671
FXUS63 KGRR 202257
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
657 PM EDT Mon Apr 20 2026
.KEY MESSAGES...
- Chance of storms south of I-96 late Tuesday
- Next best chance of rain late Friday
- Another wet system possible early next week
&&
.DISCUSSION...
Issued at 245 PM EDT Mon Apr 20 2026
- Chance of storms south of I-96 late Tuesday
We have now experienced a couple of full days of drying after the
frequent rains last week. High pressure at the sfc centered over the
area this morning is responsible for the mostly sunny skies and
light winds, with cool conditions persisting from the weekend. We
will see a significant bump in temperatures Tuesday as compared to
today as winds will be increasing from the SW and bringing in much
warmer air. 850 mb temperatures will warm from around -8C this
afternoon to +8 to +9C Tuesday afternoon.
Usually with significant warm air advection like this, we see
showers and storms accompany it. This is not the case this time as
the air mass is quite dry to start out today, so it will take a bit
longer to saturate.
We see some of this show up late Tuesday and Tuesday evening in the
form of a chance of showers and a few storms, mainly south of I-96.
We see a weak short wave aloft in the NW flow that will arrive here
late Tuesday. This will support a weak front dropping down through
the area. Ahead of the front we see some moisture pooling with dew
points increasing toward 50F. In addition, we will see a 30-35 knot
low level jet focus across Illinois, Indiana and Ohio. The nose of
this jet is what focuses the chance on the I-94 area.
The threat of strong storms is a bit on the low side, but not zero
for late Tuesday afternoon and evening. The factor that is limiting
the threat a bit is the limited instability present, which is likely
to be only a few hundred J/kg. Deep layer/effective shear is decent
at 30 knots or so. This should all move out by the early overnight
hours on Tuesday night with the passage of the weak front.
- Next best chance of rain late Friday
We are looking at another fairly dry period after Tuesday night,
from Wednesday through Friday morning. We will see the long wave
upper ridge axis approach the area, and bring strong subsidence to
the area. The ridge axis does not pass the area until overnight
Thursday night. This setup only allows temperatures to warm through
the period, even in the wake of the weak Tuesday front.
The passage of the upper ridge axis will allow a long wave trough
coming in from the Pacific, and a northern stream long wave trough
from NW Canada to potentially phase well west of our area over the
Northern Plains. This low will set up the scenario for our next best
chance of rain late Friday.
The models and ensembles have been fairly consistent in showing this
system come through later Friday. This is a little surprising
considering we have a low almost cutting off with the phasing of the
two streams, and the uncertainty with upper lows. We see enough of a
push from short wave energy to push the front into the area. There
is a decent flow from the Gulf that will supply the front with
moisture. This should bring showers and storms to the area.
The degree of strength of the storms late Friday is a bit uncertain.
Models show instability not being that strong, with less than 1000
J/kg of MU CAPE. This is likely due to the limited upper level
cooling with the low staying west of the area. In addition, deep
layer shear values are not shown to be that strong with values only
around 20 knots. Not much at this time to be concerned about, but we
will watch future trends if maybe some of the upper level cooling
can make it closer.
- Another wet system possible early next week
We do not see much cooler air move in behind the front for next
weekend. Again this is because we really do not see the upper low
make it to our area. It stays to our west, and we will be able to
clear out with just slightly cooler temperatures. Instead of the 70s
on Friday, highs will be in the 60s over the weekend.
We will see additional short wave energy rotate in on under the
upper low, and then head NE toward the area by next Monday. This
wave will have a chance at drawing additional moisture from the Gulf
and into the system. This system being seven days out has time to
adjust.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 657 PM EDT Mon Apr 20 2026
A ceiling of high clouds is moving in this evening, with upstream
observations suggesting cigs in the 10-15kft range overnight. LLWS
develops early Tuesday morning as southwest winds of 40-45 knots
develop at 2kft, with increasing gusts limiting low-level shear
after 15z. Gusts to around 25 knots are likely from the southwest
Tuesday. Lower cigs arrive late in the TAF period, with a low
chance of showers and maybe even an isolated thunderstorm after
20z. Have included PROB30 for showers at AZO/BTL where the best
signal is.
&&
.MARINE...
Issued at 245 PM EDT Mon Apr 20 2026
A Small Craft Advisory is needed for the entire nearshore this
evening through much of Tuesday. Winds will be on the increase this
evening as high pressure over the area moves east. Winds will start
out this evening for the northern zones, and gradually spread down
the shoreline by midnight or just after. Waves will increase, and
then lag the decrease in winds on Tuesday, dropping below 4 feet by
mid-late afternoon.
We will see a break in headline conditions for a couple of days then
as the gradient weakens in the wake of the weak system Tuesday
evening. The next period of winds and waves that might necessitate
another SCA will be late Thursday and Thursday night.
&&
.HYDROLOGY...
Issued at 245 PM EDT Mon Apr 20 2026
We are seeing most of the rivers now in the falling stage of this
last event. The crest this afternoon has now just passed Grand
Rapids, and is heading toward Lake Michigan. The Muskegon and most
of the Grand basins should remain mostly dry through Friday now.
This will help to allow the rivers to recover a bit after the recent
frequent heavy rains.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT Tuesday for LMZ844>849.
&&
$$
DISCUSSION...NJJ
AVIATION...Thomas
MARINE...NJJ
HYDROLOGY...NJJ
NWS GRR Office Area Forecast Discussion
