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000
FXUS63 KGRR 261925
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
325 PM EDT Fri Apr 26 2024

.KEY MESSAGES...

- Showers and Thunderstorms Tonight

- Slight Risk of Severe Weather Saturday evening

- Multiple Rounds of Showers and Storms Through Mid Week

&&

.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 /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 142 PM EDT Fri Apr 26 2024

A warm front to our south today will move through tonight causing
cigs to fall from VFR to MVFR levels from 05-08z. However, some
uncertainty to the exact timing of MVFR cig development is
expected due to complications of low-level dry air and how long
that takes to erode. Rain showers will also move in after 00z
leading to occasional MVFR visibilities as well. A few embedded
thunderstorms are possible mainly for sites MKG, AZO, GRR, and
BTL, where better instability intersects shower activity. Have
included PROB30 for thunder for these sites for the move favorable
window of TSRA. Widespread rain showers will end from west to east
between 12-15z and while isolated showers and storms are possible
behind the main grouping confidence is to low to include in the
TAFs.

The other notable concern is wind. Southeast winds of 10-20 knots
gusting to 25 knots will turn southerly overnight. A strong low-
level jet also moves in after 00z meaning TAF sites approach LLWS
criteria even outside of convection. Given the borderline
conditions given already elevated surface winds will let the next
aviation forecaster make the call on inclusion of LLWS when
surface observations show how far winds fall this evening.

&&

.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 from 2 AM Saturday to 8 AM EDT Sunday for
     LMZ844>849.

&&

$$

DISCUSSION...Ostuno/Thomas
AVIATION...Thomas
MARINE...Ostuno