255
FXUS63 KGRR 111709
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
109 PM EDT Sun Aug 11 2024

.KEY MESSAGES...

- Fair weather today through Monday

- Dry through midweek; better support for late-week rain

&&

.UPDATE...
Issued at 1137 AM EDT Sun Aug 11 2024

We expanded the mention of an isolated shower today for inland
areas. Satellite imagery shows clouds developing along the I-94
corridor and radar suggests there could be a rain shower or two in
that region. Thus we added that mention to the forecast. SPC`s
meso page does show MU CAPE values off 500-1000 J/kg inland. The
latest HRRR develops isolated showers inland this afternoon so we
expanded the mention of isolated showers even for Lansing, Alma
and Mt Pleasant.

Conditions on the lakeshore were marginally hazardous at this
time. The wind was on the increase and that should help to build
the waves slightly over the next hour or two, but the pressure
gradient is expected to weaken during the mid to late afternoon
hours and that will support diminishing winds and waves. No
changes to the hazard headlines.

&&

.DISCUSSION...
Issued at 320 AM EDT Sun Aug 11 2024

- Fair weather today through Monday

Any isolated early morning light rain showers and sprinkles will
end by mid morning as the upper level trough/vort max departs. It
will be partly sunny today with pleasant high temps reaching the
low to mid 70s as per latest ensemble guidance numbers. 00Z HREF
guidance suggests sct-bkn cloud cover will be moving out by late
afternoon with skies becoming mostly clear tonight.

925-850 mb temps continue to slowly moderate Monday. A sct-bkn
fair wx cu deck will likely develop particularly near to east of
US-131 along with some sct high cloud cover. It will be several
degrees milder Monday with high temps reaching the upper 70s to
lower 80s.

- Dry through midweek; better support for late-week rain

There now appears to be growing support in deterministic and
ensemble guidance for some appreciable rainfall toward the end of
the coming week into next weekend.

A digging upper trough approaching from the nrn Plains helps to draw
up Gulf moisture (PWATs >1.5") by Thursday night although decent
spread exists regarding the amplitude/movement of the upper trough
and the strength of the sfc reflection over the weekend.

The number of EC/CMC ensemble members showing 24 hour QPF over 1"
between Thursday night and Saturday has grown substantially and NBM
pops have trended up during this period as well. Best support for
the more substantial rain amounts looks to be in the Thursday
night/Friday timeframe although GEFS not looking quite as convincing
as EC/CMC.

The slow moving trough and sfc system slowly drift through the area
over the weekend which keeps shower and tstm chances going. However
the extent and duration of continuing rain chances look to hinge on
whether or not the upper low closes off overhead/nearby or if it is
a more progressive system.

Otherwise little change in thinking regarding the stretch of dry
weather continuing through mid week with near normal temps (highs
near 80) as surface ridging/dry air mass dominates.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1240 PM EDT Sun Aug 11 2024

No changes to the TAFs. Diurnal cu will largely dissipate toward
sunset leaving FEW-SCT070. Gusty west winds will all diminish to
less than 10 knots after sunset.

&&

.MARINE...
Issued at 320 AM EDT Sun Aug 11 2024

A beach hazards statement and sca remains in effect until late
this afternoon as fairly brisk wnw winds will result in wave
heights reaching around 3 to 5 feet. Winds and waves will finally
subside tonight as the low moves further away and pressure
gradient weakens.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 5 PM EDT this afternoon for MIZ037-
     043-050-056-064-071.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for
     LMZ844>849.

&&

$$

UPDATE...MJS
DISCUSSION...Meade/Laurens
AVIATION...04
MARINE...Laurens