457
FXUS63 KGRR 181940
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
340 PM EDT Fri Apr 18 2025

.KEY MESSAGES...

- Warm with periods of showers/storms tonight

- Another wet and breezy system Sunday through Monday

- Mild with small chances of rain Tuesday through Thursday

&&

.DISCUSSION...
Issued at 340 PM EDT Fri Apr 18 2025

- Warm with periods of showers/storms tonight

Low confidence forecast with respect to severe weather potential
and coverage this evening. Warmer, more humid air continues to
flow in from the south with temps in the 70s and dew pts in the
mid to upper 50s. Despite lingering cloud cover, some sfc based
cape is now developing south of I-96 and that is expected to grow
and expand farther north with time through this evening. However
RAP guidance continues to show 200-300 J/KG of CIN persisting for
several hours.

Mid level lapse rates of 8-9 C/KM are present over srn Lwr MI so
if the cap can be broken by either the shortwave approaching from
the southwest and/or the cold front slowing leaning in from the
northwest then strong to severe storms could quickly develop.
Large hail and damaging winds are the main threat. Will have the
highest pops early this evening north and west of a MKG to MOP
line, expanding/moving south and east with the slow moving cold
front through the night.

Shower and storm threat ending late tonight or Saturday morning
as the cold front settles south of the state but considerable
cloudiness lingering, especially south.

- Another wet and breezy system Sunday through Monday

Shower potential ramping up again later Sunday and Sunday night
as wound-up low tracks from the Plains toward Wisconsin. Best
shower and storm potential should be 06Z-18Z Monday when the sfc
occlusion and negative tilt upper trough is swinging through,
although some wrap-around showers will linger in the cold
advection Monday afternoon and night. Another aspect from this
system will be winds; with brisk easterly flow preceding it and
strong westerly flow on the back side.

- Mild with small chances of rain Tuesday through Thursday

Tuesday and beyond features occasional (but for now low) shower
chances with ripply zonal flow aloft and decent baroclinicity
overhead/nearby. There are no major cold intrusions shown and
temperatures for the mid to late week period are expected to be a
bit above normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 147 PM EDT Fri Apr 18 2025

Showers and storms will be the main focus for any aviation
concerns through the TAF period. This mornings convection brought
widespread rainfall along with some strong thunderstorms. Daytime
heating should couple with the added moisture to bring several
opportunities for showers and storms this afternoon and evening.
Models show the potential for mid afternoon convection which could
bring periods of TSRA to MKG, GRR and LAN. There is more
instability through the western portion of SW MI so have VCTS at
MKG and GRR and it is more likely to see TSRA between 22Z to 00Z.
While there is the potential at LAN, it could be just west of them
so have PROB30 group accordingly.

Showers and a few storms will remains likely at all TAF sites
between 02Z to 08Z. There is some LLWS concerns out ahead of the
line so have shear in the TAF`s until 08Z.

Behind the front will be an increase of low clouds with lowering
cigs into Saturday morning. That will bring MVFR to IFR cigs
between 08Z to 12Z. IFR looks more widespread with conditions
improving to MVFR after 12Z and VFR after 15Z.

&&

.MARINE...
Issued at 340 PM EDT Fri Apr 18 2025

We`re seeing a lull in winds and waves currently but will keep
the small craft advisory going into Saturday morning since the
cold frontal passage tonight will bring a period of increased
northerly winds. Occasional thunderstorms are also expected over
Lk MI tonight.

&&

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

&&

$$

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