Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221900

Area Forecast Discussion
National Weather Service Marquette MI
300 PM EDT Fri Sep 22 2017

.SHORT TERM...(Today and tonight)
Issued at 504 AM EDT FRI SEP 22 2017

Tricky forecast today with convection potential through at least
late morning. Hi-res models have been back and forth on when and if
a line of showers and thunderstorms tracks across the U.P. If the
storms do cross the area this could keep the temperatures a bit
lower through at least the first half of the day.

Today: Strong moisture transport/moisture convergence on the nose of
a LLJ and along a warm front lifting northward through the area will
continue to be the focus of showers and thunderstorms this morning.
Some of the hi-res models try to develop an MCS over western MN
early this morning and them shift it eastward into the west half of
the area by mid morning into the early afternoon hours, but it may
be tough for the storms to make it too far east into the U.P. with
850mb ridging in place along with diminishing LLJ/convergence and a
bit lower MUCAPE over the east half of the U.P. Still worth keeping
the mention of at least scattered showers and thunderstorms in the
forecast through early afternoon. The moisture transport weakens
throughout the day as the LLJ diminishes by mid to late morning and
the associated convergence weakens and lifts to the northeast of the
area. This should bring an end to the shower and thunderstorm
activity across much of the area as a very warm nose of air slides
in aloft by early to mid afternoon. In fact, 850 temps are progged
to warm to around 25C by early afternoon, which will allow
temperatures to warm into at least the mid 80s across much of the
area. The exceptions will be over the east half of the U.P. down
wind of Lake MI on southerly winds. On top of the hot temperatures
today, increasing moisture, with dewpoints in the upper 60s to
around 70, will make it feel very uncomfortable. Many locations will
likely see heat index values around 90 or in the low 90s by mid to
late afternoon.

Tonight: A surface low over the Plains is expected to lift
northeastward to the MN/Ontario border by 06Z/23. This along with
another developing LLJ over the far western U.P./Western Lake
Superior and much of norhtern MN will allow for increasing chance of
showers and thunderstorms. Again, similar to last night into early
Friday morning, the main area of concentraition will mostly likely
be over northn MN; however, where the stronger moisture
transport/convergence is likely to set up on the nose of the LLJ.
Where thunderstorms do form, some of them may become strong to
marginally severe as effective shear increases with LLJ development.
The rest of the U.P. will remain capped and far enough away from the
main system dynamics to force any showers and thunderstorms.

.LONG TERM...(Saturday night through Friday)
Issued at 259 PM EDT FRI SEP 22 2017

Nam shows a deep 500 mb trough over the Rockies and a strong 500 mb
ridge over the ern U.S. 00z Sun. Upper air pattern changes very
little through 00z Tue with the ridge slowly moving east to New
England by 00z Tue. What this will mean is warm and humid conditions
will continue with summer like weather. Pops will remain mostly to
the north and west of the cwa with area in the warm sector for this
forecast period and some record highs are possible for this forecast

In the extended, GFS and ECMWF show a 500 mb trough in the Rockies
and northern plains 12z Tue with a ridge over the ern U.S. 12z Tue.
This trough moves into the upper Great Lakes 12z Wed and this trough
remains into 12z Thu. Starting on Wed, a cold front moves through
and brings an end to the summer like temperatures with cooler air
moving into the area. Temperatures will go from above normal on Tue
to below normal for Wed through Fri.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 132 PM EDT FRI SEP 22 2017

Challenging forecast in near term in regards to timing of
convection moving across TAF sites. Also gusty southerly wake low
winds to near 30 mph are developing behind the stronger convection
and may continue into late afternoon. T-storms have moved mostly east
of KIWD and KCMX but will affect KSAW through 20z with possible
MVFR conditions before shower activity begins to taper off at all
sites and VFR conditions finally prevail. Should be enough mixing
from southerly winds to preclude fog development tonight and keep
conditions VFR. A low-level wind max moving across the region will
result in LLWS at all TAF sites tonight into early Sat.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 504 AM EDT FRI SEP 22 2017

Low to mid 60s dewpoints sliding across Lake Superoior are expected
to linger into early next week bringing patchy fog for several days
across the lake. Some of the fog could be locally dense at times.
Expect winds to generally be below 20 knots through the early part
of next week under a weak pressure gradient.

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


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