Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 290921

Area Forecast Discussion
National Weather Service Marquette MI
521 AM EDT MON AUG 29 2016

.SHORT TERM...(Today and tonight)
Issued at 521 AM EDT MON AUG 29 2016

Water vapor imagery and RAP analysis show a shortwave trof moving
across Saskatchewan into Manitoba. In response to the wave, 30-40+kt
low-level jet per latest RAP analysis aimed ne across MN with 1000-
2000j/kg of mucape in the inflow is supporting a large cluster of
shra/tsra in northern MN early this morning. Northern end of
activity is showing signs of weakening, at least partly due to
storms on the southern and western end of the cluster increasingly
becoming aligned to disrupt low-level jet into the convection
farther n and ne. Closer to home, clear skies and good radiational
cooling for a good part of the night has allowed some fog/stratus to
form over portions of the central and eastern fcst area, typical for
this time of year. Lowest observed temp is 43 degrees nw of KERY at
Spincich Lake RAWS site.

Fcst for the morning hrs was largely constructed based on
extrapolation of the MN convection with some weighting of guidance
that has at least some resemblance to reality. As convection moves
out away from the better low-level jet forcing, expect the ongoing
weakening trend to continue, but at this point, it appears likely
pops will be warranted over the far w. Lowered pops to chc farther e
into central Upper MI and kept the e basically dry thru the aftn
with expectation of this cluster of shra/tsra never making it that
far e. What transpires after this convection moves thru/dissipates
is uncertain. While fcst maintains chc pops thru the aftn over the w
and central, it is certainly possible that there could be many hrs
with no shra/tsra under stabilizied air mass following the morning
pcpn. High res NAM window has been very insistent for a number of
runs that new convection will hold off until after sunset,
developing along the cold front that will drop se into the area.
This idea is supported by the NCEP NMM and NSSL WRF, and may offer a
reasonable solution for the aftn hrs and tonight. With deep layer
forcing here very weak as shortwave tracks well n thru northern
Ontario, coverage of new convection may be limited as suggested by
the NAM high res window/NCEP NMM and NSSL WRF. Kept pops mostly in
the chc range. As for svr storms, not expecting any svr storms this
morning as convection will be weakening. New storms that develop
either later this aftn or more likely tonight will be in an
environment of mlcape 1000-1500j/kg. While deep layer shear is
generally 25kt or less, 30-40kt shear is not far to the n and ne.
So, not out of the question that there could be an isold svr storm.

.LONG TERM...(Tuesday through Sunday)
Issued at 408 AM EDT MON AUG 29 2016

Majority of active weather should be out of cwa by daybreak on Tue.
Key whether there will be additional shra/tsra is shortwave dropping
across Northern Ontario on Tue. Even as sfc front slips south and
east of cwa on Tue morning, may be enough of a wsw component to h85
winds to keep sufficient elevated instability with mucapes up to
1000j/kg over far south cwa early to mid aftn. Effective shear is
less than 20 kts so chances of strong storms is low. Sfc and h85
fronts move well to the south Tue night into Wed. Sfc ridge center
remains well to the northwest but with pwats down to 0.50 inch on Tue
night could see chilly conditions for interior west. 925mb winds up
to 20 kts over east cwa should limit temp fall there despite mostly
clear skies.

On Wed into Wed evening shortwaves dig se toward Lk Superior within
main trough aloft across Northern Ontario. Thermal trough with h85
temps down to 5-6C glances region. Soundings indicate thin layer of
high moisture h9-h85. Suppose there could be enough daytime heating
to combine with the moist layer to lead to a few sprinkles or
showers out of widespread cu/sc field. Bigger issue will be stiff
northerly winds and higher waves that may lead to moderate swim risk
late Wed into Wed night at the Marquette and Alger county beaches of
Lk Superior.

Sfc high moves closer on Wed night but ridge axis remains west of
cwa. Thermal troughing with h85 temps still around 6c and lingering
h85 moisture could lead to setup for weak lake effect on Wed night
and even into Thu morning. NE winds in blyr would favor higher
terrain of ncntrl U.P. Would not be surprised if there a few light
showers or sprinkles at times with delta t/s around 13c and since it
will occur during diurnal min with less mixing to disrupt lake
effect processes. Moisture diminishes enough by Thu aftn and h85
temps warm sufficiently to 10c to end chances of any lake effect.
Sfc high crosses Thu night into Fri. Mostly clear skies and light
winds along with pwats lower than 0.50 inch point to chilly night
over much of inland sections on Thu night. Lowered mins toward GEM
bias corrected guidance which yielded upper 30s for favored cold

High will keep conditions dry Fri into Fri night, then return flow
could allow for initial wave of shra/tsra to lift into the area late
Sat into Sat night. Greater chances for shra/tsra move back occur
Sun night and Mon with approach of stronger low pressure trough and
axis of higher theta-e and mlcapes up to 1000 j/kg.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 117 AM EDT MON AUG 29 2016

Radiation fog could develop at SAW overnight under sfc high pressure
and near calm wind where MVFR vsby and brief IFR vsby was included.
Scattered showers/t-storms may also develop at IWD/CMX this morning
and at SAW in the afternoon with increasing warm advection ahead of
approaching trough over the Northern Plains so VCSH was mentioned.
There is less confidence in thunderstorm potential and was not
included in the TAF.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 408 AM EDT MON AUG 29 2016

Expect winds mostly under 20kt through early this week as pressure
gradient remains generally weak. Stronger NW to N winds with gusts
to 25 kts may occur on Wed as a high pressure ridge builds toward
the area in the wake of cold front passage early on Tue morning.
Eastern Lake Superior would be favored for the stronger winds. Winds
diminish to less than 20 kts rest of the week as high pressure moves
across. S to SW winds increase to around 20 kts on Sat as pressure
gradient tightens btwn the exiting high and sharpening sfc trough
over the Northern Plains.

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


SHORT TERM...Rolfson
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