Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221816

Area Forecast Discussion
National Weather Service Marquette MI
216 PM EDT FRI JUL 22 2016

.SHORT TERM...(This evening through Saturday)
Issued at 211 PM EDT FRI JUL 22 2016

WV loop shows dry air aloft over the Upper Great Lakes today. It`s
another warm day through not as humid as seen Wed and Thu. Readings
thus far have topped out in the upper 80s to lower 90s, warmest
south central. Lake breeze has brought localized cooling to Lk
Superior shoreline but with water temps in the mid 60s in the
nearshore areas, onshore flow at least for today is bringing in more
humid conditions than just inland where dwpnts are as low as the
low to mid 50s. Another sunny afternoon, though have had some cu
form over far eastern cwa on edge of troughing and cooler air aloft
over Northern Ontario.

Quiet weather is expected to continue through at least most of Sat
aftn. Upper level ridge over northern plains crosses tonight. Weak
sfc ridge crosses tonight so temps over interior will fall to around
60, maybe upper 50s. At least some wind will stir near the Great
Lakes shores so temps will remain in the 60s there. Shortwave trough
currently crossing Pacific Northwest reaches Saskatchewan to Dakotas
axis on Sat aftn. Sfc trough makes it to Manitoba and western
Minnesota by Sat evening. Weak q-vector convergence and h85 warm
advection moves into far western cwa aft 21z on Sat. A bit of theta-
e advection as well. Soundings indicate a lot of dry air remains in
place blo h6/15kft. With the dry air lingering, only included slight
chance pops for very far west cwa aft 21z. Farther east, despite
much more in the way of lake breezes compared to today, soundings
show sharp capping h8-h7 to prohibit sfc based convection so kept it
dry. High temps will not be as warm as last couple days, especially
closer to the Great Lakes with quickly developing lake breezes.
Temps over the inland west should end up in the 86-88 range. Dwpnts
may push back into the lower 60s in some areas, but inland areas with
better mixing may see dwpnts fall back into the 50s similar to today.

.LONG TERM...(Saturday through Thursday)
Issued at 446 AM EDT FRI JUL 22 2016

Currently, notable 500mb height anomalies are present for late July
across N America. A subtropical ridge with anomalies as high as 2.5
standard deviations above the long term late July avg dominates a
large part of the CONUS. To the n, an impressively deep mid level
low dominates nw Canada with heights 3.5-4 standard deviations blo
avg centered over nw Nunavut. During the long term, the subtropical
ridge will weaken across the CONUS, and then late next week, there
will be some building of heights near/just off the w coast. Although
heights will remain above normal here, there will be a trend toward
weak troffing into the Great Lakes late next week in response to the
building heights to the w. The mid level low across nw Canada will
also weaken during the long term and will eventually drift n with
time. These 2 main features will help guide a significant shortwave
currently just off the Pacific NW coast eastward to northern Ontario
and the Great Lakes region late Sun. This system will bring the best
potential of shra/tsra during the long term portion of the fcst.
Later next week as shortwaves drop into the developing weak trof,
there will be additional shra/tsra chances. As for temps, above
normal heights thru the period suggest above normal temps will
mostly prevail, especially early on, but there will be gradual
cooling next week toward near near normal for the last half of the
week as weak troffing develops. Looking farther ahead, CPC/NAEFS
outlooks indicate troffing into the Great Lakes may deepen enough to
sustain a cooler period with temps around or even slightly blo
normal in the 8-14day period.

Beginning Sat, the day will begin tranquil with high pres ridge over
the area, then attention turns to the vigorous shortwave trof
currently just off the Pacific NW coast. It will reach the
Dakotas/southern Manitoba Sat evening. In response, strengthening
s/sw flow and resulting waa/ne push of instability ahead of feature
will support shra/tsra across the Dakotas/MN during the day Sat.
While low-level wind max will still be out across MN thru late aftn,
increasing 850mb theta-e advection may bring shra/tsra into far
western Upper MI before 00z Sun. Pres falls spreading into the Upper
Mississippi Valley/western Great Lakes combined with higher pres to
the ne will aid a wind component off Lake Superior during the day,
helping to keep lakeside locations cooler. Will also be a little
cooler near Lake Michigan. Away from these areas, temps should push
well into the 80s on Sat.

As shortwave trof continues eastward and 40kt low-level jet aims
into the Upper Great Lakes, expect shra/tsra to spread across the
area Sat Night/Sun morning. Based on fcst soundings, it appears
convection will be elevated across Upper MI. While axis of greatest
elevated mucape only reaches western Upper MI late in the night,
upwards of 1000j/kg is still avbl. Deep layer shear progs are fairly
noisy, but it appears effective shear may be around 30kt which would
support strong to perhaps isold svr storms though potential should
diminish with eastward extent as storms move farther ahead of the
instability axis. Potential of svr storms may tend to increase late
Sat night over the w as greater instability advects into that area
and then over the e on Sun. If there is any kind of break in
pcpn/cloud cover on Sun before sharp mid level drying arrives and
occluded/cold front passes, mlcape increasing to at least 2000-
3000j/kg combined with 30-40kt of deep layer shear will support a
greater risk of svr storms. If clouds/pcpn dominate up until fropa,
svr risk will be lower. Otherwise, fropa/sharp mid level drying will
result in pcpn ending w to e Sun aftn/evening.

In the wake of the shortwave trof, looks like a couple of dry days
will follow for Mon/Tue. However, confidence in dry weather on Tue
is lower than on Mon as a shortwave swinging thru northern Ontario
could spark some isold convection, particularly as noted with the
ECMWF. Max temps will trend down closer to normal on Mon before
rising a bit for Tue. Dwpts will fall back to the upper 50s/lwr 60s,
still a bit on the uncomfortable side.

Heading into Wed/Thu, uncertainty in timing shortwaves into the
developing weak trof suggests using a consensus of current and
recent medium range guidance to construct pops, resulting in low chc
pops both days.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 140 PM EDT FRI JUL 22 2016

VFR conditions will prevail through the TAF period. Mid and High
clouds will increase through the day on Saturday ahead of an
approaching low pressure system. Winds will be breezy out of the
west this afternoon, especially at CMX and SAW.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 211 PM EDT FRI JUL 22 2016

Winds will remain at 20 knots or less into next week as pressure
gradient remains weak and due to high overwater stability. Patchy
fog is possible Sat night and Sun and into early next week as
another humid airmass moves over the Upper Lakes. &&

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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