158
FXUS63 KGRR 141148
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
748 AM EDT Sun Jul 14 2024

.KEY MESSAGES...

- Showers and storms through this morning

- Severe weather possible late Monday and Monday evening

- A few showers and storms still possible Tue and Wed

- Dry and pleasant weather Thursday through Sunday

&&

.DISCUSSION...
Issued at 353 AM EDT Sun Jul 14 2024

- Showers and storms through this morning

We are starting out this morning with a MCS that is steadily
weakening as it moves through the area. The line of storms had gusts
to 30-35 mph as it moved onshore, and has only weakened to just
mainly showers and embedded storms as of 330 am this morning. The
most impressive aspect of this is the MCV that is well defined over
Muskegon and Newaygo counties. Thankfully there are no known impacts
with this like a wake low wind event, or anything else. This whole
complex will continue to weaken as it does not have deep and rich
moisture available ahead of it.

The next feature we are watching is the thunderstorm complex near
the MN and WI border as of 330 am this morning. This complex has
developed at the nose of a weak secondary low level jet feature
behind the first complex from earlier. Lots of instability out
there, and it doesn`t take much to fire something off.

The expectation with this is that we will likely see showers and
storms for at least the western half of the CWFA by mid-morning.
After that, it will likely weaken and shift south and east by late
this afternoon. Severe weather possibilities with this next complex
look fairly low. Anything that is a bit stronger will likely stay
west of the area as it follows the axis of the best instability
gradient. One thing that we will watch is for the possibility of
training storms that could lead to some minor flooding. We have a
very moist air mass in place, and rainfall will be fairly efficient.

It does seem that once the second batch moves through, the threat
for organized convection for tonight and early Monday will be quite
limited. A few storms could form for southern areas that might not
experience the storms later this morning, and with some untapped
instability would be present. This would most likely happen in the
late afternoon and evening hours. Then being in between features and
during the min in instability overnight, most areas would be rather
quiet and just warm and humid.

- Severe weather possible late Monday and Monday evening

The quiet weather will linger into the first portion of Monday,
before things could get quite active Monday afternoon and evening.

The lack of activity Monday morning will allow for the atmosphere
to destabilize well with at least some sunshine, and the warm and
humid air mass remaining in place. Temperatures are forecast to
warm to around 90 and dew points will be in the low to mid 70s.
This will drive heat indices up to the upper 90s across the south,
and slightly cooler further north. Right now with our expected
temps and dew points, we think we will be just short of Heat
Advisory criteria, and will hold off for now.

We will see a couple of short waves approach later on Monday, and an
associated cold front that will be poised to push through a bit
later. Forecast CAPE`s are expected to increase to almost 4,000 J/kg
by early Monday evening. The atmosphere will be mainly capped for
much of the day. The short waves and cold front will likely provide
enough forcing to go along with some weakening of the cap to fire
convection.

Once convection does fire, severe weather is very plausible across
the entire area, with all hazards in play. Deep layer shear values
are forecast to be around 40 knots. We will have a fairly strong low
level jet pushing in that will provide for plenty of low level
shear. The degree of instability, thick CAPE profiles aloft, and mid
level lapse rates 6.5 to 7.5C/km will all bring the large hail
threat. The wind threat will develop as the storms develop their
cold pool and 40-50 knots in the mid levels help out. A tornado
threat will also exist due to the strong low level shear with the
low level jet. SRH`s are forecast to increase to 200 by 00z Tue,
with 0-1km shear values of 25-30 knots, and 0-3km values of 35
knots. The hodograph has some nice curvature in the lowest levels
with the directional and magnitude shear in the lower levels.

This will linger through the evening, until the front can pass south
of the area overnight. Any training of these storms in this high
moisture environment could also cause some flooding.

- A few showers and storms still possible Tue and Wed

A shower and tstm risk may still exist on Tuesday, mainly south and
east of GRR, before the cold front completely clears the area.
Cooler and drier air arrives behind the cold front for Wednesday but
the upper trough will be digging in with a decent shortwave arriving
at peak heating. That will support another chance of showers and
storms, although relatively limited coverage expected and mostly
favoring the Mt Pleasant and Clare areas.

- Dry and pleasant weather Thursday through Sunday

The Thursday through Sunday period is looking dry with comfortable
temperatures and humidity levels as a sprawling area of high
pressure impacts the region. Mostly sunny days and clear nights
expected with highs near 80 and lows in the 50s.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 749 AM EDT Sun Jul 14 2024

The line of storms tracking east from WI early this morning
extrapolates into MKG around 14Z and into GRR/AZO around 15Z.
Could be a wind gust to 30 kts and brief IFR vsbys for an hour or
so as this line comes through this morning. Confidence is low as
to how much it holds together and if it impacts the terminals
farther east such as LAN and JXN. Looks like a lull in convection
can be expected this afternoon after the passage of the morning
convection with VFR likely. Additional storms are possible
tonight although the timing and coverage is low confidence at
this time.

&&

.MARINE...
Issued at 353 AM EDT Sun Jul 14 2024

We do not anticipate any headlines being needed through today for
marine interests. There will be an increase in wind ahead of the
stronger front later Monday, and behind it Monday night into
Tuesday. We will continue to evaluate the need for headlines for
those times. Not enough confidence to hoist them at this time, plus
we are still probably 36 hours away, so there is some time.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ050-056-057-
     064-071.
MARINE...None.

&&

$$

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