Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251140

Area Forecast Discussion
National Weather Service Grand Rapids MI
740 AM EDT Tue Jul 25 2017


Issued at 330 AM EDT Tue Jul 25 2017

High pressure provides pleasant weather today before slipping
away on Wednesday. A frontal boundary dropping in from the north
will bring scattered showers and possible thunderstorms Wednesday
night into Thursday followed by a stretch of dry weather with
seasonal temperatures Friday through early next week.


.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue Jul 25 2017

Main focus is on rain potential late Wednesday into Thursday. The
shortwave which comes toward us on Wednesday night is originally
a monsoonal feature which drifts north from Arizona and gets
caught up in the westerlies. Extreme PWATS near 2.75 inches,
almost unheard of, are progged by both the GFS and NAM over IA and
wrn IL Wednesday night as this shortwave translates east.

Currently the models are keeping the bulk of the heavy rain with
this monsoonal feature Wednesday night well to our southwest
across IA and wrn IL, then moving it southeast from there. Given
the current model consensus, and how the low level jet is progged
to be pointed at wrn IL, it`s conceivable that we see little
impact with yet another MCS passing by to our southwest.

Still it is early and considering the excessive rainfall
potential it will need to be monitored for a northward shift. For
now will avoid likely pops Wed night but even if the MCS misses
us there should still be some scattered showers/isolated storms
along the sfc frontal boundary as it presses slowly south through
the area.

If we do get missed Wednesday night, a better chance of showers
and storms may develop on Thursday as the next upper low/digging
H5 trough drops in from the northwest. If there`s still higher
PWAT air around as this feature moves through we may see a pretty
decent coverage of convection develop, especially if the nrn
stream upper low arrives at peak heating.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue Jul 25 2017

Will keep a lingering chance for showers early Thursday night.
Although deeper atmospheric moisture will be displaced southward,
there is good model consensus on a compact upper potential vorticity
maximum traversing the area during this time. Instability looks too
meager to justify the mention of thunderstorms however.

Friday through Tuesday still looks dry with seasonal temperatures.
Northwest flow aloft across the western Great Lakes and a broad
surface high across most of the eastern U.S. will predominate. Even
though there will be transient PV maxima in the flow aloft, the
surface high will effectively shut off the Gulf of Mexico as a
source of atmospheric moisture for the area, so we do not anticipate


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 734 AM EDT Tue Jul 25 2017

VFR weather is likely today and tonight with winds below 10 knots
as high pressure dominates.


Issued at 330 AM EDT Tue Jul 25 2017

Increasing southerly flow later tonight into Wednesday on the back
side of the departing sfc high should push waves to 2 to 4 feet
north of Grand Haven. Currently not expecting advisory criteria,
but it may be a close call around Big and Little Sable Points. A
more significant northerly flow event, with waves of 4 feet or
more, appears possible for the entire nearshore Thursday
afternoon into early Friday.


Issued at 327 PM EDT Mon Jul 24 2017

A fair portion of the area has trended drier than normal over the
past 1 to 2 weeks. Late Wednesday into early Thursday appears to be
the only chance of appreciable rainfall over the next week. Local
amounts will depend greatly on the track of the potential
thunderstorm complex, though over an inch is possible where it does
track. This fairly progressive upper level shortwave trough and
associated surface front do not suggest much threat of excessive




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