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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 180535

Area Forecast Discussion
National Weather Service Marquette MI
135 AM EDT Sun Aug 18 2019

.SHORT TERM...(This evening through Sunday)
Issued at 330 PM EDT SAT AUG 17 2019

Other than the potential for some sprinkles this afternoon along
the Lake Superior breeze that has come onshore, aided by a weak
wave traversing through out ahead of the main trough still back
over in MT/Saskatchewan, benign weather prevails until the
approach of a frontal boundary tomorrow. Pre-frontal activity is
expected to grace the western U.P. with its presence by around or
just shortly after dawn, with instability already on the increase
by then. As the morning continues, look for this convective
activity to spread north and eastward, with the thunder potential
decreasing from south to north. With ample shear moving into the
area, the limiting factor for any sort of more robust activity
will be the instability, although there are some hints that
locations closest to the WI border could see a brief window by
midday tomorrow of a few feisty storms attempting to impact the
area. If the pre-frontal activity ends up slowing down more so
than currently anticipated, the stronger storm potential will
likely then increase, something to keep in mind heading into
tomorrow's outdoor activity planning. Regardless of which scenario
ends up playing out, moderate rain will be possible, with locally
heavy rain not out of the question, given the increase in PWATs
expected overnight. Some model soundings are depicting the skinny
CAPE/moist profile scenario indicative of moderate to heavy 

With dewpoints on the rise tonight, some fog will be possible in
prone locations, with lows struggling to drop below the mid 50s in
the interior, and remaining in the 60s along the lakeshores.
Expected cloud coverage by the start of the day will keep highs
tomorrow moderated, topping out in the 70s just about everywhere,
lingering on the cooler side of those 70s in the west, higher in
the east.

.LONG TERM...(Sunday night through Saturday)
Issued at 222 PM EDT SAT AUG 17 2019

A relatively benign forecast is expected through the extended 
period, with realistic precipitation chances relegated to Sunday 
night, Tuesday afternoon and evening, and late Friday afternoon into 
the weekend, with ample uncertainty in the evolution of next 
weekends forecast. Otherwise, quick moving high pressure passing to 
our south will bring warm and dry conditions Monday through Tuesday 
morning, and returning high pressure combined with a mid-level low 
spinning across northeastern Canada will bring cooler, drier 
northwesterly flow for Wednesday and Thursday. Return flow will 
begin to warm things back up again Friday. 

Sunday night, an exiting trough axis/embedded shortwave will allow 
for lingering showers and weak thunderstorms over the eastern Upper 
Peninsula, but these should exit by around or just after midnight. A 
little patchy fog can't be ruled out over the interior, but winds 
may remain just enough to keep the PBL well mixed. Surface high 
pressure will then move into the region, skirting across Wisconsin 
during the day Monday. Decent low level mixing is expected and a 
relatively dry airmass will lead to 25-30+ degree dew point spreads. 
The dry air could locally lead to relative humidities dipping below 
30 percent, but winds will be light for all locations except the 
Keweenaw Peninsula where some afternoon gusts are possible out of 
the SW. Fire weather concerns would thus be limited to the far 
northwestern UP on Monday, and even then only if enough dry air 
mixes to the surface. 

We will remain under moderate SW flow on Tuesday, and inland 
temperatures will reach the low to mid 80s ahead of a trough and 
associated cold front that should kick off a few showers and storms 
Tuesday afternoon. Could eek out enough instability for a marginally 
severe thunderstorm Tuesday afternoon/evening over the inland west. 

As high pressure builds from the Plains to the Upper Mississippi 
Valley Wednesday, a strengthening pressure gradient over the Upper 
Great Lakes will lead to gusty NW winds and could reach small craft 
advisory criteria on Lake Superior. Some models indicate a second 
wave embedded in the flow around the Canadian low that may lead to an 
isolated shower on Thursday over the east half, but better precip 
chances should hold off until later on Friday and especially 
Saturday after the high exits to the east.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 134 AM EDT SUN AUG 18 2019

VFR conditions will prevail overnight. As a frontal boundary 
approaches early today, showers and lower cigs will move in along 
with an increase in winds. Cigs should drop to or just below IFR 
during the periods of heavier rain at KIWD by late morning and in 
the afternoon at KCMX and KSAW. Thunderstorms may also occur, but 
confidence was not high enough for mention in the TAF.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 312 PM EDT SAT AUG 17 2019

Fog/low-level stratus today will continue to burn off/dissipate
across the eastern portions of Lake Superior as the day continues.
Otherwise, benign weather conditions prevail on the lake today,
with a change expected overnight as a frontal boundary approaches
the Upper Great Lakes. Winds will be on the increase overnight
through tomorrow night, with gusts approaching and perhaps
exceeding 20 knots. Winds will remain elevated into the start of 
the work week as a tight pressure gradient overhead allows
for gusts to reach toward 25 to near 30 knots on Monday. Look for
winds to drop back off to less than 20 knots on Tuesday, with a
quick return of over 20 knots reappearing by Wednesday. For
Thursday into at least the early part of Friday, winds are
anticipated to remain less than 20 knots. As for hazards to marine
interests (other than winds), thunderstorm chances exist for 
tomorrow and then again on Tuesday as disturbances pass on 

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