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263
FXUS63 KGRR 290549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Wed May 29 2024

.KEY MESSAGES...

- Risk for Showers/Thunderstorms Tonight

- Some Frost Possible North Wednesday Night

- Dry Thursday and Friday

- Periodic chances for rain Saturday through Tuesday

&&

.DISCUSSION...
Issued at 244 PM EDT Tue May 28 2024

- Risk for Showers/Thunderstorms Tonight

An approaching mid level cold pool in WI combined with surface
heating has destabilized the atmosphere over the CWA. SB CAPE
values were generally 1000-1500 J/kg. Effective deep layer shear
is weak. Thus we have been seeing scattered thunderstorms
developing. Due to the weaker deep layer shear the storms will be
pulse in nature. Small hail and cloud to ground lightning strikes
are the main forecast hazard. Locally heavy rain is possible as
these cells will be relatively slow moving. Low level convergence
is favoring areas east of US-131 for the greatest storm risk. We
did trend the forecast towards featuring a greater potential for
showers and thunderstorms for the remainder of the afternoon and
into the night. The cold pool does not arrive until tonight to
that will likely keep the risk for storms into the night.


- Some Frost Possible North Wednesday Night

A large area of high pressure will become centered just west of the
CWA Wednesday night. Northerly winds out ahead of this system will
advect down a cooler than normal airmass leading into the night.
With subsidence prevailing through a deep layer, any diurnal cloud
cover will scatter out during the evening.  With a weakening
pressure gradient and decreasing mixing, the winds will diminish as
well.  Thus we will see a good radiational cooling night.  Ensemble
guidance from the various models are coming into decent agreement
showing lows dropping into the upper 30s for north parts of the CWA.
 For now we will feature patchy frost and not go with a headline.

- Dry Thursday and Friday

Confidence remains high that we will see a couple of dry and sunny
days with moderating temperatures for Thursday and Friday. The upper
ridge axis over the Rockies today will slowly build to the east to
be over the area by Friday afternoon. Strong subsidence with this
ridge, and drier air advecting in from the NE initially will ensure
the dry and mostly clear skies. 850 mb temperatures in the upper
single digits C Thursday, and lower teens C Friday, will support max
temps around 70 on Thursday, and well into the 70s for Friday.

- Periodic chances for rain Saturday through Tuesday

Confidence is also becoming high that we will see our next chance of
rain arrive on Saturday, with periodic rain chances then through the
end of the period next Tuesday.

The models and their ensemble means are all showing the upper ridge
responsible for our nice days Thursday and Friday will be flattened
out by a strong upper jet expected to traverse across Southern
Canada. This will result in a zonal flow starting Saturday and
lingering through the end of the period.

The leading short wave that will help to flatten the upper ridge
will be our first chance of rain on Saturday. The wave will be just
strong enough, and there will be just enough moisture advecting in
from the south, to bring a decent chance of some mainly rain
showers. These could be enhanced a bit by diurnal heating.
Instability is pretty much lacking that a thunder threat looks
minimal.

With the decent wave coming through Saturday, there will be a decent
short wave ridge building in over the area for Sunday. This should
be strong enough to keep most locations dry on Sunday. The blend
continues to kick out some 20 pops for Sunday, which looks to be
mainly a pop up afternoon shower.

Beyond Sunday, timing of individual short waves and chances of rain
will be difficult to pin down. The flow will remain zonal, with
short waves continuing to move through at times. Chances are that it
will remain more dry than wet from Monday and Tuesday. Each day does
have a legit chance of rain. The best chance of rain right now looks
to move in late Tuesday with a more pronounced wave forecast to
approach the area.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
-- Changed Discussion --
Issued at 149 AM EDT Wed May 29 2024

VFR weather is expected to prevail through Wed evening with cloud
bases generally between 5000 ft and 8000 ft. Light rain will hang
on for much of the overnight hours around AZO/BTL, possibly
pivoting into JXN for a time as well. However the rain is light
and not causing much reduction to vsbys/cigs.

The rain over far srn lwr MI moves out toward 12Z, but cannot
rule out a few isolated diurnal showers redeveloping Wednesday
afternoon. A tstm is not completely out of the question either but
the chance is too low to mention in any of the TAFs at this time.
Skies clearing out Wed evening after 00Z.
-- End Changed Discussion --

&&

.MARINE...
Issued at 244 PM EDT Tue May 28 2024

Northerly flow will be on the increase through tomorrow leading to
hazardous conditions developing in the nearshore waters and
several surf zones. We will go ahead and issue headlines for parts
of the region based on the forecast of increasing winds and waves.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
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MI...Beach Hazards Statement from noon EDT today through this evening
     for MIZ064-071.
MARINE...Small Craft Advisory from 5 AM early this morning to 11 PM EDT
     this evening for LMZ844>848.
-- End Changed Discussion --

&&

$$

DISCUSSION...MJS/NJJ
AVIATION...Meade
MARINE...MJS