Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 211136

Area Forecast Discussion
National Weather Service Marquette MI
736 AM EDT Mon May 21 2018

.SHORT TERM...(Today and tonight)
Issued at 439 AM EDT MON MAY 21 2018

Water vapor imagery and RAP analysis show a deep northern stream
trof over eastern Canada. The flow is split over western N America
with a ridge over western Canada and a trof over the western CONUS.
In the sw flow downstream of the trof, a couple of shortwaves are
over the central Plains. One of the fcst concerns during the short
term will be whether these shortwaves will spread any shra into the
fcst area late today or this evening. Prior to that, fire wx will be
a concern. Currently, skies are clear across the fcst area, though
some high thin clouds are beginning to spread out of WI into Upper
MI ahead of the aforementioned shortwaves. A wide range of temps is
noted with some interior locations down in the low/mid 30s while
temps are as high as the low/mid 50s at some locations near Lake
Superior. Warmest conditions are in the Marquette area.

Some high clouds, mostly thin, will spread across the area today.
Mid clouds should then follow into s central Upper MI during the mid
and late aftn hrs as upstream shortwaves move closer. With high
clouds not providing much restriction to solar insolation, deep
mixing of drier air down from aloft will lead to another day of low
RH. Similar to yesterday, incorporated lower dwpts based on mixing
heights along with bias corrected guidance to arrive at aftn dwpts.
With high temps rising well into the 70s, min RH will likely be in
the 17 to 25pct range for much of the fcst area. Sustained winds
should be up around 9-13mph with gusts in the 15-20mph range,
strongest over the central fcst area. As a result, wildfire
potential will be elevated sufficiently to warrant a special weather
statement to heighten awareness for much of the area today,
particularly the central counties where winds will be strongest.
Under se winds, coolest conditions this aftn will be along Lake MI
and the east side of the Keweenaw.

Shortwave will weaken/shear e across the Great Lakes region tonight
in the more confluent flow across this region. As a result, moisture
transport gets shunted eastward rather than northward into Upper MI.
So, shra potential looks quite limited. As with the late aftn hrs,
will only include shc shra mention across southern Menominee County
this evening. Otherwise, with more cloud cover around tonight,
bumped min temps up a few degrees from previous fcst. 40s will be
the rule.

.LONG TERM...(Tuesday through Sunday)
Issued at 417 AM EDT MON MAY 21 2018

Dry with a warming trend to start the extended then still looks like
pattern could become more unsettled with increasing chances of rain
late this week into the holiday weekend as upper level trough
starting this week over the southwest CONUS moves to the northern
Plains and eventually the Upper Great Lakes. Initially Tue, Wed and
possibly into Thu focus will remain on fire weather concerns. Min RH
values should be 20-30 pct as daytime temps inland reach the 70s
Tue, well into the 80s over the interior west half on Wed and maybe
into the lower 80s on Thu depending on cloud cover. High pressure
ridge persisting will result in lake breezes Tue and Wed with gusts
inland reaching 15 mph. Later Thu, initial push of stronger moisture
advection could support some showers trying to move into western
Upper Michigan. Soundings indicate weak forcing and good deal of dry
air to overcome in low-levels so not expecting much rain on Thu. At
the least, clouds should thicken up over the west through the day.

Attn Thu night into Fri will be on shortwave trough and sfc low
slowly crossing the northern Plains and extending into scntrl
Canada. With the sfc low well to the northwest of here, increasing
south to southwest flow should result in increasing instability into
the Upper Great Lakes. Late Thu into Fri, Upper Great Lakes will be
on edge of elevated mixed layer with mid-level lapse rates over
7C/km. Would expect t-storm potential during this time to be driven
by where strongest moisture transport develops and also by any
convectively induced shortwaves that emerge from t-storms over the
northern Plains to the Upper Mississippi River Valley. With the
increasing instability could also see t-storms develop along lake
breezes over especially western and central Upper Michigan. MLCAPE
to 1000j/kg seems possible on Fri as sfc dwpnts climb into the 50s
to near 60F. Admittedly early to pin down shear forecasts, but
models are giving around 30-35 kts at this time. Seems that there
could be some stronger storms Fri if these forecasts of instability
and shear continue to hold. Main upper trough moves through in
northwest flow on Sat as sfc low crosses north of Lk Superior
swinging a cold front across Upper Michigan. Should see decent
coverage of showers and t-storms on Sat, though is is possible
chance of stronger storms could be held down as plume of steeper
lapse rates and greatest instability may advect farther south and
east by that time as low-level jet veers to the west.

Will keep chance of showers going Sat night into Sun until upper
trough axis exits east of Upper Michigan. Though most of the weekend
will be unsettled, good agreement that high pressure building back
over the region will bring dry weather for Memorial Day. Gone today
is the idea of cooler air plowing in over the region as well so
could be pretty warm Memorial Day, especially inland away from
Great Lakes.

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 736 AM EDT MON MAY 21 2018

With high pressure and a dry air mass lingering, VFR conditions will
prevail at KIWD/KCMX/KSAW through this forecast period. Light winds
will increase some today, especially at KSAW where gusts to
around 17kt are expected in the aftn.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 439 AM EDT MON MAY 21 2018

A weak pres gradient will dominate for much of this week, leading to
winds less than 20kt across Lake Superior. On most days, winds will
be under 15kt across much of the lake. A low pres system or trough
moving across the western Great Lakes on Sat may lead to somewhat
stronger winds at some point Fri/Sat.

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


SHORT TERM...Rolfson
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