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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

                            
000
FXUS63 KMQT 180756
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
356 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 
rainfall.

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...(Monday through Saturday)
Issued at 356 AM EDT SUN AUG 18 2019

Zonal flow, interrupted by a couple of potent shortwaves later this 
week, will prevail this week into next week. The arrival of these 
shortwaves will bring with them quite the fluctuations in 
temperatures across the Upper Peninsula, a brief chances for 
precipitation. Otherwise, dry conditions look to prevail through 
much of next week.

On Monday, high pressure will track eastward across Wisconsin and 
Lower Michigan ushering in gusty southwest winds and very dry 
conditions across the Upper Peninsula. The combination of increasing 
warm air advection and southwest gradient winds will make for a 
classic downslope warming day across the west half of Upper 
Michigan, especially near the Lake Superior shoreline where 
temperatures will climb into the 80s. As mentioned above, a very dry 
air mass is expected to be in place. While there is some uncertainty 
in the magnitude of drying given the strengthening subsidence 
inversion throughout the day, ample diurnal mixing and cloud-free 
skies will aid in mixing down of gustier winds. The strongest winds 
are expected around Isle Royale and over the Keweenaw Peninsula, but 
forecast soundings do show the potential for gusty winds across much 
of the Upper Peninsula. Depending on how much rain we see across the 
Upper Peninsula today (Sunday), we could see elevated fire weather 
concerns across northwestern parts of Upper Michigan on Monday. 

Monday night into Tuesday, boundary layer winds will remain on the 
turbulent side so expect overnight lows to be mild. On Tuesday, a 
cold front will push eastward across the Upper Peninsula, bringing 
back chances for showers and thunderstorms. While it's more common 
for this pattern to bring fire weather concerns in the spring time, 
gusty southwest winds and warm conditions will prevail ahead of the 
front. With how dry we've been as of late, how low RHs get on 
Tuesday ahead of the front will need to be monitored for fire 
weather concerns. For both Monday and Tuesday, there is some support 
with HDW creeping up into the 90th percentiles. As for convection 
along the cold front, not out of the question that there could be 
some stronger storms. Deep-layer shear doesn't appear to be a 
problem, but will need to see just how much moisture can return 
across the area and boost instability levels. 

Tuesday night through Thursday, behind the cold front a strong punch 
of cold air advection will bring fall-like temperatures to the Upper 
Great Lakes and another stretch of dry weather. Given the CAA, cloud 
cover may end up becoming more robust than currently forecast. Did 
bump winds up across the area as this pattern favors breezy 
northwest winds, especially Wednesday as the pressure gradient 
continues to look fairly strong ahead of the main surface ridge off 
to the west. Thursday into Friday morning, surface ridging will 
traverse the Upper Great Lakes, slackening the winds. The 
combination a cool, dry conditions and light winds Thursday 
night/Friday morning looks to allow for very chilly overnight lows. 
Adjusted the NBM down during this time period, as model guidance is 
hinting towards the potential for lows to fall into the upper 30s 
across the interior west.  

This cool down will not last long. For the end of the weekend into 
early next weekend, temperatures will be on the rebound as we find 
ourselves under another bout of return flow from the southwest, as 
high pressure drops southeast of the region and another shortwave 
lifts across the area. This transition back to warm air advection 
and increasing moisture will also bring back chances for 
precipitation, especially towards the end of the weekend into early 
next week.
&&

.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 
through.
&&

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

$$

SHORT TERM...lg
LONG TERM...Ritzman
AVIATION...JLB
MARINE...lg