254
FXUS63 KGRR 021132
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
632 AM EST Mon Nov 2 2026
.KEY MESSAGES...
- Small rain chances through Tue; Rain Likely Tue night/Wed
- Cooler with rain chances Thursday and Friday
- Limited forecast certainty this weekend
&&
.DISCUSSION...
Issued at 246 AM EST Mon Nov 2 2026
- Small rain chances through Tue; Rain Likely Tue night/Wed
No changes to previous thinking in terms of overall expectations.
Areas northwest of Grand Rapids, particularly around Ludington,
could see precipitation beginning early Tuesday morning shortly
after midnight. However this precipitation is expected to remain
out of most of southwest Lower Michigan.
The best chances for rain will be late Tuesday night and Wednesday.
Both SPC and machine learning guidance suggests that isolated
thunderstorms are possible, which seems reasonable given that
extremely strong integrated water vapor transport (based on the
ECMWF ensemble) and isentropic ascent will aid in elevated
convective destabilization. Elevated stability-altering processes
like these don`t tend to be parameterized well by global models,
including the GFS, so this is where machine learning guidance can
have an advantage by leveraging analogs associated with the
overall moisture and kinematic environment.
Forecast precipitation totals continue to decrease with successive
model runs. Instantaneous rainfall rates could be impressive; this
would be quite concerning if the expected warm cloud depth was
greater. Rain totals should be kept in check by this being a
progressively moving system.
The lower expected rainfall appears to be related to the trough
transitioning into a cutoff low over the midwest. At the same
time, at the southern extent of the deteriorating trough, there
looks to be a cyclonic wave break over the Lower Mississippi
Valley associated with a separate upper PV max. Hence, the best
forcing for ascent and resultant precipitation amounts now look to
occur in the Gulf Coast states and TN Valley area. This also
would reorient the low level moisture transport vectors to point
more east of our area via low level PV generation associated with
latent heat release in the precipitation area.
The final thing to note about Tuesday is that it will be extraordinarily
warm with highs now expected to be in the mid 70s. Guidance continues
to increase highs during this time. Wednesday also looks warm
with highs approaching 70s.
- Cooler with rain chances Thursday and Friday
We may have a break in rain Wednesday night, as noted previously,
but this is neither certain nor likely to be long duration. This
is because the expected dry slot may miss us to the east. In any
case, colder lower tropospheric air pours into the area Thursday
night into Friday with 850mb temperatures dropping close to 0C.
This will yield delta-T values in the lower/mid teens which is
sufficient for lake effect rain. Based on wind direction,
precipitation will be primarily across far southwest Lower MI.
- Limited forecast certainty this weekend
The upper pattern during this time looks wobbly and complex with
ephemeral cutoff lows rotating through a broader trough over the
Great Lakes. With steep lapse rates underneath the colder air
aloft, it would be easy to squeeze out rain showers from even
modest upper PV forcing. The latest guidance still does keep
Saturday dry and Sunday a little wetter, but given the extremely
poor predictability with this pattern, the weekend forecast will
be subject to change a lot during the coming week.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 632 AM EST Mon Nov 2 2026
Main changes this update was to was to speed up the deterioration
of ceilings into MVFR range this morning, with fuel alternate
ceilings below 2000 feet AGL now being possible as early as 16Z.
Next, some detail was added after 00Z, including chances for rain
showers as well as for low level wind shear. It seems increasingly
likely that IFR ceilings will be realized across much of southwest
Lower MI around or shortly after 00Z tonight and will likely
remain that way for the rest of the valid period of the TAFs.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 7 PM this evening to 7 PM EST Tuesday
for LMZ844>846.
Small Craft Advisory until 7 PM EST Tuesday for LMZ847>849.
&&
$$
DISCUSSION...TJT
AVIATION...TJT
NWS GRR Office Area Forecast Discussion
