Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KGRR 231905

Area Forecast Discussion
National Weather Service Grand Rapids MI
305 PM EDT Sun Jul 23 2017

Synopsis/Short Term/Long Term/Marine

Issued at 305 PM EDT Sun Jul 23 2017

A few showers/thunderstorms possible across south central and south
eastern michigan through this evening. Quiet weather early this week
followed by a more active pattern for the end of the work week.


.SHORT TERM...(This evening through Tuesday night)
Issued at 305 PM EDT Sun Jul 23 2017

Not a ton of instability to aid in shower/thunderstorm development
with the greatest risk for any storms this afternoon remaining
mostly to the east/southeast of the Grand Rapids forecast area.
Ongoing showers...mainly over jackson county should exit by 5pm
or so with little/no severe threat expected before then. As the
showers move off...high pressure begins to build in with a
pleasant and less humid start to the work week expected. Cloud
cover should be abundant for most of the day Monday with Tuesday
seeing more sun than clouds.

.LONG TERM...(Wednesday through Sunday)
Issued at 305 PM EDT Sun Jul 23 2017

The main challenge in the long term deals with the timing and
strength of the convection Wednesday into Thursday.

Models are showing a series of mid level shortwaves arriving
Wednesday night. The atmosphere becomes moist and unstable during
the day on Wednesday with PWAT values forecasted to climb to close
to 2 inches and lifted index values down to at least -2 deg C.
However the cold front does not push in until later at night or
Thursday morning. Any stronger deep layer shear does not arrive
until after midnight and it is shown to weaken with time, which is
when the instability will be weakening.  Thus the severe weather
risk seems somewhat diminished at this time.  As a result will
continue to feature the potential for storms Wednesday into Thursday
with the highest POPs for Wednesday night.

The new High Res Euro supports a slower departure of the last mid
level wave to track through the CWA.  This model would favor keeping
a potential for showers/storms going into Friday.  The GFS is faster
and supports dry weather for Thursday night into Friday. I will hold
onto a risk for showers for the eastern CWA Thu night. Trends will
need to be monitored here.

Steady mid level height rises are forecasted for the weekend, which
should translate into a warming trend.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 142 PM EDT Sun Jul 23 2017

The atmosphere has destabilized through the day. A cold front will
push through the region this afternoon. The most favorable setup
for thunderstorms is inland...closer to the KLAN...KBTL and KJXN
TAF sites. I have included vcts for these site for a few hours
this afternoon.

A risk for low clouds and fog to redevelop exists tonight. The low
level humidity values will be relatively high to start the
evening. Then as we cool down...the fog and low clouds will likely
develop. The TAF sites will feature MVFR or lower conditions later


Issued at 305 PM EDT Sun Jul 23 2017

Northerly winds increase overnight tonight with building waves by
early monday. Winds should begin to slowly back off starting mid
monday morning as high pressure builds in.

Could see a short period early in the day where hazardous beach
conditions exist...but feel at this time the majority of the peak
beach hours will see weaker winds and smaller waves. Should winds
take a bit longer to start to diminish...beach hazard statement
may be needed...but will hold off for now.


Issued at 111 PM EDT Sun Jul 23 2017

No flooding concerns for the next 7 days. A frontal passage
Wednesday night into Thursday may bring thunderstorms but this is
not the setup that favors high basin average rainfall amounts.
Therefore, the rivers should behave for the foreseeable future,
especially with a cooler and drier pattern likely to follow for
late in the week and weekend.




MARINE...Maczko is the U.S. government's official web portal to all federal, state and local government web resources and services.