Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251817
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
217 PM EDT Tue Apr 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 302 AM EDT Tue Apr 25 2017

A low pressure system developing over the Southern Plains region
will track northeast through Thursday...reaching the Western Great
Lakes. Southerly winds ahead of this system will draw up a warm
and increasingly moist airmass. As a result the dry weather
pattern that we have seen over the past few days will give way to
showers and thunderstorms by the Thursday.

&&

.SHORT TERM...(Today through Thursday)
Issued at 302 AM EDT Tue Apr 25 2017

Models are indicating an increasing potential for showers and
thunderstorms...although the trend continues to support a delay in
onset.

It looks like the greatest potential for showers and thunderstorms
will be Wednesday night into Thursday. This is when a strong low
level jet moves in from the southwest. This...coupled with
instability and some stronger deep layer shear may support a few
stronger storms. SPC has the marginal risk over parts of Southwest
Lower MI...mainly for later Wednesday night. Models do show a mid
to upper level wave taking on a negative tilt as it moves in from
the southwest later Wednesday night into Thursday. This is when I
will feature the highest POPs. Will also mention the potential
for stronger storms in the Hazardous Weather Outlook.

I did raise temperatures slightly for the daytime periods today
and Wednesday. With the delayed arrival of the precipitation along
with continued warm air advection...rather warm conditions will
move in. I would not be surprised to see a few 80 degree readings
on Wednesday...especially Battle Creek to Jackson region.

.LONG TERM...(Thursday night through Monday)
Issued at 302 AM EDT Tue Apr 25 2017

An active wx pattern will develop through most of the long range
fcst period.

A weak high pressure ridge will build in Thursday night into
Friday and bring a brief period of dry wx. However a warm front
draped across the lower Great Lakes region will focus development of
rain and perhaps some convection Saturday through Saturday
night.

A slow moving low pressure system will move into the Great Lakes
region Sunday through Sunday night and focus development of more
widespread rain and thunderstorms. Some of the rainfall
Sunday through Sunday night could be heavy as ample gulf moisture
will move north into our region.

The cold front will most likely move through Sunday night with
cooler weather to follow for early next week as the upper level
trough axis moves over the Great Lakes region Monday. Temperatures
should average near to slightly above normal Friday through the
weekend before cooling to slightly below normal by Monday.

$$

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 217 PM EDT Tue Apr 25 2017

VFR weather is forecast the next 24 hours with cloud bases at or
above 4000ft through the period. There will be some times, namely
this evening and again into the midday hours of Wednesday, when we
see ceilings around 4,000-5,000ft. Otherwise, mid and high clouds
are expected with bases at or above 10,000ft.

Winds will be from the south-southeast around 10 knots this
afternoon and evening. An increase in wind is expected late
tonight and into Wednesday, picking up into the 10-20 knot range
with gusts to around 25 knots.

&&

.MARINE...
Issued at 302 AM EDT Tue Apr 25 2017

The southerly flow will set up today and strengthen into Wednesday
as the low pressure system approaches from the southwest. The
longer fetch will favor the northern zones for higher wave
heights. Right now conditions are forecast to become marginally
supportive of a small craft advisory for Wednesday. Will hold off
on the issuance at this time.


&&

.HYDROLOGY...
Issued at 126 PM EDT Mon Apr 24 2017

Most river streamflow rates are running between the 75th and 85th
percentiles for April 24, so they are still running above normal
despite most having fallen below bankfull. An active weather pattern
will return late Wednesday and continue into next week. The concern
for rebounding river levels and possible flooding remains,
especially after the rain event likely to occur between Saturday to
Monday. A majority of the latest GFS and ECMWF ensemble members
produce at least 2 inches of rainfall over the area by next
Monday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...Laurens
AVIATION...Duke
HYDROLOGY...CAS
MARINE...MJS


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