246
FXUS63 KGRR 151142
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
742 AM EDT Sat Jun 15 2024

.KEY MESSAGES...

- Hotter and More Humid Sunday

- Heat and Humidity Still in the Forecast for Sunday and Next Week

- A Few Chances for Showers and Storms Next Week

&&

.DISCUSSION...
Issued at 335 AM EDT Sat Jun 15 2024

- Hotter and More Humid Sunday

High pressure will bring fair wx today with mostly clear to partly
cloudy skies and high temps in the upper 70`s to lower 80`s. Fair
wx will continue tonight as the high pressure ridges moves east of
our region.

It will become hotter and more humid Sunday as southerly flow waa
develops on the back side of the departing ridge. H8 temps
moderate to 18-20 C and high temps will reach the 85 to 90 degree
range tomorrow.

An overall shorter range guidance consensus shows potential for
scattered showers and perhaps a few thunderstorms tomorrow mainly
north of I-96 as a mid to upper level disturbance moves in from
the west. However convective potential will be mitigated
significantly by weak instability. The 00Z HREF shows stronger
instability tomorrow will stay well to the west to sw of our area.

- Heat and Humidity Still in the Forecast for Sunday and Next Week

So, while the heat and humidity still look on track for next week
there are certainly mixed signals that lead to slightly lower
confidence overall. The mixed signals are that while 500mb heights
rise into the 590s dm next week there are still disparities in high
temperature output. The ECMWF is still very bullish on 90s each day
while the GFS holds in the 80s. 590s heights do not happen that
often, so those are anomalous values. Conversely, the 850mb
temperatures are not all that rare by summer standards in Michigan.
A combination of the GFS and ECWMF operational 850mb temperatures
range between +16C and +21C from Sunday through Friday. These are
very typical 850mb numbers during warm spells, certainly not off the
charts. High 850mb temperatures would be in the +22C to +26C range
and we are just not seeing that. Ensemble high temperatures at GRR
are completely in the 80s in the GFS over the next 10 days. The
highest is 89 on Monday. The ECMWF ensemble guidance has 91 almost
every day between Sunday and Friday with 94 on Monday being the only
outlier.

The bottom line is that it will be a warm spell with upper 80s to
lower 90s temperatures for highs. Nighttime lows will remain in the
70s for days which does not happen all that often. A prolonged
period of warm weather with little relief coming at night, but
nothing too atypical for a mid summer warm spell. People without air
conditioning will need to be checked on through the week though as
the cumulative affect of the warmth will take its toll. Folks
working outdoors will need to be prepared for the warmth as well.

- A Few Chances for Showers and Storms Next Week

The GFS and ECWMF both have a boundary that sags into the area in
the mid to late week. Too early to be very confident in how
precipitation chances work out though. Moisture associated with the
front and potential precipitation could aid in keeping high
temperatures in check a bit. We do not have any pops in the forecast
that are above 20-30 percent.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 743 AM EDT Sat Jun 15 2024

VFR weather is expected the next 24 hours. Mid and high clouds
will stream in from the west through the forecast period with
bases at or above 15,000 feet. No restrictions to visibility are
anticipated. Southeast winds of 5 to 15 knots are in the forecast
today.

&&

.MARINE...
Issued at 335 AM EDT Sat Jun 15 2024

Rather minimal wave heights and wind speeds are forecast today.
Winds will veer to the southeast and begin to strengthen somewhat
late tonight. Winds will become southerly and ramp up to 15 to 25
kts causing wave heights to build particularly across our
northern marine zones. A small craft advisory will be needed Sunday.

&&

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

&&

$$

DISCUSSION...Duke/Laurens
AVIATION...Duke
MARINE...Laurens