413
FXUS63 KGRR 151940
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
340 PM EDT Wed May 15 2024

.KEY MESSAGES...

- Chilly night; showers and storms return late Thursday

- Above normal temps with a low risk of showers into the weekend

- Potentially stormy early next week

&&

.DISCUSSION...
Issued at 340 PM EDT Wed May 15 2024

- Chilly night; showers and storms return late Thursday

Dry air mass with sfc dew pts in the 30s/40s continues to
infiltrate the state from the north/northeast. As winds slacken
off tonight under mostly clear skies, expect chilly overnight low
temps in the lower to mid 40s. Some thin cirrus is expected to
arrive from the west late.

After a fairly sunny start to the day, the approach of a
shortwave from the west Thursday brings increasing clouds in the
afternoon along with a chance of a shower or storm by late in the
day. Developing southerly flow draws up sfc dew pts in the lower
50s which could set off a few diurnal showers and storms after
21Z or so. CAMs look to favor the area from GRR to the south
especially AZO.

Limiting factor for any stronger/svr storms looks to instability
with only about 500 J/KG SBCape or so vs 1500 J/KG to our west
over WI where SPC Day2 MRGL risk exists. Deep layer shear does
increase however to near 40 kts by the end of the day.

Shower/tstm coverage becoming more numerous for Thursday night as
the shortwave and associated sfc front draws closer and the
remnant WI convection heads our way. Again instability looks too
meager to support any stronger storms despite existence of decent
shear.

- Above normal temps with a low risk of showers into the weekend

The risk for spotty showers and storms will linger into Friday and
Saturday, though overall synoptic forcing will be weak. For Friday,
expect weakening low pressure north of Lake Superior, with an ill-
defined front/boundary trailing south across the Great Lakes. This
feature, albeit weak, will still support a low chance (20-30%) for
convection, particularly during the afternoon with the addition of
daytime heating. Low chance (20%) for showers continues Saturday
with daytime heating and weak upper low pushing into Ohio Valley
likely to throw moisture north in the region.  At this time, rain
chances appear very low for Sunday.

Overall, the Friday/Saturday/Sunday period will likely be more
indicative of an early summer pattern; though small chances for
convection will exist, sky conditions during the day should average
partly to perhaps mostly sunny, and highs will reach the 70s to near
80 /some 4-8F above normal/.

- Potentially stormy early next week

Deterministic and ensemble model output has been relatively
consistent the last few runs showing a strong mid level impulse (at
least for the month of May) progressing steadily ENEwd from the
California coast late Sunday to the Upper MS Valley and Great Lakes
region by Tuesday/Wednesday. Strong dynamics, low level moisture
advection in advance of surface feature, and May sun angle point to
the potential for storminess in West Michigan about Tuesday (give or
take) before cooler air arrives Wednesday-ish.

Not surprising at this forecast projection, much uncertainty exists
regarding timing/strength, though it will be worth monitoring as we
head toward early next week. High temperatures nearing 80 Monday and
Tuesday will cool by Wednesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 130 PM EDT Wed May 15 2024

VFR conditions and mainly light winds will prevail at all SW Lower
MI TAF sites through the valid period. Patchy mid level clouds
across far southern Lower MI will thin this afternoon through
early evening, with only some thin higher clouds expected tonight
into early Thursday. NE surface winds of 5-10 kts will become
light E tonight, before veering to SE Thursday morning.

&&

.MARINE...
Issued at 340 PM EDT Wed May 15 2024

Typical diurnal enhancement to the wind field in the marine
environment has occurred this afternoon as earlier northeast
breezes have turned to the north-northwest with some gusts now up
to 20 kts. Wave heights have responded and now seeing 2-3 footers
along much of the coast. These enhanced winds/waves will continue
through sunset before relaxing and turning offshore again. Other
than that, not really seeing any periods of hazardous winds and
waves for the remainder of the week and actually through the bulk
for the upcoming weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Meade/Smith
AVIATION...Smith
MARINE...Meade