Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 231151
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
651 AM EST Thu Feb 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 319 AM EST Thu Feb 23 2017

A weak cold front moving through the area will bring cooler
temperatures compared to what was experienced on Wednesday. Rain
will move in from South to North tonight as a much stronger system
approaches from the Southwest. Rain could become a wintry mix across
Central Lower Michigan tonight and Friday morning with cold temps at
the surface.

Thunderstorms will become likely late tonight and especially Friday
through Friday evening as the system moves through. Severe weather
will be possible Friday afternoon south of a line from Holland to
Lansing where much warmer air will be found. Strong winds will be
the main threat. Much colder air will filter in across the area
Friday night and Saturday. Rain showers will transition over to snow
showers with some light accumulations likely.

Another strong storm system will affect the area beginning Monday
night and lasting through Tuesday night. This will bring mostly rain
to the area, after starting out as a possible brief wintry mix up
north.

&&

.SHORT TERM...(Today through Saturday)
Issued at 319 AM EST Thu Feb 23 2017

Our main issues in the short term revolve around p-type issues up
north tonight, severe threat Fri afternoon/evening down south, and
pcpn changeover Fri night/Sat. We are issuing a Winter Weather
advisory for tonight and Fri morning for much of Central Lower due
to freezing rain potential. The SPC has expanded the Enhanced Risk
of Severe weather a bit to the north for Fri afternoon/evening.

We will have the proverbial calm before the storm in place today,
before the interesting weather starts tonight and lasts right
through the end of the short term on Saturday. Temps are quite warm
first thing this morning with temps well into the 50s at most
locations with a warm SW wind occurring. We will see the cold front
just coming into the NW portion of the CWFA as of 08z push through
the area this morning. There looks to be a few sprinkles at most
with the passage as the moisture is quite shallow in the lower
levels. What it will do is cool us off, with most seeing their high
temps for the day early this morning.

This front will stall out across IN and OH before moving back north
as a warm front tonight and bringing a nice surge of pcpn with it.
This will occur as a strong system will move into the Plains, and
draw a good deal of moisture north out of the Gulf. Most of the area
will see the pcpn fall as rain. However, Central Lower will see
enough cold air come in via low level NE flow to change the pcpn
over to some freezing rain and sleet. There looks to be enough from
around midnight tonight through noon Fri that some impacts will
likely occur. So we will be issuing the Winter Weather Adv for most
of the two northern rows of counties, except Oceana for around a
tenth of an inch of ice.

All areas will change to rain by Fri afternoon, however most of the
CWFA will see it as a cold rain. Thunder will be possible, with much
of it being elevated in nature. The exception to this will be the
Srn two rows of counties where the warm sector is expected to move
up to. We are expecting temps to approach 70 south of the front late
in the afternoon and early in the evening. Models differ a bit on
the instability with some showing thin CAPE profiles (GFS) where the
NAM has over 1000 j/kg of Sfc based CAPE. If the higher CAPE comes
to fruition, severe weather will be much more likely with strong
wind/shear profiles leading to mainly a wind threat.

We will get dry slotted once the front moves through Fri evening,
leading to some drizzle or light showers. Better coverage of pcpn
will move back in Sat morning with the wrap around moisture coming
in from the NW. This will likely be mostly light snow with some
light accumulations possible. Warm ground from the recent spell of
warm weather will likely mitigate accums a bit, in addition to it
falling during the day.

.LONG TERM...(Saturday night through Wednesday)
Issued at 319 AM EST Thu Feb 23 2017

High pressure over the Tennessee valley will ridge northward at the
start of the period providing mainly dry but cool weather. Highs in
the mid 30s Sunday will rise into the 40s Monday as the ridge moves
east and southwest flow develops.

The next system moves in from the southwest Monday night. ECMWF is
quicker than the gfs in the warm air advection pattern Monday night.
It`s also possible that the pcpn could transition to a period of
light freezing rain and/or sleet Monday night although confidences
isn`t high on that yet. The ecmwf really strengthens that low as it
moves northeast toward western Lake Superior early Wednesday. We`ll
see mixed rain and snow with this early before changing to rain
Wednesday as temps climb into the mid 40s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 651 AM EST Thu Feb 23 2017

The first order of business for aviation interests this morning
is low cloud cover. We have one area that is exiting to the SE,
one area that is spreading in from the NW, and another trying to
form and move in from the SW. We have a period of IFR this morning
at all sites except KJXN where the clouds do not move back in
after they move out in the next hour or so. These low clouds will
gradually lift later this morning and early this afternoon.

There will be a break in the low clouds until rain moves back in
from the SSW later this evening and overnight. We expect a fairly
quick return of the low clouds and IFR conditions when they move
in. Rain is expected, and some thunder will be possible,
especially across the south prior to 12z Fri.



&&

.MARINE...
Issued at 319 AM EST Thu Feb 23 2017

The Small Craft Advisory in effect for this morning will be allowed
to expire on time as winds are on the downward trend.

The next event that we are looking at likely marine headlines for
will be the period from overnight tonight through Friday morning
ahead of the incoming system. Offshore flow and warm air advection
points toward this being an advisory situation vs. a Gale although
it could come close.

After a brief break on Friday, winds and waves will pick up once
again as the colder air rushes in behind the cold front.


&&

.HYDROLOGY...
Issued at 1201 PM EST Wed Feb 22 2017

Snowmelt in the headwaters of the Muskegon River basin has caused
the river to rise to above normal for late February. The Grand and
Kalamazoo rivers are running near normal. Showers and storms on
Friday may put down swaths of rainfall in excess of a half or
perhaps 1 inch. Some rivers would be susceptible to rising above
bankfull if that amount of rain falls in their respective basins.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from midnight tonight to 11 AM EST
     Friday for MIZ037>040-044>046.

LM...Small Craft Advisory from 10 PM this evening to 11 AM EST Friday
     for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...04
AVIATION...NJJ
HYDROLOGY...CAS
MARINE...NJJ



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