Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 141138

Area Forecast Discussion
National Weather Service Marquette MI
738 AM EDT Thu Sep 14 2017

.SHORT TERM...(Today and tonight)
Issued at 507 AM EDT THU SEP 14 2017

Water vapor imagery and RAP analysis show a trof extending from
central Canada to southern BC and the Pacific NW. Ahead of this
feature, wsw flow is developing toward the Upper Great Lakes early
this morning. At the sfc, stationary front extends from SD across
northern MN and Lake Superior. To the n of the sfc boundary, a
subtle shortwave acting on 850mb cape gradient/theta-e gradient is
currently generating a cluster of shra/tsra to the nw of Lake
Superior. Otherwise, across Upper MI, it`s a quiet and mild early
morning for mid Sept. Actually, it`s warm in the s to sw wind
downslope locations near Lake Superior as temps are still locally in
the mid/upper 60s. In the interior, temps have fallen off to the
lower and mid 50s. Some patchy fog, locally dense, has formed across
the s central and near Lake MI.

During the short term, main concern will be potential of shra/tsra.
Ongoing shra/tsra to the nw of Lake Superior will brush northern
Lake Superior and may impact Isle Royale this morning. Otherwise,
stationary front across Lake Superior will move little today though
developing lake breeze may tend to effectively push boundary into nw
Upper MI this aftn. Convective temps fcst to be at least in the
upper 80s will not likely be achieved this aftn. So, at this point,
don`t foresee any convection developing across Upper MI today. In
fact, may not see any CU develop, just some CI spreading across the
area at times. Shra/tsra today should be confined farther n and nw
of the stationary front where elevated convection will be forced.
Expect another day of summer warmth/humidity with max temps
generally in the low/mid 80s for much of the area. Will be a little
cooler n of the Portage Canal and closer to Lake MI.

Convection that will be firing in northern MN late this aftn/evening
will track eastward along stationary front tonight. These
shra/storms should largely ride along the northern edge of the 850mb
cape gradient that will be situated across Lake Superior and
adjacent MN/northern Ontario. Southern edge of this convection may
brush nw Upper MI with the Keweenaw obviously located more
favorably. Effective shear for elevated convection is under 20kt, so
not expecting any svr storms if any do reach Upper MI tonight.
Expect another warm night for mid Sept with mins in the mid 50s to
mid 60s.

.LONG TERM...(Friday through Wednesday)
Issued at 318 AM EDT THU SEP 14 2017

Upper air pattern consists of a trough in the western U.S. and
Rockies with a ridge over the upper Great Lakes and southern plains
and a trough in New England 12z Fri. The trough in the western U.S.
moves into the northern plains 12z Sun. The deeper moisture and
stronger dynamics appear to be north and west of the area this
forecast period. Will continue with slight chance to low chance pops
for the north and western cwa this forecast period before better
chances come into the whole cwa Sat night as the cold front nears.
Temperatures will stay above normal this forecast period with higher
humidity values.

In the extended, GFS and ECMWF show a 500 mb shortwave in the upper
Great Lakes 12z Sun with a cold front moving through the area. Broad
500 mb troughing remains across the western U.S. into Mon and then
the troughing digs into the western U.S. 12z Tue as the trough
amplifies. This builds a ridge back into the upper Great Lakes 12z
Wed. GFS is more amplified and faster with this upper trough while
the ECMWF is further west 12z Thu. Feeling is that the GFS is too
fast considering how amplified the upper pattern is and that the
slower ECMWF will verify. Temperatures start out near normal at the
beginning and warm to above normal this forecast period.

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 737 AM EDT THU SEP 14 2017

VFR conditions should prevail thru the fcst period at
KIWD/KCMX/KSAW. However, there is some concern that upslope
southerly winds tonight at KSAW could yield ocnl fog/stratus and
IFR/LIFR conditions, similar to last night. Also, there is a small
potential of shra/tsra tonight at KCMX, but at this point, potential
is too low to include a mention in fcst.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 507 AM EDT THU SEP 14 2017

Nearly stationary front across Lake Superior through Sat will
occasionally lead to locally stronger winds. NE winds up to 15-25kt
will occur at times over western Lake Superior while southerly winds
up to 15-25kt will occur at times over eastern Lake Superior. Cold
front will then sweep across Lake Superior on Sun, bringing a period
of 15-25kt winds. Winds will then diminish Sun night with light
winds under 15kt following into Mon as sfc high pres builds over the
Upper Lakes.

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


SHORT TERM...Rolfson
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