Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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691
FXUS63 KGRR 290024
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
824 PM EDT Fri Apr 28 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 333 PM EDT Fri Apr 28 2017

A weak wave will move along a stationary boundary through the Ohio
Valley late this evening into Saturday morning. This will bring a
round of light precipitation, mainly affecting southern sections of
Lower Michigan. The bigger story will come over the weekend as a
deepening upper level low swing from the plains into the Midwest.
Abundant moisture will surge northward, resulting in periods of
showers and thunderstorms from late Saturday into Monday. Much
quieter weather lies beyond Monday with below normal temperatures.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 333 PM EDT Fri Apr 28 2017

A heavy rain event is looking more likely beginning Saturday
afternoon and extending through the second half of the weekend.
Otherwise, light rain showers are possible late this afternoon
into early Saturday morning.

Visible satellite imagery continues to show extensive cloud cover
streaming in from the south this afternoon. Light to moderate rain
has developed along a quasi-stationary boundary, which stretches
from Central Illinois eastward to Central Ohio. This boundary will
continue to meander south of Lower Michigan through early Saturday.
In the meantime, a disturbance moves along the boundary late this
evening with rain showers lifting northward in Lower Michigan. Much
of the activity will be light in nature into Saturday morning before
a lull between rainfall late Saturday morning and early Saturday
afternoon.

Front begins to lift north as a warm front Saturday afternoon with a
strengthening ridge developing over the Southeastern U.S. The
boundary remains south of Lower Michigan with several waves of
energy moving along the boundary from SW to NE. Much of the rainfall
will be convective in nature over MO/IL. As it travels north, it
will provide a broad area of rainfall with some embedded
thunderstorms Saturday afternoon and evening.

The boundary lifts further north Sunday with copious amounts of
moisture streaming northward out of the gulf. The front will also
play a large role in highs reaching the 70s near the MI/IN border
and 40s through central Lower Michigan. PWATs reach well above one
inch late Saturday and stay there through all of Sunday,
especially through the heart of the CWA. Guidance in good
agreement with placing the heaviest rainfall into the SW corner of
Lower Michigan. Total rainfall amounts look to reach the 2-4 inch
realm through early Monday morning. Localized amounts higher than
4 inches are possible, especially in/near any convection.
Therefore, a flood watch will be issued from Saturday afternoon
through early Monday to cover flood possibilities for low lying,
flood prone areas.

.LONG TERM...(Monday through Friday)
Issued at 333 PM EDT Fri Apr 28 2017

The rain will gradually lighten up and become more scattered through
the early part of next week.  We will see a chilly period Monday
night through Thursday when some patchy overnight frost will be
possible. Then a drier and slightly warmer period is expected
late in the week.

Surface and upper low should be over NE IA Monday morning.  This
heads northeast into the U.P. by Monday night.  Monday morning rains
look likely still, but it should become lighter and more scattered
Monday afternoon.  The system only slowly heads into Canada, so it
will probably take until Tuesday afternoon or evening before we
finally see the rain completely end.

Chilly air follows the system, with H8 temps dropping to around -3C
by Tuesday night.  As skies clear we may have the risk of frost late
Tuesday night and again Wed and Thu nights.  At this point low temps
appear to be in the mid 30s each night, so the risk to area fruit
trees should be low, but stay tuned.  A short wave comes through Thu
night or Fri, but it appears the surface reflection is well south,
so will keep the forecast dry for now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 823 PM EDT Fri Apr 28 2017

A warm front will sharpen just south of the Great Lakes tonight
and especially on Saturday. The TAF sites across Southwest Lower
Michigan will see ceilings lower and thicken the next 24 hours.
VFR ceilings and mainly dry weather should be in place tonight.
There is a small chance at some MVFR ceilings tonight however we
did not feel the threat was high enough to include in the TAFs.
Ceilings should gradually lower tonight from 7,000-10,000ft to
around 3,500ft by Saturday morning.

On Saturday, the ceilings should lower into the MVFR range with
rain developing from south to north. Rain should spread into
southern Lower Michigan around 15z and move into the I-96 corridor
around 18z.

&&

.MARINE...
Issued at 333 PM EDT Fri Apr 28 2017

Winds will continue to shift this afternoon, predominantly coming
from the north-northeast tonight through much of the day Saturday.
Speeds will generally be 5-15 knots, increasing to 15-25 knots
Saturday afternoon. Locally higher winds may occur in/near
thunderstorms, but offshore flow should keep waves under SCA
criteria. Otherwise, the main concern will continue to be shower
and thunderstorm chances extending from late Saturday into Monday.

Monday brings the likelihood for hazardous conditions. Low pressure
will approach the area with better support for high wind and wave
action into early next week, especially with winds out of the south-
southwest.

&&

.HYDROLOGY...
Issued at 333 PM EDT Fri Apr 28 2017

In general, a fairly widespread 2" to possibly 4" of rain is
expected this weekend. This will certainly lead to river rises and
some areas may reach flood stage by early next week. At this point
no major flooding is anticipated. Forecasts will continue to be
adjusted with the projected rainfall and once the rain gets into the
basins the accuracy of the forecasts will increase. It is important
not to focus on the exact crest values necessarily since they may
change with the daily updates as the rain gets closer to the region
and eventually begins occurring overhead.

The greatest impacts at this point look somewhat similar to earlier
this month for the Sycamore Creek and Looking Glass River. Rises
above flood stage look likely. On the Grand, the river may hold just
below flood stage. If rainfall ends up being more 3"-5" across this
basin then higher crests would be achieved and flooding would likely
materialize.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from Saturday afternoon through Monday morning for
     MIZ043>046-050>052-056>059-064>066-071-072.

LM...None.
&&

$$

SYNOPSIS...JAM
SHORT TERM...JAM
LONG TERM...JK
AVIATION...Duke
HYDROLOGY...Hoving
MARINE...JAM



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