000
FXUS63 KGRR 270618
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
218 AM EDT Sat Apr 27 2024

.KEY MESSAGES...

- Showers and Thunderstorms Tonight

- Slight Risk of Severe Weather Saturday evening

- Multiple Rounds of Showers and Storms Through Mid Week

&&

.UPDATE...
Issued at 1002 PM EDT Fri Apr 26 2024

As expected the initial batch of showers weakened as it
encountered the dry low level airmass in place here in MI. It
looks like there`s a gap in the precipitation moving in however a
larger area of showers/storms was headed our way from IL. Thus
later tonight we will see the precipitation on the increase and
towards daybreak, the instability increases steadily so that is
when the potential for storms ramps up.

Looking at the rest of the weekend, there is some indications that
a potential for excessive rain could evolve. Corfidi vectors
become short and a very moist airmass with low lcl`s and thin/deep
CAPE exists at times. Also a low level jet sets up both Saturday
night and Sunday night with a low level boundary around. It does
look like the models may be catching onto this risk with the 00Z
HRRR now showing some swaths of over 2 inches of rain by 00z Mon
here in the CWA.

&&

.DISCUSSION...
Issued at 325 PM EDT Fri Apr 26 2024

- Showers and Thunderstorms Tonight

An area of isentropic ascent in strong warm advection pattern is
bringing showers and embedded thunder into northern Illinois this
afternoon and this will be moving northeast through Lower Michigan
tonight. The storms are expected to remain elevated overnight. By
Saturday morning the steadier rain is done with just isolated
showers through the day as the warm front will focus shower
activity north of the forecast area.

- Slight Risk of Severe Weather Saturday evening

Convection will be limited across much of the forecast area
through Saturday afternoon under shortwave upper ridging, with a
capping inversion noted in model soundings, but we will have to
watch the northwest zones for initiation of convection during the
evening along a prefrontal trough aligned across central or
northern Lake Michigan. There is 30 knots of shear present in this
area along with 500 to 1000 J/kg of CAPE, so any convection that
initiates could become organized enough to present a severe
threat. Main threat at this point would be hail and isolated wind.

There could be an isolated tornado threat with some model
guidance showing potential for a triple point low across the
northwest zones during the evening.

- Warm With Multiple Rounds of Showers and Storms Through Mid Week

Additional showers and storms are likely Sunday into Monday
associated with forcing from an upper-level jet streak and aided by
a frontal boundary sitting across northern Michigan and a shortwave
from the parent trough ejecting through the region. Convection will
be favored across Central Lower for our CWA closer to the warm
frontal boundary, with MUCAPE values north of 500 J/kg suggesting
there will be an attendant thunder risk. SPC currently has us in
general thunder which is reasonable given that the favored region
instability is separated from deep later shear and the highest
likelihood of showers/storms.

Widespread showers then expand into the remainder of the CWA Sunday
night and continue into early Tuesday as a cold front drifts across
the area. MUCAPEs suggest thunder chances continue. Rainfall by the
time all is said and done Monday night looks to be from 0.3-0.4
inches in the southeast CWA to 1-1.5 inches up towards Ludington.

Dry conditions then take over later Tuesday. as a high pressure
system quickly pushes through the area. Conditions then become more
active Wednesday as we see a cold front driven through Lower
Michigan by a northern stream shortwave followed by additional rain
chances into Thursday as a surface low ejects north into the upper
Ohio Valley.

Temperature wise, highs in the 70s are expected to continue into mid
week. By late week, expect highs to fall back to near normal in the
60s as a thermal trough slides into the central Great Lakes.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 219 AM EDT Sat Apr 27 2024

A warm front stretches from Iowa southeastward into Northern
Illinois and Southern Indiana at 06Z. The front will steadily
work its way north and east through Southwest Lower Michigan
today. Typical weather associated with a warm frontal passage in
the spring can be expected...namely rain showers, embedded
thunderstorms and lower ceilings.

Lower ceilings will press into the TAF sites towards daybreak,
with MVFR conditions prevailing by 14Z-15Z. Showers will be likely
in the 08Z to 14Z time frame with some occasional thunderstorm
activity mixed in as well.

The MVFR conditions should try to lift out in the afternoon as we
surge into the warm sector of the system. Another round of storms
appears likely after 00Z, but much of this activity should remain
north of the TAF sites through 06Z Sun.

Winds will veer from southeast to southwest today with the passage
of the warm front. Wind gusts may eclipse 30 knots this afternoon
from the southwest.

&&

.MARINE...
Issued at 325 PM EDT Fri Apr 26 2024

Hoisted a Small Craft Advisory for later tonight through Saturday
night. Southwest winds should hit 25 knots and perhaps 30 knots at
times. Marine fog is possible as well with dew points in the mid
to upper 50s although the winds may be able to mix out the
inversion and disperse the fog to some extent.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for LMZ844>849.

&&

$$

UPDATE...MJS
DISCUSSION...Ostuno/Thomas
AVIATION...Duke
MARINE...Ostuno