Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 231823
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
223 PM EDT SAT JUL 23 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 258 AM EDT Sat Jul 23 2016

A southwesterly flow of very warm and humid air will continue
into tonight. Well above normal temperatures are forecasted as a
result. A cold front will approach from the northwest Saturday
night and Sunday. This feature will then push through the region
Sunday night. With an unstable airmass in place...there will be
some scattered showers and thunderstorms around for the second
half of the weekend.  Dry weather returns for Monday.

&&

.SHORT TERM...(Today through Monday)
Issued at 258 AM EDT Sat Jul 23 2016

Despite the temperatures likely to climb into the 90s today...the
dewpoints stay mainly in the 60s. As a result...it looks like we
will fall short of the need for a Heat Advisory. Southern counties
will need to be monitored given their proximity to the moisture.

Its hard to say how the convection will evolve tonight into Sunday
night. The models are not handling the current setup very
well...especially the convective complex over Nebraska. What I do
see in the models that lines up with the stronger convection is an
850 mb low level jet. The nose of this feature intersects the axis
of instability...resulting in a complex. Looking ahead 24 hrs from
now...this low level jet strengthens as it pushes northeast
through WI and into the UP. Thus...it does appear another complex
will develop in that region tonight. The outflow from this feature
should push into part of my CWA later tonight and/or Sunday
morning. Will downplay the pops to start tonight...but keep them
relatively high for tonight.

The forecast area ends up on the divergent backside of the low
level jet Sunday and Sunday night. So somewhat of a limiting
factor is forecasted for widespread convection. Still the surface
front pushes into a warm and unstable airmass. Some synoptic lift
is forecasted as the mid to upper level wave pushes through...but
the trend is for weaker lift from this feature. Will keep a risk
for storms going. Stronger mid to upper level subsidence arrives
for later Sunday night into Monday. Thus the precipitation should
diminish quickly.

I did feature patchy dense fog in the morning forecast for today.
Observations show some around. The good radiational cooling will
continue for a few more hours...so the fog should expand somewhat.

.LONG TERM...(Monday night through Friday)
Issued at 258 AM EDT Sat Jul 23 2016

The long term portion of the forecast will start out dry and very
warm. It will then transition just a little cooler with some
intermittent chcs of rain showing up from mid-week and beyond.

The hot and steamy weather should be well south of the area by the
beginning of the long term as the cold front will be at least across
IN and OH. We will still maintain very warm temperatures with less
humidity. A short wave ridge aloft and associated sfc ridge will
keep the area dry through at least Tue night.

The chance of rain will begin on Wed, however we are not looking at
a real good chance until Wed night and especially on Thu. The
ridging will shift east of the area later on Tue, and some troughing
will start to work into the area. It will take a while for
sufficient moisture to advect into the area as the low level flow
will need to become srly to tap enough moisture for pcpn. Pcpn does
not look to be an all day event.

There will be chcs of showers/storms through the remainder of the
long term through Friday, but nothing looks too ominous at this
time. Heights will lower a little and the upper flow will become
more W/NW allowing for some cooler air to seep into the area. The
somewhat zonal flow will bring chances for showers/storms via
embedded short waves riding the jet stream from the Pacific NW.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 223 PM EDT Sat Jul 23 2016

VFR weather is expected the remainder of the afternoon hours and
through the evening as well. The only clouds will be a few
cumulus with bases around 4000ft and some cirrus from storms well
west of our area with bases above 20000ft. Winds will be light
for the most part this afternoon and evening outside of a lake
breeze near MKG where southwest winds to around 10 knots are
likely.

Storms will try to push into the area off of Lake Michigan
near MKG late tonight after about 09z-10z. These storms may push
southeast through the remainder of the TAF sites then through the
course of the morning hours of Sunday. Forecast has VCTS and VFR
weather at this point, but obviously local short term conditions
will dip into the MVFR or IFR category if/when storms move through
the TAF sites. Again storms will sag southeast through the area
Sunday morning between 10z and 18z.

&&

.MARINE...
Issued at 258 AM EDT Sat Jul 23 2016

I did feature patchy dense fog for the marine forecast to start
the day today. Observation sites along the lakeshore show some
thick fog in places. HRRR suggests this fog may extend over parts
of the lake. Mid lake buoy has an RH of 100 percent right now.

The pressure gradient is rather weak...and will stay that way for
the first half of today. The gradient tightens up this afternoon
and evening as the next wave of low pressure approaches. A
stronger low level jet pivots up through WI and the UP tonight. A
complex of storms will likely impact parts of the nearshore waters
later tonight or Sunday morning...resulting in locally higher
winds and waves.


&&

.HYDROLOGY...
Issued at 1256 PM EDT Sat Jul 23 2016

No river flooding is expected through next week. Up to three
quarters of an inch of precipitation is possible tonight into
Sunday night. A small chance of rain is also in the forecast
Wednesday through Friday. River levels are at or below normal for
this time of year, so this rain should not bring any rivers near
flood. Strong thunderstorms could produce localized rainfall
totals over 1 inch and lead to localized ponding of water.
Rainfall totals will probably vary substantially over short
distances.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...NJJ
AVIATION...Duke
HYDROLOGY...63
MARINE...MJS



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