Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241729
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
129 PM EDT SAT SEP 24 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sat Sep 24 2016

High pressure north of Lake Huron will provide fair weather today
and through most of Sunday. A cold front will pass through the
state on Sunday night and early Monday, bringing showers and a few
thunderstorms. Breezy and cool weather will follow behind the
front on Monday with scattered showers and highs only in the 60s.

&&

.UPDATE...
Issued at 902 AM EDT Sat Sep 24 2016

Forecasts were updated to account for a greater amount of cloud
cover to start the day. Mid level clouds were dropping
southeastward through the CWA and should persist for a few hours.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Sep 24 2016

Main issue in the near term is cloud trends. Higher potential for
sunshine today - especially this afternoon - as surface ridging and
drier air press southward through the region. Diurnal cu schemes are
not particularly strong today, scattered at best, although there
should be some mid/high cloudiness streaming in from the northwest.

Increasing clouds expected Sunday from west to east, although a good
chance for areas east of GRR to remain sunny much of the day. Low
chance pops arriving late in the day for MKG/LDM areas.

Nighttime frontal timing/limited instability (MUCAPEs below 500
J/KG) should keep thunderstorm coverage/chances fairly low Sunday
night. However the probability of showers will be high as axis of
high PWAT air over 1.5 inches precedes the front.

Upper low/cold pool aloft supports scattered showers on Monday
and perhaps even some thunder as steeper mid level lapse rates
arrive. A very fall like day for sure.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Sep 24 2016

We are looking at a period of cool and unsettled weather for at
least the first portion of the long term. We will see the wrn trough
that will drive the sfc front through in the short term, try to
close off over the Great Lakes as additional energy dives in. This
will drive the jet south of the area, bringing the cold pool aloft
and cyclonic flow overhead. This will keep the threat for showers in
through Wednesday. Some lake enhancement will be likely with plenty
of over water instability with Lake Michigan still in the lower 70s.

There has been decent agreement that the area would see conditions
dry out and temperatures moderate beginning Thursday. This was the
result of a strong enough wave rotating around the upper low, and
taking it east of the area. This was never a sure thing considering
we are dealing with an upper low that is always tough to forecast
the movement. We are starting to see some evidence that this low may
not kick out as quick as earlier expected, and linger around the
region. We are not adding rain chcs yet for Thu and/or Fri, but will
be monitoring. If the low takes longer to kick out, temps will
remain cooler than advertised right now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 124 PM EDT Sat Sep 24 2016

A nearly stationary band of MVFR clouds over KAZO should gradually
diminish over the next couple of hours as mixing slowly erodes the
clouds. Otherwise...the low level moisture is forecasted to remain
limited...which supports a VFR forecast. Showers will be pushing
in from the west after 18z Sun as deeper moisture starts to
arrive.

&&

.MARINE...
Issued at 330 AM EDT Sat Sep 24 2016

Offshore flow will keep wave heights below advisory criteria through
the weekend. Waves will begin to build Sunday night with the passage
of the cold front and westerly wind shift/increase, then significant
wind/wave action is high confidence Monday in cold advection/
cyclonic flow pattern.

Wave heights could easily approach 10-12 feet Monday afternoon
considering how warm the water still is (72F at the srn lk mi buoy).
This will create very steep lapse rates/deep mixing over the water.
Will also need to monitor waterspout potential although at this time
is appears the winds may be too strong on Monday. Gale
watches/warnings may eventually be needed for Monday.


&&

.HYDROLOGY...
Issued at 1140 AM EDT Sat Sep 24 2016

River levels are around normal for the time of year. Showers and
thunderstorms are expected Sunday into Monday night with additional
rain possible Tuesday into Wednesday. Up to around one inch of rain
is expected and therefore rivers and streams should remain below
bankfull through the week.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

UPDATE...MJS
SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...NJJ
AVIATION...MJS
HYDROLOGY...63
MARINE...Meade


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