-liquid ratios. This snow will obviously
cause issues with the roads, and could cause some power outages as
the snow could weigh down power lines and snap tree limbs.

The snow should then let up in intensity on Saturday, and will
likely even change to a wintry mix, and then rain/drizzle for areas
along and south of I-96. This happens for a couple of reasons. The
first reason is the surface low will come up into the area, and
bring a brief shot of warmer air. This will come in aloft first, and
could bring a brief bout of some freezing rain. This should not be a
problem for roads falling on top of snow.  Also, the deeper moisture
will peel away, and could end up as some drizzle as the dgz becomes
unsaturated.

-- Lake effect snow showers to affect the area Saturday night into
Monday --

Where it does change over to rain, it will be brief as the low moves
east very quickly, and colder air is quick to rush in behind the
low. This will change precipitation back to some snow, and
eventually lake effect as sufficiently cold air advects in. The flow
regime ends up as W/NW, which would favor areas toward Ludington,
and between I-96 and I-94. Additional accumulations will be expected
as the deep cold air on the cyclonic side of the upper jet will be
overhead, and overlake instability will be in the mid to upper teens
C. The lake effect potential will linger into early Monday
morning before it shifts offshore.

-- Next system to bring some rain and snow next Thursday and
beyond --

We should have a couple of quiet days with moderating temperatures
for Tue and Wed, before the next system moves in beginning Thursday.
High pressure will hold over the area as a decent upper ridge builds
through the region. As this ridge moves by, we will see southwest
flow tap Gulf moisture in the lower levels ahead of the next front.
With temperatures and melting layers near p-type thresholds, we
could see a mixture of p-types occur. Details are still uncertain a
week out, so will keep precipitation generic for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1249 PM EST Fri Jan 17 2020

Conditions are VFR across the area at 18z this Friday afternoon,
but conditions will go downhill pretty fast this evening between
700pm and 1100pm. MVFR conditions will spread in quickly during
this time frame with conditions headed for IFR late tonight and
Saturday morning.

Snow will be the culprit for the IFR conditions. The snow will be
steady and occasionally heavy tonight into Saturday morning. Once
the snow begins a solid 9 to 12 hours of dense wet snow is
expected. Intermittent precipitation is expected on Saturday with
bursts of snow intermingled with some light rain and drizzle at
times. IFR conditions, with lower ceilings especially will persist
into Saturday afternoon.

Winds will increase tonight and ramp up further into Saturday
morning. Southeast winds will increase to 15 to 30 knots into
Saturday morning. The winds will increase further Saturday
afternoon and evening to 20 to 40 knots.

&&

.MARINE...
Issued at 300 AM EST Fri Jan 17 2020

Headlines for both the nearshore waters, and the lakeshore
flooding/erosion both look good and will not be changed this morning.
As winds pick up today, they will have an offshore component which
will limit the wave heights and flooding/erosion. This will change
quickly Saturday morning as the system moves by, and winds and waves
becoming westerly and will start being impactful. Waves will peak up
around 14 feet Saturday night. This is expected to flood the
immediate lakeshore, and cause erosion on the sand dunes. The winds
and waves will slowly improve through Tuesday.


&&

.HYDROLOGY...
Issued at 330 PM EST Thu Jan 16 2020

The crest on the Grand River is currently passing through Grand
Rapids. Minor flooding is occurring in Comstock Park and also in
Robinson Township. Other locations along the lower portion of the
Grand River (downstream of Lansing) is near bankfull, but no
additional flooding is expected. Minor flooding also continues on
the Maple River near Maple Rapids.

Flooding in Robinson Township is being amplified by a push of
backwater up the Grand River from the gusty winds happening along
the lakeshore right now. The winds will diminish greatly tonight,
and some drop in the river levels in Robinson are expected as a
result. However, we will probably stay above flood stage through the
first part of next week.

With cold temperatures expected late this weekend and next week, the
rivers should have a chance to drop down below bankfull at all
locations. However, cold temperatures also bring the growth of river
ice, so some freezeup ice jam issues are possible next week,
especially in some of the most favored areas such as on the Muskegon
River downstream of Big Rapids.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Warning from 7 AM Saturday to 7 PM EST Sunday
     for MIZ037-043-050-056-064-071.

     Winter Weather Advisory from 7 PM this evening to 7 PM EST
     Saturday for MIZ064>067-071>074.

     Winter Weather Advisory from midnight tonight to 7 PM EST
     Saturday for MIZ037>040-043>046-050>052-056>059.

LM...Gale Warning from 1 AM Saturday to 10 AM EST Sunday for
     LMZ844>849.

&&

$$

UPDATE...Duke
SYNOPSIS...NJJ
DISCUSSION...NJJ
AVIATION...Duke
HYDROLOGY...AMD
MARINE...NJJ



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.