316
FXUS63 KGRR 110533
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
133 AM EDT Sat May 11 2024

.KEY MESSAGES...

- Cloud forecast for aurora tonight

- Showers moving through tonight into Saturday

- Back to warm springlike pattern starting Sunday

- Rain chances on Monday and Friday

&&

.DISCUSSION...
Issued at 457 PM EDT Fri May 10 2024

- Cloud forecast for aurora tonight

Chances of an aurora are high tonight given the levels of various
indices that are monitored like the planetary kP index. Values
have reached 8 this afternoon which is a high confidence event
over Lower Michigan. The issue for folks in Southwest Lower
Michigan is the amount of clear skies we will have between
reaching darkness and before clouds advance into the area. For
instance, sunset in Grand Rapids is 853 pm this evening, but we do
not get to complete darkness until around 1005 pm. Clouds per the
HREF are advancing into Kent County going on midnight. So, the
opportunity in the metro area may be a couple of hours. To the
northwest towards Ludington, clouds come in even earlier which may
spoil the potential show. Best chances may be for an hour or two
from near Grand Rapids off to the south and east. Bottom line, once
it gets dark its worth a look to see if skies are clear. Given the
magnitude of this event, auroras are likely through the weekend.
Saturday night will be a better chance at mainly clear skies. We
will have to see whether the aurora chances continue into Saturday
night. Monitoring the kP index online may be the best way to see if
conditions remain favorable. Anything over a 6 is good for Lower
Michigan. 7 to 8 values are much better. The auroral oval forecast
is another way to monitor trends online. Final point...the band of
clouds in Wisconsin advancing our direction for tonight is fairly
narrow, so it may be worth trying to be opportunistic overnight to
look for breaks in the cloud cover.

- Showers moving through tonight into Saturday

A compact system will sweep through Southwest Lower Michigan
tonight and into Saturday morning. It looks to have increased in
speed and we will likely dry out quicker for Saturday afternoon
and evening than was expected yesterday. We have high pops
overnight when the main band of rain showers moves through.
Precipitation amounts look to be on the order of a tenth or two,
so fairly light. Any threat for thunder looks to be fairly small
given the time the precipitation is moving through away from the
diurnal max. An isolated thunderstorm cannot be ruled out tonight
however.

Saturday night looks to be mainly clear and cool. Patchy frost is
possible across Central Lower Michigan into Sunday morning, but at
this point holding off on any headline as our current lows are
mainly upper 30s.

- Back to warm springlike pattern starting Sunday

Deep upper troughing over the eastern CONUS will steadily deamplify
starting late this weekend and generally continue through next week.
This will gradually shift our mean flow away from the chilly
northwesterlies we`re in this weekend, and move in favor of a more
typical springlike southwesterly flow pattern. This will allow the
return of warmer 850 temperatures into Lower Michigan. Normal high
temperatures this time of year are in the upper 60s in Grand Rapids,
but we`ll spend much of the upcoming week in the lower to mid 70s.

- Rain chances on Monday and Friday

There are two main chances for rain for next week. Late Sunday night
and during the day Monday Lower Michigan will get pinched between a
shortwave passing to our north and a stronger 500 mb wave sliding
eastward out of Missouri. While we could see a few showers from the
northern wave Sunday night and Monday morning, we`re more likely to
see areas of rain form as the southern wave moves through later
during the day on Monday. This is not looking like a heavy rainmaker
at all, it`ll probably be enough to make for a gloomy wet day for
many folks on Monday.

Much of the middle part of the week will be very pleasant as we come
under the influence of some upper ridging moving into our area from
the west. For late in the week, we start to bring a more robust
upper trough through the Great Lakes. As it encounters the warm and
somewhat humid air that will have worked in here during the midweek
period, we`ll need to be alert for thunderstorm potential late next
week as better dynamics work their way into the area. Overall, this
is a typical springlike pattern and it looks like the classic battle
between cool and warm air will continue in our area over the next
10 days.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 129 AM EDT Sat May 11 2024

A line of showers with some vicinity thunder moves through
overnight with WNW wind gusts to 25 or 30 kts possible. Cloud
bases are expected to lower following the passage of this line of
showers. Model guidance is suggesting ceilings should hold above
IFR but will likely be in MVFR for most. A breezy afternoon is in
store with gusts once again reaching the 25 to 30 kts range.

&&

.MARINE...
Issued at 346 PM EDT Fri May 10 2024

Have opted to not issue a Small Craft Advisory tonight into
Saturday, but it will be close. A increase in southwest winds will
occur for a couple hours this evening, followed by a cold front
sweeping through overnight. Winds may remain elevated on Saturday
for a time as well. The issue with this potential event is that
winds do not stay up over a longer duration to produce a
substantial wave field. The best opportunity may be Saturday
morning behind the cold front. The WaveWatch3 produces a couple
hours of waves around 4 feet midday on Saturday before they
subside once again. Given the borderline wave heights and short
duration have held off on the Small Craft Advisory for now. If
these levels are maintained we may need to issue a SCA for a time
on Saturday.

Sunday looks like a better chance at needing a Small Craft
Advisory headline as winds ramp up out of the south. The mid lake
BUFKIT point even shows a brief period of gales being possible.
Given this is a warm air advection event have low confidence in
gales.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for
     LMZ844>847.

&&

$$

DISCUSSION...Duke/AMD
AVIATION...Hoving
MARINE...Duke