Area Forecast Discussion

FXUS63 KMQT 190006

Area Forecast Discussion
National Weather Service Marquette MI
706 PM EST Fri Jan 18 2019

.SHORT TERM...(This evening through Saturday)
Issued at 419 PM EST FRI JAN 18 2019

...Snow showers with poor visibility ramp up along Lake Superior...

Cold front bringing in the the arctic air has dropped across Upper 
Michigan today. Temps have settled into the single digits above zero 
over the west half but stronger onshore flow off Lk Superior has 
kept temps over east half in the teens. Lake Superior certainly has 
modified the incoming airmass as temps over northern MN and over 
Ontario north of Lk Superior are still well below zero this aftn. 
Was a brief burst of snow showers along the front as it moved 
through this morning, but otherwise lake effect has been the main 
story. Thus far despite H85 temps dropping below -22c, shear in the 
lake effect convective layer has led to disorganized LES with very 
light snow accumulations. However, due to the arctic air and smaller 
snowflake size, snow showers have dropped vsby to a half mile or 
less at times. Away from Lk Superior are seeing plenty of mid clouds 
to the north of the system bringing banded synoptic snow to southern 
MN and southern WI. No big impacts from that system as it should 
stay to our south into Sat. High pressure ridge from Saskatchewan 
and Manitoba to north shore of Lake Superior is resulting in NW flow 
LES into Upper Michigan. 

As we move through tonight, ridge so close by will result in land 
breezes developing off northwest WI and western Upper Michigan and 
also over eastern Upper Michigan as temps there overnight drop well 
below zero. High res models are fully picked up on these land 
breezes and indicate strongest convergence developing along and just 
offshore of western Upper Michigan (Little Girls Pt, Porcupine Mts 
and toward Freda) and over scntrl Lk Superior vcnty of eastern 
Marquette to western Alger County (Big Bay/Marquette as far east 
as Au Train). Interesting that if HRRR/RAP and wrf-ARW are 
correct, main focus for LES band will impact mainly Marquette 
County from Big Bay to Harvey while land breeze pretty much 
clears out Alger County. Based on expected inversion heights of 
3-6kft and delta t/s over 20C and various model qpfs, expect 
moderate snowfall amounts of 2-4" later tonight through early Sat 
in these stronger convergence bands. On Sat, as high centers more 
over Manitoba and weak low pressure trough, possibly lake induced,
forms over southeast Lk Superior, increasing N-NNW winds will 
bring all these convergence zones more onshore, so out west more 
toward Ironwood, Ontonagon and Bergland and for Alger County more
into Munising and Shingleton. Snow could fall moderate to heavy 
at times, but for most part, looking at 2- 4"/3-5" type amounts. 
Low vsby will be perhaps the bigger factor as where the snow 
showers persist, vsby should easily drop to 1/2sm with any 
stronger winds bringing vsby down to 1/4sm or even less. Based on 
expected snow amounts and more so the low vsby, went with winter 
weather advisory for Marquette and Alger counties later this 
evening and based on coordination with long term forecaster, ran 
that advy through Sat night as conditions should not change too 
much if not even get better with shortwave moving through. Out 
west, since most snow does not get into those areas until Sat 
daytime, will hold off on any advy, but will put SPS out.

Away from LES off Lk Superior should be a chilly day with partial 
sunshine and highs mainly in the single digits. Since winds will 
overall be light under 10 mph, no real wind chill issues are 

.LONG TERM...(Saturday night through Friday)
Issued at 310 PM EST FRI JAN 18 2019

For tomorrow night, ongoing lake-effect snow showers will be
impacting the northern wind snow belt regions, becoming more
northwesterly by early Sunday morning. There are several factors
that went into the issuance of the Winter Weather Advisory for LES
that continues into this time frame; for that discussion, see
above. Specific to Saturday night, LES will get quite a boost from
an upper trough axis swinging through along with a vort max. LES
bands initially feeding into Alger County tomorrow night will
translate eastward into Marquette County, looking to drop at least
3" to 5" along the lakeshore, with some terrain enhancement
assisting in the higher amounts. Higher snow totals may end up
coming to fruition, especially if snow ratios tick upward, thanks
to another shot of arctic air with the aforementioned trough.
Bottom line for Saturday night into Sunday morning for these two
counties: expect hazardous driving conditions as a reduction in
visbys occurs due to smaller yet abundant flakes. Elsewhere, LES
is anticipated to impact locations all along Lake Superior, 
especially the western U.P. into the Keweenaw, although amounts 
there overall look less than further east. Locations in the south-
central U.P. should remain generally snow-free, other than some 
passing flurries and/or rogue light snow showers that are able to
track further inland. As the trough exits the area and winds 
taper off later Sunday, LES activity will follow suit. 

Weather should be fairly benign on Monday as ridging briefly makes
an appearance. However, amplifying upper trough traversing through
the Dakotas/Saskatchewan/Manitoba by early Tuesday looks to 
trigger cyclogenesis, according to the 12Z run of the GFS, as 
this feature approaches the Upper Great Lakes region. This low 
is then depicted to end up phasing with a southern low pressure 
system tracking across the Central Plains into the Lower Great 
Lakes region, yielding a marked increase in atmospheric moisture. 
With a definitively cold airmass already in place, widespread 
snow looks likely regardless of whether or not this phasing 
occurs, although still a bit too far out at this point to nail 
down anticipated snow amounts. As this merged low pressure system 
continues its trek northeastward, LES should take over once again 
on its backside under NW flow on Wednesday. Despite the
discrepancies between the models from Tuesday onward, an active
pattern is likely for the forecast area given the broad agreements
in wave after wave marching through.

Attention should also be paid to the cold temperatures much more
typical of this time of year expected to overtake Upper Michigan 
through this forecast period, with bitterly cold lows expected Sunday
night into Monday morning. Widespread lows in the negative single
digits are anticipated tomorrow night, with negative teens likely
in the interior, and lakeshore spots hanging out just above zero 
degrees tomorrow night. With the reinforcing shot of arctic air
(above) taking a swipe at the U.P. Sunday night, even colder temps
will blanket the area, with widespread negative teens in the
interior locations. Don't be surprised if lows drop off even more
where partial clearing occurs outside of the snow belts. Despite
relatively light winds anticipated, wind chills could still easily
drop close to advisory criteria; regardless of whether or not it
does, anyone planning on being outdoors during this time frame
should do all they can to stay warm. Single digit to teen highs on
Sunday will bounce back up quickly to upper teens and 20s by
Monday afternoon, even though the morning initially starts out so
cold. As for the remainder of next week, plan on temps overall
remaining near or slightly below normal for mid to late January.

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 703 PM EST FRI JAN 18 2019

Lake effect snow is expected to persist this evening at IWD and 
CMX before land breezes push the snow showers more over Lake 
Superior later tonight. North winds increasing will allow lake 
effect to return to both of these terminals Saturday. At SAW, LES 
will prevail through the rest of the TAF period. At all sites when
lake effect is expected to prevail, expect mainly MVFR cigs/vsby 
with only ocnl IFR vsby. 


.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 419 PM EST FRI JAN 18 2019

Occasional winds to 30 kts are expected into next week but no 
widespread gales will occur through the period. Heavy freezing spray 
will continue at times into Monday.

Upper Michigan...
  Winter Weather Advisory until 7 AM EST Sunday for MIZ005-006.

Lake Superior...
  Heavy Freezing Spray Warning until 7 PM EST Sunday for 

  Heavy Freezing Spray Warning until 1 PM EST /noon CST/ Sunday 
     for LSZ162-240>248-263>265.

Lake Michigan...