Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 200229
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1029 PM EDT Sun Mar 19 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 325 PM EDT Sun Mar 19 2017

A cold front will move across the state Monday triggering some light
rain and perhaps a thunderstorms south of I-95. Dry and colder
weather is expected Wednesday with highs only in the mid 30s. Then a
warm up into the 50s will occur by the end of the week.

&&

.UPDATE...
Issued at 1028 PM EDT Sun Mar 19 2017

I have added the chance for thunderstorms to our western CWA
tonight as there is an area of elevated instability that shows up
nicely in the RAP soundings. The instability is coming from air
above 700 mb so nearly no chance of mixing this the ground but
above 700 mb there is 700 to 900 j/kg crossing the western CWA
between midnight and 4 am or so. This is on the nose of the best
1000/850 moisture transport. There are thunderstorms out there now
based on lightning data and surface observations (over NE WI and
soon northern Lake Michigan). Some brief down pours are surely
possible from these storms and small hail would not be out of the
question as there is a fair amount of the cape in the -10 to -20c
range.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 325 PM EDT Sun Mar 19 2017

Forecast concerns deal with pcpn chances later tonight and Monday.

A cold front currently over the Mississippi Valley will move east
through the cwa Monday. Ahead of it, instability has developed over
Missouri and some of this instability will move toward far southern
Lower Michigan tonight. We`ll see showers develop ahead of the
approaching front and a few elevated storms are possible tonight
south of I-94. Upper level support is lacking with this system; it
remains in Canada. Thus pcpn amounts will be limited. However, as a
wave develops along the front over Illinois tonight, moderate to
high pops seem warranted Monday. After the front passes, high
pressure quickly builds in and Monday night through Tuesday night
will be dry.

.LONG TERM...(Wednesday through Sunday)
Issued at 325 PM EDT Sun Mar 19 2017

The main challenge with the long term deals with the precipitation
type for Thursday night. The latest incoming data suggests this will
be mainly a rain event. The initially low wet bulb temperatures from
the High Res Euro...could support a brief period of snow...but the
warm air advection is strong and is shown to quickly warm up the
soundings...even for Harrison.  The GFS is too warm for snow there
through the night with 800 mb dewpoints of 3.7 deg C at 06z for
Harrison. We will need to monitor the surface
temperatures...especially the interior northeast zones. The pattern
does suggest a small risk for zr if we end up with surface
temperatures a few degrees cooler.

It looks like a rather cool day for Wednesday.  The 925 mb thermal
trough will be in place to start the day with values around -12 to
-13 deg C.  Despite the abundant sunshine the weak flow with high
pressure overhead will support only slow modification of the
airmass.  Some locations look likely to stay below freezing.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 731 PM EDT Sun Mar 19 2017

It would seem to this forecaster that for the most part the
showers will largely bifurcate the GRR TAF sites overnight. Some
of the convection is exiting northeast across Lake Superior as I
write this, that will stay well north of here. Meanwhile a
southern stream shortwave will track it`s convection largely south
of Michigan overnight. I could see a few scattered showers coming
through the AZO and BTL TAF sites even so. While an elevated
thunderstorm is not out of the question a quick look at the SPC
SREF makes is clear the thunderstorms will be south of I-94
overnight.

There is just the slightest hint that afternoon convection,
developing just north of the warm front associated with the
developing low over western IL could make it as far north of I-94
Monday afternoon, I did not play this in the TAFs but you should
be aware of this. If this makes it into Michigan these have a
better chance of being thunderstorms.

Once the convention misses the TAF sites to the south (more or
less) low clouds will follow and hold most of the day. Drizzle i
not out of the question. I would expect clearing around or just
after 00z Tuesday.


&&

.MARINE...
Issued at 325 PM EDT Sun Mar 19 2017

Southwest winds 10 to 20 knots will create 2-4 foot waves during the
next 24 hrs. A thunderstorm is also possible


&&

.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...None.
&&

$$

UPDATE...WDM
SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...63
MARINE...04


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