-- Discussion containing changed information from previous version are highlighted. --
506
FXUS63 KGRR 311038
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
638 AM EDT Fri May 31 2024

.KEY MESSAGES...

- Dry and mostly sunny Friday

- Showers and chance thunderstorm moving in Saturday afternoon

- Medium confidence in timing of shortwave features in progressive
flow regime next week

&&

.DISCUSSION...
Issued at 343 AM EDT Fri May 31 2024

- Dry and mostly sunny Friday

With the surface high pressure center slipping east of our area
today, high temperatures will be several degrees warmer than
Thursday with light southerly winds. Some cirrus clouds will be
streaming in, and those should be the only clouds given a very dry
middle and lower troposphere. Afternoon relative humidity is
expected to drop below 40 percent except near the cooler Lake
Michigan shore.

- Showers and chance thunderstorm moving in Saturday afternoon

A southern stream wave of low pressure over Okla/Ark today/tonight,
augmented by its associated convection, may move northeast toward
Indiana on Saturday, while northern stream troughing also impinges
on the Great Lakes. Low-level moisture surging north into Lower
Michigan during Saturday afternoon is likely to fuel showers and
possibly thunderstorms depending on the depth of instability that
can be achieved with modest lapse rates.

There remains considerable spread among the global and high
resolution ensembles in QPF max amount and placement by Saturday
night, given the uncertainty in how the southern wave`s propagation
may be tugged by its own convection amid weak upper-level flow.
Plausible rainfall amounts across the area range from 0.1 to 0.5
inches, with a chance of a swath of over 1 inch occurring. Southern
Michigan, including the Grand and Kalamazoo river basins, has a
relatively higher probability of receiving heavier amounts compared
to farther north.

- Medium confidence in timing of shortwave features in progressive
flow regime next week

Ensemble spread is decreasing and run to run consistency is
indicating higher confidence in the details for sensible weather
next week.

There continues to be a signal for rain late Monday as a shortwave
trough approaches and minors out...then a stronger signal on
Wednesday/Thursday as a better-defined trough or cut off low
approaches from the Northern Plains. This low figures in the
evolution of a longwave trough by the end of the week with cooler
than normal temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
-- Changed Discussion --
Issued at 637 AM EDT Fri May 31 2024

FR conditions will continue into Saturday morning. Winds will be
from the south AOB 10 knots today then light and variable tonight.
-- End Changed Discussion --

&&

.MARINE...
Issued at 343 AM EDT Fri May 31 2024

A gentle breeze from the south/southwest today will bring waves up
to 1 foot, perhaps 2 feet north of Whitehall. Hazardous winds and
waves are not expected Saturday either, though a thunderstorm may
develop over southern Lake Michigan during the afternoon. The next
chance of hazardous winds and waves is on Monday north of Grand
Haven.

&&

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

&&

$$

DISCUSSION...Ostuno/CAS
AVIATION...Ostuno
MARINE...CAS