Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221457
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1057 AM EDT Sat Apr 22 2017

LATEST UPDATE...
Hydro

.SYNOPSIS...
Issued at 309 AM EDT Sat Apr 22 2017

A large area of high pressure located in the Upper Plains will
track slowly eastward into the Great Lakes Region through the
weekend. This fair weather system will act to keep it dry.
A weak cold front will try to slip down from the north Sunday
night...but this feature is expected to diminish as it moves in.
A better shot for rain arrives for the middle part of the week
when a low pressure system tracks in from the southwest.

&&

.SHORT TERM...(Today through Monday)
Issued at 309 AM EDT Sat Apr 22 2017

Models are in relative agreement in tracking a high pressure
system in from the west through the weekend. The main issue
appears to be frost. Overall it looks like somewhat of a higher
risk tonight. This is because the cloud cover will be less and
with lighter winds. So...I added patchy frost to the for the
region tonight.

A weak backdoor cold front slips down from the north Sunday night.
At this time no precipitation is forecasted as this system will be
weakening...feature little or no lift and the atmosphere will
remain dry.

.LONG TERM...(Monday night through Friday)
Issued at 309 AM EDT Sat Apr 22 2017

A busy weather pattern returns to the region by mid-week with
several waves of precipitation possible through the end of the week.
A couple of these events could include heavy rain and stronger
thunderstorms.

High pressure will continue to exit east Monday night. The zonal
pattern begins to erode with southwest flow advecting warmer air
into Lower Michigan through the day Tuesday.

The first wave will be surface low that was originally expected to
arrive into the area Tuesday night. This system continues to shift
northwest in the latest guidance. Better dynamics stay west of Lower
Michigan until at least Wednesday, when a cold front tries to push
eastward. There are some timing differences between two models as we
go through the day. Forecast soundings point to a unidirectional
flow regime, which would suggest a linear pattern to storm mode.
Timing could make a big difference if storms could tap into any
afternoon instability. ECM guidance is much slower at pushing the
front through with a more south-to-north track in surface low, which
could keep rain in the forecast through early Thursday.

The second wave moves in Friday with much less confidence on
placement. Both the ECM/GFS diverge with solutions spreading
somewhere between Iowa and Ohio. This system will be patterned with
a much strong upper jet core that is crossing through the central
plains Friday. A warm front extending east of the low will result in
developing showers and thunderstorms for the Lower Michigan with
precipitable watter values pushing well over an inch. While the GFS
solution would be more progressive to a south-north precipitation
track, the ECM would point to a longer duration heavy rainfall
event. Given recent rain, high river levels and Wednesday`s system,
this will certainly be something to watch.

A third and final wave will depend on which model solution is right
on Friday`s system. The GFS would provide another cold front
convective line for Saturday, while the ECM would suggest lead to
showery remnants behind the back side of the system. This could also
have a great impact on temperatures. Should the ECM verify,
temperatures could be suppressed to the 60s, as opposed to the milder
GFS.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 617 AM EDT Sat Apr 22 2017

Relatively quiet weather forecasted for the TAF sites. VFR clouds
will be around today...along with winds generally under 10 knots
as high pressure will be building in from the west. An onshore
flow could develop along the lakeshore.


&&

.MARINE...
Issued at 309 AM EDT Sat Apr 22 2017
With high pressure in control of our weather...no marine headlines
are forecasted.


&&

.HYDROLOGY...
Issued at 1057 AM 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 or 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.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...JAM
AVIATION...MJS
HYDROLOGY...CAS
MARINE...MJS


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