Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200814

Area Forecast Discussion
National Weather Service Marquette MI
414 AM EDT Sun May 20 2018

.SHORT TERM...(Today and tonight)
Issued at 413 AM EDT SUN MAY 20 2018

Water vapor imagery and RAP analysis show a pair of shortwaves
swinging across northern Ontario. Lead wave, heading into Quebec,
sent associated cold front across Upper MI yesterday. Ahead of sfc
high pres ridge currently extending from ND to just nw of Lake
Superior, much drier air noted on the 00z CWPL/KINL soundings is now
advecting into the area and is working to clear out postfrontal low
clouds from nw to se.

Sfc high pres and a very dry air mass will settle over the area
today and tonight. As a result, low clouds will clear out of the
rest of the fcst area during the early morning, followed by
thinning/clearing of high clouds, leading to a sunny aftn and a
clear night tonight. A very dry air mass thru a deep layer will
support falling dwpts during the day today. Based on mixing heights,
interior dwpts have the potential to fall well down into the teens
this aftn. Incorporated this mix down potential with bias corrected
guidance to bottom out dwpts in the low/mid 20s in general in the
interior. As temps rise into the 60s to around 70F, this leads to
min RH in the 15-25pct range for much of the fcst area this aftn
with the lowest readings over the interior w. Fortunately, the
blustery winds of yesterday aftn and earlier in the night will not
be around during the day today to aggravate fire wx concerns. With
high pres building over the area today, winds will generally be at
or blo 10mph as peak heating and min RH approach. As the high builds
over the area, lake breezes will rule the aftn, leading to cooler
conditions lakeside. Along the lake east of Marquette, temps may not
get out of the 40s with onshore gradient winds this morning,
followed by lake breeze winds this aftn.

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.
Favored the lowest of avbl 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.

.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 06Z TAFS through 06Z Sunday night)
Issued at 135 AM EDT SUN MAY 20 2018

A very dry air mass is currently spreading into the Upper Great
Lakes. This drier air has already cleared out low clouds at
KIWD/KCMX. At KSAW, high IFR/low MVFR cigs will clear out in the
next hr or so per satellite imagery. With a very dry air mass
dominating, VFR conditions will prevail at all terminals today and

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 413 AM EDT SUN MAY 20 2018

Sfc high pres ridge building into the Upper Lakes from the w will
lead to winds under 15kt today across most of Lake Superior.
However, with the ridge axis setting up across southern Lake
Superior, sw winds over the n central part of the lake will increase
to 15-25kt this aftn. 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...


SHORT TERM...Rolfson
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