030
FXUS63 KGRR 090728
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
228 AM EST Sat Nov 9 2024

.KEY MESSAGES...

- Rain Expected Saturday Night into Sunday Night

- Another Round of Rain Wednesday/Wednesday Night

&&

.DISCUSSION...
Issued at 227 AM EST Sat Nov 9 2024

- Rain Expected Saturday Night into Sunday Night

Ridging and dry air looks to keep conditions dry through early
Saturday. A few CAMS try to spark off isolated showers ahead of the
main system but given a dry profile this seems to not be realistic.
After midnight deep moisture arrives. Forcing to start precipitation
will be driven by a wave currently visible on water vapor satellite
imagery over the Desert Southwest ejecting into the Upper Great
Lakes. Widespread rainfall will overspread the area, with PWATs over
1 inch and additional LLJ forcing warranting PoPs greater than 70%
across much of the area. No instability precludes any thunder from
the forecast.

Showers decrease for a time during the day Sunday as the dry slow of
this occluded system works across the area. The upper-level cold
pool and low-level moisture will keep scattered showers around, but
coverage much lower than overnight. As the dry slot exits later
Sunday precipitation coverage increases once again. The good news is
that the upper-level cold pool isn`t really that cold with 850mb
Temps only falling by 2-3 degrees. This will keep highs solidly in
the 50s and low 60s.

- Another Round of Rain Wednesday/Wednesday Night

At this point the extended forecast is mainly dry with high pressure
over the area through most of the Monday through Friday timeframe.
There will be another cold front moving through Monday and with some
lingering low level moisture we could see some shallow light rain
showers. Otherwise attention turns to the middle of the week as a
deeper trough moves through the Great Lakes Region. The timing of
this mid week system is varying between during the day Wednesday and
Wednesday night. There should be plenty synoptic support with upper
level jet divergence, positive vorticity advection, and warm air
advection. GEFS members are more progressive with the trough and low
pressure system while other ensemble members are slower bringing it
in Wednesday night. Hence the better probabilities (greater than 50
percent) for measurable precipitation at this time are Wednesday
night. This system will be better sampled once it moves into the
northwest CONUS Monday with timing becoming clearer for the Tuesday
morning forecast. Chances for thunderstorms with this round of rain
will be dependent on the timing.

Ridging quickly fills back in once the system passes ending the week
with pleasant fall weather. Highs next week will be mainly in the
50s with lows in the 20s and 30s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1140 PM EST Fri Nov 8 2024

VFR expected through the TAF period as FEW cirrus overnight
increase into Saturday with ceilings lowering to near 10-15kft by
the end of the TAF period. East to Northeasterly winds tonight
become southeasterly Saturday with winds of 5-10 knots. Isolated
SHRA cannot be ruled out ahead of the front according to the
latest high resolution models however low confidence in terminal
impacts precludes TAF inclusion. More widespread rainfall arrives
just after the TAF window, though some uncertainty on how fast
rainfall begins on either side of 06z at MKG prompts the inclusion
of a PROB30 group.

&&

.MARINE...
Issued at 227 AM EST Sat Nov 9 2024

The lingering influence of a departing high pressure system will
keep winds and waves below small craft advisory criteria until
Sunday morning. Then, a low-pressure system tracking across the
upper Great Lakes will lead to winds increasing Sunday afternoon
into Monday. Winds look to be 20-25 knots gusting to 30 knots from
the southwest and west. A Small Craft Advisory will be needed for
the winds and resulting waves. However given the event is still
about 36 hours out, will defer that for a future forecast package.
Winds then subside into Tuesday as a brief high pressure
system crosses the region.

&&

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

&&

$$

DISCUSSION...RAH/Thomas
AVIATION...Thomas
MARINE...Thomas