Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 230521

Area Forecast Discussion
National Weather Service Grand Rapids MI
121 AM EDT Sun Apr 23 2017


Issued at 328 PM EDT Sat Apr 22 2017

Dry high pressure will be over Michigan the next few days resulting
in mainly clear skies. Patchy frost is again possible tonight as
temperatures fall into the 30s. Chances for rain will increase
Tuesday night as a cold front approaches. Temperatures will climb
into the 70s Tuesday ahead of the cold front before slipping back
into the 50s toward the end of the week.


.SHORT TERM...(This evening through Monday night)
Issued at 328 PM EDT Sat Apr 22 2017

Forecast concerns are minimal and mainly deal with the frost
potential tonight.

Satellite imagery shows some high clouds over the southern cwa,
otherwise mostly clear skies were noted. Once again today, dewpoints
were lower than guidance suggested due to good mixing. With clear
skies again expected tonight we`ll see temperatures fall into the
30s. I expect patchy frost again, but not widespread with RH the
limiting factor. Temperatures will be a degree or two warmer tonight
than last night. Coupled with limited low level moisture, we`re
likely to see patchy frost.

Mostly clear skies again Sunday through Monday. Temps will warm a
few degrees each day and night. Highs in the mid 60s Sunday and near
70 Monday are expected.

.LONG TERM...(Tuesday through Saturday)
Issued at 328 PM EDT Sat Apr 22 2017

This is more and more looking like a stormy period of weather for
Southwest Lower Michigan. There are three storms that come through
this area. The most significant will be the last in the series,
which could impact us in the Sunday to Monday time frame. All three
storms could produce severe weather but the more likely outcome will
be heavy rain. For this entire period it is very possible some
locations could see over 3 inches of rain. There will likely be wide
swings in temperature as we get into the warm sector at least with
the Wednesday and Sunday storms. This will be followed by brief cold
periods before the next storm arrives.

As I have been writing about for the past few days, our old friend
the East Asian Jet (EAJ) sends a series of shortwaves and their
assoicated jet cores into the western CONUS.  There are actually
only two jet segments with this EAJ.  We get three systems because
the lead wave kicks out system now just offshore of western North
America, as far south as California.  The first jet core digs a deep
trough over the Rocky Mountains by Tuesday.  The second one digs
into the trough created by the first one in the Thursday time frame.
That retrogrades and deepens this this trough. It is that event that
sets the stage for the Sunday event (being the most impactful for
our area).

The CIPS extended analogs and the experimental SPC CFS Severe
Weather Guidance for several days now have been very consistent with
all three of these phases. It shows the southern 1/3 of Lower
Michigan in the northern edge of the severe threat area. The CIPS
analogs and the WPC 5 to 7 day QPF forecast, the GFS, the GFS
ensembles, the ECMWF and the ECMWF ensembles all show an area of 2+
inches of rain into Lower Michigan between Wednesday and next

The Wed system has a coupled jet to help its cause (departing
northern stream and incoming southern stream jets) the Fri system
has a jet exit region and the Sunday system has the main core of the
EAJ rounding the base of the trough creating an enhanced coupled jet
feature over our area. Each event has high precipitable water values
assoicated with them, each has at least a 40 to 50 knot low level
jet and all three have the 1000/850 moisture transport vectors aimed
at us.  The Sunday system is the most impressive. Which makes sense
given it has the core for that EAJ feature coming at us.

What is a little different on today`s runs from yesterday is that
the Wednesday system is stronger (does not shear out as fast) so
that could result in a bigger impact for our area.  The Friday
system is farther south so we do not get into the warm air, but if
the warm front gets close to us we would have an enhanced tornado
risk. The Sunday system still looks powerful and will need to be
watched closely.

So, my bottom line is storm in the Wed to Sunday time frame.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 121 AM EDT Sun Apr 23 2017

VFR conditions will continue through Sunday.

Winds have become light and variable in many locations tonight.
Winds are likely to remain near or less than 5 knots through much
of the day Sunday. The exception will be at KMKG and KGRR, where
winds could increase between 5-10 knots as they eventually turn
out of the northwest during the afternoon. Dry air will provide
for clear skies and unlimited visibilities through the period.


Issued at 328 PM EDT Sat Apr 22 2017

High pressure will be over Michigan the next few days resulting in
relatively light winds and waves less than 3 feet.


Issued at 328 PM EDT Sat Apr 22 2017

The 7 river forecast points out of their banks are near crest or
already falling. Dry weather through Tuesday will allow rivers to
recede below bankfull on some but not all rivers. An active weather
pattern is probable for the region the latter half of the upcoming
week. There is a chance for basin-average rainfall to exceed 1-2
inches by next weekend, though there is low confidence exactly where
the axis of heaviest rain will set up. Many rivers will still be
running higher than normal going into this active pattern, so they
will be susceptible to at least minor flooding again if heavy rain
does occur.




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