Area Forecast Discussion

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FXUS63 KMQT 201739
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1239 PM 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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1238 PM EST TUE NOV 20 2018

Mainly MVFR conditions are expected at KIWD/KCMX/KSAW thru this fcst 
period. A period of -sn this aftn, producing ocnl IFR vis especially 
at KIWD/KCMX, will give way to lake effect shsn tonight thru Wed 
morning in the wake of a passing arctic cold front. A brief period 
of shsn/+shsn with IFR or even LIFR vis may occur at KCMX as the 
front passes early this evening. As is typical for lake effect shsn, 
conditions tonight/Wed will be variable, fluctuating btwn MVFR and 
IFR at times. A heavier band of shsn will likely impact KSAW Wed 
morning, leading to prevailing IFR conditions and potentially brief 
LIFR. Gusty nw winds behind the arctic front will gust to around 
25kt at KCMX 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...Rolfson
MARINE...JLB