Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241827

Area Forecast Discussion
National Weather Service Marquette MI
227 PM EDT Tue Apr 24 2018

.SHORT TERM...(Today and tonight)
Issued at 459 AM EDT TUE APR 24 2018

WV imagery and RAP analysis indicated a split flow pattern with an
upstream northern stream shortwave trough from nw Ontario into ne
North Dakota and a compact mid level low just to the south over wrn
South Dakota. At the surface, a cold front extended from ne lake
Superior through the Keweenaw Peninsula into nw WI. Mostly clear
skies prevailed across Upper Michigan with only some high clouds
over the se. Clouds were thickening over nw MN ahead of the shrtwv,
but no pcpn was observed.

Today, expect clouds to increase as the shrtwv approaches, per
upstream satellite trends. Although moderate 850-700 mb fgen slides
se into Upper Michigan this afternoon, and exits the se by late this
evening, with only limited moisture availability and llittle/no
inflow, only slight chance POPs at best are expected. Since the
low levels remain relatively dry, mainly just a few sprinkles
would be expected. Northerly flow CAA will bring cooler air into
the area with highs only in the 40s north near Lake Superior to
the upper 50s south.

Tonight, models suggest that skies will clear from west to east
during the evening with drier air moving in. However, upslope
northerly flow aided by some lake moisture will support increasing
clouds north central late.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 222 PM EDT TUE APR 24 2018

The next week or so looks to be our version of spring before we
swing into a summer-like pattern with highs in the upper 60s to
lower 70s with periodic chances for precipitation (dare I say
thunderstorms?) However, we`ll have to get through couple of days
of colder temperatures and maybe even some light snow before
pulling out the shorts.

First thing is first...A cold front is expected to swing through the
upper Great Lakes Thursday afternoon and evening ushering in
relatively colder air compared to the past few days. Numerical model
guidance paints anywhere from a trace to 0.25" of QPF along the
front with the GFS most "heavy." Given antecedent conditions (as
well as the mostly dry cold front coming through today), the
inclination is to keep qpf low--generally less than 0.05" area
wide. As for precipitation type, light rain is expected to
transition to light snow (if not heavy flurries) as colder and
drier air filters in along the backside of the front. No snow
accumulations are expected. The biggest impact of the frontal
passage will likely be strong north to northeasterly winds gusting
over 30-35 mph Thursday evening and into early Friday morning
across the west and north central shores of Lake Superior.
Temperatures are expected to reach the upper 50s to lower 60s
before the front sweeps though.

A secondary shortwave trough and associated compact low pressure
system will sneak into the area Friday with a narrow ribbon of
anywhere from a 0.05" to 0.15" of QPF. Earlier model runs indicated
mainly light rain along the northwestern side of the low but 850 mb
temperatures/max wet bulb temperatures may hover at if not just
below freezing leading to a mix of rain and snow. To make matters
a bit more complicated, forecast soundings indicate a layer of dry
air (max dew point depressions of 11 C or so) from about 850 mb
down to the surface as the main forcing from the low passes
through. All in all, there is low confidence in just how much
precipitation will make it to the ground. As such, kept QPF fairly
low in the grids for now to give time to iron out the details.

Saturday looks quiet and dry with highs in the forties along the
Lake Superior shore to lower fifties along the Wisconsin border.

The real warm up begins on Sunday as deep upper-level ridge builds
into lower central Canada enabling broad southwesterly low- to
mid- level flow across the western Great Lakes. Monday and Tuesday
look quite warm with 850 mb temperatures shooting up to +10-12 C,
giving way to highs in the low to mid 70s (if not warmer) and
lows in the lower 40s. Model guidance also depicts dew points
increasing quite a bit owing to the aforementioned southwesterly
flow. By and large the warmer and moister conditions will start
the vanishing act of the remaining snowpack across Upper Michigan.
The big question is just how long the upper-level ridge will last
(especially for fire weather concerns). A quick peak at a
northern hemispheric perspective of the forecast upper-level flow
next week reveals that a pair of cut-off lows off the western and
eastern CONUS *should* keep the wave train moving aided by a
shortwave trough in between. However, it would not be surprising
for the ridge to move slower than currently depicting in the
models (as they often do). Even so, when the shortwave trough
embedded in the longwave pattern pushes into the Great Lakes, the
expectation is that at least portions of the area may get in on
heavier precipitation which, when combined with snow melt, may
cause some minor river flooding problems. Stay tuned.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 155 PM EDT TUE APR 24 2018

Northerly winds will prevail into Wed behind a cold frontal
passage. Although there is a slight chance of showers this
afternoon, mainly just mid clouds are expected with a low
confidence of pcpn, especially that would restrict vsby or lower
cigs. Persistent upslope flow of colder air into north central
Upper Michigan late tonight into Wed morning is expected to bring
a period of low-end VFR to high-end MVFR cigs to KSAW late in the
forecast period.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 459 AM EDT TUE APR 24 2018

Northwest winds will increase to around 25 knots over central and
eastern Lake Superior late this afternoon into this evening and then
diminish overnight. Wednesday through Thursday, winds are expected
to remain below 20 knots across all of Lake Superior. Winds will
then pick up to 20 to 30 knots Thursday night with the passage of
another cold front.

Issued at 222 PM EDT TUE APR 24 2018

After a 24-hour period of highs in the lower 70s and lows in the low
to mid 30s (e.g. above freezing), the snow pack has lost 3-5 inches
across much of Upper Michigan.  The snow pack will continue to melt
today but at a slower pace mostly driven by the sun (when not
blocked by clouds). Most rivers across Upper Michigan have seen
manageable rises in water levels thus far, except for a minor ice
jam reported on the Ford river in Escanaba that has since broken
apart. Precipitation chances over the next several days look
somewhat bleak (collectively less than 0.25"). However, temperatures
next week will increase dramatically with an accompanying increase
in moisture likely leading to a rapid decrease in snow cover
across the area. There are indications of heavier precipitation
toward the middle to end of next week, though uncertainly remains
on exactly where and how much will fall. All in all, the snow pack
is expected to shrink considerably next week which may lead to
minor river flooding in the usual rivers prone to spring flooding.


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


LONG TERM...Borchardt
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