Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202016

Area Forecast Discussion
National Weather Service Marquette MI
316 PM EST Fri Jan 20 2017

.SHORT TERM...(This evening through Saturday)
Issued at 310 PM EST FRI JAN 20 2017

Murky conditions over much of Upper Michigan today with moist
easterly low-level flow to the north of weakening sfc low pressure
system over Ohio Valley. Shearing out shortwave trough and area of
isentropic lift is leading to slow northward push of light rain into
southern Upper Michigan. Despite temps at or blo freezing this
morning as the rain moved in, there were not many icing issues
reported as main roads were mostly wet. Cold ground temps likely led
to slippery non treated surfaces as was occurring over northern WI.
As weakening shortwave continues to drift north expect the shield of
steady light rain to do so as well. Should be pretty rainy evening
for northern Upper Michigan but the rain should taper off by late
evening or after midnight. Due to the moisture from the rain that
will have occurred and/or potential light drizzle at times, temps
falling into the low to middle 30s could lead to icy conditions on
untreated surfaces tonight. Plan to cover this with special weather
statement and mention in the hazardous weather outlook.

On Sat, the damp and murky conditions will continue. Temps will rise
into the upper 30s or near 40 by the aftn. At this point, with
minimal insolation, thinking 40 will be a stretch. Low level flow
remains weak as weakening area of low pressure lifts toward Upper
Mississippi river valley and warm front slides to the western Great
Lakes. Another shortwave currently over the central Plains lifting
in along with the low-level forcing/lift should enhance light rain
especially in the aftn. May see drizzle at times before the next
surge of rain on Sat. Since sfc temps will be around freezing could
still see icy conditions at times on untreated sfcs at least during
the morning hours.

Other larger issue is fog. Fog was very widespread near Lk Michigan
and the Bay of Green Bay into early aftn with widespread reports of
vsby less than 1/4sm. Fog has lifted this aftn though with vsby now
more in the 1-3sm range as the more widespread rain moved in,
scouring out the tiny fog droplets. However, weak east to southeast
low-level flow and sfc temps/dwpnts above freezing flowing across
ice on Bay and sfc temps in the mid 30s over the open waters of Lk
Michigan should result in more dense fog forming again near Lk
Michigan by this evening as the steadier rain lets up. Moist ESE
flow and an ongoing melting snowpack will likely allow this fog
to expand over much of cntrl Upper Michigan and across the
Keweenaw later tonight (especially once the rain ends) and similar
wind trajectories and dwpnts on Sat indicate the fog could
persist through much of the day. Went with dense fog advy for all
but far western cwa (since downslope E-SE flow not as favorable
there) through midday Sat. Widespread dense fog probably will not
develop until after the steady rain lifts out later this evening.
Later shifts can extend or cancel the advy as needed.

.LONG TERM...(Saturday through Thursday)
Issued at 425 AM EST FRI JAN 20 2017

As negative height anomalies continue to expand from AK s across the
western CONUS to northern Mexico over the next few days, a strong
positive height anomaly now centered over northern Ontario will
strengthen and become centered over Hudson Bay. During the early and
middle part of next week, this positive height anomaly will expand
to cover most of Canada. This will prevent any build up of arctic
air in Canada and will even shunt bitter cold conditions currently
over AK and far northern Canada even farther n. 850mb temps will
peak over the next couple of days, supporting continued unseasonable
warmth. With cloud cover to dominate and with a lack of any low-
level caa, expect some record high min temps to be set. 2 or 3 days
should see min temps failing to fall to 32F. As for pcpn, a series
of vigorous shortwave trofs will impact the western CONUS thru early
next week. As they shift e, the strong positive height anomaly to
the n will do 2 things, either force that energy on a track well s
of here or weaken shortwaves that do lift ne thru the Plains. End
result will be that Upper MI should be spared from receiving any
significant pcpn thru early next week. Despite it being late Jan,
the unseasonable warmth will mean that pcpn that does occur will be
only liquid, very unusual for the climatologically coldest period of
the year. Beginning Mon, but more so Tue/Wed, gradual height falls
rather than advection of a colder air mass will lead to a cooling
column, supporting a ptype transition from rain to eventually all
snow. Toward the middle of next week, there are still indications
that the final batch of energy in the series impacting the western
states will make a stronger run into the Great Lakes than its
predecessors. Given the persistence of the positive height anomaly
to the n, it remains to be seen if a system lifting thru the Plains
will manage to bring significant pcpn into Upper MI. At a minimum,
expect at least light accumulations of snow in the midweek period.
Farther down the line, it appears that the positive height anomaly
dominating Canada early next week will consolidate into western
Canada, allowing for development of eastern Canada troffing late
next week thru the last days of this month. This may send a decent
shot of colder air into the area for next weekend, dropping temps
back to near normal and certainly generating LES. Canadian ensembles
indicate some deamplification after the cold shot next weekend, so
temps will probably end up a little above normal heading to the
1st of Feb.

