Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 182022

Area Forecast Discussion
National Weather Service Marquette MI
422 PM EDT Mon Sep 18 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 421 PM EDT MON SEP 18 2017

High pressure brought dry weather to start the day but am now seeing
rain move back into western Upper Michigan. Rain is tied to
shortwave and right entrance region of upper level jet lifting
through in persisting southwest flow aloft. Expect the rain over the
west to slowly slide into the central and eastern forecast area
through the evening. Since forcing is not strong and the rain is
running into a dry airmass as seen on 12z raob from Green Bay WI,
expect the rain to diminish steadily as it moves through the area
this evening. As upper jet continues to lift north of Upper Michigan
overnight, expect any rain to end by that time. Did increase pops
through the evening as rain is expected, but again not looking at
much rain with most areas seeing less than a tenth of an inch of
rain. Clouds will hang around most of the night but should see
partial clearing overnight. If clearing occurs earlier in the night
there would be risk of shallow ground fog.

Improvement continues on Tuesday and this will be the start of
warming trend as well. H85 temps rising up to 12C will support highs
well into the 70s, especially inland west. High pressure sliding
east and approaching low pressure trough and warm front will result
in increasing east to southeast wind with strongest gusts over the
more exposed Keweenaw Peninsula.

.LONG TERM...(Tuesday night through Monday)
Issued at 358 PM EDT MON SEP 18 2017

High amplitude trough/ridge pattern setting up over the CONUS
particularly by the end of the week will keep the western Great
Lakes in a warm south-southwest flow which will result in well above
normal temperatures throughout much of the extended period. The best
chances for showers and thunderstorms will be Wednesday into early
Thursday as a cold front slowly pushes across the area.

Continued large scale anticyclonic flow will maintain dry conditions
Tue night. The warming trend will continue Wednesday and Thursday,
with high temperatures expected to climb into the 70s. Precipitation
chances will increase late on Wednesday through Thursday as a cold
front slides southeast across Upper Michigan. With MLCAPE values
upwards of 1000-1500 j/kg and deep layer shear of 30-40 knots there
will be a risk for strong to possibly severe thunderstorms Wed
afternoon into Wed night over the western two thirds of the fcst
area. Not surprisingly, this is the area where SPC has a marginal
risk for severe storms on the day3 convective outlook. During the
day on Thursday, models indicate the cold front slowing its
eastward/southward progress and then pushing back northward into
Upper Mi as warm front Thu night. This could bring isolated
showers and t-storms back into the area.

Friday through Sunday look to be the warmest days of the week. As
the warm front lifts well north of the area strong warm air
continues to stream northeast into the Upper Great Lakes region.
Models indicate 925-850mb temperatures at or above 20 C. These warm
temperatures coupled with southerly winds of 10 to 20 mph to enhance
mixing should easily allow temperatures to climb 10 to 20 degrees
above normal for this time of year, especially for downsloping areas
along Lake Superior. Southerly flow in warm sector ahead of frontal
boundary over the Plains will also tap into Gulf moisture and bring
it northward through the central CONUS into the Great Lakes region.
As a result, expect the humidity to increase as well making for
rather warm and muggy conditions over the weekend. However, cap of
warm air aloft will likely inhibit formation of convection for the
most part, despite increase in moisture and instability. By Sunday,
model uncertainty increases regarding progression of frontal
boundary eastward into Upper Mi. The operational GFS is definitely
quicker than the GFS ensemble mean or the 12z ECMWF/GEM-NH but would
anticipate there could be a few storms popping up at least over the
western cwa as frontal boundary draws closer from the Plains.

Would expect showers and thunderstorms to increase in coverage
heading into next Monday as there is better model agreement that the
front will move eastward into central Upper Mi.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 142 PM EDT MON SEP 18 2017

A relatively dry low-level air mass should allow VFR conditions to
prevail thru the fcst period at KIWD/KCMX/KSAW. A disturbance
approaching the area will spread some -shra into w and central Upper
MI this aftn/evening. If -shra occur at any of the terminals,
conditions won`t fall out of VFR given that the pcpn will be light.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 421 PM EDT MON SEP 18 2017

High pres over the Upper Lakes will lead to winds mostly under 15kt
across Lake Superior through tonight. As the high shifts e on Tue
and a low pres trof moves out over the Plains, winds will begin to
increase a bit on Tue, but much more so Tue night and Wed as the
trof moves closer. SE to S winds will increase to 20-25kt across
much of the lake Tue night and will increase up to 30kt over north
central and eastern Lake Superior on Wed. With passage of the trof,
winds will drop off quickly to under 15kt from w to e Wednesday
night with these lighter winds lingering thru Thu.

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


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