159 
FXUS63 KGRR 230535
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
135 AM EDT Fri Apr 23 2021

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 233 PM EDT Thu Apr 22 2021

- Not as cold tonight as Upper Trough Moves East

- Rain on Friday night and Saturday as Low Pressure tracks south 
  of Lower Michigan

&&

.DISCUSSION...(This evening through next Thursday)
Issued at 233 PM EDT Thu Apr 22 2021

- Not as cold tonight as Upper Trough Moves East

Instability snow showers have moved east of the forecast area
this afternoon and even flat cu is dissipating as upper trough 
moves out and heights rise. After the last two nights in the 20s,
low temperatures tonight are expected to be in 30s with most 
places near or above freezing. 

Warm advection continues on Friday with moisture return beginning
on Friday but dry air in place during the day and any precip
should hold off until Friday night.

- Rain on Friday night and Saturday as Low Pressure tracks south 
  of Lower Michigan

Area of isentropic ascent and return flow moisture transport from
the Gulf/Southern Plains associated with southern stream low will
increase rain chances Friday evening. The low will be tracking 
south of Lower Michigan on Saturday and the northern edge of the
precip shield should reach our forecast area with a quarter to
half inch of QPF expected, mostly in the 12 hour period between 
12Z Saturday and 00Z Sunday.

Model soundings show general lack of instability and thunder is
not included in the forecast at this time. Colder air on the back
side of the low Saturday night arrives after the deep moisture
pulls off to the east, with the DGZ unsaturated after 00Z Sunday.
So at this point it looks like the potential for any snow across 
the northern zones is low on Saturday night despite thermal
profiles below freezing.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 135 AM EDT Fri Apr 23 2021

VFR expected through the forecast period. Only challenges are low
level wind shear between the ground and 1500 feet through about
1200Z this morning, which will transition to being wind gusts 
that mix down to the ground during the day. High altitude clouds
will increase during the day and gradually lower, becoming VFR to
MVFR ceilings by late Friday night.

&&

.MARINE...
Issued at 233 PM EDT Thu Apr 22 2021

After a spell of fairly tranquil conditions could be hazardous to small
craft on Sunday into Monday with winds over 25 knots and waves 4
to 6 feet.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Ostuno
DISCUSSION...Ostuno
AVIATION...CAS
MARINE...Ostuno