Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 182337
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
737 PM EDT Sat Mar 18 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 319 PM EDT Sat Mar 18 2017

Precipitation will exit the area by early tonight. Sunday will be
dry with persistent clouds. Precipitation returns to the forecast
Sunday night into Monday. The rest of the week looks dry with
seasonal temperatures. However Thursday night through Saturday looks
milder and wet with highs in the 50s.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 319 PM EDT Sat Mar 18 2017

Satellite imagery shows warming cloud tops with strong subsidence
aloft overspreading the area. Already weak radar returns continue to
diminish over the southeastern forecast area. Thus, little if any
additional precipitation is currently expected. Have a slight chance
mentioned for our eastern zones this evening.

There is small possibility for brief clearing of our overcast skies
early Sunday morning. However, this is very uncertain and more
likely we will see extensive low cloudiness persisting for most of
the the day.

No real change in thinking regarding rain Sunday night into Monday.
Rain should fall mainly between midnight and early Monday afternoon,
with precipitation totals rather light at a tenth of an inch or
less.

.LONG TERM...(Tuesday through Saturday)
Issued at 319 PM EDT Sat Mar 18 2017

The long term period will start off with a very large high
pressure system tracking out of the Canadian Prairies and into
Michigan. This fair weather system will become centered over the
state on Wednesday. With a low level northeast flow ahead of this
system...a shallow cool and dry airmass will filter in from
Ontario. This will support a cooling trend with temperatures
ending up well below normal for Wednesday.

Warm air advection develops on the backside of the departing high
pressure system for Thursday.  The temperature will start to
rebound...but moisture will be on the increase.  By Thursday night
some precipitation will be moving in from the southwest. Forecast
soundings suggest that if any snow/mix falls that it will not last
long as thermal profile largely remains above freezing. Although it
is worth noting that the new High Res Euro is stalling the surface
front over the CWA on Friday...with the main impact from that being
perhaps a longer period of wintry precipitation for northern zones.
At this point surface temperatures are shown by all models to be
mostly above freezing. Thus it appears that this will be mostly a
rain event.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 737 PM EDT Sat Mar 18 2017

Currently MVFR cigs prevail across the TAF sites in SW MI. If you
put the winds in the 200 to 400 mb layer over the IR / VIS images
you can quickly convince yourself that the low clouds clear once
the anticyclonic side of the polar jet crosses the area. So, this
has been true all day today (see what is happening in WI) and I
have no reason to believe this will fail tonight or Sunday. So, I
would think by mid morning we should see clearing from west to
east across SW Michigan. The models seem a little reluctant to
clear the low clouds that fast but this seems to work so I went
for it the TAFs. If I am correct we get to see the sun set Sunday
evening without having to be in a jet plane.

Unlike last night I do not see enough low level moisture around to
result in much fog so I so have some MVFR fog but thats should be
about it.

&&

.MARINE...
Issued at 319 PM EDT Sat Mar 18 2017

Expiration times of current Small Craft Advisory headlines look to
be within an hour or two of wave heights dropping below thresholds
according to the morning WaveWatch3 output, so no headline changes
planned. The wind forecast also basically unchanged.


&&

.HYDROLOGY...
Issued at 1047 AM EDT Sat Mar 18 2017

River levels are running around normal to a little below normal.
With less than a half inch of precipitation expected through this
weekend and then no additional precipitation until Friday, no
flooding is expected across the area into next weekend. The
precipitation next weekend may be enough to push river levels up,
but they should remain below bank full.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT this evening for LMZ847>849.

     Small Craft Advisory until midnight EDT tonight for LMZ844>846.

&&

$$

SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...63
MARINE...TJT



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