Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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576
FXUS63 KGRR 291735
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
135 PM EDT Wed Mar 29 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 309 AM EDT Wed Mar 29 2017

A ridge of high pressure will track eastward through Michigan
today. This fair weather system will provide the region with dry
weather. Clouds will thicken up during the day as a low pressure
system approaches from the southwest. This system will spread a
mixture of precipitation types to the area late tonight...that
will transition to all rain during the day on Thursday. The wet
and cool weather will then persist into Friday.

&&

.SHORT TERM...(Today through Friday)
Issued at 309 AM EDT Wed Mar 29 2017

The main challenge in the short term deals with the potential
impacts for later tonight through Thursday. Overall it appears
parts of interior Lower Michigan could see some impacts mainly
from wet snow.

We are going to have to monitor this system carefully and may have
to make bigger adjustments to the forecast with time. The cooling
and drying airmass that we currently have in place is lowering the
wet bulb temperatures down ahead of the approaching storm system.
This will act to create more of a snow sounding when the steadier
precipitation moves in later tonight. Fgen strengthens
overhead...with favorable upper jet setup suggests the
precipitation could organize into a band...especially after
midnight or Thursday morning. Up high...weakness in the stability
could support a period of higher snow rates.  Currently the
northern row or two of zones in my CWA look to be at the greatest
risk with the main window from 09z to 18z. This would include the
area along and north of a Mount Pleasant to Big Rapids line. Still
some uncertainty as mixed precipitation could occur and low level
temperatures may struggle to fall below freezing possibly
limiting impacts. We will continue to highlight the potential in
the hazardous weather outlook and social media.

Low level wet bulb temperatures are still not far from snow going
into Thu Evening. If this system trends a little colder...snow
could persist even into Thu afternoon and evening.  Stay tuned.

.LONG TERM...(Friday night through Tuesday)
Issued at 309 AM EDT Wed Mar 29 2017

There may be a few lingering showers Friday night as low pressure
moves east across northern Ohio, otherwise the weekend looks dry with
highs in the 50s as high pressure builds in behind the departing low.

The next chance for measurable rain comes late Monday and Monday
night as low pressure moves from the Plains east across the Ohio
Valley. Most of the precipitation associated with this system will
stay south of Michigan. However, the southern cwa will see the
highest chances for light rain. Highs Monday and Tuesday will be in
the 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 135 PM EDT Wed Mar 29 2017

Little question it will be solid VFR at all taf sites through
around 06z. Also there is little question of solid IFR in rain
Thursday after about 15z or so. Between 06z and 12z is when there
are some forecast issues.

The precipitation shield around the storm, currently centered in
southern Kansas, will begin to move into our taf sites in the 06z
time frames. It is possible that MKG and GRR could start with a
mix of rain and snow as there is enough dry air to allow wet bulb
cooling at the leading edge for those locations. I put mixed rain
and snow at MKG but not GRR through since the risk seemed higher
at MKG than GRR. All TAF sites will we solid IFR in rain with a
gusty east wind (15-25 knots). The rain will be moderate to heavy
at times after about 16z tomorrow so there more than likely will
be visibilities under 2 miles Thursday afternoon at all taf sites.

&&

.MARINE...
Issued at 309 AM EDT Wed Mar 29 2017

With a largely offshore wind...no marine headlines are expected
today to tonight.


&&

.HYDROLOGY...
Issued at 1158 AM EDT Wed Mar 29 2017

Widespread precipitation is expected across West Michigan from
late tonight through Friday. Basin average amounts of three
quarters of an inch to an inch can be expected. Area rivers levels
are currently elevated from the previous rainfall event...with
advisories in place for Ionia, Hastings, and Holt. While most local
rivers should experience falling stages through tonight...the
precipitation over the next 36 hours will create a new round of
rises to develop. Current advisory products attempt to illustrate
this scenario.

Some of the 12Z model output suggests heavier precipitation than
currently included as input to the river models. These higher
amounts...if they materialize... could produce above bankfull
rises on many more rivers and streams across West Michigan. Those
with interests on area rivers should closely monitor the
situation.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...WDM
HYDROLOGY...MWS
MARINE...MJS



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