385
FXUS63 KGRR 310645
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
245 AM EDT Sat Oct 31 2026
.KEY MESSAGES...
- Slight chance for rain this weekend
- Warmer and wetter by mid-week
- Limited forecast certainty from mid-week onward
&&
.DISCUSSION...
Issued at 245 AM EDT Sat Oct 31 2026
- Slight chance for rain this weekend
Current radar this morning shows isolated and mostly light elevated
showers crossing Lake MI and entering Lower MI. Upstream VWPs such
as KMKX/TMKE indicate strong lower tropospheric veering indicative
of forced isentropic ascent. The 31/00Z DTX sounding showed a dry
lower troposphere; this should result in spotty precipitation
amounts around a trace for Lower Michigan into today. Trick or
treating tonight does not appear at risk of a washout.
Sunday looks similar in terms of hit or miss light rain. A weak and
poorly phased upper trough and attendant PV max will cross Lower MI.
It`s not out of the question that a better coverage of rain will
result, but ensemble guidance such as the ECE has been trending
drier and this may speak to the continued dry lower tropospheric
conditions still expected.
- Warmer and wetter by mid-week
GOES-W satellite shows a phasing and meridionally deep upper trough
off the west coast about to move onshore. It will cross the Rockies
when a well developed Bermuda High allows increasingly favorable
moisture transport from the Gulf. The moist transport will be
augmented by troughing in the lee of the Rockies in response to the
approach of the upper trough. Consequently, we will be looking at
seasonably very large precipitable water values by Monday night,
with ECE mean values reaching or exceeding the 99th percentile
relative to climatology.
Not surprisingly, precipitation chances go up considerably around
this time thanks to the increased moisture and forcing for ascent.
Precipitation efficiency will be good but there is some question
about total amounts given that the trough will be fairly
progressive. Nonetheless, this is normally when fall leaves and
storm drains do their annual clogging dance. Thus, nuisance
flooding is certainly possible from quick rainfall accumulations
of even an hour or less. Severe weather is not expected and there
is some question about whether there will be enough conditional
instability for any thunderstorms in the first place.
We still expect anomalously warm temperatures early this week. To
illustrate, an expected high of 70 at Grand Rapids on Tuesday would
be about 15 degrees above normal.
- Limited forecast certainty from mid-week onward
Starting in the Wednesday timeframe, the previously mentioned
organized and phased upper trough appears to weaken while at the
same time there is background unphasing of the northern and
southern streams. There is a wide variety of possible forecast
scenarios during this transition. One tricky possibility would be
the development of a cutoff low to focus precipitation chances.
However, predictability for a targeted and relatively impactful
outcome such as this is very poor, so the best compromise at this
point is keeping PoPs in the 20 to 30 percent range for the latter
part of the week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 126 AM EDT Sat Oct 31 2026
No changes to previous thinking.
Probability of VFR at all terminals through 12Z: 95 percent
Probability of VFR at all terminals through 18Z: 90 percent
Probability of IFR at any terminals through 18Z: 3 percent
Brief light rain is possible at some of the terminals this
morning with no associated visibility or ceiling restrictions
anticipated.
As noted previously, fog this morning looks unlikely due to a
combination of increasing low to mid-level cloudiness and
stronger nocturnal boundary layer winds; these factors should
mitigate outgoing longwave radiation flux necessary for radiation
fog.
&&
.MARINE...
Issued at 245 AM EDT Sat Oct 31 2026
No concerns in the short term. Winds and waves could reach or exceed
Small Craft Advisory criteria as early as Monday afternoon however.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...TJT
MARINE...TJT
NWS GRR Office Area Forecast Discussion
