812
FXUS63 KGRR 092334
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
634 PM EST Sat Nov 9 2024

.KEY MESSAGES...

- Showery and Unsettled through Monday

- Tame Week of Weather for mid-November, Rain Chances Wednesday

&&

.DISCUSSION...
Issued at 330 PM EST Sat Nov 9 2024

- Showery and Unsettled through Monday

Nebraska upper low continues lifting northeast, reaching nrn Lwr MI
by Sunday evening then Quebec (as more of an open wave) by Monday
morning. Another nrn stream shortwave diving southeast from wrn
Canada follows on its heels reaching Lake Superior by Monday morning
then Quebec by Monday night.

Widespread rain associated with the warm advection pattern ahead
of the vertically stacked Nebraska low sweeps through late tonight
into early Sunday, bringing one quarter to one half inch of rain
to areas south and east of GRR and generally only a tenth of an
inch or less north of GRR.

The rain lasts only 3-4 hours at most locations before the mid
level dry slot arrives by mid morning Sunday. Low clouds and
patchy drizzle follow behind that and temps could briefly exceed
60 degrees before the sfc cold front/occlusion pass through in the
afternoon.

Decent cold advection pattern develops later Sunday afternoon in
the wraparound/comma-head of the upper low, with H8 temps near 2C
rushing in from the west by 00Z. The arrival of the H5 cold pool
near -25C supports steeper mid level lapse rates around 7 C/KM
for a time during the early evening which combined with lake
effect may support some fairly robust showers. Would not rule out
a rumble of thunder or small hail as equilibrium levels poke up
above 15K ft for a few hours.

Things calm down with the passage of the upper low/shortwave
later Sunday evening but low pops continuing for scattered
lighter showers in the cool/cyclonic flow off the lake. Breezy
Monday with a continued risk of a few showers as the clipper
system brushes by to the north.

- Tame week of weather for mid-November, rain chances Wednesday

After Monday, the remainder of the week is favored to be rather low-
impact weather with temperatures near to a little above normal.
Normal highs/lows for mid November are upper 40s / lower 30s, and
that is about where we will be on Tuesday then trend a little milder
during the latter half of the week.

Some questions remain regarding how much rain is expected on Wed to
Wed night and how late in the day it might arrive. The synoptic wave
pattern, while progressive and full-latitude across the CONUS, is
also tending toward splitting and remaining neutrally tilted over
the eastern US. The 12Z ECMWF exemplifies a drier possibility for us
as 500 mb vort maxima pass both north and south of Lower Michigan.
The middle 50 percent of QPF outcomes among the ECE and GEFS are for
around 0.1 to 0.3 inch totals, so a period of rain remains likely
though it is not a slam dunk. A handful of ECE and GEFS members, and
more among the CMC and the latest 12z ECE, are staying rain-free.
There remain outlier solutions for 0.5 to 1.0 inch of rain, though
dwindling in number.

There is medium confidence in mild temperatures continuing into next
weekend also, as high pressure and warmer temperatures build in the
southeastern US with troughing with cooler temperatures are favored
in the western US. In this pattern would loom precip chances for
latter part of the weekend or early next week as a low-pressure
system develops in the Plains/Midwest.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 629 PM EST Sat Nov 9 2024

Active weather for the TAF sites over the next 24 hours here in SW
Lower MI. Cloud bases and visibilities will be lowering down to
IFR and lower as a band of showers moves in by daybreak Sunday.
Then the showers diminish to drizzle and IFR and lower conditions
for much of the morning as a moist axis arrives. Cloud bases will
lift Sunday afternoon as front moves in from the west. However
showers along the front could lower conditions at times for the
afternoon. The wind will veer to the southwest to west behind the
departing showers late in the afternoon and become gusty with
values over 25 knots possible.

&&

.MARINE...
Issued at 330 PM EST Sat Nov 9 2024

A lengthy period of hazardous conditions is expected on Lk MI
beginning Sunday afternoon and continuing through Monday night and
a Small Craft Advisory will be issued. This starts as strong
southwesterly winds behind a frontal passage Sunday afternoon
which go westerly Sunday night then northwest on Monday and
northerly Monday night. Winds and waves finally subside and go
offshore on Tuesday as high pressure arrives from MN/WI.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 1 PM Sunday to 7 AM EST Tuesday for
     LMZ844>849.

&&

$$

DISCUSSION...Meade/CAS
AVIATION...MJS
MARINE...Meade