Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 151140
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
740 AM EDT Sat Jul 15 2017

.SHORT TERM...(Today and tonight)
Issued at 355 AM EDT SAT JUL 15 2017

All remains quiet early this morning across the Upper Peninsula.
Satellite imagery shows mostly clear skies across the bulk of the
area; however, to the northwest a boundary was beginning to approach
and IR imagery indicates mid-level clouds trying to thicken. With
the lack of mixing yesterday afternoon, coupled with the clear skies
and calm winds overnight, radiational fog has developed across the
central/southern portions of the U.P. In a few areas visibilities
prior to daybreak may fall to around one half mile, otherwise expect
just some minor reductions to visibilities. Temps will continue to
radiate into the upper 40s to lower 50s, with the exception of areas
of the Keweenaw Peninsula where the cloud cover has already begun to
arrive. The focus for later today will be on the potential for
showers and possibly thunderstorms developing, along with much
warmer temps.

Shortly after daybreak guidance indicates the surface ridge will
continue to sag south across the Ohio Valley, allowing the
approaching frontal boundary to nudge closer to the U.P. The
stronger shear and vorticity within the mid/upr levels, which would
support better organization/development to thunderstorms will not
arrive until aft 18z. Guidance has been consistent with this
thinking, which could pose some forecast challenges this afternoon
once lake breezes form and push inland. This would introduce
additional low-level convergence to increasing instability, and
coupled with increased moisture, could help to enhance the vertical
component to thunderstorms along with intensity. But again the
timing and coverage will be a challenge, due to the delayed arrival
of the upper level support. So the best timing for thunderstorms
will likely be aft 18z thru 00z, and focused along and south of a
Iron Mountain to Gwinn line. SPC continues to highlight the far
southern areas of Menominee County in a marginal risk for severe
storms, which seems plausible given the aforementioned atmospheric
conditions and timing of upper level support. With Td`s on the rise
this afternoon, advecting north ahead of the frontal boundary, any
rain/storms that develop could easily produce brief downpours. Storm
motion does appear to be around 15-20kts to the southeast, but this
could still pose a minor concern for areas that have seen heavy
rainfall in the southern CWFA.

Temps quickly warm into the 70s by late morning, then approach the
low 80s for many areas early this afternoon. With the steadily
increasing low-level moisture, this should slow the rate of warming,
and with precip chances increasing in the afternoon this could hold
temps in the upper 70s.

.LONG TERM...(Sunday through Friday)
Issued at 452 AM EDT SAT JUL 15 2017

Models suggest nw flow through the nrn Great Lakes this weekend
downstream from a ridge over wrn NOAM will become more zonal next
week as a strong shortwave trough advancing from srn BC to Hudson
bay by late Monday flattens the ridge. Toward the end of the
week, the pattern will amplify slightly as a trough edges eastward
from the Pacific Northwest.

Sunday, Behind the cold front from Saturday, expect a pleasant
conditions with highs from the mid 60s to lower 70s and dewpoints
down again into the comfortable upper 50s to lower 50s. Onshore
nrly gradient flow will bring the coolest air into the north.

Monday, although a strong inversion will limit the mixing depth, WAA
with developing srly flow will help push temps into the upper 70s,
except where onshore flow prevails near Lake Michigan. The gradient
should remain weak enough to allow lake breeze development from Lake
Superior over the east half of the cwa.

Tuesday, a cold front is expected to move through Upper Michigan.
The ECMWF remained slightly faster with this feature compared to
the GFS/GEFS/GEM. Temps in the lower 80s with MLCAPE values of 1k-
2k J/Kg could again support some stronger storms althoug there is
some uncertainty with the potential for thicker clouds to limit
sfc heating/instability. There may also be a threat for heavy
rain alont a slow moving west to east boundary as PWAT values
climb aoa 1.75 inch and westerly inflow of low level moisture may
favor training cells.

Wednesday-Friday, Confidence remains low with the handling of the
frontal position and associated pcpn chances. Although there is
trend toward wnw mid/upper level flow which might keep the front to
the south, it will remain close enough to maintain a threat for
additional shra/tsra especially if any stronger shortwaves emerge
from the nrn plains.
&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 730 AM EDT SAT JUL 15 2017

VFR conditions will prevail at KIWD/KCMX/KSAW thru this aftn. A
cold front dropping se across the area today may spark a few
shra/tstms, but confidence in coverage and location of development
is low. Right now, it appears central Upper MI has a better
potential of seeing sct pcpn development than western Upper MI.
Have thus included a VCSH mention during the mid/late aftn at
KSAW. Passage of cold front and development of cool upslope flow
may result in low MVFR or IFR cigs for a time this evening,
especially at KSAW.

&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 355 AM EDT SAT JUL 15 2017

Ahead of an advancing cold front, winds will increase to 15 to 20
knots across the western and northern half of Lake Superior early
this morning. Further to the east during the same time period, winds
will be 10 to 15 knots. As the front pushes south of the area, winds
will become north-northeasterly this evening into Sunday around 15
to 20 knots. Sunday afternoon winds will weaken to around 10 to 15
knots. Next week we could see a day or two with wind speeds up to 15
to 20 knots, otherwise winds will remain around or less than 15
knots.
&&

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

$$

SHORT TERM...Beachler
LONG TERM...JLB
AVIATION...Beachler
MARINE...Beachler



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