242
FXUS63 KGRR 090532
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
132 AM EDT Thu May 9 2024

.KEY MESSAGES...

- Rain Thursday

- Rain Expected Saturday

- Lower Certainty Pattern Into Next Week

&&

.UPDATE...
Issued at 926 PM EDT Wed May 8 2024

Trends in the latest HRRR suggest this dry air currently in place
will play a more significant role in the timing and amount of
precipitation we end up seeing. Through 12z, there`s almost no qpf
seen in the CWA. Based on this, I trended POPs downward for
tonight and also shifted them further south, closer to the
moisture.

&&

.DISCUSSION...
Issued at 254 PM EDT Wed May 8 2024

- Rain Thursday

Clear skies this evening will give way to increasing clouds
tonight as low pressure over Oklahoma begins to get caught up in
the upper flow over of the northern MS Valley trough. Given the
east-west elongated nature of the trough, it will take at least 24
hrs for the low and its precipitation to move out of the cwa.

Model trends track the low across the north side of the OH Valley
tomorrow developing rain in the far southern cwa around 12z and
then moving north. Little in the way of instability means thunder
should stay south of the cwa. QPF totals have trended down a bit
and range from a couple of hundredths near US-10 to around a half
in near I-94. Light rain will end Friday evening.

Below normal temperatures are expected Thursday with highs in the
upper 50s. There could also be some patchy frost in low lying
areas near US-10 Thursday night as temperatures fall into the
upper 30s there.

- Rain Expected Saturday

Friday brings dry weather to West Michigan as high pressure and
ridging aloft shifts through the Central Great Lakes. It will be
slightly cooler than normal with highs in the low to mid 60s.

Our next chance of rain begins early Saturday as a shortwave drives
a surface low across the region. Rain showers are expected with the
best coverage Saturday morning as the low itself crosses the area.
However, some diurnal enhancement on the backside of the low is
possible Saturday afternoon as the upper-level cold pool passing
overhead given steep mid-level lapse rates in the 7C-8C range. If we
can get a shower with a better updraft, those lapse rates suggest
that isolated thunderstorms are possible.

- Lower Certainty Pattern Into Next Week

Dry weather is expected for the day on Sunday as a brief period of
shortwave and upper-level ridging slides through the state.
Precipitation chances do increase somewhat Monday as a shortwave and
cold front enter the region, however the timing and placement of
these features is uncertain. Ensemble means and deterministic
guidance do suggest a longwave trough develops but there remains
notable spread in model guidance as to the specifics of how the
pattern evolves. This gives lower confidence as to forecast details
in the days 5-7 timeframe.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 132 AM EDT Thu May 9 2024

VFR conditions will prevail through Thursday evening. Showers will
move in from the south during the morning but ceilings are
expected to stay above 5 kft AGL. East to northeast winds 10 to 15
knots through tonight.

&&

.MARINE...
Issued at 254 PM EDT Wed May 8 2024

East winds will develop tonight and could be gusty for a brief
period during the late morning/early afternoon Thursday but will
hold off on a headline due to the limited nature of it.

Colder air moving southeast early Saturday may result in 3-5 foot
waves south of Grand Haven for a period as well.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...MJS
DISCUSSION...04/Thomas
AVIATION...Ostuno
MARINE...04