Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201725

Area Forecast Discussion
National Weather Service Marquette MI
125 PM EDT Fri Oct 20 2017

.SHORT TERM...(Today and tonight)
Issued at 446 AM EDT FRI OCT 20 2017

Today will be sunny, dry, and breezy. We won`t see nearly as dry of
conditions today as yesterday, but minimum RH values will be as low
as the mid 30% range over the interior west. With southerly winds
today, the east half will be considerably more moist with minimum RH
values in the 50-60% range. Those southerly winds will gust to 15-25
mph, strongest over the W and in downslope areas near Lake Superior.
Temps today will be around 20 degrees above normal with highs in the
70s W half and mid-upper 60s E half. Temps tonight will also be
about 20 degrees above normal with lows in the 50s and increasing

.LONG TERM...(Saturday through Thursday)
Issued at 420 AM EDT FRI OCT 20 2017

Autumn has been dominated by periods of unseasonable warmth with blo
normal temp days quite rare. The current pattern is once again
supporting unseasonably warm conditions across the Upper Great
Lakes. This warm pattern will last for a few more days as 500mb
positive height anomalies of 220m over the Upper Great Lakes this
morning shift ene and increase to 300m over Quebec by Sun morning.
This occurs in response to a shortwave trof swinging across the
western CONUS today and reaching the central CONUS by Sun morning.
Although this trof weakens as it pushes across the area on Sun, it
will herald an overall cooler pattern that will set in next week as
there will be 2 periods of trof amplification into the
central/eastern CONUS downstream of a mean ridge developing near the
w coast of N America. By the end of next week, there will be a broad
central N America trof btwn ridging over the Gulf of Alaska and off
the E Coast. Although turning colder, temps won`t fall much blo late
Oct normals. As for pcpn, the weakening trof reaching the area on
Sun will bring some shra this weekend. Energy in the southern
portion of this trof will briefly separate out of the main flow and
drop into the Lwr Mississippi Valley late in the weekend. The first
trof amplification next week will then pick up this energy.
Depending on how sharply the trof amplifies will determine whether
this southern energy will spin up a strong storm system that could
affect the Great Lakes region in the Mon/Tue time frame. Whatever
happens, the larger scale trof amplification will lead to colder
weather and at a minimum some lake effect pcpn late Mon/Tue. The
next trof will amplify Thu/Fri, sending another cold front across
the area on Thu. Lacking moisture, there may not be much shra
activity with the front. Behind the front, influx of colder air
should generate some lake effect pcpn into Fri.

Beginning Sat, strong, deep southerly flow will be in place ahead of
approaching shortwave trof and associated cold front. Deepening
moisture may lead to some -shra over the w, closer to approaching
front, but overall limited moisture depth, lack of much isentropic
ascent/deep layer forcing suggest nothing higher than low chc pops
is warranted at this time. Better potential of shra (likely to
categorical pops) will spread from w to e Sat night/Sun as cold
front sweeps across the area. With a few hundred j/kg of elevated
CAPE avbl, there may be a few thunderstorms. Even with more cloud
cover, Sat will be another warm day with high temps mostly in the
upper 60s/lwr 70s. Sun will turn cooler as cold front passes. Expect
highs generally in the upper 50s/lwr 60s.

Mon into Tue, attention turns to the trof that will be amplifying
from the Northern Plains to the Mississippi Valley, Ohio Valley, and
Great Lakes region. Operational models have mostly trended away from
this trof amplifying sufficiently to phase early on with the
aformentioned energy over the Lwr Mississippi Valley, which would
lead to a strong storm system lifting far enough w into the Great
Lakes region to impact the weather here significantly. While there
are a few CMC/GFS ensembles that show such a storm system, the trend
is for less members to show it. Will still be something to monitor,
but for now it appears the fcst area will mostly just be influenced
by the amplifying trof. For the last 2 runs, the CMC is much
stronger with the deepening of the trof over the Upper Mississippi
Valley. It develops a closed mid-level low over the western Great
Lakes with associated sfc low organizing over WI, resulting in a
soaking rainfall for the fcst area late Mon into Tue. There is
really not any support for this solution from the ensembles. At this
point, it looks like pcpn will be light as it develops later Mon
thru Tue under amplfiying trof with an increasing lake component to
pcpn with time as 850mb temps fall to perhaps as low as -4 or -5C.
May see some snowflakes mix in Tue night.

As trof shifts e on Wed, shortwave ridging will build toward the
Upper Great Lakes ahead of the next shortwave trof dropping thru sw
Canada into the northern Rockies. This will lead to a trend to dry
weather on Wed. Thu will be warmer, though timing of the cold front
associated with the next trof amplifying into the central CONUS will
determine how warm. If it`s slow, temps will rebound back into the
60s. Might be a few shra along the front, but better chc of pcpn
will develop after fropa when colder air arrives to generate lake
effect pcpn off Lake Superior Thu night into Fri. Right now, it
appears this surge of colder air late next week will be the coldest
of the week and will offer a better chc of seeing more of the lake
effect pcpn become LES.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 125 PM EDT FRI OCT 20 2017

VFR conditions will continue. LLWS is expected at all sites tonight.
A cold front will approach the western TAF sites late in the TAF
period which will introduce ceilings; however, they should remain
VFR through this issuance.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 446 AM EDT FRI OCT 20 2017

Today through Monday, winds will remain mostly between 20 and 25
knots. There is potential for gusts up to 30 knots late Saturday.
North gusts to 30 knots (and maybe some gales) are possible late Mon
night into Tue night

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


LONG TERM...Rolfson
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