Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 130044
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
844 PM EDT Tue Mar 12 2024

.KEY MESSAGES...

- Warm Temperatures Continue for Wednesday

- Showers and Storms Likely Late Wednesday into Friday

- Cooler This Weekend with low snow chances

&&

.UPDATE...
Issued at 844 PM EDT Tue Mar 12 2024

No need for an update to the forecast for tonight. High clouds are
moving through ahead of a weak cool front that will drop through
tonight. The air mass is quite dry, so no rain is expected with
this front.

&&

.DISCUSSION...
Issued at 219 PM EDT Tue Mar 12 2024

- Warm Temperatures Continue for Wednesday

The 925 mb temperatures are shown to warm up to 12 to 13 deg C on
Wednesday. Mixing to that level supports high temperatures into
the 60s once again. These values are at least 20 degrees above
normal for this time of the year. Ensemble max temperature plots
for GRR from multiple models show values in the 60`s and with a
slight upward trend from the previous runs. So confidence is high
that we will top the 60 degree mark. RH values are trending lower
for Wednesday. It`s looking like we will see some of the CWA drop
into the 20 percent range during the afternoon. Right now the
lowest readings are favored for interior Lower MI.



- Showers and Storms Likely Late Wednesday into Friday

Widespread showers remain likely late Wednesday into Friday with a
stationary front stalling in the southern part of Michigan or
northern part of Indiana. A slight uptick in QPF with the 12z
guidance with a generally 0.4-0.8 inch total, though there are low
(15-25% chances) of 1 inch or more. Higher amounts will be best
realized in any convective or frontogenetical enhancement. As of now
given how dry soils are at present, and the fact that the rain is
spread out, not expecting notable hydro impacts with this event.

The other piece of note is thunder potential. Elevated instability
continues to suggest thunder chances across Central and Southern
Michigan, particularly near and south of I96 and Thursday afternoon
and evening. 12z guidance continues to suggest that the main area of
surface based instability remains south of us. However a few models
suggest a slightly more northerly front and SBCAPE making it to the
I94 corridor so if this trend holds, wouldn`t be surprised to see
the marginal risk to our south be brought into this area, especially
if the destabilization process occurs more than expected. Overall
given the current expectations for frontal placement, the severe
weather threat looks to remain confined to our south towards the
Indiana border.

- Cooler This Weekend with low snow chances

A notable pattern shift occurs this weekend as upper-level troughing
drops through the area. A leading vorticity maximum and cold front
are forecast to drop through lower Michigan later Saturday bringing
20-30% chances of rain, mainly across Central and Northern lower
Michigan.

After that, the main trough becomes established keeping the area in
cyclonic flow. The associated Cold Air advection brings temps
falling into the upper 30s - low 40s by early next week. There is
the potential for Lake Effect snow showers by Sunday Night as a
vorticity maximum rotates through and low MUCAPE builds over the
Lake. However, ensemble 850mb temp guidance continues to show
temperatures that are marginal for Lake Effect formation. Given
this, lake effect snow is possible, mainly across Southwest Michigan
Sunday Night into Monday morning. However, certainty remains low at
this point in the forecast.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 713 PM EDT Tue Mar 12 2024

There could be some low level wind shear initially this evening
as surface winds weaken. Otherwise expect VFR conditions with SCT
to BKN ceilings around 25000 feet. Tomorrow winds become light and
variable for most of the TAF sites. FEW to SCT clouds around 5000
to 7000 feet are possible.

&&

.MARINE...
Issued at 219 PM EDT Tue Mar 12 2024

The vad wind profile from GRR is showing 25 to 30 knots up around
4k feet and we are mixing to that level, even on the lakeshore.
Thus we will maintain the small craft advisory. The mixing height
and winds at those levels do diminish this evening so we are
forecasting a weakening trend to the winds then.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 10 PM EDT this evening for LMZ844>849.

&&

$$

UPDATE...NJJ
DISCUSSION...MJS/Thomas
AVIATION...RAH
MARINE...MJS


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