418
FXUS63 KGRR 220739
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
339 AM EDT Sun Sep 22 2024

.KEY MESSAGES...

- Showers and isolated storms this afternoon, then dry and cooler

- Rain chances Monday Night through Wednesday

- Model differences in latter half of work week

&&

.DISCUSSION...
Issued at 339 AM EDT Sun Sep 22 2024

- Showers and isolated storms this afternoon, then dry and cooler

A cold front is slowly moving east across central WI early this
morning. Showers and thunderstorms continue to develop ahead of
this front and we`ll likely see rain this afternoon as the front
moves over the cwa.

Based on forecast soundings, instability is the lacking
ingredient this afternoon. LI`s are largely above 0c and CAPE
values are generally a couple of hundred joules/kg as the front
moves through. There is good moisture convergence along the front
thanks to a 40 kt LLJ and precipitable water values that climb to
near 2 inches. Shear values are decent, though, at 40 kts. We`ll
continue with the idea of most locations seeing rainfall. Roughly
a quarter to half inch of rain is expected before the front moves
through and precipitation moves east.

RH progs suggest that clearing will occur from the northwest late
tonight and spread across the cwa Monday. After highs in the mid
70s today, highs will be around 70 Monday.

- Rain chances Monday Night through Wednesday

Shortwaves in both the southern and northern streams will converge
on the Great Lakes in the early to mid week time frame. A surface
low will move into the area on Tuesday lingering in the area Tuesday
night. Deeper moisture can be seen on GFS Bufkit overviews from
Monday night through much of Wednesday. We have 30-60 pct chances
for precipitation (highest south) as the low moves through the area.
PWAT values reach the 1.00 to 1.50 inch range with the low, so
precipitation amounts could be locally towards 1.00 inch, but most
areas will stay well below that.

- Model differences in latter half of work week

Differences between the ECWMF and GFS begin to show up Wednesday
night in terms of how the upper pattern evolves. The GFS has more in
the way of ridging through the Thursday through Saturday time frame,
while the ECMWF has an upper low nudging our direction from the mid
Mississippi valley. Bottom line at this point is we will feature dry
weather for much of the Wednesday and Thursday time frame. Model
blends give us isolated chances for rain Friday and Saturday. We
will roll with that at this point, as confidence is low in the most
likely solution at this point for day 6 and 7.

Temperatures will be near normals early in the week with the clouds
and precipitation, warming to above normal once again by the end of
the week. 70s for highs look likely Thursday and Friday.


&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 214 AM EDT Sun Sep 22 2024

A cold front is located upstream tonight stretching from portions
of Central Wisconsin into Eastern Iowa. VFR weather is occurring
well east of the front here in Southwest Lower Michigan with
scattered areas of MVFR near the front off to our west. Showers
and thunderstorms are occurring at 06z especially over southern
Wisconsin. The front will make steady progress to the east today
and move through Southwest Lower Michigan in the afternoon and
evening hours. MVFR conditions will show up this afternoon as
lower ceilings fill in, which will trend to IFR in the late
afternoon and evening. Ceilings will dip below 1,000 feet between
21z and 02z near and just behind the front. At this point have
showers in the forecast, but we may need to add some thunder with
time as the threat gets closer. The thunder threat is not
significant or high, but will come between 18z and 23z. Isolated
to scattered storms are possible.

&&

.MARINE...
Issued at 339 AM EDT Sun Sep 22 2024

North winds will increase behind the cold front today. Wave progs
indicate waves will increase to 4-7 feet north of Whitehall this
afternoon. The higher waves will work south with time. We issued a
Small Craft Advisory and Beach Hazards Statement from this
afternoon through Monday morning for the hazards.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from this afternoon through Monday
     morning for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 4 PM this afternoon to 11 AM EDT
     Monday for LMZ844>849.

&&

$$

DISCUSSION...Duke/04
AVIATION...Duke
MARINE...04