Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 120002

Area Forecast Discussion
National Weather Service Marquette MI
702 PM EST Thu Jan 11 2018

.SHORT TERM...(This evening through Friday)
Issued at 359 PM EST THU JAN 11 2018

...Very icy conditions across Upper Michigan this evening...

A very complicated pattern across Upper Michigan today, with a 35F
temp spread between the Houghton and St. Ignace earlier this
afternoon. Sub-freezing temps have quickly advected eastward,
resulting in a flash freeze across the western CWA this afternoon.
This will continue eastward across the remainder of Upper Michigan
through this evening.

The last shield of synoptic moisture ahead of the main northern
trough is edging into the western CWA this afternoon. An associated
deformation band is expected to produce moderate to heavy snow
roughly north and west of a line from Iron River to Marquette
through early evening. Snowfall rates of 1"/hr are expected. Have
therefore allowed the Winter Storm Warnings to continue across the
western tier of counties. Winter Weather Advisories also continue
for the next tier of counties to the east, along with Marquette and
Alger counties. Law enforcement and NWS employees have confirmed
multiple vehicle accidents where temperatures have fallen below
freezing across the west half.

Though frozen precip has been and will be minor for the remainder of
the CWA, wet roadways from rain and melting snow will be of concern
as temperatures fall well-below freezing through this evening. Have
issued a Special Weather Statement highlighting the expected rapid
onset of icy conditions this evening.

After synoptic moisture departs early this evening, snow will
transition to light to sometimes moderates LES for the NNW wind snow
belts. Shallow inversions should mitigate heavier lake effect snow
rates, but a period of higher SLR snow will be possible across the
west this evening before arctic air reduces SLRs overnight into
Friday. Will allow the western warnings to expire at 06Z, but they
may need to be replaced with an advisory if conditions warrant
overnight into early Friday morning. Farther east, gustier winds and
slightly higher inversions supports holding on to advisories into

.LONG TERM...(Friday night through Thursday)
Issued at 359 PM EST THU JAN 11 2018

After a few days of warmer weather that began this past Sun, pushing
temps to around or above normal, a switch back to blo normal
temps/cold weather is currently underway and will last thru the
first half of next week. This change is in response to another
strongly building ridge (upwards of 350m above normal at 500mb) over
western N America, which will force a deepening eastern N America
trof. Arctic air mass settling into the Upper Lakes won`t be as cold
as what was experienced in late Dec, and it will much shorter-lived
as the ridge breaks down quickly. This will occur due to developing
ne Pacific troffing shifting to the W Coast, forcing rising heights
downstream and a return to lower amplitude flow that will drive more
Pacific dominated air masses across the CONUS as next week
progresses. This would be consistent with the signal from the
current active MJO over the Indian Ocean, moving from phase 2 to 3,
which favors western N America troffing and eastern N America
ridging. Unless the MJO weakens, it will be a forcing mechanism for
mild conditions/above normal temps over the Upper Lakes for at least
the next couple of weeks, suggesting any cold spells thru the end of
Jan will be short-lived. As for pcpn, after the synoptic pcpn event
today, pcpn will be largely lake effect driven thru the first half
of next week. However, there will be a decent shortwave dropping
into the western Great Lakes early next week that will likely
provide a period of widespread light snow as well as hvy lake
enhanced snow off Lake Superior, affecting n central and western
Upper MI. Will probably see a period of hvy snow off Lake MI on the
front side as well. LES will wind down/end midweek as warmer air
arrives, and late week should be uneventful. With Pacific energy
moving across the CONUS in the overall mild pattern during the last
half of the month, there should be more frequent opportunities for
storm systems/pcpn to affect the area, but unfortunately, that may
include mixed ptypes.

Beginning Fri night/Sat, With 850mb temps of -20 to -25C, LES will
prevail into Sat under nw to n low-level flow. DGZ will be
suppressed to near the sfc over the w and in the low part of the
convective layer over the e, resulting in smaller snowflakes that
are more effective at reducing vis, especially w. A shortwave trof
is still fcst to swing across the Upper Lakes Fri night/early Sat
with height falls of at least 60m at 500mb in 12hr. While fcst
soundings show inversions roughly around 4kft w and 6kft e thru Sat,
there is a slight lifting of the inversion for a time in response to
the shortwave as would be expected. Overall, LES will be light thru
Sat, but do expect an uptick in LES (greater coverage/some increase
in intensity) for a short time Fri night/Sat morning as shortwave
passes. Should generally see 1-3in/12hr snowfall rates, locally up
to 4in with the shortwave passage. Highs Sat will be in the 5-15F

