Area Forecast Discussion

FXUS63 KMQT 211156

Area Forecast Discussion
National Weather Service Marquette MI
756 AM EDT Sat Jul 21 2018

.SHORT TERM...(Today and tonight)
Issued at 401 AM EDT SAT JUL 21 2018

...Dreary and Soggy Saturday across portions of Upper Michigan...

The main forecast concerns over the next 24 hours are additional 
chances for rain showers, mainly across the central and east, areas 
of fog near Lake Superior, and then the development of moderate to 
high swim risk for Lake Superior beaches in Marquette and Alger 
counties. High temperatures today will be a bit cooler than 
yesterday, likely only climbing into the 60s and lower 70s. Cooler 
temperatures are expected near the shoreline of Lake Superior as 
northerly flow ushers in a cooler, more stable airmass. 

Fog: Webcams across far western Upper Michigan show areas of patchy 
dense fog this morning, especially across Gogebic County. With 
observations showing flow off of Lake Superior through much of the 
night, the combination of upslope/onshore flow and radiational 
cooling as clouds/showers broke up earlier has allowed for this fog 
to develop. Expect the fog to remain in place until flow veers more 
north-northeasterly later today. Further to the east across the 
north central, the majority of high-res guidance is showing a period 
of reduced visibilities as upslope/onshore flow coupled with rain 
showers moving inland later this morning. 

Precipitation: Early this morning, the main surface low was ever so 
slowly rotating across southern Lake Michigan. A branch of warp-
around moisture continued to pump northwest from Lake Huron over 
into eastern Upper Michigan. This wrap-around moisture allowed 
fairly widespread rain showers and a few isolated rumbles of thunder 
to develop and drift westward towards central Upper Michigan early 
this morning. Models are all fairly consistent with the areas of 
showers currently across the east pivoting over central Upper 
Michigan through the mid/late morning hours, then as lingering wrap-
around moisture teams up with upslope flow across the north central, 
additional rounds of rain showers will be possible through tonight. 
The better instability, and chances for isolated thunderstorms, will 
be across the east as flow off of Lake Superior in the north central 
will result in increased stability and reduced chances for 
thunderstorms. Given the fairly good model-to-model agreement with 
the track of these numerous rounds of precipitation, have increased 
QPF - especially over the north central where a few models are 
showing upwards of three quarters to just over one inch of rain 
today. While it may be challenging to get rainfall totals of that 
magnitude given the stable environment coming off of Lake Superior, 
it certainly is not out of the question if rain showers train over 
the same areas. 

Swim Risk: As winds continue to funnel towards the shoreline of Lake 
Superior today across Marquette and Alger Counties, a moderate to 
high swim risk is expected to develop. Through much of the day 
today, the swim risk is expected to remain in the moderate category, 
until ramping up this evening through the overnight hours. Given 
that the timing of the high swim risk is quite late in the day, and 
the fact that today is not the ideal beach day (temperatures less 
than 65F and intermittent rain showers expected), have opted to hold 
off on issuing a beach hazard statement for today. Keep in mind, if 
conditions ramp up quicker, the day shift may need to issue a 

.LONG TERM...(Sunday through Friday)
Issued at 339 AM EDT SAT JUL 21 2018

Generally low impact weather expected over the extended period. 
Models suggest that a mid-level low over Alberta will slowly 
slide eastward to northern Ontario by Wed and then to James Bay by
Friday. The mid-level low over the central Great Lakes into the 
Ohio Valley is expected to sink to the south and become cutoff 
over the se CONUS early next week. 

Beginning Sunday, northerly flow will weaken as a sfc high pressure 
ridge builds in from the west. Models indicate drying/subsidence 
associated with mid-level/sfc ridging by the afternoon so expect 
clouds to dissipate. Increasing sunshine will allow temps to climb 
back into the upper 70s to around 80 inland and to around 70 near 
Lake Superior.

Monday and Tuesday, a shortwave and associated weak cold front 
moving out of the Northern Plains could bring some isolated showers 
and maybe a thunderstorm into the far west late afternoon/evening. 
However, moisture transport and instability will likely be limited 
as forcing weakens along/ahead the front as it moves into the 
northern Great Lakes. Another shortwave moving through the area 
could produce a few isolated showers/T-storms Tue afternoon as 
diurnal instability builds. 

Tue night-Wed, As the mid-level low from Canada sinks south the next 
significant shortwave and sfc front is expected to move into the 
region by Wed bringing another chance of shra/tsra. With limited 
moisture inflow, only lighter rainfall amounts would be expected 
with mainly scattered shower coverage. Cooler and drier air will 
then move in for the end of the week.

Thu-Fri Cyclonic mid-level flow through the Upper Great Lakes from 
trough/mid-level low centered over northern Ontario will bring 
additional weak shortwaves through the area producing periodic light 
showers. High temperatures will trend slightly cooler than normal, 
mainly in the 70s.

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 755 AM EDT SAT JUL 21 2018

Today will be one of those days where amendments may be necessary as 
complex weather continues across Upper Michigan with significant 
impacts on visibilities and ceilings. KIWD has gradually come up to 
2SM this morning, but ceilings are more stubborn to lift. Expect 
this trend to continue through the day today with gradual 
improvements to ceilings, perhaps towards low-end MVFR; however, 
visibilities should improve quicker. KCMX is a bit of a wild card as 
ceilings have just rapidly come down this morning. With ceilings 
already plummeting at KCMX, they will likely hold on through the 
morning hours before gradually improving this afternoon. KSAW is 
also rather challenging this morning with north-northeast flow 
coming in off of Lake Superior and a band of moderate rain just 
starting to nudge into the terminal. As the moderate rain pivots 
over the terminal through the next few hours, ceilings and 
visibilities may improve slightly. However, with the north-northeast 
flow off of the lake continuing throughout the day and into tonight 
confidence is not high in regards to how visibilities and ceilings 
will evolve. For now keep mostly IFR ceilings and MVFR visibilities. 
However, if the marine layer can push up towards KSAW, visibilities 
could end up being lower than what is currently in the TAF.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 401 AM EDT SAT JUL 21 2018

As the main surface low over far southern Lake Michigan slowly digs 
southeast today, expect winds to remain between 10 and 20 knots 
today and tonight. There was an observation showing reduced 
visibilities over western portions of the lake earlier this morning, 
so expect areas of patchy fog. It is possible areas of persistent 
rainfall over eastern Lake Superior over the next 12-24 hours could 
result in areas of widespread fog. High pressure will move in for 
the end of the weekend, bringing lighter winds less than 15 knots on 
Sunday. Expect winds to remain around or less than 15 knots through 
much of next week.

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


SHORT TERM...Ritzman