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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 181752

Area Forecast Discussion
National Weather Service Marquette MI
152 PM EDT Sun Aug 18 2019

.SHORT TERM...(Today and tonight)
Issued at 543 AM EDT SUN AUG 18 2019

Water vapor imagery and RAP analysis show a mid-level low centered 
along the northern portion of the Manitoba/Saskatchewan border with 
a shortwave extending s into the Dakotas. Ahead of this feature, a 
shortwave that was over the Plains has been convectively 
strengthened during the night, and it is now moving across se MN 
into western WI. On a side note, the ECMWF had a good handle on this 
wave for at least a couple of days. The wave has a classic radar 
signature with a rotating area of shra/embedded thunder on the 
northern portion, centered vcnty of the Twin Cities. Stronger storms 
then arc s then sw across IA. Closer to home, fog, locally dense, 
has developed from s central into eastern Upper MI during the night. 
This fog appears to be lifting and/or thinning a bit under 
increasing gradient flow ahead of approaching shortwave. 

Aforementioned shortwave moving into western WI will lift across 
Upper MI this morning/early aftn. While shra on the northern portion 
of the circulation are showing signs of weakening/diminishing in 
coverage, well-defined circulation should maintain a fairly solid 
area of shra and some embedded thunder as it lifts across Upper MI 
during the morning and into the early aftn. Extrapolated movement of 
the vort max based on radar trends suggests the nw half of Upper MI 
will be on the more favorable n side of the vort track and should 
thus see the most widespread/heavier rainfall, perhaps general 0.25-
0.5 inch rainfall with isolated higher amounts. Shra 
coverage/rainfall amounts over the se half are more uncertain with 
that area s and se of vort track. Shortwave trof across the Dakotas 
will reach the area during the aftn. It may spark a few additional 
shra/tsra after passage of the pcpn associated with the lead 
shortwave. Not anticipating any svr storms today as instability will 
likely be held in check by abundant cloud cover. In fact, thunder 
coverage may end up being quite limited.

Any lingering pcpn over the e will end this evening. Subsidence and 
sharp drying in the wake of the second shortwave will lead to 
clearing skies from w to e tonight. Center of sfc high pres will 
reach se MN/sw WI by 12z Mon. Decent pres gradient btwn the high and 
low pres vcnty Hudson Bay will keep wind stirring across the n and e 
tonight. Although precipitable falls to around one-half inch, about 
50pct of normal, to enhance radiational cooling over the interior w, 
it won't be an ideal radiational cooling night with the high off to 
the sw. Even so, opted to favor the low side of avbl guidance which 
puts min temps down into the low/mid 40s over the interior w. Temps 
will range up to around 60F along Lake Superior from the Keweenaw 
eastward. Given the time of year with warm lakes, streams and swamps 
and longer nights, could be some patchy ground fog late tonight over 
the interior w toward the MI/WI state line.

.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 18Z TAFS through 18Z Monday afternoon)
Issued at 146 PM EDT SUN AUG 18 2019

MVFR ceilings are currently dominating at all three terminals,
with improvements expected later this afternoon at KIWD/KCMX, and
this evening at KSAW. In the meantime, showers with perhaps some
lightning will persist. Westerly winds, already breezy at KIWD 
and KSAW, will pick up at KCMX as the low responsible for today's 
active weather moves off to the northeast, with a tight pressure 
gradient on the [leading edge as well as the] backside. Surface 
high pressure will be trekking into the Great Lakes region tonight
through tomorrow, leaving Upper Michigan on its windy side 
through the remainder of this TAF period, but ushering in dry air 
aloft to clear out clouds relatively quickly. Expect VFR 
conditions to prevail late tonight into tomorrow.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 543 AM EDT SUN AUG 18 2019

Low pres trough will move across Lake Superior today. Small low pres 
wave riding ne along the trough makes for a challenging wind fcst 
due to the uncertain strength of this small scale low pres center. 
Given the current presentation of this feature on 
satellite/radar/sfc obs, opted to raise winds for today across much 
of the lake. Could be a brief period of southerly 20-30kt winds 
ahead of the trough across the e half of Lake Superior. In its wake, 
probably looking at a period of 15-25kt w to nw winds into tonight, 
particularly over the e half of the lake. Not out of the question 
that high obs platforms could see an hr or two of marginal gale 
gusts immediately in the wake of the low if the low ends up a little 
stronger. While winds will diminish on the east half of the lake on 
Mon, sw winds up to 20-30kt are expected over western Lake Superior 
btwn the Keweenaw and Isle Royale. Winds will then generally fall 
off blo 20kt into Tue. Cold front passing on Tue will usher in a 
cool air mass for Wed into Thu. With unstable conditions developing 
btwn the warmer water and cooler air moving over the lake, winds may 
reach the 15-25kt range at times. High pres will arrive on Thu to 
bring diminishing winds.

Upper Michigan...
  Beach Hazards Statement until 11 PM EDT this evening for MIZ014.

Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
LONG TERM...Ritzman