462
FXUS63 KGRR 060207
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1007 PM EDT Sat Oct 5 2024

.KEY MESSAGES...

- Chance of showers or a thunderstorm late tonight

- Breezy Sunday, increasing fire weather concerns

- Cool and dry next week, then warmer

&&

.UPDATE...
Issued at 1006 PM EDT Sat Oct 5 2024

Will lower overnight pops a bit especially south of Highway M-46
and will considering removing them entirely south of I-96. Strong
to severe convection currently in north central WI is firing in
area of stronger 700 mb theta-e advection, and all of this
activity is lifting northeast into Upper MI where the better
moisture/lift is present closer to the upper low/trough. However
there is narrow corridor of 700 mb RH greater than 70 percent
ahead of the incoming front which comes through our area overnight
and could touch off a few showers and storms mainly north of
M-46. HRRR runs have been consistent in keeping convection well to
our north and the 3KM NAM which had been the most ambitious CAM
for our area is backing off as well in the new 00Z run.

&&

.DISCUSSION...
Issued at 324 PM EDT Sat Oct 5 2024

- Chance of showers or a thunderstorm late tonight

The risk for an isolated severe wind gust for the US-10 area is
still conditional on there being thunderstorms developing this far
south. The overall thoughts on this setup haven`t changed much in
the past day. Most 12Z convection-allowing models are still shy of
developing robust convection near and south of US-10. The better
chances are in northern Michigan where better mid-level moisture
transport convergence and upper-level divergence will be.

However, given moderately steep lapse rates and somewhat higher
ambient relative humidity expected in the mid to upper levels, there
is a decent depth of potentially effective updraft parcels around
700 mb. Depending on the degree to which inhibition can be overcome,
the door is open for the possibility of high-based convection to
realize 500-1000 J/kg of CAPE concentrated in the hail growth layer.
Model forecast temperature profiles in surface-850 mb layer, while
too stable for potential updrafts, does not appear to be overly
stable to any hail-laden downdrafts that might occur. The low and
strong southwesterly low-level jet ahead of the cold front, with 45
to 50 knot winds just 1000 to 2000 feet above ground, would be
liable to be mixed down in isolated spots if stronger convective
pulses do occur. The main time for this threat will be between
midnight and 5 AM.

Even without showers or storms tonight, there may be a few hour
period of 40 mph gusts spilling to the surface, off the top of the
marine layer, within a few miles of Lake Michigan between Holland
and Ludington.

- Breezy Sunday, increasing fire weather concerns

After weeks of dry weather, the conditions Sunday afternoon will
approach Red Flag in a portion of central to southern Lower
Michigan, as humidity drops to around 30 percent and west winds
increase to 15 to 20 mph with gusts over 30 mph. Areas east of a
line from Mount Pleasant to Kalamazoo are most concerning for fire
weather conditions.

- Cool and dry next week, then warmer

We are in for another stretch of dry weather next week.

An upper trough Sunday into Monday over the Great Lakes will usher
in cooler air to the region. Highs in the lower to mid 60s will be
common Monday through Wednesday. However, a warming trend will
develop mid week and carry us into the weekend as high pressure at
the surface and a building ridge aloft bring in warmer air from the
south. Friday and Saturday will see highs in the lower to mid 70s.
Dry weather is expected through the period.

Frost is possible over the northern cwa Monday night through
Wednesday night as lows dip into the lower to mid 30s.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 742 PM EDT Sat Oct 5 2024

Forecast remains fairly consistent. A strong LLJ will create wind
shear for several hours tonight ahead of a cold front that will
move through after 06z. Shower activity is still expected along
the front with storms possible to the north. There remains some
uncertainty as to whether the precip will extend southward enough
to reach the terminals. Have continued the use of VCSH at GRR. The
wind shear will intensify between 06Z until it relents around 11Z.
Gusty winds will continue for much of Sunday with the chance for a
stratocu deck to move in late in the day Sunday, after 21Z.
Though, that low cloud deck should remain VFR.

&&

.MARINE...
Issued at 324 PM EDT Sat Oct 5 2024

Not much change to previous thinking. The small craft advisory has
started for gusty winds from the southeast today. Will become more
from the south, southwest, then west later tonight.

Previous discussion...

Strong southerly flow ramps up today into tonight and gradient flow
increases with the approach of a low pressure system. Offshore flow
dominates through much of the afternoon with gusts of 20-25 knots.
This evening, a 50 knot low level jet likely brings gusts of 35-40
knots north of Holland, even with marginal mixing conditons. A Gale
Warning has been issued from 00z-09z. South of Holland, Gusts around
30 knots are expected starting this afternoon resulting in the
issuance of a Small Craft Advisory. Isolated gusts to gales cannot
be ruled out South of Holland however short duration and low
confidence preclude the issuance of a gale warning. Scattered
showers and thunderstorms could also bring locally higher winds.

Small craft advisory conditions are likely to continue across the
entire nearshore waters after the Gale Warning expires through
Monday afternoon. The advisory south of Holland currently runs
through 21z Monday and an advisory will need to be issued upon the
expiration of the Gale Warning to cover the continuing gusty winds
north of Holland.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT Monday for LMZ844-845.
     Gale Warning until 5 AM EDT Sunday for LMZ846>849.

&&

$$

UPDATE...Meade
DISCUSSION...04/CAS
AVIATION...04/Ceru
MARINE...CAS/Thomas