Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 202338
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
738 PM EDT Thu Apr 20 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 322 PM EDT Thu Apr 20 2017

Showers and thunderstorms will end this evening as a cold front
moves across Lower Michigan. High pressure will then build into the
region providing sunshine from late Friday through the end of the
weekend. Night time tempeatures will be cool Friday night and
Saturday night and patchy frost is possible.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 322 PM EDT Thu Apr 20 2017

Forecast concerns deal with convection this evening and the
potential for frost Friday night and Saturday night.

Latest sfc obs shows low pressure over Lake Michigan with a warm
front extending southeast from near Grand Haven to just south of GRR
to north of Jackson. The cold front stretched from the low south to
near the Il/In border.  An area of showers/storms was moving east
across the eastern cwa producing small to medium size hail. This
precipitation will move east of the cwa by 4 pm or so. Then what? It
appears as though we`ll have a couple of hours in which the
atmosphere may be able to destabilize again before the cold front
sweeps east. Latest hi res vis loop shows clearing skies developing
over far southwest Lower Michigan. If this continues the I-94
corridor may see storms redevelop in a couple of hours and these
storms could be strong/severe too. Moderate shear 40-50kts exists
along with 500-1000 j/kg sbcape in the warm sector. The HRRR indeed
shows storms developing over Calhoun county around 5 pm and moving
east by 7 pm. The current severe thunderstorm watch remains in
effect until 8 pm.

Mostly cloudy skies will continue tonight as the upper trough swings
through. Friday will be chilly with highs 45-50. Skies will
gradually clear Friday afternoon setting the stage for cold
temperatures Friday night. We expect temperatures to fall into the
mid 30s both Friday night and Saturday night. Given the abundant low
level moisture in place, frost seems like a real possibility
along/south of I-96; we added patchy frost to the grids both nights.


.LONG TERM...(Sunday through Thursday)
Issued at 322 PM EDT Thu Apr 20 2017

The beginning of this period will have near normal temperatures and
dry weather.  However toward the end of this period we get back into
a warm and wet period with thunderstorms likely.

The big picture is similar to yesterday, our East Asian Jet will be
weak early in the period.  That allows the upper low over Hudson Bay
to dig just far enough south (southern edge of the upper level
circulation) into the Upper Great Lakes over this coming weekend so
as to blocks the next Pacific system to our south.  This will also
allow dry weather with a warming trend early next week for Southwest
Michigan.

By early next week the East Asian jet feature comes back across most
of the Pacific and that digs a western trough. Over time that trough
slowly moves inland enough to bring showers and thunderstorms with
warmer temperatures to this area by Wednesday.  This will be just
the begging of an extend wet period that will likely last more than
a week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 738 PM EDT Thu Apr 20 2017

Most of the region was VFR behind the thunderstorms, but some
areas across Central Lower still was seeing IFR conditions.

The ceilings will trend down overnight, with MVFR, fuel alternate
ceilings developing. At this point expect there will be enough
wind to help keep ceilings from falling into the IFR range.

Into Friday morning the ceilings will lift, expecting a return to
VFR by the 14-17Z time frame. The VFR should continue for the rest
of the day.

WNW winds will continue at 15 to 20 knots through the next 24
hours.

&&

.MARINE...
Issued at 322 PM EDT Thu Apr 20 2017

No changes to the headline. Waves will slowly diminish Friday as
high pressure builds over the lake.

&&

.HYDROLOGY...
Issued at 1142 AM EDT Thu Apr 20 2017

Thursday morning rain totals surpassed 1 inch in Mason, Ottawa,
and northern Kent counties. Generally two thirds of an inch fell
upstream of Croton and one third fell upstream of Evart.
Expecting only a slight additional rise at Evart, while Croton
could reach bankfull on Friday. Looking Glass and Sycamore avoided
the heaviest rain while Maple caught some of it. While flood
stage being reached is not the most likely scenario, Looking Glass
appears to be the most vulnerable of all the rivers if it gets
repeated storms Thursday afternoon. Fortunately, dry weather is
expected Friday into early next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 6 PM EDT Friday for LMZ844>849.

&&

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...WDM
AVIATION...JK
HYDROLOGY...CAS
MARINE...04



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