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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KGRR 230549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Tue Apr 23 2024

.KEY MESSAGES...

- Showers Tonight; Marginal Svr Risk Tuesday

- Another round of cold air mid-week

- Warm and potentially stormy next weekend

&&

.DISCUSSION...
Issued at 345 PM EDT Mon Apr 22 2024

- Showers Tonight; Marginal Svr Risk Tuesday

Breezy, mild and very dry conditions are in place currently with
sfc RH values of 15-25 percent and southwest winds gusting to
around 25 mph. Fuels have dried out considerably over the last
24-36 hours per land management officials and a Red Flag Warning
remains in effect through 8 PM.

The current dry conditions creates questions about rain shower
coverage later tonight as digging upstream trough and frontal
system begin to move in our direction. Guidance consensus is for
pops ranging from 80 pct around LDM and MKG where QPF should be
0.10 to 0.20, to 40-50 pct around LAN and JXN where amounts under
a tenth of an inch are anticipated.

Some clearing is expected on Tuesday in the wake of the departing
band of morning showers. Then the arrival of the upper trough and
cold pool aloft later in the afternoon initiates a batch of
diurnal convection, peaking between about 5 PM and 10 PM.

Steep mid (and low) level lapse rates on the order of 7.5 to 8
C/KM and deep layer shear as high as 80 kts will support a hail
risk. High sfc T/Td depressions (T/Tds roughly 65/40F) and
potential inverted V type soundings with higher LCLs could also
yield some localized stronger gusty winds. SPC has added the area
north of I-96 in the recent DAY2 update to a MRGL risk as
scattered to numerous storms move through during the peak diurnal
cycle.

Low topped convection waning quickly toward midnight Tuesday
night with loss of heating then another push of cold air arriving
overnight on the heels of northerly winds behind the front.
Advection freeze possible in northern sections of the area before
daybreak.

- Another round of cold air mid-week

We may have some brief residual effects of the Tuesday system
leftover Wednesday morning in the form of some clouds. There is good
agreement that the clouds in the morning will push out of the area
by Wednesday afternoon. The sun will come out, but much cooler air
will have overspread the area with highs barely reaching 50. This
cooler air will also set the area up for another night of some frost
and freezing temperatures with clear skies and light winds allowing
temps to drop quickly in the dry air mass.

We will start to see temperatures recover on Thursday and Friday as
the return flow setting up will bring the warmer temperatures aloft
over the area. We should see mostly clear/mostly sunny skies into
Friday before clouds will increase and thicken up ahead of the next
system.

- Warm and potentially stormy next weekend

There is good agreement that we are going to see a pattern change
for the area beginning Friday night and lasting into early next
week. The upper flow from the NW that has been in place over the
last week is going to lift north of the area. This occurs as the
broad upper ridge to our west is going to build over the area as a
long wave trough moves over the western portion of the country. The
ridge axis will eventually move east of the area, setting the area
up under a deep SW flow.

The SW flow is expected to live up to its typical warm and wetter
weather for the region beginning Friday night, and continuing into
Monday of next week. We will see multiple short waves eject out of
the main trough, and lift NE toward the area. We will be on the warm
side of the system most of the time as the sfc front stalls out to
our west with the waves riding along it.

This set up will also be a wet one as there will be a fairly steady
feed of Gulf moisture riding up ahead of the waves. The exact timing
and track of these waves this far out are tough to pinpoint with any
good degree of accuracy. The best thing to do at this point is to
get across that it will be warm and wet. We can not rule out some
severe weather with the approach of the waves. We will also have to
keep an eye on rainfall trends as this tends to be a pattern where
we see a better chance of some flooding over time.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
-- Changed Discussion --
Issued at 137 AM EDT Tue Apr 23 2024

A first batch of showers is moving onshore from Lake Michigan and
will move west to east across the area during the rest of the
overnight period. No thunder is expected in this batch, but gusty
winds are picking up associated with the arrival of the showers,
and even strong winds a few thousand feet above ground will
produce some wind shear conditions through 12z or so. VFR
conditions will continue throughout most of the day Tuesday,
although mid-level ceilings will linger for most of the day.
Additional showers and a few thunderstorms may develop in the
afternoon hours and move through Lower Michigan ahead of a cold
front that finally comes through Tuesday evening and switches
winds back to a northwesterly direction.
-- End Changed Discussion --

&&

.MARINE...
Issued at 345 PM EDT Mon Apr 22 2024

An active/hazardous period on Lake Michigan is expected from
tonight through Wednesday. Initially we will have south winds to
30 kts tonight ahead of an approaching frontal boundary, which
becomes southwest and decreases slightly on Tuesday as the front
nears. Winds shifting northerly to 30 kts behind the front Tuesday
night into Wednesday, possibly flirting with gales at times.
Hazardous winds and waves subsiding Wed night and Thursday as a
sfc ridge/high arrives.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
MI...None.
MARINE...Small Craft Advisory until 8 PM EDT Wednesday for LMZ844>849.
-- End Changed Discussion --

&&

$$

DISCUSSION...Meade/NJJ
AVIATION...AMD
MARINE...Meade