Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201135
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
635 AM EST Tue Nov 20 2018

.SHORT TERM...(Today and tonight)
Issued at 457 AM EST TUE NOV 20 2018

WV imagery and RAP analysis indicated an amplified pattern with a
ridge over western North America and a broad mid/upper level trough
from Hudson Bay and northern Quebec through the Great Lakes and ern
CONUS. The next upstream shortwave trough was located over nrn
Manitoba. At the surface, diminishing nrly flow prevailed across
Lake Superior as a weak ridge builds into the area ahead of low
pressure over sw Manitoba. Lake induced troughing has focused the
more prominent remaining LES bands into Alger county. With weak acyc
nw flow into the western Upper Michigan, mainly just flurries were
observed.

Today, The strongest forcing (700-300 mb qvector conv and isentropic
lift) associated with the Manitoba shrtwv will remain north of Upper
Michigan. However, some light snow is still expected over the west
half with accumulations of a half inch or less, mainly this
afternoon. As a trough trailing from the low shifts through the
northwest late today into this evening, low level conv as winds
veer sharply nw, a brief period of heavier snow will be possible
with a quick inch or two. With the entrenched cold airmass, even
with breezy sw winds, highs will only climb into the low to mid
20s.

Tonight, After the trough moves through the rest of Upper Michigan,
winds becoming nnw to n with 850 mb temps to around -20C will
support at least moderate multiple wind parallel LES through the
north half of Upper Michigan. Additional snow accumulations of 1 to 3
inches will be common with the higher snowfall rates over the west
in the evening and into north central Upper Michigan overnight. With
the DGZ coincident with the convective layer, fluffy LES with high
SLR values are expected. Although inversion heights to 6k ft would
only favor moderate LES, land breeze convergence overnight and
potential for Lake Nipigon conditioning should bring the higher
snowfall potential to areas between Marquette and Munising with some
local amounts in the 3 to 5 inch range.

.LONG TERM...(Wednesday through Monday)
Issued at 408 AM EST TUE NOV 20 2018

Models suggest that the amplified pattern with a mid/upper level
ridge off the West Coast and trough from Hudson Bay into the Great
Lakes will become slowly progressive with the ridge building into
the Plains by the middle of the week. As troughing develops over the
western CONUS and into the southern Plains ridging will extend into
the Great Lakes by late week. As a result, the colder air over the
region through Wednesday will also give way to warming as the cold
recedes to eastern Canada and northern New England.

Beginning Wed, Winds veering from nw to n early in the morning will
push preconditioned Lake Nipigon les band from western Alger into
Marquette County likely clipping Keweenaw County as well. With the
DGZ favorably positioned within the convective layer could see
several inches of fluffy snow accumulation which may push snow
totals near advisory levels at some locations. Increasingly
anticyclonic low-level flow as Arctic high pres builds over northern
Ontario on Wed will cause LES to diminish steadily through the
afternoon hours. It will end over the far w as winds veer easterly
there during the aftn. It will be a very cold day for late Nov with
850mb temps of -17C to -22C from w to e across the fcst area at
midday. Highs will only range from the low/mid teens northwest and
north central over high terrain to the lower 20s south central.
Record low max temp of 15F here at NWS Marquette could certainly
fall.

As the high shifts e Wed night and winds continue to veer, will
probably see some flurries/-shsn into south central Upper MI Wed
night into Thu morning under shallow se flow across Lake MI.
Elsewhere, it will be a very cold night if skies can clear anywhere
for a few hours. However, it appears there will be little/no gap
between the loss of lake stratocu and arrival of high/mid clouds
under developing waa regime. Eastern fcst area would likely have
best opportunity for temps to plummet toward zero.

Thanksgiving Day...waa will strengthen thru the day. Despite decent
isentropic ascent, sharply anticyclonic mid-level flow should keep
pcpn from being a concern. Under breezy conditions, temps will
rebound into the mid 20s to lower 30s. Plenty of clouds and mixing
from winds will result in very little fall in temps Thu night.

Shortwave trough will move across the Mississippi Valley late Fri
evening and reach the western Great Lakes early Sat. While models
continue to show differences in the structure/timing of trough,
there is good agreement for pcpn to occur at some point Fri
night/Sat. Ignoring the faster outlier GFS solution which has pcpn
arriving Fri aftn, expect pcpn to arrive Fri evening and continue
into Sat. Looks like column may cool sufficiently for at least a mix
of rain/snow with the potential for a change to all snow. Doesn`t
look like a headline event, but if pcpn ends up as mainly snow, the
wet snow will make for sloppy travel at times.

Models and ensembles indicate there should see a break in pcpn for
most areas on Sun as weak ridging moves across the region. 00z
models still show next shortwave lifting across the mid-MS Valley
and spinning up an Ohio Valley/Great Lakes low pres system Sun
night/Mon. Operational models and ensembles exhibit plenty of
uncertainty on the track and strength of this low and its
potential impacts on the Upper Great Lakes for Mon-Tue. The 00Z
GFS shows a deeper developing sfc low tracking farther nw into
Lower Mi with a greater potential for perhaps a longer lake
enhanced snow event into Upper Mi on its backside. Meanwhile, the
farther se tracking 00Z ECMWF sfc low looks closer to EPS and GEFS
ensemble means, which would probably result in minimal impacts
from lake-enhanced snow for our area. This will certainly bear
watching to see how the model runs trend with this developing
system over the next several days.
&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 633 AM EST TUE NOV 20 2018

Mainly MVFR cigs are expected at KIWD/KCMX as sw winds become gusty
today. As a front moves through with veering winds, lake effect
snow showers will drop vsby to IFR or near IFR, especially at
KCMX. At KSAW, VFR conditions will give way to MVFR as light snow
moves into the region. Conditions could drop to IFR late tonight
as winds veer to the nw or nnw late tonight.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 457 AM EST TUE NOV 20 2018

Winds will become southwesterly and increase back to about 25 knots
this afternoon ahead of an approaching surface trough. Behind that
trough, winds will veer to northwesterly and then northerly for
tonight and Wednesday morning but remain at about 25 knots over the
western lake and 30 to 35 knots over the eastern lake. A few widely
scattered gale-force gusts are possible over eastern Superior early
with the trough passage this evening and toward Wednesday morning.
With the stronger winds and very cold air, freezing spray will
develop and may become heavier over the northern lake. Winds across
the lake weaken below 20 knots Wednesday afternoon. Winds stay light
through Thursday morning as a high pressure ridge drops south out of
Canada across the lake. As the high departs to the southeast
Thursday afternoon, winds become southerly and increase back to 25
to 30 knots for Thursday night into Friday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...JLB
LONG TERM...Voss
AVIATION...JLB
MARINE...JLB



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