Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 121805
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
105 PM EST Sun Nov 12 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 308 AM EST Sun Nov 12 2017

A weak area of low pressure will track through the region today
and tonight. This system will lead clouds and some light
precipitation. The weak storm system moves east of the area for
Monday. It will be replaced by a high pressure system that will
then dominate the weather into Tuesday.

&&

.UPDATE...
Issued at 1000 AM EST Sun Nov 12 2017
Updated pops to reflect current radar trends. There is some
sleet falling on areas south of I-96, but impacts will be limited
due to sfc temps above freezing. Otherwise, mostly rain is
expected this afternoon along/south of M-46 and mostly dry
conditions north of M-46.

UPDATE Issued at 701 AM EST Sun Nov 12 2017

The precipitation has picked up in intensity over the past hour
from South Haven to near Jackson. A recent flight out of DTW
shows lower wet bulb temperatures below the cloud layer. Thus the
risk for some sleet/snow has increased over the past hr for
southern zones. Will issue an update to reflect these trends.
Surface temperatures to remain above freezing so not expecting
impacts at this time.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 308 AM EST Sun Nov 12 2017

The main challenge in the short term deals with the type and
location of the precipitation today. Overall this looks more like
a liquid event rather than frozen and the axis of steadier
precipitation is trending further south.

Radar shows little in the way of precipitation around SW Lower MI
at this time. One band in NRN IN was lifting northeast and a few
surface obs are showing light rain. What aircraft data is out
there...shows a stronger warm layer aloft. Thus as the snowflakes
fall through this warm layer...they are melting...and mostly
drying up before reaching the ground. With some wetbulbing likely
going on aloft...this has not translated to falling surface
temperatures.  In fact most locations are steady or rising.  It
seems like the fact that the precipitation is very light...the
wetbulb process is not that efficient today. Still surface
temperatures right now are around 32 for parts of
Jackson...Ingham...Eaton and Clinton Counties with another hour or
two before any precipitation moves in. So...some light zr may
occur. Surface temperature are several degrees above
freezing...therefore the risk for impacts at this time looks low.
Elevated surfaces may be most prone to icing. The LAN observation
just went up to 33 degrees.  Will likely issue an SPS once the
precipitation moves in for these locations mentioning patchy slick
spots possible.

High res models do increase the precipitation across southern
parts of the CWA during the morning...with little north of
Interstate 96. Will focus the highest POPs further south as a
result.

.LONG TERM...(Tuesday night through Saturday)
Issued at 308 AM EST Sun Nov 12 2017

It will be a rather active pattern for the mid to late week period.
Two systems will impact the region, starting on late Tuesday night
through Wednesday, and a second more powerful system arriving for
Friday and Saturday.

The first system will be a cold front that will pass through the
area Wednesday afternoon.  Surface low pressure will track across
Southern Canada keeping us well into the warm side of the system. So
this will bring mostly rain to the area, probably steadiest
Wednesday morning.  A few flurries may come on the back side of the
system Wednesday night across Central Lower.

We will see a briefly cooler period Wednesday night and Thursday,
with dry weather.  But we will already be warm advecting by Thursday
night ahead of the next system.  Still some timing differences with
this one, but we should begin to see more pcpn late Thursday night
into Friday.  All models show an intensifying southern stream
surface low that tracks from roughly SE IA into Lower MI Friday
evening.  Outside chance we could even see some lightning Friday
evening.  The low continues to intensify once it has passed the
region on Saturday making for a windy day.

As far as pcpn it should begin late Thursday night.  A mixture will
be possible in the warm advection wing that may last into Friday
morning.  But then all rain should occur Friday afternoon and
evening with the surface low expected to cross Central Lower.  On
it`s current track and timing, much colder air should arrive late
Friday night or Saturday morning, changing the rain to snow from
west to east.  H8 temps are progged to be around +4C Friday, then
plunge to -8C by Saturday.  Falling temps and lake enhanced snow
should kick in by Saturday afternoon.  Some light accums will be
possible by Saturday evening.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 105 PM EST Sun Nov 12 2017

IFR conditions will become more widespread this afternoon as rain
mixed with snow continues. LIFR is possible as well, particularly
south and east of GRR.

There is also a risk of the mixed precipitation changing to
predominately snow after 21Z for a few hours before ending which
would result in reduced vsbys. Moderate icing in the clouds can
expected with freezing levels at, or falling to, around 1000-1500
ft.

Considerable IFR/LIFR will probably linger tonight after the
precipitation ends, especially south and east of GRR. Improvement
to MVFR is expected on Monday, with the slowest improvement
around JXN.

The exception to all of this will be at MKG where dry conditions
are prevailing, although MVFR cigs are still likely here.

&&

.MARINE...
Issued at 308 AM EST Sun Nov 12 2017

I decided to cancel the small craft advisory that was in effect
for parts of the area. The pressure gradient has been weakening
through the night. This has resulted in diminishing winds. The
waves have fallen as well with the buoy off of Ludington now under
4 feet.


&&

.HYDROLOGY...
Issued at 1025 AM EST Sat Nov 11 2017

No flooding is expected through the week. Rivers have fallen to near
normal levels in all but Southwest Lower Michigan. Less than a half
inch of precipitation is expected through mid-week. This should
allow rivers to continue to fall. Looking like up to a inch of
precipitation late in the week into the weekend. This might cause
river levels to rise some next weekend.

&&

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

$$

UPDATE...04
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...JK
AVIATION...Meade
HYDROLOGY...63
MARINE...MJS



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