Winds will begin to back Sat aftn continuing into Sun with passage
of sfc high pres ridge. As the winds back to the sw by Sun aftn, LES
will shift offshore from w to e Sat night thru Sun morning. Arrival
of sfc high pres ridge and loss of lake stratocu should result in an
excellent radiational cooling night over the w and central interior
Sat night. Some 12z bias corrected guidance are now showing mins blo
-20F, and will favor this lower side of guidance. Would not be
surprised at all to see some traditional cold spots fall to -30F.

Next shortwave digging se into the eastern trof will arrive Mon.
Medium range models are in good agreement showing this shortwave
working to close off a broad mid-level low over the western Great
Lakes during the day Mon. With 850mb temps of -16 to -20C and deep
layer forcing/moisture overspreading the area, looks like a great
setup for hvy lake enhanced snow to develop over the Lakes. It now
appears that winds will back to a southerly direction in advance of
the shortwave to lead to a period of hvy snow downwind of Lake MI
into the eastern counties late Sun into early Mon. Depending on how
sharp sfc trof and circulation around potential sfc low become over
the western Great Lakes, winds may back around enough to swing the
lake enhanced snow off Lake MI into central Upper MI before lake
enhanced snow off Lake Superior sweeps into n central and western
Upper MI on ne to n winds during Mon and Mon night. Overall, the
setup looks really good for some spots to see very impressive
snowfall. So, the late Sun to early Tue period will definitely be a
period to monitor. Away from areas impacted by lake enhancement,
expect a period of light snow.

LES off Lake Superior will then diminish later Tue into Tue night
before ending w to e Wed under developing waa regime and backing
winds. The warming will push temps above normal late week.

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 651 PM EST THU JAN 11 2018

KIWD AND KCMX: Expect LIFR/IFR conditions to quickly improve this
evening and then continue to improve late tonight into Friday
morning to MVFR as synoptic snow transitions to lake effect snow.

KSAW: With synoptic snow ending, expect general improvement in
conditions through the evening. Developing lake effect snow bands
may cause a temporary lowering of conditions overnight before
winds back slightly by Friday morning, shifting most of the lake
effect snow east of the terminal. Expect improvement to VFR by Fri

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 359 PM EST THU JAN 11 2018

Much colder air sweeping across Lake Superior in the wake of passing
cold front will lead to northerly gales of 35-40kt over all of Lake
Superior except the far west this evening. Winds will diminish to
blo gale force overnight across western Lake Superior and early Fri
morning over central and eastern Lake Superior. Brisk n to nw winds
of 20-30kt will then prevail into early Sat morning before
approaching high pres ridge brings diminishing winds to under 20kt w
to e Sat/Sat night. With the cold air and brisk winds, heavy
freezing spray is expected over much of Lake Superior tonight, then
lingering over the e half into early Sat morning. S to sw winds will
increase to 20-30kt on Sun ahead of the next approaching low pres
trof. While winds will diminish for a time as the trof moves over
the lake Sun night/Mon morning, winds will ramp back up toward 30kt
from the ne to n Mon into early Tue as trof exits. Heavy freezing
spray will also develop again late Mon into Tue morning.

Upper Michigan...
  Winter Weather Advisory until 1 AM EST Friday for MIZ004-084.

  Winter Storm Warning until 1 AM EST /midnight CST/ Friday for

  Winter Weather Advisory until noon EST Friday for MIZ006.

  Winter Weather Advisory until 6 AM EST Friday for MIZ005.

  Winter Weather Advisory until 6 PM CST this evening for MIZ010.

Lake Superior...
  Heavy Freezing Spray Warning until 6 AM EST Saturday for LSZ244-

  Gale Warning until 7 AM EST Friday for LSZ251-267.

  Gale Warning until 7 AM EST Friday for LSZ248>250-265-266.

  Gale Warning until 4 AM EST Friday for LSZ243>245-264.

  Heavy Freezing Spray Warning until 10 AM EST /9 AM CST/ Friday
     for LSZ241>243-263.

  Gale Warning until 1 AM EST Friday for LSZ242-263.

  Heavy Freezing Spray Warning until 1 AM EST /midnight CST/
     Friday for LSZ162.

Lake Michigan...


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