901
FXUS63 KGRR 212325
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
725 PM EDT Tue Apr 21 2026
.KEY MESSAGES...
- Showers and a few storms yet through this evening
- Showers and storms Friday afternoon and Friday night
- Confidence increasing in a wet system late Monday into Tuesday
&&
.DISCUSSION...
Issued at 235 PM EDT Tue Apr 21 2026
- Showers and a few storms yet through this evening
The line of showers and a few isolated storms that developed to our
North and West have done so a bit earlier than expected. Mesoscale
analysis of typical parameters like MU CAPE indicates no instability
around, even with lightning ongoing. Forecast soundings show a
couple hundred J/kg of CAPE based around 650 mb or so. Mid level
lapse rates of 8.0-9.0C/km are also helping the cause. It seems that
the threat with any storm this afternoon would be some hail, or
downburst given the dry low levels that could help accelerate and
downward wind.
It seems that the band of showers and isolated storms should push
south of the forecast area by mid evening as a sfc front becomes
involved, and helps to push it out, along with the developing cold
pool.
We are then looking at a couple of mainly dry and warm days coming
up for the area tomorrow and Thursday. We see the long wave upper
ridge push toward the area, helping to bring a good deal of sunshine
toward the area. Even though the front moves through this evening,
we will actually warm a couple of degrees on Wednesday compared to
today. That is because of the building heights, more sunshine, and
really no cold air advection behind the front. The front will lift
back north as a warm front on Thursday. It is then that we will see
temperatures make a run at 80 degrees again. There is a non-zero
chance of a shower on Thursday as the warm front moves through.
- Showers and storms Friday afternoon and Friday night
We are still expecting the next batch of showers and storms to
arrive Friday afternoon and evening for the forecast area. We are
still expecting northern and southern branch energy to phase over
the Northern Plains. We then see left over energy from the southern
stream get steered NE toward the area on Friday. This is what will
drive the front in. The timing of the front is favorable coming in
during peak heating. Instability could build to over 1000 J/kg ahead
of the front. However, effective deep layer shear is quite low, less
than 20 knots. This lack of shear will limit the amount of potential
severe weather. Also, we do not see a good solid short wave come
right at us, as it will be more focused to our NW.
Showers and a few storms will linger into Friday night, before
clearing out by Saturday. We then are in between systems from
Saturday through the first part of Monday as the upper low stays
over the Upper Midwest, and we have to wait for additional energy to
arrive early next week for our next good chance of rain. It does
cool off some behind the Friday night front, but not much as the
much colder air stays up in Canada.
- Confidence increasing in a wet system late Monday into Tuesday
The upper low does look to drive the next bit of southern stream
energy coming in off of the Pacific up toward the area late on
Monday. This has been fairly consistent over the last couple of days.
The system will have a low level flow that will draw a good deal of
moisture out of the Gulf. This looks to be a fairly wet system for
much of the forecast area. Too early to tell if a severe weather
threat will be present given the uncertainty 7 days out.
&&
.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 725 PM EDT Tue Apr 21 2026
VFR conditons are ongoing, with fog likely to develop overnight as
skies clear out and winds slacken. Most TAF sites will reach
MVFR to IFR, with the potential exception of MKG. Periods of LIFR
are possible, mainly along I-94, with the probability 20-30% at
present. The one complicating factor is the development of a
Lake Huron-induced moisture boundary. Wherever this sets up will
determine how long restrictions last and the extent of visby
reduction. Highest uncertainty is for the I96 terminals
(MKG/GRR/LAN) invof of this boundary. Higher confidence in a
period of IFR and lower restirctions at AZO/BTL/JXN due to
moisture pooling south of the boundary. Any fog burns off by late
Wednesday morning with VFR conditions following through the rest
of the TAF period.
&&
.MARINE...
Issued at 235 PM EDT Tue Apr 21 2026
We will be leaving the ongoing Small Craft Advisory up this
afternoon to go until its expiration time. We are still getting a
few SCA wind gusts at the lakeshore, and the wave model shows we
drop below 4 ft around expiration time.
Our next marine headline event looks to ramp up in the Thursday
night time frame ahead of the incoming front. It is expected to
possibly last then into Friday night behind the front, before
diminishing.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...NJJ
AVIATION...Thomas
MARINE...NJJ
NWS GRR Office Area Forecast Discussion
