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099
FXUS63 KGRR 111932
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
332 PM EDT Tue Jun 11 2024

.KEY MESSAGES...

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- Small rain chances tonight, Wednesday night

- Chance of showers and storms Thursday, strong to severe possible

- Summertime heat on the way
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&&

.DISCUSSION...
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Issued at 330 PM EDT Tue Jun 11 2024

- Small rain chances tonight, Wednesday night

Band of rain showers continues to march east across WI ahead of a
mid level shortwave and sfc frontal boundary. These features move
our way this evening but are generally weakening and the air mass
over MI is quite dry with sfc RHs in the 20s/30s. Expectation is
for mainly virga/sprinkles although not impossible some locations
see minor measurable amounts of a few hundredths so will carry 20
pct pops.

Clouds decrease early Wednesday as the shortwave departs and sfc
front washes out, leaving a mostly sunny and warmer day with
highs in the lower 80s. Another chance of rain arrives for late
Wednesday night as higher PWATs and a plume of steeper mid level
lapse rates arrive ahead of the next shortwave embedded in the
northwest flow aloft. Will carry 30-50 pct pops for showers and
tstms mainly west and north of GRR after Midnight.

- Chance of showers and storms Thursday, strong to severe possible

Bottom line up front: There remains a chance of showers and storms
out ahead of an approaching cold front Thursday afternoon. This
system could have enough wind shear and instability to allow storms
that form to become strong to severe.

In depth discussion:  An upper level trough at 500 mb with good
baroclinicity through the mid and low levels will be trekking
through the upper Great Lakes Thursday. In conjunction with this
upper level trough will be a positively tilted elongated mid level
trough that current models have extending all the way into the
Great Plains. Latest trends show a tightening gradient as the
system moves into the region along with a decent low level jet.
ECMWF mean PWATS are upwards of 1.25 inches with +1 standardized
anomalies. This is a good indication of ample moisture for
showers and storms and could mean the potential for heavy rain
along with any storms. Another factor is that daytime temperatures
should get into the 80s and there could be some surface humidity
from any precipitation late Wednesday night.

There are some caveats to the storm potential. Among them is that
while there are strong lapse rates of 7 to 8 c/km through the mid
levels, latest model soundings show some weak inversions that
could inhibit storm formation. Another is that early in the day
convection could limit daytime heating. This all parallels with
SPC`s marginal risk for Thursday. If storms do form there is the
potential for them to become strong to severe.

- Summertime heat on the way

High pressure will build over the intermountain west Friday into
Saturday. The building high will cause downsloping flow across Lake
Michigan and the lower peninsula. This should bring some gusty
winds Friday. Temperatures will remain around normal Friday and
Saturday before they rise 10 to 15 degrees above normal Sunday
through Tuesday. So summertime temperatures should arrive with Max
temperatures in the 90s through at least early next week. The
models begin to diverge on a solution as far as precipitation into
next week especially given the potential for the passages of some
MCS`s. Given the track of those systems will determine
precipitation chances early next week. So have slight chance
precip chances given currently depending on an future solutions.
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&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 131 PM EDT Tue Jun 11 2024

VFR cigs and vsbys will continue tonight through tomorrow with a
wind change around mid morning tomorrow.

&&

.MARINE...
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Issued at 330 PM EDT Tue Jun 11 2024

Waves build later tonight as southerly flow increases, but
current expectation is for winds and waves to remain below
advisory criteria. Another round of increased southerly flow
occurs on Wednesday night into early Thursday before veering
southwest then west on Thursday with a frontal boundary sinking
south through the GrtLks Rgn.

A Small Craft Advisory and Beach Hazard Statement may be needed
on Thursday and there may also be a few stronger storms with the
frontal passage. The t-storm threat ends for Friday but an
increase in north-northwest winds is expected Friday afternoon
behind the front in an advancing sfc high scenario, which may
necessitate additional marine headlines.
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&&

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

&&

$$

DISCUSSION...Meade/Ceru
AVIATION...Ceru
MARINE...Meade