722
FXUS63 KGRR 220030
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
730 PM EST Thu Nov 21 2024

.KEY MESSAGES...

- Only light precip tonight

- Potential for Showers Monday into Tuesday

- Turning colder with winter impacts possible towards the end of
  next week

&&

.DISCUSSION...
Issued at 355 PM EST Thu Nov 21 2024

- Only light precip tonight

The big upper low is moving east and sfc cyclogenesis is
occurring across southern New England as the remnant low moves
south over Lake Michigan with an eye-like warm core feature. It
will continue to weaken and gets absorbed into the larger
circulation tonight, taking its precip with it. There could be
some brief clearing overnight which would allow for some icy
patches to form on pavement, otherwise travel impacts will
continue to be negligible.

North flow will keep most of the lake effect showers offshore
this evening with some movement inland later tonight and on
Friday. Model soundings suggest these showers will be liquid as
the DGZ loses saturation and wet bulb zero heights climb to 2 to 3
kft.

- Potential for Showers Monday into Tuesday

Models are showing a mid level wave digging into the Great Lakes
Region on Monday and tracking it east of the region Tuesday.  They
also show a negative tilt to the system so it will likely be
featuring stronger lift. Gulf moisture does get drawn into the
system with PWAT values shown to approach an inch along the MI/IN
border 18z Mon.  Ensemble qpf values still support a quarter inch or
less of qpf, so impacts look unlikely from this event.  Temperature
trends also support this event to be mainly rain.  The colder air
that wraps in behind the departing system may draw in enough cold
air to mix some snow in for northern zones.

- Turning colder with winter impacts possible towards the end of
next week

Models are in fairly good agreement in showing a deepening mid level
low over the Canadian Prairies Friday into Saturday next week.  If
this happens, we would see arctic air flowing into the Great Lakes
Region for the end of the week.  That would support an increased
risk for winter impacts.  The CPC 8 to 14 day outlook reflects this
trend by showing an increase potential for colder than normal
temperatures and above normal precipitation. Ensemble total
snow plumes also indicate this pattern change as well. Given the
upcoming holiday period, this will be something that we will need
to monitor closely going forward.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 727 PM EST Thu Nov 21 2024

Expect skies to slowly lift this evening with MVFR cigs lingering
until around 02 to 04Z. VFR will then prevail through most of the
overnight period. Early tomorrow morning, between 09Z to 12Z the
northerly flow on the backside of the departing storm will lead to
showers and a return to MVFR conditions, especially closer to the
lakeshore. Gusty winds upwards of 20 to 25kts will mix down after
15Z with MVFR enveloping the region through tomorrow. Periods of
IFR cigs will be possible Friday evening.

&&

.MARINE...
Issued at 355 PM EST Thu Nov 21 2024

Based on current obs and trends, the Gale Warning was replaced
with a SCA for all but the southern marine zone where the Gale
Warning was kept, but the expiration time moved up to 03Z. The SCA
end time was moved forward to Saturday afternoon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Gale Warning until 11 PM EST this evening for LMZ844.
     Small Craft Advisory until 1 PM EST Saturday for LMZ845>849.

&&

$$

DISCUSSION...MJS/Ostuno
AVIATION...MJS/Ceru
MARINE...Ostuno