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Area forecast discussion 
National Weather Service Grand Rapids Michigan
325 PM EDT Thursday Aug 27 2015

Latest update...
synopsis/short term/long term/marine

issued at 325 PM EDT Thursday Aug 27 2015

After a nice Friday we will be entering a wetter period Friday night
into Saturday night. Some heavy rain could occur...especially
toward Highway 10. Temperatures will remain mild with daytime highs
in the 70s.

Next week should be warmer with highs mainly in the 80s. Rain
chances should be low.


Short term...(this evening through Saturday night)
issued at 325 PM EDT Thursday Aug 27 2015

A frontal system is expected to slowly move into the region Saturday
afternoon and linger over the area into early next week. The air
mass appears to be quite moist along with persistent forcing and
some heavier rains could occur.

It will remain quiet over the next 24 hours as high pressure drifts
to our east. Can not rule out a few showers or a storm over the northwest
County Warning Area late Friday afternoon due to moisture advecting in behind the

Main period for showers and storms through the short term will come
Friday night through the first half of Saturday night. A warm front
will be over central Indiana by Friday evening and it will continue
to move slowly northward...reaching the southern County Warning Area Saturday
evening...and near I-96 by early Sunday morning. High precipitable
water values move in ahead of this front...reaching 1.50 to 1.75
inches by late Friday evening. These values remain over the region
through Saturday night.

With this moist air mass in place there is also persistent
forcing...leading to concern for heavy rain north of the front. The
right entrance region of the upper jet moves overhead Friday evening
and remains over the area into Saturday evening as it becomes more
defined. Combined with the upper jet...a low level jet intersects
the warm front by late Friday night and displays persistence over
central lower into Saturday evening. This seems like a very good
set up for training or persistence showers and storms rolling east
on the north side of the warm front. Expect most areas will see
0.50 to 0.75 inches of rain...but heavier totals seem likely at this
point toward Highway 10.

Long term...(sunday through thursday)
issued at 325 PM EDT Thursday Aug 27 2015

Upper shortwave trough is still overhead on Sunday with its weak
surface reflection (boundary) situated through the forecast area.
Have maintained small probability of precipitation on Sunday...20/30 the boundary
slides southeast/washes out. Dew points are pooled in the middle to
upper 60s across the southern County Warning Area...which is where we should see the
isolated/scattered showers and storms form.

After Sunday...the surface pattern becomes quite diffuse with a
building upper ridge overhead. Have a dry forecast from Sunday night
all the way through Thursday. High temperatures should warm into the
upper 80s which is what we have in the forecast middle next week. Could
see needing to push highs more to around 90 as confidence increases.

The items to watch will be whether we need to add some small chances
for afternoon showers and storms next week in the building heat and
humidity. Hard to find much of a trigger at this point...but it is
not out of the realm of possibilities in the afternoon/evenings. At
500mb...the GFS and European model (ecmwf) try to maintain a weak low aloft off to
our east and south depending on the model. Hard to put a lot of
stock in these weak features at this point. Rolled with the dry
forecast given surface and upper level ridging.


Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 219 PM EDT Thursday Aug 27 2015

Ceilings have become more cellular due to diurnal heating and
have even scattered out in some areas. Ceilings are VFR across
central lower Michigan and are still MVFR across south central
lower Michigan. Have tempo groups at some of the taf sites for a
few hours to cover the MVFR ceilings before they lift above 3000ft
due to additional heating.

Tonight feel ceilings will scatter out area wide and leave VFR
conditions in place. There is a threat for fog overnight...left it
out of the tafs at this point...but could see the need to add it
moving forward. Friday should be VFR in the morning after any fog


issued at 325 PM EDT Thursday Aug 27 2015

Minimal wind and wave concerns on Lake Michigan with wind speeds
expected to be 15 knots or less through the short term. However
scattered thunderstorms will be possible late Friday afternoon into
Saturday night.


issued at 325 PM EDT Thursday Aug 27 2015

Dry weather expected through Friday. Much of the County Warning Area should see
under an inch of rain over the weekend...however portions of central
lower could see heavier rains. At this point river levels should
remain low into next week. However nuisance type flooding in low
lying areas will be possible across central lower into Saturday and
Saturday night.


GRR watches/warnings/advisories...


short term...jk
long term...Duke

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