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FXUS63 KGRR 081728
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
128 PM EDT Sat Jun 8 2024

.KEY MESSAGES...

- Showers Today, Breezy Sunday

- Risk for some Thunderstorms Thursday Evening

&&

.DISCUSSION...
Issued at 251 AM EDT Sat Jun 8 2024

- Showers Today, Breezy Sunday

Presently, shortwave ridging is keeping the area dry and clear
causing temps to fall into the 50s. However, rain showers are
beginning to develop across the northern Mississippi River Valley
thanks to a 700mb shortwave. These will continue to develop and
spread southeastward into West Michigan starting across Central
Lower this morning and expanding south through the day. Given LIs
staying positive today into tonight and little to no MUCAPE have
removed thunder from the forecast. HREF LPMM progs suggest 0.25"-
0.5" is possible north of I96 while less is expected south. Showers
wind down by 2am as the mid-level wave exits the area.

Sunday will be generally dry. A weak shortwave crosses through the
area in the afternoon causing increased clouds especially north of
I96. An isolated shower cannot be ruled out, however any coverage
would be to low to justify any PoPs in the forecast at present. A 20-
35 knot LLJ moves overhead Sunday, and when combined with mixing
heights climbing to over 5kft gusts of 20-30 mph are possible. Highs
today and Sunday will generally be from the upper 60s to mid 70s.

- Risk for some Thunderstorms Thursday Evening

Models are advertising a cold front dropping down from the northwest
during this time.  Zonal flow out ahead of this feature draws in an
unstable air mass into the CWA during the afternoon/evening.  A low
level jet is shown to strengthen over MI as this front moves in.
Also, a mid level jet streak of 50 to 70 knots moves in which will
lead to stronger deep layer shear. However the limiting parameter
for organized convection is the instability with ensemble surface
based CAPE values shown to remain well under 1000 J/kg.  If the
instability trends upward with time, we could end up with stronger
storms, which will need to be monitored.  For now, we will feature
chance POPs in the forecast for Thursday evening, which is supported
by the latest ensemble qpf trends.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
-- Changed Discussion --
Issued at 128 PM EDT Sat Jun 8 2024

Light rain is beginning to move through central lower Michigan
this afternoon. Along with these showers, expect slightly reduced
visibility and periods of MVFR and IFR cigs, especially southeast
of GRR. Lightning does not look like a major concern, but a few
flashes of lightning are not out of question. Drier air will move
into the region tonight leading to the return of VFR for Sunday.
Looking into Sunday, wind will turn gusty during the late morning
to afternoon.
-- End Changed Discussion --


&&

.MARINE...
Issued at 251 AM EDT Sat Jun 8 2024

Weaker gradient winds and diminished winds aloft will keep winds and
waves below levels hazardous to small craft today. The next day to
watch for potential conditions hazardous to small craft would be
later Sunday into Monday. A high pressure system across Central
Canada drifts south increasing gradient winds. Uncertainty as to the
extent winds increase for any sustained period of time exists, as
well as how well we can mix gusts down. This will be monitored for
the next 24 hours for the need for a Small Craft Advisory or a Beach
Hazards Statement if confidence increases.

&&

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

&&

$$

DISCUSSION...MJS/Thomas
AVIATION...Thielke
MARINE...Thomas