Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210820

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

.SHORT TERM...(This evening through Monday)
Issued at 346 PM EDT SUN MAY 20 2018

Water vapor imagery and RAP analysis show a split flow pattern over
the western CONUS with a wnw confluent flow aloft into the Upper
Great Lakes region and sfc high pressure dominating. Lake breezes
have kept conditions cooler this afternoon near the Great Lakes
shores (40s and lower 50s) while much farther inland under sunny
skies and deeper mixing temps have risen in the upper 60s/lower 70s
along the WI border.

Winds will diminish to calm/near calm tonight, setting the stage for
a chilly night as dry air mass (precipitable water as low as one-
quarter to one-third inch) aids radiational cooling potential. Will
continue to favored the lowest of available guidance, bias corrected
mos guidance and bias corrected CMC global which is normally a
superior performer on radiational cooling nights. Traditional
interior cold spots should fall into the upper 20s/around 30F.

Sfc high pressure will remain in control continuing the dry
conditions on Monday. With the center of the high moving east
southeast gradient winds will increase near 10 mph with gusts
reaching over 15 mph at times over the west half of the fcst area.
The winds combined with high temps reaching into the lower 70s and
minimum RHs lowering into the 20 to 25 percent range will contribute
to elevated fire weather concerns especially over the west half.
Shortwave lifting ne from the Central Plains could bring some mid-
high clouds into s central portions in the afternoon, although any
showers associated with this system should remain south on Monday.

.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 06Z TAFS through 06Z Monday night)
Issued at 131 AM EDT MON MAY 21 2018

With high pressure and a very dry air mass dominating, VFR
conditions will prevail at KIWD/KCMX/KSAW through this forecast
period. Light winds will increase this morning and become gusty
at times this afternoon at KSAW.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 346 PM EDT SUN MAY 20 2018

Sfc high pres ridge over the Upper Lakes has led to winds under 15kt
today across most of Lake Superior this afternoon. However, with the
ridge axis setting up across southern Lake Superior, sw winds over
the n central part of the lake could gust as high as 20kt late this
afternoon. High pres will then remain over the Great Lakes region
into Tue, resulting in winds mostly under 15kt. Although a cold
front will drop s across Lake Superior Tue night/Wed morning, it
will be weak, and winds will likely remain mostly under 15kt thru
Wed and into Thu.

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


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