Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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084
FXUS63 KGRR 280021
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
821 PM EDT Thu Apr 27 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 334 PM EDT Thu Apr 27 2017

In the grand scheme, the pattern will remain very active. Much
cooler air has settled into the region today with near to below
normal temperatures expected to extend into next week. A brief
period of dry weather is expected this evening through early Friday.
A weaker disturbance passing over Indiana will lead to a round of
light rain late Friday into early Saturday. A more vigorous upper
wave over the plains will send copious amounts of moisture northward
into the Midwest over the later half of the weekend. Heavy rain is
possible from late Saturday into Monday.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 334 PM EDT Thu Apr 27 2017

Relatively quiet weather is expected tonight into the first half
of Friday. We will see mainly dry conditions with the exception
to a few widely scattered/isolated showers lingering well behind
the upper low, as it rotates north into Canada.

Much cooler air continues to work into the area today. A boundary
settles to our south, which stretches through the Midwest and
Ohio Valley for the early portion of the weekend. A weaker
surface low travels along the boundary through Indiana late
Friday into Saturday. GFS is a little more spread out on precip
chances with probabilities stretching pretty far north into the
CWA. Higher res guidance, along with the ECM keep much of the
precipitation along and south of I-94. Despite probabilities being
carried through the entire area, the highest likelihood for
rainfall will be through the southern third of the state. Rain
chances should be minimal late Friday night as the wave moves
east and weakens.

The second round of precip comes in late Saturday and marks the
beginning of what could be a very wet period. As the upper level
jet lifts north, surface ridging begins to build over the eastern
conus. An area of overrunning precip is likely to develop as the
exit region of the low level jet approaches. Rainfall could be
heavy at times overnight Saturday with the gulf opening up and
PWATs exceeding one inch. A steady, widespread rain (at this
point) could extend into Sunday morning.

.LONG TERM...(Sunday through Thursday)
Issued at 334 PM EDT Thu Apr 27 2017

The wet scenario continues into the first part of next week.  An
upper low near Kansas City will continue to pump warm and very moist
air.  Meanwhile a front remains stationary near the MI/IN border.
Over riding across the front will be persistent and with
precipitable water values holding around 1.5 inches, a steady and
dredging rain seems likely Sunday and Sunday night.  Hydro issues
will likely persist into much of the week with 1 to 3 inches of rain
likely by early Monday morning.  The surface boundary finally lifts
north on Monday as the low drifts northeast into the NW Great Lakes.
This should result in lighter and more scattered rains on Monday.

The surface and upper low continues to drift NE into Ontario and
Quebec by Tuesday.  With the troughiness over the Great Lakes the
light rain should continue into tuesday, but gradually diminish
through the day.

The upper flow becomes more zonal with high pressure helping to dry
us out.  We may see a chance of light rain again by Thursday as low
pressure develops over the SE U.S. and moves northward.

Temps will cool down by Monday and remain chilly into Thursday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 820 PM EDT Thu Apr 27 2017

MVFR should persist through the evening with ceilings 1500 to 2500
feet AGL. There will be areas of IFR as well, mostly near MKG
early this evening as low clouds and light showers persist near
Lake Michigan. Conditions will improve to VFR on Friday morning.

Winds will decrease tonight with some gusts over 20 knots early
this evening then southwest winds around 10 knots through Friday
afternoon.

&&

.MARINE...
Issued at 334 PM EDT Thu Apr 27 2017

The cold front that was responsible for gusty winds through
Thursday morning has pushed east of Lake Michigan. Though
southwest winds will continue to be up around 25 knots this
afternoon, they will gradually subside as the evening progresses.
Waves of 3-6 feet will be common through the afternoon before
dropping to the 1-3 feet range Friday morning. The small craft
will continue until then.


&&

.HYDROLOGY...
Issued at 334 PM EDT Thu Apr 27 2017

All major medium range models continue to indicate a solid swath of
rainfall across our region late this weekend, with 1"-3" or more
expected. The heaviest amounts may fall across the central and
western reaches of the Muskegon, Grand, and Kalamazoo River basins.
We are expecting within bank rises at the least and a possibility of
flood stage being reached at some locations. If 4" or 5" ends up
falling across portions of these basins then a more significant
flood threat would result with even greater impacts.

There is about a 36 hour window when the vast majority of this rain
will fall from Saturday night into Monday morning. Small rivers and
streams may rise abruptly so residents along these types of
waterways should monitor closely throughout the day Sunday and
Monday in particular.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 2 AM EDT Friday for LMZ844>849.

&&

$$

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



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