Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191125
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
725 AM EDT Sat Aug 19 2017

.SHORT TERM...(Today and tonight)
Issued at 256 AM EDT SAT AUG 19 2017

An area of scattered showers with some isolated thunder moved into
far northwest portions of Upper Michigan this morning as a
shortwave continued to move across western Lake Superior. Through
the morning hours, these scattered showers and thunderstorms will
continue to push southeast into central portions of Upper
Michigan, primarily the north central, before diminishing over the
next few hours. Elsewhere, lingering cloud cover was observed
early this morning.

Later today, as the main upper-level wave lifts out of the region,
cloud cover will gradually start to wane from west to east. With
increasing insolation and a somewhat dry air mass overhead, expect
temperatures to warm nicely into upper 70s and low 80s. Locations
that see temperatures climb into the low 80s will likely be confined
to areas of better downsloping. Given the increased insolation, lake
breeze boundaries are expected to develop and push inland through
the afternoon and evening hours. Increased convergence along the
lake breeze boundaries and area of more substantial terrain, and
along lake breeze interactions, will allow for afternoon showers and
thunderstorms to develop. While there will be a small chance that a
few of these storms may develop across the north central portions of
the area, the main focus should remain where the Lake Superior and
Michigan breeze converge across the central and east. A weak PV
anomaly/shortwave is progged to clip the area this afternoon and
should also provide some additional lift for afternoon convection.
It will also help increase the amount of deep-layer shear as well,
with 0-6km shear increasing to around 30 to 40 knots by the mid-
afternoon hours. Along these lake breeze boundaries, low-level
moisture is progged to pool with dew points climbing into the low
60s. Therefore, it looks like around 1000 to possibly upwards of
1500 J/kg of MUCAPE will develop. These ingredients should allow for
some storms to remain organized, and possibly strong at times,
especially considering the shear orientation will remain quasi-
perpendicular to where the lake breezes are progged to interact.

Tonight, any lingering showers and thunderstorms across the south
central and east will push out over Lake Michigan. Temperatures will
remain mild as winds become southwesterly ahead of an approaching
cold front.

.LONG TERM...(Sunday through Friday)
Issued at 457 AM EDT SAT AUG 19 2017

Models suggest that a slowly progressive pattern will prevail into
next week with a transition from zonal flow this weekend to a more
amplified pattern as a trough over Alaska drifts through the Gulf of
Alaska to BC/Alberta late next week. The resulting downstream
ridge/trough will bring mainly nw flow through the wrn Great Lakes
from Tue night into Friday. Above normal temps Sunday into Monday
will give way to seasonably cool conditions from Tuesday through the
rest of the week.

Sunday, a shortwave trough moving through nw Ontario will drag a
cold front into the nrn Great Lakes. Increasing srly flow WAA ahead
of a front edging into the region will help boost temps into the mid
80s (850 mb temps to near 17C). Although MLCAPE values may climb to
around 1500 J/Kg, capping will be strong enough to limit convection
potential/coverage, so that only lower end POPS with isold/sct
shra/tsra are expected over mainly the north and west from the late
afternoon into the evening. There is also low confidence whether any
weak shrtwvs in the zonal flow will be able to enhance shra/tsra
chances. Storms that develop may become strong or possible severe
given the amount of instability and 0-6km shear in the 30-40 knot
range.

Monday, the combination of a frontal boundary developing over the
area combined with the likelihood of a stronger shortwave emerging
from the nrn plains will bring greater shra/tsra chances over the
area. However, confidence with any timing is low given model
differences. Models have also trended farther south with the front
position and associated pcpn chances keeping the higher POPs over
the srn cwa. Sky cover confidence is also low given pcpn potential
but there may be a period of some sunshine especially over the
northern cwa.

Monday night into early Tuesday, a stronger shortwave trough is
expected to drop into the nrn Great Lakes as the pattern amplifies
bringing another round of pcpn. However, with the front to the south
of the area the best chance of rain will remain over the southeast
half of Upper Michigan.

Expect drier conditions again by later Tuesday that should persist
through the end of the week with the mid level trough developing to
the east. As is often the case with nw flow patterns some light
showers may be possible with any weak shrtwvs moving through the
area, especially Wednesday before the sfc high strengthens over the
region.
&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 724 AM EDT SAT AUG 19 2017

VFR conditions are expected to prevail over the next 24 hours.
Westerly winds will become breezy at times at KIWD and KCMX later
this afternoon. At KSAW, the lake breeze is expected to push inland
today, which may result in afternoon shower and/or thunderstorm
activity. However, Confidence in overall coverage was not high
enough to include anything other than VCSH at KSAW for later this
afternoon.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 256 AM EDT SAT AUG 19 2017

Winds are expected to remain 10 to 20 knots through the weekend.
Early next week, winds will relax to around or less than 15 knots.
Tuesday and Wednesday as the surface pressure gradient is progged to
increase across the area, winds will pick up to around 20 knots.
Then towards the latter half of the week, high pressure will take
over and winds are expected to remain under 15 knots.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...JLB
AVIATION...Ritzman
MARINE...Ritzman



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