Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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173
FXUS63 KGRR 281722
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1222 PM EST Tue Feb 28 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 311 AM EST Tue Feb 28 2017

Low pressure moving through the Great Lakes today and Wednesday
will bring a variety of weather. Rain and thunderstorms are
expected today and tonight then colder air moves in on Wednesday
with rain changing to snow. Snow showers can be expected Thursday
into Friday.

&&

.SHORT TERM...(Today through Thursday)
Issued at 311 AM EST Tue Feb 28 2017

First batch of showers moving in this morning as broad area of
warm advection/isentropic ascent ahead of slowly developing Plains
low will be across Lower Michigan through tonight. Primary forecast
problem is determining the northward extent of stronger
thunderstorms this afternoon and evening.

Shear and instability profiles are as impressive as the storm this
past Friday, so some strong storms are possible across at least
the southern half of the forecast area this afternoon and evening.
The OOZ GFS continues to show most of the heavier QPF across
central Indiana and Ohio, suggesting that moisture transport into
Michigan could be disrupted, while the OOZ Euro has the axis of
heaviest QPF across southern Lower Michigan.

Colder air moves in from the northwest on Wednesday morning with
rain changing to snow. Axis of f-gen forcing across the northern
zones implies snow bands Wednesday afternoon could drop 3 to 5
inches northern half of the forecast area with 1 to 3 possible
across the south.

Northwest flow lake effect snow showers on Thursday will be
enhanced during the afternoon by shortwave trough axis swinging
through. Bumped up POPS to likely for the afternoon across the
favored northwest flow lake effect areas.

.LONG TERM...(Thursday night through Monday)
Issued at 311 AM EST Tue Feb 28 2017

Colder air will be flowing over the lake as we start the long term
period as a clipper moves over far southern Lake Michigan. We`ll
continue with likely pops west of US-131 Thursday night and Friday.
Instability will be high over the lake due to h8 temps near -18c and
the upper trough in place will aid in lift. Additionally, inversion
heights around 4k ft will be sufficient for lake effect snow
development. By Friday afternoon the upper trough begins to lift out
and sfc ridging moves in; we`ll see the snow showers diminish.

A northward moving warm front may generate a shower Saturday night
or Sunday but the more substantial threat of rain will arrive Sunday
night and Monday. A deeper surface low coupled with a compact upper
wave moves over the western Great Lakes during this time. Models
show some elevated instability with this and we may need to add
thunder to the grids if this feature persists.

Highs will climb from around 30 Friday to the mid 50s by Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1222 PM EST Tue Feb 28 2017

It seems to me ifr conditions will rule the day and the night
over all of the taf sites. The area of convection coming out over
Lake Michigan at I write this (1718z) should stay north of all of
the taf sites this afternoon. Even so IFR cigs should spread
north and east to cover all of the TAF sites by 21z or so. The
rain and scattered thunderstorms with the warm front will move
into the taf sites after 00z and last until around 09z or so. I
would expect the rain to be moderate to heavy at times in the 04z
till 08z time frame. Once the rain ends some fog and low ceiling
should persist until the cold front comes through around 16z.

Expect low level wind shear tonight as 40 to 50 knots winds will
be just above the surface till around 09z. Also, while there is a
marginal risk for severe storms, at this point I feel they will
stay south of all of our TAF sites overnight.

&&

.MARINE...
Issued at 311 AM EST Tue Feb 28 2017

A small craft advisory or gale warning will be needed for for late
tonight or Wednesday as winds and waves increase.


&&

.HYDROLOGY...
Issued at 330 PM EST Mon Feb 27 2017

Many rivers in the region continue to experience higher flows due to
continued runoff from rainfall late last week.  Additional rises
will develop later this week as another rainfall event brings one
half to one inch of rain across a large portion of West Michigan.
Flooding is not expected at time...but several locations will see
above bankfull rises.

&&

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

$$

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



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