Lansing, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

326
FXUS63 KGRR 141813
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
213 PM EDT Wed May 14 2025

.KEY MESSAGES...

- Scattered Showers and Storms into this Evening

- Round of Strong to Severe Storms Thursday Evening

- Additional Chances for Showers and Gusty Winds

&&

.DISCUSSION...
Issued at 213 PM EDT Wed May 14 2025

- Scattered Showers and Storms into this Evening

This afternoon Mixed Layer CAPE values of 500-1000 J/kg and high
precipitable values around 1.4 inches will be present. Shear
however is lacking, therefore only expecting general thunderstorms
with heavy downpours as seen my the moist sounding profiles. Best
coverage could be along the lake breeze as it will aid in a source
of lift this afternoon with isolated to scattered coverage
elsewhere. Thunderstorms should taper off after sunset as the
inversion builds in with light and variable winds overnight. The
moisture trapped below the inversion could develop into areas of
fog into Thursday morning.

- Round of Strong to Severe Storms Thursday Evening

During the day, Thursday is expected to be dry as warm air aloft
prevents any thunderstorm. Dew points will continue to be in the
60s as we remain in our moist environment with precipitable water
values around 1.5 inches. Warm air advection ahead of the
925-850mb front will help erode our CAP allowing for thunderstorms
to tap into 2000 J/kg + of CAPE and 30-40 knots of shear Thursday
evening. There is ample directional shear in the low levels
creating plenty of spin in the environment which is favorable for
storms to rotate. Mid level lapse rates will also be favorable
for hail development. With these variables large hail (30 percent
chance of 2 inch diameter hail or larger), damaging winds, and
tornadoes.

The main window for severe storms will be between 8pm Thursday to
2am Friday from west (US 31) to east (US 127). There is some
uncertainty with the southern extent due to some drier air in the
mid levels, either way if storms develop they have a high
probability of becoming severe. With storms occuring overnight,
make sure you have a way to receive warnings and that you have a
plan to take shelter.

- Additional Chances for Showers and Gusty Winds

Friday should be breezy with a good amount of sunshine, though
ensemble members are far from settled whether this will be a day
with gusts around 30 mph or 40-45 mph. A shortwave trough rounding
the base of the low and a proximate cold front may touch off a
quick round of showers late Fri evening, perhaps thunderstorms in
Southern Michigan given the potential for instability rebuilding
to 500-1000 J/kg.

Saturday does have the potential to be another breezy day,
though the magnitude of peak gusts is still questionable among the
ensembles, dependent on the pressure gradient between the low over
the northern Great Lakes and the high over the SE US. Lingering
showers are possible through the morning hours before drying out
during the afternoon.

Canadian sfc high builds in early next week with potential for
scattered frost Sunday night and Monday night.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 131 PM EDT Wed May 14 2025

Scattered showers are ongoing across West Michigan, with isolated
thunderstorms possible at all terminals. Confidence in direct
impacts to a terminal is low, but IFR conditions are possible if a
storm does impact a terminal. Will monitor TAFs and amend as
needed.

Tonight, increasing dewpoints will lead to areas of MVFR fog,
particularly at MKG, LAN, and JXN, and possibly MVFR cigs as
well. The likely timeframe is 09z-13z before any fog mixes out
bringing MVFR conditions through the remainder of the period.

&&

.MARINE...
Issued at 213 PM EDT Wed May 14 2025

Areas of fog continue over the lake as moist air moves over the
waters. Have extended the Dense Fog Advisory through 00z (8pm ET)
and cannot rule out needing further extensions into the overnight
hours until winds increase Thursday morning.

Thunderstorms are likely Thursday Evening as a cold front moves
across the lake. Strong to severe storms are possible, with severe
storms capable of gusts in excess of 40 knots and large hail.

Southerly winds Friday veer to westerly by Saturday with winds of 15-
20 knots. Gusts to 30 knots and waves in excess of 4 feet are likely
to bring conditions hazardous to small craft.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Dense Fog Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

DISCUSSION...RAH
AVIATION...Thomas
MARINE...Thomas