Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251655
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1255 PM EDT Tue Jul 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
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
precipitation.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1256 PM EDT Tue Jul 25 2017

I expect solid VFR conditions to prevail through Wednesday
evening at all TAF sites. Departing high pressure has rather low
dew points for this time of year so I do not see much of fog
threat for tonight. The moisture return on the back side of the
surface high is such that any convection would not reach this area
until well after midnight Wednesday (early Thursday). Winds
should for the most part be 10 knots or less till midday Wednesday
when winds should increase out of the south to around 10 knots.

&&

.MARINE...
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.


&&

.HYDROLOGY...
Issued at 1055 AM EDT Tue Jul 25 2017

With near- to drier-than-normal conditions lately and a dry pattern
setting up for the next week, scattered showers and thunderstorms
Wed and Thu will be a welcomed sight to those looking for rain.
This does not look like a guarantee for everyone to get appreciable
rainfall amounts. But with 1.5 to 2.0 PW values nosing in and
relatively slow storm cell movement, it`s possible for some
locations to receive over an inch or two of rain in a couple hours.
Excessive rainfall to the point of flooding does not appear likely
due to a questionable storm coverage extent over the area.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...TJT
AVIATION...WDM
HYDROLOGY...CAS
MARINE...Meade



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