Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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084
FXUS63 KGRR 222029
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EST Wed Feb 22 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 329 PM EST Wed Feb 22 2017

Mild weather will continue with highs in the 50s both Thursday and
Friday, and lows mainly 40 to 45.  However rain showers will arrive
Thursday night and linger through Friday night.  Some thunderstorms
will also be possible, with some of these storms possibly severe
into Friday evening.

Colder air moves in late Friday night into Saturday, and the rain
will be switching over to snow.  Some light snow accumulation is
possible Saturday.  Another chance of rain and snow moves back in by
Tuesday night and Wednesday.  Cooler for the weekend and into early
next week with highs mainly be 35 to 40.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 329 PM EST Wed Feb 22 2017

A few light showers will be possible tonight with a cold front
passing through.  It won`t be as warm Thursday behind this front,
but it will still be in the 50s.  Then a wet and stormy system
arrives for Thursday night through Friday night.

The moisture does not look that impressive with tonight`s front and
most areas probably stay dry. but will carry low POPs along and
north of I-96.  A northerly wind moves in for Thursday, keeping us
slightly cooler.  Mid 40s for Central Lower to around 60 for South
Central Lower.  After a cloudy start on Thursday we should see some
sun into the afternoon, but no pcpn is expected.

Main story will be the system approaching and moving through
Thursday night through Friday night.  Still appears to be potential
for severe storms, with the evening looking most favorable.  We see
a coupled jet move in by late afternoon, with a low level jet
arriving into the evening.  CAPE values are only modest, but with
the amount of dynamics believe we will see storms.  It seems like
the highest potential for severe storms will be along and south of I-
96 where dew points will manage to reach the 50s as this area gets
into the warm sector.  However it may be somewhat questionable,
whether the best dynamics reach us during the highest instability.
If the LLJ is delayed too much, much of the action could be to our
south.  If we see severe storms, damaging winds will be the main
hazard.

It will be a wet system with rain totals expected to be around an
inch.  Perhaps higher in West Central Lower.  At the onset of the
pcpn Thursday night we may see a bit of rain/snow mix over Central
Lower, but this should be brief and not cause issues.

Later in the event, the colder air arrives in the west just prior to
daybreak Saturday, so have included the chance of snow mixing in
late Friday night there.

.LONG TERM...(Saturday through Wednesday)
Issued at 329 PM EST Wed Feb 22 2017

The long term period will start off with the low pressure system
pulling away from the region on Saturday.  After being dry
slotted...the wrap around moisture will pivot through the CWA during
the day and into the evening.  Thus...higher POPs are warranted.
Based on the thickness values this looks to be a mainly snow
event...but some rain could mix in especially early on. Surface
temperatures will largely be above freezing...so impacts will likely
be limited.  It appears later Saturday...as the temperature starts
to drop off below freezing...that the risk for impacts will be
elevated. This is also when the precipitation will be winding down.

Sunday into Monday the risk for precipitation looks low. One storm
tracks up the OH valley for Monday.  Overall the trend of this track
has been further south...so this system should miss our region. Then
on Tuesday another storm will be approaching from the west.  Will
feature increasing POPs for Tuesday.  This system has trended
warmer...so it is currently looking like a rain event.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1245 PM EST Wed Feb 22 2017

As the low level moisture diminishes somewhat this afternoon...an
overall trend toward MVFR is expected. Close to Lake MI...the flow
has back for KMKG and that that may nudge the IFR and lower
conditions slightly to the west of that site. As the winds veers
southwest again this evening...the low clouds and fog should
return back to KMKG by then. Then tonight as temperatures cool off
a few degrees...the low clouds leading to IFR may return again. A
cold front will drop down from the north late tonight and Thursday
morning...causing a wind shift. This front could trigger a few
showers and thunderstorms. Confidence was not high enough to go
with them at the TAF sites at this time.

&&

.MARINE...
Issued at 329 PM EST Wed Feb 22 2017

The fog over the lake was slowly mixing out and vsbys will continue
to improve.  The fog advisory goes through 5 PM.  At that point will
hoist a small craft advisory as SSW winds come up to around 20 knots
as the cold front approaches.  It will be a brief advisory as winds
and waves diminish again toward daybreak Thursday.

&&

.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...None.
LM...Dense Fog Advisory until 5 PM EST this afternoon for LMZ845>849.

     Small Craft Advisory until 4 AM EST Thursday for LMZ845>849.

&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...CAS
MARINE...JK



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