Lansing, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

416
FXUS63 KGRR 171943
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
343 PM EDT Thu Apr 17 2025

.KEY MESSAGES...

- Round of storms late tonight/early Friday

- Severe storms possible Friday evening

- Additional showers Sunday/Monday

&&

.DISCUSSION...
Issued at 343 PM EDT Thu Apr 17 2025

- Round of storms late tonight/early Friday

Complicated forecast next 36 hours with main fcst challenge being
convective trends/timing and strength.

Northward moving warm front, incoming 50-55kt low level jet, and
leading edge of higher PWATs sends a band of showers through the
area this evening. This is followed by increasing chances for
thunder overnight as MUCapes over 1000 J/KG arrive.

Various CAM runs have been hinting at the possibility of a decent
nocturnal MCS rolling through between 4 am and 9 am, favoring
areas near and north of I-96. The main threat with these elevated
storms would be small hail, heavy downpours and lightning although
some isolated stronger wind gusts cannot be ruled out. If Gravity
Wave Associated Convection (or GWAC) were to develop/occur then
some high gusts could reach the ground despite stable/cool
boundary layer conditions. (See recent paper by Borchardt et al
on the GWAC subject in Weather and Forecasting.)

After any early morning storms depart, we`ll have to watch for the
possibility of a few additional stronger, discrete cells
developing near the northward moving warm front/on the northern
edge of the incoming cap. Guidance shows a few updraft helicity
swaths north of I-96 from late morning through mid afternoon,
before the warm front lifts far enough north for the cap to become
better established. If those storms occur and can become rooted
in the boundary layer then a TOR threat may exist for a few hours.
There could also be a mesoscale outflow or two still floating
around from any earlier convection.

- Severe storms possible Friday evening

Presence of a capping inversion around 5K ft and CIN values of
200-300 J/KG will likely limit convective convective potential
between 18Z and 00Z Friday; possibly longer. The main impetus for
new development after 00Z will be the incoming, slow moving sfc
cold front but questions remain regarding the coverage and
strength of Friday evening convection since the really good mid
level lapse rates of 8-9 C/KM may be departing to the east around
that same time. If some overlap can exist then damaging winds
and/or large hail may occur. Svr potential wanes after Midnight as
instability drops off and sfc cold front works through.

- Additional showers Sunday/Monday

Upper low tracking from the srn Plains to WI brings another chance
of showers Sunday and Monday. Sfc warm front lifts back north
Sunday night but gets quickly pinched off by occlusion/cold front
sweeping from the west early Monday, so the thunder and svr threat
with that system looks quite low at this time.


&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 224 PM EDT Thu Apr 17 2025

Mid to high clouds will continue to increase with southerly gusty
winds through the afternoon. The big forecast concern will be the
frontal system moving through overnight. LLWS is expected after
00Z with a 55kt jet overhead. Expect 40 to 55kts of shear between
00Z to 12Z. Showers are expected to move through along the western
TAF sites beginning around 02Z to 04Z. Thunder is expected but
whether it moves over the TAF sites is the question. As such have
used PROB30 for timing for now. Periods of MVFR to IFR in
thunderstorms is expected. Some of the strongest storms could be
severe with damaging hail and winds possible. Best chance of
storms will be between 08Z to 12Z beginning at MKG and then
through JXN. Behind the front lower ceilings will then move
overhead with MVFR cigs possible after 15Z.

&&

.MARINE...
Issued at 343 PM EDT Thu Apr 17 2025

A period of hazardous winds and waves is expected on Lk MI through
Saturday morning. Strong southerly winds tonight and Friday
eventually shift northwesterly on Friday night with a cold frontal
passage. Also, rounds of thunderstorms will pose a hazard to
mariners from late tonight through Friday night. Can`t rule out
some areas of fog too once the warmer and more humid air mass
arrives on Friday.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 11 AM EDT Saturday for LMZ844>849.

&&

$$

DISCUSSION...Meade
AVIATION...Ceru
MARINE...Meade