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Area forecast discussion 
National Weather Service Grand Rapids Michigan
746 am EDT Thursday Jul 31 2014

Latest update...
aviation

Synopsis...
issued at 329 am EDT Thursday Jul 31 2014

A slow warm trend will continue right into the weekend across the
area with a slight increase in humidity levels. Low rain chances
will persist into the weekend as weak waves of low pressure will
affect the area. Most areas will not see much rain with
showers/storms expected to be rather isolated to scattered. The best
chances will be further inland away from Lake Michigan during the
afternoon and early evening hours.

&&

Short term...(today through saturday)
issued at 329 am EDT Thursday Jul 31 2014

The main focus of the forecast continues to be convective trends through
the period...and determining if there is a severe weather threat or not.

Conditions for today do not support a significant concentration of
storms or a severe weather threat. We have one of the main lobes of the
long wave trough that is in the process of exiting the area to the
east this morning. A shower is possible up north this morning before
it exits...but nothing of significance. Cool air aloft remains over
the area. With temperatures inland inching up to 80 or so and dew points in
the middle 50s...a few showers/storms will develop this afternoon and
last into early this evening. An inversion resulting from the
subsidence in the wake of the lobe may keep things limited until
later afternoon when a short wave approaches. That said...cape is
very thin...winds in the middle levels are light so we expect some
small hail and some sub-severe wind gusts at worst today.

The threat for precipitation will remain over the area through the day on
Sat. Short wave energy coming into North Dakota this morning will
carve out another trough over the region by Friday. This trough
overhead and what looks like an elevated mixed layer of instability
moves overhead tonight. There is no major feature coming in...but
any mesoscale focus could pop a shower/storm overnight tonight.

Probably the best chance of precipitation in the period and the potentially
strongest storms of the short term will come on Friday. The new trough
will move overhead...cooling the middle levels down a bit. At the same
time temperatures will inch into the lower 80s and dew points will increase
to almost 60. These conditions will produce convective available potential energy over 1000 j/kg
with a good chunk of that cape in the -10 to -30c layer. This would
support some bigger hail.

The chance of rain will persist into Friday night and Sat...but the chance
will diminish slightly. The trough over the area on Friday will slowly
shift east by Sat afternoon. Some ridging builds and and temperatures aloft
warm a little. This will limit the instability some...and result in
a lower severe threat for Sat after a slight chance of a pop up shower
or storm Friday night with the trough still overhead at that time..

Long term...(saturday night through wednesday)
issued at 329 am EDT Thursday Jul 31 2014

Upper trough is finally lifting out of the area to the east and
northeast at the beginning of the long term period (saturday night).
For the remainder of the long term period upper ridging nudges
toward the Great Lakes from the plains states with a general
west-northwest flow in place. This will mean an end to the diurnal
type showers and storms that we have been experiencing and a
transition into a more progressive pattern.

Features to key on will be a frontal boundary that sags south into
the area on Monday...which lingers across the area into Tuesday.
Have sided with the slower evolution with this front via the European model (ecmwf).
Both the GFS and European model (ecmwf) then develop a surface low on the front and
bring this through the region middle week. The European model (ecmwf) is quicker with
the low into the area which seems plausible given the more
progressive flow that will be in place.

Bottom line in terms of sensible weather...dry Saturday night and
Sunday as surface high pressure drifts through the area. Chances for
showers and storms each forecast period Sunday night through
Wednesday as the front pivots into the area and then
stalls...followed by a low moving from west to east along the
boundary. Best chances for precipitation will likely be middle next
week as the low moves through.

Temperatures will be near normals for this time of year through the
period.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 739 am EDT Thursday Jul 31 2014

Marine fog continues to be an issue this morning off of Lake
Michigan. Kmkg has been in and out of LIFR...with the current
trend being upwards. Feel we could be looking at some LIFR
conditions for another hour or two...before conditions improve
with daytime mixing. Winds off the lake today may keep the stratus
and fog lingering a bit longer into the morning than it did
yesterday however.

Otherwise...VFR conditions are expected the next 24 hours. Ceilings
of 4000-6000ft are expected. Some widely scattered showers are
possible this afternoon and tonight. Covered this low end threat
with vcsh wording.

&&

Marine...
issued at 329 am EDT Thursday Jul 31 2014

Marine concerns in the short term will be limited to fog potential.
Tough to tell how the fog is trending this morning on coastal web
cams due to the darkness and a lack of visible satellite imagery. Fog
does remain a distinct possibility with light winds out on the water
and an air mass that is moist enough compared to the colder water at
the surface. This remains possible into the weekend...although winds
will be increasing some to help mix the atmosphere.



&&

Hydrology...
issued at 300 PM EDT Wednesday Jul 30 2014

No major hydrology issues expected. The precipitation is forecasted
to be scattered. As a result not much basin average rainfall
predicted. Will need to monitor the possible wave for Thursday night
into Friday. Trends could support a steadier rain event.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...dense fog advisory until 11 am EDT this morning for lmz844>846.

&&

$$

Synopsis...njj
short term...njj
long term...Duke
aviation...Duke
hydrology...mjs
marine...njj

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