AFOS product AFDGRR
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Displaying AFOS PIL: AFDGRR
Product Timestamp: 2021-04-23 07:30 UTC

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317 
FXUS63 KGRR 230730
AFDGRR

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

LATEST UPDATE...
Synopsis/Discussion/Marine

.SYNOPSIS...
Issued at 330 AM EDT Fri Apr 23 2021

- Milder temperatures and a rainy Saturday

- Warm Tuesday then potential for heavier rain mid/late week

&&

.DISCUSSION...(Today through next Thursday)
Issued at 330 AM EDT Fri Apr 23 2021

-- Milder temperatures and a rainy Saturday --

Sunshine today will become increasingly filtered through 
cirrostratus and altostratus. A plume of slightly warmer air at 850 
mb will be over us, allowing high temperatures to reach near normal 
for the first time since Sunday.

Rain on Saturday (especially the all-day washout kind) is not 
guaranteed for everyone, and there remain considerable differences 
in rainfall amounts among HREF and ECMWF ensemble members ranging 
from less than 0.10 to as much as 0.75 inches even at any one 
particular location. The upper level trough is not fully phased as 
it passes over Michigan, with the two distinct vorticity maxima 
located over the Ohio Valley and northern Wisconsin/Michigan. The 
greatest potential for rain will develop amid a plume of mid-level 
moisture from the southern stream undergoing isentropic ascent over 
southern Michigan. It's this area of steady, more stratiform rain 
where models are most disagreeing with both amounts and northward 
extent, but this would provide the greatest potential for an all-day 
gently soaking rainfall. More showery (shallow convection) and 
spotty rain amounts may develop later in the day farther north in 
central Michigan associated with the northern upper level trough and 
surface cold front.

-- Warm Tuesday then potential for heavier rain mid/late week --

After a cool Sunday behind the cold front, temperatures rebound on 
Monday as strong warm-air advection resumes. There is a fair amount 
of spread among the ensembles for Monday's high temperature 
depending on how quickly the warm air can return, though a majority 
of ECMWF members give areas south of I-96 temperatures well into the 
60s, with central Michigan staying a little cooler.

Tuesday appears to be the day with greatest predictability next
week, with a sharp Rossby wave trough carved out in the western
CONUS and a building ridge over the Midwest.

&&

.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 330 AM EDT Fri Apr 23 2021

Models are showing 30 to 40 knot winds just 1000 feet above the 
water prior to sunrise this morning, however, the temperature 
inversion between that height and the water will prevent the winds 
from mixing down. Lake water temperatures are about 40 to 43 
degrees, insufficient to enhance mixing as temperatures at 1000 feet 
are about 45 degrees. No plans to issue a small craft advisory this 
morning, however, in warm advection environments with southwest 
winds, gusty winds can still occur in the harbors despite the 
inversion. Can't rule out some gusts from the southwest at 20-25 
knots this morning. Otherwise, conditions hazardous to small craft 
will hold off until Saturday night into Sunday.

&&

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

$$

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