Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221042
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
642 AM EDT Wed Mar 22 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Wed Mar 22 2017

It will be chilly today and tonight, by late March standards, with
highs mainly in the mid and upper 30s and lows in the teens. However
skies will remain mostly clear.  We will see a warmup by Thursday,
but it will come with some rain by late in the day and into Thursday
night and Friday.  Temperatures will be in the 40s Thursday, and
Friday will see upper 40s across Central Lower to the mid 60s over
far Southern Lower.

It appears the wet period will continue through much of the weekend,
before we finally dry out early next week.  Highs are largely
expected to be in the 50s for this period.

&&

.SHORT TERM...(Today through Friday)
Issued at 330 AM EDT Wed Mar 22 2017

Temps will be about 10 degrees below normal today and tonight.  Then
we warm Thursday through Friday, with rain building in.  There will
be a slight chance the pcpn starts as freezing rain in the far NE
Thursday evening.

Center of Canadian high pressure drifts across Northern Lower this
afternoon.  Under a very dry air mass we will again see a fairly
large diurnal temp swing.  However with starting out in the teens,
highs today will only reach the mid and upper 30s.  Lows again
tonight in the teens.

Strong warm advection commences Thursday, along with moisture
advection by late in the day.  Noting some upper divergence by the
end of the day, so feel we may see an earlier on set to scattered
pockets of rain.  Added low POPs for the latter half of Thu. However
the main trust of pcpn arrives after nightfall Thursday.  The models
have trended warmer and feel the forecast legacy grids are too cool
as the pcpn arrives.  Still can not rule out some freezing rain at
the onset of the pcpn over the far NE CWA, but feel if this happens
it will only be for a couple of hours.  Temps will continue to rise
overnight, leading to all rain after midnight.

By late Thursday night into Friday a surface boundary will slowly
sag over Central Lower and much of the rain will focus there. Some
elevated instability shows up, but for now have left out thunder.
The southern portion of the CWA will probably only see a tenth of an
inch, while Central Lower sees a more persistent rain, with amounts
perhaps exceeding a half inch.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EDT Wed Mar 22 2017

A nearly stationary boundary will be draped across central Lower
Michigan Friday night. This will be the focal point for shower
activity through much of Saturday. Mild temperatures will support a
decent, soaking rain. Rainfall amounts Friday night through Saturday
evening may approach half an inch.

The weakening upper level wave is then expected to swing our
direction Saturday night into Sunday. This will keep rain chances
respectable through the remainder of the weekend. With high pressure
situated just to the north of Lake Superior, there has been some
concern for freezing rain over the far northeastern corner of the
forecast area after midnight Saturday and again after midnight
Sunday. A couple of things are working against any long duration
freezing rain. The main inhibitors are that no strong cold advection
process is taking place and the high itself is progressive- it will
not be pumping colder air in for very long. Rain may very briefly
mix with freezing rain, but much of any side effect at 31 or 32
degrees would be on elevated surfaces.

Low pressure continues to weaken as is pushes east of Lower Michigan
Monday. A few light rain showers will be possible, but more of the
hit-or-miss variety. A weak are of low pressure passes to our south
on Tuesday with chances for light rain. A weak front then pushed in
from the north, shifting winds out of the northwest by late Tuesday.
Temperatures, however, will largely stay near 50.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 642 AM EDT Wed Mar 22 2017

VFR conditions will prevail over the next 24 hours, with only some
mid and high level clouds around. NNE winds will remain under 10
knots today, becoming east, and then SE tonight.

&&

.MARINE...
Issued at 330 AM EDT Wed Mar 22 2017

Small craft advisory until noon, as winds and waves gradually
diminish.  We may need another advisory by Thu and Thu night over
the Points region with a brisk southerly flow.

&&

.HYDROLOGY...
Issued at 247 PM EDT Tue Mar 21 2017

Thursday night into next week is looking like an active period with
multiple opportunities for rain. Rainfall amounts in excess of an
inch by early next week are possible. At this time it`s unknown
exactly where the heavier rain amounts will fall. But this will bear
monitoring, as certain rivers could climb above bankfull if heavy
rain falls within their basins.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until noon EDT today for LMZ844>849.

&&

$$

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


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