Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 190235
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1035 PM EDT Fri May 18 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 318 PM EDT Fri May 18 2018

Low pressure will move north from the Ohio Valley spreading rain
into Lower Michigan tonight and Saturday. The low will pull away
on Saturday night but another low will bring more showers late
Sunday into early next week. Fair weather should return by the
middle of the week.

&&

.UPDATE...
Issued at 1035 PM EDT Fri May 18 2018

Overall our on-going forecast looks fine. I did some minor touch
ups to timing of the rainfall and increased the chance for thunder
Saturday afternoon as the latest NAM has nearly 1500 j/kg of
MUCAPE near JXN by mid afternoon. The LI index falls to around -3c
then too.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 318 PM EDT Fri May 18 2018

Timing the rain moving up from the south tonight is the primary
forecast challenge. Slowed down the arrival a bit from the
previous forecast based on current radar and short range model
trends. Otherwise, no major changes were made to the previous
forecast.

Thunder chances tonight and Saturday are low given limited
instability. Rain should be ending from west to east on Saturday
night with surface ridging bringing fair weather and near normal
temperatures for Sunday.

.LONG TERM...(Monday through Friday)
Issued at 318 PM EDT Fri May 18 2018

Flow regime does not change much through next week with the
persistent upper troughing across eastern Canada holding in
place. We will continue to see occasional bouts of rain
interspersed with fair weather as sfc lows move along the wavy
front that has been across the Great Lakes/Ohio Valley for the
past few weeks.

After a weak sfc low moves through early in the week with some
showers we can expect a stretch of mostly fair weather Wednesday
into Friday as a sfc high builds south from Canada. The high moves
east with return flow by the end of the week along with an
increasing chance of showers.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 741 PM EDT Fri May 18 2018

An area of low clouds and showers is moving northward into
Michigan from Ohio Valley and really from the northern Gulf a few
days ago. This system has a lot of moisture given it`s origin. So
there will be periods of rain into midday Saturday. The showers
may be heavy at time causing visibility`s to be IFR in the
heavier showers.

Convective instability (enough for thunderstorms) enters the
picture near and southeast of I-69 Saturday afternoon. I put VCTS
in the JXN TAF for this and considered but did not put it in the
LAN, BTL and AZO TAFS.

I expect widespread IFR ceilings by morning across the and it may
take until Sunday afternoon to lift those clouds out of the area.
The heaviest rain should be between 05z and 12z at most TAF
locations.

Winds at 2000 feet above ground level increase to around 40 knots
by 06z so I have included LLWS in our TAFs too. This should let up
by 12z.


&&

.MARINE...
Issued at 318 PM EDT Fri May 18 2018

Offshore winds will continue through Saturday and then go north
with waves expected to remain below 4 feet through Sunday.


&&

.HYDROLOGY...
Issued at 318 PM EDT Fri May 18 2018

River levels are high across southern Lower Michigan. The rivers in
central Lower Michigan are near to a little above normal. No river
flooding is ongoing. We are not expecting significant amounts of
rain, with less than an inch of rain expected through Monday for
most locations. This may lead to a slowdown or pause of the river
level falls.

&&

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

$$

UPDATE...WDM
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Ostuno
AVIATION...WDM
HYDROLOGY...63
MARINE...Ostuno



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