Beginning Sat/Sun, abundant low cloudiness will prevail behind the
shortwave swinging n thru the area today/tonight. Along with low
cloud cover, precipitable water in the upper portion of late Jan
climatology will support unusually high min temps which will likely
fail to fall to freezing. Record high min temps at NWS Marquette are
28F, 31F, 35F, respectively for the 21st to the 23rd. If low clouds
do dominate as they should, max temps won`t rise much from the mins.
Could certainly see only 2-3 degree swings from mins to maxes,
something like mins of 33/34 and maxes of 35/36. One or more
shortwaves lifting n, mainly to the w of the area, Sat/Sun may
generate some -ra. Otherwise, expect some -dz at times thru the

A much more significant shortwave/low pres system will track
underneath the positive height anomaly in Canada, from TX late Sat
to the se CONUS by Mon. While this system will be much too far s and
se of the area to bring pcpn, sfc/mid level troffing extending back
to the Upper Mississippi Valley should work to maintain some chc of
-ra thru Mon. Best chc of rain will be along and e of the sfc trof.
Exact location of the sfc trof is uncertain, but right now, it
appears that it may cut nw to se across Upper MI from the Keweenaw
to northern Lake MI. So that will mark the position for denoting
higher pops. Cooling column under height falls may support a mix
with wet snow over the higher terrain of the w.

Models still indicate that the last significant shortwave in the
series impacting the western states will lift ne, reaching the Great
Lakes midweek. Continued falling heights and cooling column will
mean a ptype transition to just snow, if not for Tue, certainly by
Wed. CMC continues to be more suppressed with the wave than the GFS,
and indicates the main synoptic pcpn shield staying s of Upper MI.
The 00z ECMWF has shifted a bit farther n, but not as far n as the
GFS. Both would bring the synoptic snow shield into Upper MI, though
the GFS much more aggressively. GFS ensembles overall support the
operational GFS, but a number show an even farther n track. A good
number of the CMC ensembles are similar to the GFS track, just
delayed about 24hrs. So, it would seem there is a decent potential
for a period of widespread synoptic snow at some point in the Tue
Night to Thu time frame. Whatever happens, the positive tilt of the
large scale trof in which the stronger shortwave is emedded suggests
that a wrapped up strong system is unlikely. So, snow accumulations
midweek will not be significant, but more in the light to mdt range.
Some LES should follow the system.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1234 PM EST FRI JAN 20 2017

Light rain will gradually lift across Upper Michigan through this
evening, affecting all the TAF sites. Low cigs and low visibility
in light rain and fog will result in IFR to LIFR conditions into
Sat. Upslope flow will result in potential for VLIFR conditions at
SAW and possibly CMX. Could see conditions at both sites fall blo
flight minimums.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 310 PM EST FRI JAN 20 2017

A relatively weak pressure gradient over the Upper Great Lakes in
the absence of any strong weather systems will result in winds under
20 kts over Lake Superior most of the time into early next week.
Abundant low-level moisture will result in fog over northern Lk

Upper Michigan...
  Dense Fog Advisory from 10 PM EST /9 PM CST/ this evening to 1
     PM EST /noon CST/ Saturday for MIZ001-003>007-010-011-084-

  Dense Fog Advisory until 1 PM EST /noon CST/ Saturday for

Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 1 PM EST Saturday for LMZ221-248-250.



LONG TERM...Rolfson
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