Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180526

Area Forecast Discussion
National Weather Service Marquette MI
126 AM EDT Wed Sep 18 2019

.SHORT TERM...(This evening through Wednesday)
Issued at 346 PM EDT TUE SEP 17 2019

A relatively high amplitude mid-level ridge stretches
north to south from Hudson Bay to the Mid-South region this
afternoon, with a shortwave trough currently located near the
Arrowhead of Minnesota riding up the western periphery of the ridge.
This produced showers and thunderstorms throughout today, but the
stable air of the lake has kept the thunder to the west thus far. A
brief sprinkle near Ironwood or across the northern Keweenaw through
this evening are possible, otherwise the thick cirrus shield has
kept temperatures a few degrees cooler over the west. Highs have
been generally in the 70`s except some lower 80s where downsloping
southerlies have helped raise temps and some 60s where low clouds
and flow off Lake Michigan have hindered a diurnal warm-up.

Tonight, a somewhat drier low-to-mid-level airmass will move into
Upper Michigan as a strong SWerly LLJ kicks in. If any fog were to
redevelop tonight, it would likely be over the east, advecting in
from Lake MI. But low stratus seems more likely to dominate these

Another shortwave will push SW to NE across MN late tonight into
tomorrow in association with low pressure centered over Lake
Manitoba. This will increase the pressure gradient over Upper
Michigan leading to a breezy daytime with gusts of 15-25 mph,
locally to 30 mph over the west and north, though there are
significant differences in gust potential between models. The GFS is
indicating a much weaker inversion than the NAM and thus stronger
gusts, and the forecast has been nudged a little in that direction.
But looking at upstream soundings from today, the GFS forecast
inversion seems a little unrealistic so, as usual, reality will
likely be somewhere in between.

In terms of precipitation, it looks like overnight showers and
storms will fall apart before reaching the UP, with only a slight
chance for a shower to hold together into Ironwood in the late
morning or early afternoon. POPs slowly increase through the late
afternoon over the western third of the area, and a rumble of
thunder or two will be possible. Temps during the day will be
similar to today, with low 70s near Lake MI, and mid 70s to low
80s elsewhere.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 255 PM EDT TUE SEP 17 2019

The main story from the middle of the week into the weekend is the
continued well above normal temperatures and humid conditions. Upper-
level ridging which builds across the western Great Lakes today will
shift slightly east on Wed and then remain fairly stationary across
the Great Lakes through the end of the work week. A couple of
shortwaves and associated sfc low pressure systems ejecting out of
the western CONUS trough into the western/northern Plains and then
into central Canada will favor a southerly flow of very warm, moist
air into the western Great Lakes region, tapping into moisture all
the way from the Gulf of Mexico. The first shortwave lifting from
the northern Plains into central Canada will push a weak frontal
boundary into Upper Mi Wed night into Thu, which will tend to stall
out over or near the area through Fri. The stalled out frontal
boundary will result in chances for showers/storms Wed night into
Fri, along with continued warm and humid conditions. A stronger
shortwave and associated cold front is expected to move through the
area late Sat into Sun, likely bringing a better chance for
widespread showers/t-storms before drier, cooler and much less humid
air moves in behind the front Sunday night into Monday.

Wed night, weak frontal boundary just west of the cwa finally gets
propelled into Upper Mi Wed night as a shortwave and associated sfc
low over southern Manitoba late Wed lifts to James Bay by 12Z Thu.
Ahead of the cold front late Wednesday into Wednesday night, 1000-
1500 j/kg of instability and 20 to 25 knots of deep layer shear may
allow for a few stronger, pulse thunderstorms to develop. Given the
unidirectional flow along the frontal boundary, and PWATs running
1.5+, heavy rain especially over areas that may see training
showers/storms could become a possible flooding concern. However,
with the front weakening as it moves overhead and shortwave dynamics
lifting well north of the area, shower coverage may ultimately end
up being more scattered which would limit potential flood concerns.

Thursday into Friday, models indicate the above mentioned cold front
will continue to weaken overhead and essentially stalls out and
transitions into a stationary front Thu into Fri, but then pushes
back northward into Canada on Friday night as prevailing s-sw flow
strengthens on backside of mid-upper ridge axis. Lingering moisture
and humid conditions along the stalled out frontal boundary Thu-Fri
will lead to enough instability for periodic isolated to scattered
showers/t-storms through the period. Nothing severe is expected as
shear will be weak through the period. Best chance of pcpn may
end up being Thu afternoon into Thu night when many models
indicate the passage of a weak shortwave across the area which
could aid formation of convection along the frontal boundary.

Fri night into early Sat, with the stationary frontal boundary
expected to lift north of the area Fri night with the strengthening
prevailing s-sw flow off the sfc, expect a period of quieter weather
Fri night into Sat morning before the next shortwave pushes a
stronger cold front across the area bringing increasing chances
of showers/t-storms late Sat into early Sun.

Sat-Sun, the movement of the longwave trough toward the Upper Great
Lakes will funnel an additional round of strong WAA and moisture
transport across the region late Fri night into Sat. Operational
models differ on timing/advancement of long wave trough and its
associated cold front into the Upper Great Lakes this weekend. The
12Z GFS and 12Z ECMWF are certainly faster than the 12Z Canadian
with the advancement of the cold front, bringing the front into
western Upper Mi late Sat and then across the rest of Upper Michigan
through 12Z Sun. Meanwhile, the slower 12Z Canadian and the previous
00Z ECMWF run really don`t have the front advancing across area
until late Sat night into Sunday which generally agrees better with
the GEFS ensemble members and means. If models trend toward this
slower solution, showers/t-storms may not end up impacting the U.P.
until Sat night into Sun time frame. Again, with PWATs around 1.5
inches ahead of and along the cold front expect the potential of
brief heavy rain with any of the t-storms.

Behind the system, CAA wrapping around behind the system as it pulls
off to the north should finally bring us some relief from the muggy
and very warm conditions later Sun into Monday and return us to more
fall-like weather. Models and ensemble forecasts generally support
another day of dry weather on Tue as WAA from the west allows the
airmass to slowly moderate.

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 125 AM EDT WED SEP 18 2019

VFR conditions are expected at CMX and IWD through the forecast
period. SAW though will see some upslope clouds from Lake Michigan.
LIFR cigs were in earlier and they could still be nearby and have
few005 to account for this, but will have them be transient for now
and keep SAW VFR through the period. Originally thought fog would be
a problem at SAW with upslope, but feel that this moisture will
instead try to form low clouds. LLWS will continue overnight at all
three sites.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 346 PM EDT TUE SEP 17 2019

As low pres lifts into Manitoba tonight and to Hudson Bay Wednesday
night, southerly winds will continue to gradually increase across
Lake Superior, especially over the e half. Gusts of 15-25kt tonight
will increase to 25-30kt on Wed over the east half. Winds will
generally be lighter over western Lake Superior. Over far western
Lake Superior, ne winds may persist thru tonight. Since the cold
front associated with the low pres will dissipate as it crosses Lake
Superior Wed night/Thu, winds will fall back to under 15kt on Thu.
Winds should be under 15kt on Fri, then increase again Sat as the
next cold front approaches. May see gusts to 20-30kt again on Sat.

Occasional fog will remain possible until the frontal passage. Most
likely locations for fog occurrence will be over approximately the
eastern quarter of the lake as well as locations near the MN

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


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