684
FXUS63 KGRR 081145
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
745 AM EDT Mon Jul 8 2024

.KEY MESSAGES...

- Occasional Showers and Storms Through Tuesday

- Rain showers, some heavy, possible Tuesday night into Thursday

- Unsettled, warm weather continues into next weekend.

&&

.DISCUSSION...
Issued at 343 AM EDT Mon Jul 8 2024

- Occasional Showers and Storms Through Tuesday

Regional water vapor imagery shows a weak vorticity maxima across
Wisconsin that will slide into lower Michigan over the next few
hours. Combined with upper-level divergence showers will develop
across the northwest CWA near daybreak. An isolated rumble of
thunder is possible but confidence is low.

More widespread shower and thunderstorm chances arrive this
afternoon into the evening as a shortwave ahead of a parent trough
initiates convection off of a lake breeze convergence zone draped
across the CWA. We remain in the D1 general thunder as while MLCAPES
exceeding 750 J/kg are expected with MUCAPEs exceeding 1000 J/kg,
deep layer shear is marginal at 25-35 knots. Model soundings also
show modest mid-level lapse rates which means updrafts will struggle
somewhat as they develop. Cannot rule out isolated strong storms
(wind/hail risk) but that would be the exception and not the norm.
Showers and storms then subside overnight.

Latest trends Tuesday suggest that a front crossing into the area
stalls as the mid-level wave driving it shears out, as well as the
front undergoing frontolysis. Scattered showers and storms are
possible, mainly across the southeastern CWA where the dying front
stalls, however much of the area will be dry. While instability is
present, shear under 30 knots aided by near moist adiabatic mid-
level lapse rates will keep the occasional embedded thunderstorm non-
severe (if any convection can develop at all). Approaching 00z
Tuesday, the deformation rain bands associated with the remnants of
Beryl begin to approach the I94 corridor.

- Rain showers, some heavy, possible Tuesday night into Thursday

The models continue to hone in on the track and course of Beryl.  As
Beryl becomes extra tropical and moves to the northeast, there
continues to be run to run variability in both the ensembles and in
the operational models on the track. The NHC cone overall covers
most, if not all, of these potential outcomes. The biggest driver
for Beryl will be two fold. First the 300mb jet stream will move
through the midwest with a 100 kt jet moving over Michigan by
Wednesday night. Stepping down to 500 mb the remains of Beryl
becomes engulfed in the trough and should ride up into a weak
negatively tilted ridge. The biggest question is where the core of
the low goes from there. Ensembles and latest models continue to
waffle between various courses. However, even given the differences
between the runs, the overall course brings persistent tropical
moisture and showers through southern Michigan Tuesday night through
Wednesday and into Thursday. WPC has the region in a slight risk for
excessive rainfall and half one to two and a half inches over time
frame. So while some potential changes lurk on the horizon, a wet
period is ahead through mid week.

- Unsettled, warm weather continues into next weekend.

No major changes through the latter half of the week with slightly
warmer than normal Max temperatures ahead with periods of showers
and storms possible as a zonal flow will bring successive troughs
through the region. This should allow for potential for afternoon
convection through the latter half of the week and into next
weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 732 AM EDT Mon Jul 8 2024

Scattered showers and storms will be the main aviation concern
today. The first round is moving through with MVFR to IFR cigs
and vsbys at MKG for the next few hours. Another round of showers
and storms is possible this afternoon. The main TAF sites that
will be affected will be MKG and GRR.

&&

.MARINE...
Issued at 343 AM EDT Mon Jul 8 2024

Weak gradient winds keep winds and waves below small craft
advisory/beach hazard statement levels today into Tuesday. The next
timeframe of concern will be Wednesday and Wednesday night as the
remnants of Beryl approach the Central Great Lakes. Notable
uncertainty in the track of this system, and by extension the
positioning and strength of the gradient pattern exists. The trend
across 00z guidance is for a more easterly low track which would
reduce the impact of gradient winds across the lake. However, the
NAM and to some extent the Canadian model do suggest northerly winds
at least approaching small craft criteria. Bottom line is marine
interests may be impacted by the remnants of Beryl mid-week,
however uncertainty in the extent of this remains high. Stay tuned
to future forecast updates as the low track becomes clearer.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Ceru/Thomas
AVIATION...Ceru
MARINE...Thomas