Area Forecast Discussion

FXUS63 KMQT 172231

Area Forecast Discussion
National Weather Service Marquette MI
631 PM EDT Tue Sep 17 2019

.SHORT TERM...(This evening through Wednesday)
Issued at 346 PM EDT TUE SEP 17 2019

A relatively high amplitude mid-level ridge stretches 
north to south from Hudson Bay to the Mid-South region this 
afternoon, with a shortwave trough currently located near the 
Arrowhead of Minnesota riding up the western periphery of the ridge. 
This produced showers and thunderstorms throughout today, but the 
stable air of the lake has kept the thunder to the west thus far. A 
brief sprinkle near Ironwood or across the northern Keweenaw through 
this evening are possible, otherwise the thick cirrus shield has 
kept temperatures a few degrees cooler over the west. Highs have 
been generally in the 70's except some lower 80s where downsloping 
southerlies have helped raise temps and some 60s where low clouds 
and flow off Lake Michigan have hindered a diurnal warm-up. 

Tonight, a somewhat drier low-to-mid-level airmass will move into 
Upper Michigan as a strong SWerly LLJ kicks in. If any fog were to 
redevelop tonight, it would likely be over the east, advecting in 
from Lake MI. But low stratus seems more likely to dominate these 

Another shortwave will push SW to NE across MN late tonight into 
tomorrow in association with low pressure centered over Lake 
Manitoba. This will increase the pressure gradient over Upper 
Michigan leading to a breezy daytime with gusts of 15-25 mph, 
locally to 30 mph over the west and north, though there are 
significant differences in gust potential between models. The GFS is 
indicating a much weaker inversion than the NAM and thus stronger 
gusts, and the forecast has been nudged a little in that direction. 
But looking at upstream soundings from today, the GFS forecast 
inversion seems a little unrealistic so, as usual, reality will 
likely be somewhere in between. 

In terms of precipitation, it looks like overnight showers and 
storms will fall apart before reaching the UP, with only a slight 
chance for a shower to hold together into Ironwood in the late 
morning or early afternoon. POPs slowly increase through the late 
afternoon over the western third of the area, and a rumble of 
thunder or two will be possible. Temps during the day will be 
similar to today, with low 70s near Lake MI, and mid 70s to low 
80s elsewhere.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 255 PM EDT TUE SEP 17 2019

The main story from the middle of the week into the weekend is the 
continued well above normal temperatures and humid conditions. Upper-
level ridging which builds across the western Great Lakes today will 
shift slightly east on Wed and then remain fairly stationary across 
the Great Lakes through the end of the work week. A couple of 
shortwaves and associated sfc low pressure systems ejecting out of 
the western CONUS trough into the western/northern Plains and then 
into central Canada will favor a southerly flow of very warm, moist 
air into the western Great Lakes region, tapping into moisture all 
the way from the Gulf of Mexico. The first shortwave lifting from 
the northern Plains into central Canada will push a weak frontal 
boundary into Upper Mi Wed night into Thu, which will tend to stall 
out over or near the area through Fri. The stalled out frontal 
boundary will result in chances for showers/storms Wed night into 
Fri, along with continued warm and humid conditions. A stronger 
shortwave and associated cold front is expected to move through the 
area late Sat into Sun, likely bringing a better chance for 
widespread showers/t-storms before drier, cooler and much less humid 
air moves in behind the front Sunday night into Monday.  

Wed night, weak frontal boundary just west of the cwa finally gets 
propelled into Upper Mi Wed night as a shortwave and associated sfc 
low over southern Manitoba late Wed lifts to James Bay by 12Z Thu. 
Ahead of the cold front late Wednesday into Wednesday night, 1000-
1500 j/kg of instability and 20 to 25 knots of deep layer shear may 
allow for a few stronger, pulse thunderstorms to develop. Given the 
unidirectional flow along the frontal boundary, and PWATs running 
1.5+, heavy rain especially over areas that may see training 
showers/storms could become a possible flooding concern. However, 
with the front weakening as it moves overhead and shortwave dynamics 
lifting well north of the area, shower coverage may ultimately end 
up being more scattered which would limit potential flood concerns. 

Thursday into Friday, models indicate the above mentioned cold front 
will continue to weaken overhead and essentially stalls out and 
transitions into a stationary front Thu into Fri, but then pushes 
back northward into Canada on Friday night as prevailing s-sw flow 
strengthens on backside of mid-upper ridge axis. Lingering moisture 
and humid conditions along the stalled out frontal boundary Thu-Fri 
will lead to enough instability for periodic isolated to scattered 
showers/t-storms through the period. Nothing severe is expected as 
shear will be weak through the period. Best chance of pcpn may 
end up being Thu afternoon into Thu night when many models 
indicate the passage of a weak shortwave across the area which 
could aid formation of convection along the frontal boundary. 

Fri night into early Sat, with the stationary frontal boundary 
expected to lift north of the area Fri night with the strengthening 
prevailing s-sw flow off the sfc, expect a period of quieter weather 
Fri night into Sat morning before the next shortwave pushes a 
stronger cold front across the area bringing increasing chances 
of showers/t-storms late Sat into early Sun.  

Sat-Sun, the movement of the longwave trough toward the Upper Great 
Lakes will funnel an additional round of strong WAA and moisture 
transport across the region late Fri night into Sat. Operational 
models differ on timing/advancement of long wave trough and its 
associated cold front into the Upper Great Lakes this weekend. The 
12Z GFS and 12Z ECMWF are certainly faster than the 12Z Canadian 
with the advancement of the cold front, bringing the front into 
western Upper Mi late Sat and then across the rest of Upper Michigan 
through 12Z Sun. Meanwhile, the slower 12Z Canadian and the previous 
00Z ECMWF run really don't have the front advancing across area 
until late Sat night into Sunday which generally agrees better with 
the GEFS ensemble members and means. If models trend toward this 
slower solution, showers/t-storms may not end up impacting the U.P. 
until Sat night into Sun time frame. Again, with PWATs around 1.5 
inches ahead of and along the cold front expect the potential of 
brief heavy rain with any of the t-storms. 

Behind the system, CAA wrapping around behind the system as it pulls 
off to the north should finally bring us some relief from the muggy 
and very warm conditions later Sun into Monday and return us to more 
fall-like weather. Models and ensemble forecasts generally support 
another day of dry weather on Tue as WAA from the west allows the 
airmass to slowly moderate.

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 630 PM EDT TUE SEP 17 2019

VFR conditions are expected at CMX and IWD through the forecast 
period. SAW though will again see upslope fog from Lake Michigan 
which will take the visibility down to IFR this evening through Wed 
morning before VFR conditions there return. LLWS will set up 
overnight at all three sites.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 346 PM EDT TUE SEP 17 2019

As low pres lifts into Manitoba tonight and to Hudson Bay Wednesday 
night, southerly winds will continue to gradually increase across 
Lake Superior, especially over the e half. Gusts of 15-25kt tonight 
will increase to 25-30kt on Wed over the east half. Winds will 
generally be lighter over western Lake Superior. Over far western 
Lake Superior, ne winds may persist thru tonight. Since the cold 
front associated with the low pres will dissipate as it crosses Lake 
Superior Wed night/Thu, winds will fall back to under 15kt on Thu. 
Winds should be under 15kt on Fri, then increase again Sat as the 
next cold front approaches. May see gusts to 20-30kt again on Sat.  

Occasional fog will remain possible until the frontal passage. Most 
likely locations for fog occurrence will be over approximately the 
eastern quarter of the lake as well as locations near the MN 

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