Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201946

Area Forecast Discussion
National Weather Service Marquette MI
346 PM EDT Sun May 20 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...(Monday through Saturday)
Issued at 319 AM EDT SUN MAY 20 2018

Upper air pattern starts off this week with ridge over western
Canada and shortwave trough over the southwest CONUS. Flow looks
generally zonal downstream of these features including over the
Great Lakes. Generally sfc high pressure that expands across the
upper Great Lakes today will remain in place the first part of the
week. Still some hint that weak shortwave over the plains along
with increasing mid-level moisture H85-H6 could result in a few
showers Mon night over scntrl. Forcing is very weak with this
system though so may be nothing more than a few sprinkles if
precip occurs. Weak system exits east of area on Tue morning. Weak
ridging staying in place should promote lake breezes for all
areas by Tue aftn. Both Mon and Tue will feature elevated wildfire
potential due to low RH values in the 20-30 pct range inland.
Wind gusts on Mon could top out in the 13-18 mph range, strongest
over the central with enhanced southeast lake breeze off Lk
Michigan. Winds on Tue should be lighter.

By Wed, flow pattern aloft turns more northwest as troughing expands
Hudson Bay to Quebec. As sfc high pressure builds across northern
Ontario and Quebec, more dry weather will continue over Upper
Michigan. With high to the north and east of Lk Superior, northeast
winds may be enhanced closer to Lk Superior leading to temps in the
50s. However, inland toward MI/WI state line at LNL and IMT, temps
will push above 80F. Once again RH values will be in the 20-30 pct
range but winds should stay light where the warmest temps/lowest RH
values line up.

Late in the week, still looks like chances for rain will increase as
shortwave trough that begins the week over the southwest CONUS
meanders to the northern Plains and eventually heads toward the
western Great Lakes. Since high pressure over the area most of the
week moves east and troughing develops over the central Plains,
return flow should begin to bring increasing low-level moisture
northward, though will still have potential for lower RH values on
Thu over east half due to dry air lingering with departing high.
Late Thu into Fri, as low pressure deepens over the northern Plains
and moisture transport increases into Upper Great Lakes should start
to see at least chances for showers and maybe a chance for t-storms
as well. This far out, it is hard to gage if there could be stronger
t-storms, but at least based on forecast MLCAPES seems there may be
a potential, especially Sat. We will have to see if there is enough
deep layer shear around to support organized stronger storms though.

Chances for rain should continue into much of Sat as the northern
Plains low slowly crosses the Upper Great Lakes. Rain chances will
begin to diminish later in the weekend but it may take until Sun
aftn or Sun evening. Though there is decent agreement on
temperatures on Sun with 50s near Lk Superior and 70s inland, the
extent of cool down behind the low by Memorial Day is very
uncertain. Likely will depend on how far south and west the upper
level trough over eastern Canada progresses. Spread in models is
high at this point with coldest guidance suggesting highs in the 50s
inland on Memorial Day while warmest guidance shows temps in the

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 122 PM EDT SUN MAY 20 2018

With high pres and a very dry air mass dominating, VFR conditions
will prevail at KIWD/KCMX/KSAW thru this fcst period.

.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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