Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221133

Area Forecast Discussion
National Weather Service Marquette MI
733 AM EDT Sun Sep 22 2019

.SHORT TERM...(Today and tonight)
Issued at 552 AM EDT SUN SEP 22 2019

Water vapor imagery and RAP analysis show a trof extending from
Manitoba/northern Ontario to the southern Rockies. Trof has several
more well-defined shortwaves within it. One is moving from se
Manitoba into northern Ontario, another is over eastern MT and a
third is over eastern CO. The latter 2 will play a role in the fcst
here later tonight into Mon morning as they phase while moving into
the western Great Lakes. Sfc cold front has been moving into Upper
MI rather uneventfully during the night. There were some tsra that
moved across west and central Upper MI earlier in the night, but
they have all dissipated over the last few hrs despite plenty of
instability (MUCAPE in the 1000-2000j/kg range). It is an
unseasonably warm/humid early morning with many locations still
reporting temps around 70F with dwpts in the upper 60s.

Cold front will continue eastward today, clearing the eastern fcst
area early aftn. Shra development will remain possible ahead of the
front this morning. Even after it exits, it will be close enough for
a continued risk of shra, especially in light of a subtle shortwave
lifting ne today in addition to upper diffluence which both support
shra expansion on the cool side of the sfc cold front. This pcpn
signal is already present across nw MO into IA where shra are
already widespread with trends toward northeastward development.
Upstream development/movement will need to monitored. Could end up
with a few hrs of steady shra from roughly KMNM to KERY during the
aftn. Instability will be fading with passage of cold front, so
isold thunder will only be possible far se fcst area until about mid
aftn. Given the warm start to the day, today will still be warm with
highs generally upper 60s/lwr 70s. Will be turning less humid from w
to e, especially nw half which will see dwpts fall to the low/mid
50s this aftn. Will be breezy on Keweenaw today under favorable post-
frontal westerly winds. All models have toned down mixed layer winds
from previous runs. Still, some gusts to 30-35mph will be possible.

Tonight, the shortwave currently over eastern MT and the one over CO
will phase, leading to a mid-level low weakly closing off over nw WI
and then moving over Upper MI by 12z Mon. Decent 12hr 500mb height
falls up to 120m occur into the western Great Lakes tonight with
increasing deep layer forcing developing over Upper MI per q-
vectors. Left exit of accompanying upper jet will also place Upper
MI under favorable upper diffluence. Given the abundance of moisture
still in the vcnty to be taken advantage of (precipitable water of 1-
2 inches from se WI across Lwr MI into eastern Upper MI this
evening), the general, overall model trends toward more expansive
pcpn developing tonight seem on track. ECMWF has been leading the
other models on this scenario and has been increasing pcpn amounts
in each successive run. The 0.5 to 1 inch totals the 00z run shows
across Upper MI tonight/Mon morning could very well work out. Expect
shra to expand back across the fcst area tonight, mostly during the
overnight hrs.

.LONG TERM...(Monday through Saturday)
Issued at 415 AM EDT SUN SEP 22 2019

The long-term period forecast starts off with some drama right away
Monday. There`s been a distinct trend towards a quick developing low
spinning up roughly over the Mackinac Straits on Monday that while
not yet in all of the guidance is starting to emerge as a likely
solution. Some of the time-lagged model blends are not picking this
up yet, so relied on the raw deterministic guidance for POPs and QPF
Monday, resulting in about a quarter to a half inch of rain from
Sunday night through Monday night for the central and eastern U.P.
As the pressure gradient tightens up quickly, there could be a window
for some 20-25+ mph gusts as well on Monday, especially over the

precip clears Monday evening but some clouds linger into Monday
night east. At the same time, mid to upper-level ridging builds in
behind the system with drier air aloft, so hedged cool with Tuesday
morning lows west and central and then hedged slightly warmer east
where that clouds cover may linger a bit longer. As the winds go
light and the skies clear, there will probably be some areas of fog
as well, especially where it rained during the day Monday.

We have one definitely dry day Tuesday as that upper-level ridging
passes directly overhead. But the next system moves in quickly
Tuesday night. As a cold front barges southward through Ontario
towards the Upper Great Lakes, a strong upper level jet pushes into
the Northern Plains and spins up a surface cyclone along the
boundary. This becomes the focus for a line of showers and
thunderstorms trekking across the U.P. Tuesday night into Wednesday
morning. The NBM looked too low on precip (every major model has
this yet it had POPs maxing out at 40% in some areas) so blended
towards WPC and the raw models. Should be enough MUCAPE for some
embedded thunder as well but right now this looks like primarily a
9scattered) heavy rain even rather than a strong/severe storm event.

Look for decent CAA behind the system Wednesday afternoon into
Thursday - albeit with the exact FROPA timing still uncertain.
Regardless, it will eventually get much cooler. The deterministic
GFS drops 850 mb temps all the way down to -1 C by Thurs morning.
The EC is not as cold (about +3 C) and the GEFS mean is closer to +1
C, but no matter what it looks like a chilly day. Highs could be in
the upper 50s to 60 if we get enough sunshine, which is likely, but
could be stuck in the low 50s without. There`s also a brief window
for some lake-effect showers over the west and Keweenaw before drier
air aloft advects in. Went with just slight chance to chance POPs
for now, and whatever does materialize should be wrapping up by mid-
morning. With that CAA and steep lapse rates, should be pretty
breezy late Wed. into Thurs., especially on the Keweenaw where 30+
mph gusts certainly look possible.

The active pattern continues with another rain-maker modeled for the
end of the week. This doesn`t look like as much a well-defined
system as a wave slowly ridging along a slow-moving boundary, so
this could be another chance for a widespread soaking rain with
locally heavy rainfall possible on or around Friday.

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 732 AM EDT SUN SEP 22 2019

With a somewhat drier air mass moving into the area today, VFR
conditions should prevail at KIWD/KCMX. MVFR cigs may hang on at
KSAW for a few more hrs before conditions become prevailing VFR.
West winds will be gusty to 25-30kt at KCMX today. A disturbance
moving into the Upper Great Lakes tonight will spread shra back
across the area with cigs falling to MVFR at KCMX/KSAW. IFR cigs
could develop late at both terminals.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 552 AM EDT SUN SEP 22 2019

In the wake of a passing cold front, expect wind gusts generally in
the 15-25kt range today across Lake Superior. Winds will diminish a
bit tonight/Mon, but some gusts to 20-25kt may still occur over
portions of eastern Lake Superior. A period of light winds under
15kt is expected Mon night under passing high pres ridge. Winds will
then begin to increase Tue ahead of the next approaching cold front.
With a deepening low pres developing along the front and lifting to
Hudson Bay, expect winds to increase to 20-30kt Tue night/Wed. Not
out of the question that gales could occur over parts of the lake in
the wake of the front on Wed, especially over eastern Lake Superior.

Any lingering patches of dense fog on Lake Superior will dissipate
today as drier/cooler air arrives.

Upper Michigan...
  Beach Hazards Statement until 7 PM EDT this evening for MIZ014.

Lake Superior...
Lake Michigan...


SHORT TERM...Rolfson
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