Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212339
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
739 PM EDT Thu Sep 21 2017

.SHORT TERM...(This evening through Friday)
Issued at 301 PM EDT THU SEP 21 2017

19Z Visible satellite reveals that patches of fog still linger
over portions of Lake Superior this afternoon, especially eveident
over south central and eastern Lake Superior. Patchy fog/stratus
still lingers over portions of Luce County as well. Elsewhere
across Upper Mi, sunshine and associated mixing have scoured out
any lingering morning fog/stratus.

Tonight, the cold front which stalled out just east and south of the
fcst area this morning is poised to pivot and lift back northward
across the Western Great Lakes later tonight as a warm front. As
this occurs, strong warm air advection and moisture transport will
lift north-northeast across the area bringing back chances for
showers and thunderstorms overnight. Higher dew points with the warm
front combined with nocturnal cooling will also lead to areas of
fog, which could become widespread and possibly dense over southeast
portions of Upper Mi in a developing upslope sse flow. Given the
strong moisture transport and steepening mid-level lapse rates,
upwards of 1500-2000 J/kg should develop mainly over western
portions of Upper Michigan, and extending out across western and
central Lake Superior. While the effective shear is on the marginal
size around 20 knots, enough directional shear looks to be in place
that may sustain updrafts and aid storm organization at times.
Therefore, a few strong to marginally severe storms will be
possible. Given the elevated nature of the convection, hail should
be the primary concern with any stronger cells.

Fri, could see some lingering scattered convection in the morning
mainly over the nw fcst area associated with the warm front and pool
of elevated cape lifting n of the area. If convection does linger
thru Fri morning, pcpn/cloud cover and disruption of sfc wind field
could hold back the rising of temps initially on Fri. However, still
would expect enough sunshine Fri afternoon as warm front lifts north
and core of 925 mb temps near 25c moves overhead that most of the
area should still realize highs in the mid to upper 80s with the
exception of 70s to lower 80s readings downwind of Lake Mi in a
southerly flow.

.LONG TERM...(Friday night through Thursday)
Issued at 321 PM EDT THU SEP 21 2017

No significant hazards expected in the long term, but there are some
significant temperatures anomalies in the first 2-3 days of the long
term.

Similar to the setup that resulted in record and near-record warmth
last week, we will start the long term with an upper ridge over the
CWA and a SFC trough/front stalled out across or near western Lake
Superior into northern Lake Superior. This will result in convection
mainly W and N of Upper MI through at least Sun and probably through
Mon, but possibly skirting W/NW Upper MI resulting in slight to
chance pops in those areas. It is possible that some stronger storms
could move across the western and northern lake, but that is not
expected at this time. The front looks to move through on Tuesday as
a stronger shortwave and SFC low moves up the front.

Temperatures will be the big story as highs are currently forecast
into the upper 80s over portions of the central and west (warmest in
downsloping areas near Lake Superior). This is the only place
changes were made changes to the blended initialization, where some
warmer temps were drawn into the downslope areas. There is a good
portion of guidance that shows highs in the low to maybe even mid
90s, which may occur if cloud cover is minimal. Should shatter the
record high and record high-low values of 82 and 60.

Current forecast highs for Sun are as warm as mid 80s over portions
of the central and west. If skies are clear, could see those needing
a bump closer to 90, but even as is we should break the record high
and high-low of 84 and 60.

Temps cool more for Mon as models show a cooler airmass and some
show some precip, but even with forecast highs in the mid 70s to low
80s we are forecast to break the record high of 75.

Will see temps back to below normal for Wed and Thu.
&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 739 PM EDT THU SEP 21 2017

Another forecast with multiple challenges. VFR conditions will
gradually diminish as fog on Lake Superior spreads into the Keweenaw
Peninsula and low clouds move north into the Upper Peninsula along
the approaching warm front. The timing is the question, but all three
sites will see lower cigs and restrictions to visibilities tonight,
with KSAW seeing the biggest impact with IFR/LIFR visibilities. The
development of the LLJ will bring potential for LLWS at KIWD and
KCMX, plus there is a possibility for thunderstorms activity to
develop and move into those areas on nose of LLJ and in area of
better elevated instability. Best chances for thunder remain at KIWD
and then KCMX, but cannot completely rule it out at KSAW either,
although confidence is less there. The fog and low clouds exit the
area shortly after daybreak, with VFR conditions returning for the
remainder of the forecast.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 301 PM EDT THU SEP 21 2017

Latest visible satellite still reveals patches of fog over portions
of Lake Superior which could linger into tonight. With lower to mid
60s dewpoints moving across the area and lingering into early next
week, patchy fog could persist for several days across the lake.
Other than a brief increase this evening in winds to 20 to 25 knots
over the western part of the lake, expect winds to generally be
below 20 knots through the early part of next week under a weak pres
gradient. As a warm front lifts north across the area tonight,
scattered thunderstorms will be possible over mainly the western
half of the lake and a few could contain large hail.
&&

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

$$

SHORT TERM...Voss
LONG TERM...Titus
AVIATION...RJT
MARINE...Voss



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