-- Discussion containing changed information from previous version are highlighted. --
662
FXUS63 KGRR 280553
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
153 AM EDT Tue May 28 2024

.KEY MESSAGES...

- Potential for a few Thunderstorms Tonight

- Increasing potential for rain Tuesday Night, locally heavy

- Small lingering rain chances south Wednesday

- Dry and warmer period Thursday through Friday

- Occasional small rain chances Saturday-Monday

&&

.UPDATE...
Issued at 1027 PM EDT Mon May 27 2024

Tweaked POPs/Weather grids based on current radar trends showing
showers departing east-central forecast area and additional
showers moving in from the west. There have been a couple
lightning strikes that past hour over Wisconsin and southern Lake
Michigan. Convective instability is limited so only isolated
thunder is expected overnight, primarily across the southwest
forecast area.

&&

.DISCUSSION...
Issued at 223 PM EDT Mon May 27 2024

- Potential for a few Thunderstorms west  Tonight

Satellite WV imagery loops show a potent wave dropping out of the
Upper Plains towards Lower MI. Mid level height falls occur
overnight and models are showing 300 to 500 J/kg of MU CAPE
advecting into western zones. Forecast soundings become fairly
saturated. Thus an increased potential for a few thunderstorms
will exist then, especially west of US-131. SPC has this region in
a general thunder risk.

- Increasing potential for rain Tuesday Aftn into the Night, locally
heavy

A mid level low will be digging down into Lower MI later Tuesday and
into Tuesday night.  Lift increases and deepens as this feature
moves into the area.  Forecast soundings show deep moisture with low
lcl`s and thin deep CAPE that does not reach the trop.  Based on
this, there is an increased risk for the rainfall to become
efficient with relatively warm cloud tops.  The main question is
where the bands of rain will set up.  With the models varying on the
location of the pockets of heavier rain, it`s too early to say at
this time where they will ultimately set up, but it is something we
will need to monitor. The models seem to be catching on
to this potential by showing ensemble mean qpf values trending up.
The SPC`s HREF LPMM 24 hr qpf values show a couple of locations
with amounts approaching an inch, mainly over southeast and
northeast parts of the CWA.  For now we will increase the
potential for rain in this period.

- Small lingering rain chances south Wednesday

The trend over the last 24 hours is for the upper low complex,
currently over the area, to hold on just a little west than
previously thought. What this will do is keep temps aloft a tad
cooler, allow for short wave energy on the western flank of it to
linger over the area, and ultimately keep a small chance of P.M.
rain showers in.

- Dry and warmer period Thursday through Friday

We are still looking for a warmer and drier period for Thursday and
Friday. The upper ridge axis will be a bit closer to the area, and
the low level sfc flow will be from the NE ahead of the incoming sfc
high, bringing in much drier air. This may initially allow for some
cool temps Thu morning, especially across the cooler interior
portions of Central Lower where some frost will be possible.

After the frost early Thursday morning, we should be looking at dry
weather with warming temperatures. A short wave looks to clip the
eastern area on Thursday, but there will be no moisture for it to
work with. The broader scale ridging building in with the ridge axis
to our west will keep things dry also. The ridge axis will then be
overhead on Friday, likely bring a mostly clear day other than maybe
some cirrus spilling over the ridge.

850 mb temperatures are forecast to increase from the upper single
digits C on Thursday, to lower teens C on Friday. These temps aloft
should translate to highs around 70 on Thursday, and well into the
70s on Friday.

- Occasional small rain chances Saturday-Monday

A first look at the forecast with rain chances each day from
Saturday through Monday would seem fairly pessimistic. However, each
of the rain chances do not look impressive with a fairly zonal and
low amplitude pattern expected to be in place. Much of the period
will remain dry next Saturday through Monday with a few brief
chances.

The upper ridge bringing the dry and warming weather Thursday and
Friday will get pushed east, and will get knocked over by an
increasingly zonal flow across the northern half of the country.
This will allow some weak short waves to approach and move through
the area from Saturday through Monday.

The initial wave does look like it will have a chance to grab some
Gulf moisture as it moves by. In reality though, the wave is weak
and it is forecast to mostly miss the area to the south. Sunday is
the day with the lowest chances of rain, as there is some semblance
of weak ridging being over the area between short waves. It is tough
to accurately determine the track and timing of short waves this far
out, so will have a small chance in. There is a better wave that
looks to arrive toward Monday, but again details are too uncertain
to get to specific at this time.

It does look like we will stay mild to warm next week with no real
cold air in the area with the zonal flow in place.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
-- Changed Discussion --
Issued at 153 AM EDT Tue May 28 2024

Predominately VFR conditions prevailing overnight as scattered
showers overspread the area from WI. There is no lightning in
this activity currently and while the chance of thunder is non-
zero, believe the threat is too low to include in any of the TAFs
at this time.

There is some indication that MVFR cigs could become more
numerous between about 10Z and 15Z this morning, mainly south of
I-96, with even a low chance of some patchy IFR.

Mostly VFR anticipated for this afternoon although building
instability could lead to a few tstms developing. The threat
looks to favor the LAN and JXN terminals between about 21Z and 02Z
where better sfc convergence will be present.
-- End Changed Discussion --

&&

.MARINE...
Issued at 223 PM EDT Mon May 27 2024

Waves are running in the 4 to 5 feet range in the nearshore zones
at this time and winds are gusting over 20 knots. We will maintain
the Small Craft Advisory and Beach Hazards as a result. The
pressure gradient weakens later this afternoon so we should end up
with conditions falling to under criteria levels close to the 00z
Tue end time.

&&

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

&&

$$

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