Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 271447

Area Forecast Discussion
National Weather Service Marquette MI
1047 AM EDT Thu Apr 27 2017

Issued at 1047 AM EDT THU APR 27 2017

Wintry weather will continue for portions of central and western
U.P. this morning, and may persist into this afternoon for the
Keweenaw Peninsula. Temperatures have held steady across the area in
the lower 30s from Marquett to Escanaba and points east, while
further west of this line temps have held in the mid/upr 20s. The
steady feed of deep moisture continues to pivot from southeast to
north/northwest across the western half of the U.P. With the
aforementioned temps, this is causing considerable ice build-up on
elevated surfaces and in some locations on area roads. In addition
the far western U.P. and the Keweenaw Peninsula have been cold
enough that the precip has been falling as all snow and at times
moderate/heavy snow with visibilities between 1/2sm and 3/4sm. GOES-
16 satellite imagery indicates cloud tops are showing some warming
along the eastern periphery of the moisture feed, which is poised to
pivot further west. In addition some heating from aloft was
occuring, and expect this to help to very slowly diminish the
intensity of freezing rain/sleet and eventually snow. But until we
get to this point additional accumulations may occur and some
additional light ice build-up. Through early this afternoon an
additional 2-4" of snow is possible for the Keweenaw Peninsula south
through Gogebic and Iron counties. Further east an additional 0.05
to 0.10" of ice may occur.

Hi-res forecast guidance continues to indicate the shortwave that is
producing the abundant moisture will lift north over the Keweenaw by
19z, with wrap-around moisture and a cold front pivoting east across
the western U.P. This could bring a brief slug of steady snow to the
Keweenaw and other portions of the U.P. west of Marquette before
spreading east later this evening. Then the upper level system will
finally begin to lift north into Ontario with flow turning
southwesterly and bringing drier and slightly more milder air back
to the U.P. by Friday.

.SHORT TERM...(Today and tonight)
Issued at 457 AM EDT THU APR 27 2017

...Complicated mixed precip with main impacts of icing and snow...

Deepening upper level trough will become negative tilted as it lifts
across Upper Great Lakes into this evening. Sfc low is currently
near Chicago. Expect the low to lift to northern Lk Michigan this
morning and to northern Lk Superior this evening. Rain streaming
north within the deepening trough will only expand north and west
into this aftn with the strengthening system and as coupled jet
structure develops through the morning.

Warm side of the track of the low MQT-ESC eastward should just see
rain today. Thunder possible early this morning far east. Cold side
of the low track will see mixed precipitation with snow, sleet,
freezing rain and associated icing. Thus far main surprise has been
snow as ptype from IWD to CMX since late Wed evening. Web cams in
higher terrain areas show at least a coating of accumulation
overnight. Earlier call to Gogebic sheriff in Bessemer indicated
roads were fine but snow was accumulating on grassy areas. Majority
of guidance, even short range high resolution models seem too warm
with max tw aloft. ECMWF was colder showing h85 0c isotherm near IWD
at 12z and racing across Keweenaw by early aftn and over eastern cwa
by late today as precip exits to the north with departing sfc low.
Leaned toward colder ECMWF which resulted in more snow far west. In
fact now have several inches of snow over Ontonagon and Houghton
counties. Farther east warm layer aloft at 5-7c will result in
liquid ptype so then it comes down to sfc temps to determine rain or
freezing rain. Bullseye for heaviest rain sets up over along border
of Baraga/Iron and Marquette/Dickinson counties. This area is
already seeing temps blo freezing so looking at freezing rain and
potentially significant icing. Heaviest icing potentially over one-
quarter inch is forecast on axis from Iron River to Michigamme
Highlands, including Amasa, Republic, Champion with Ishpeming and
Negaunee on eastern edge of more significant icing. As icing went on
Wed, expect most icing on trees and powerlines. Gusty NW winds will
play a role though with ice so could see some power outages. Cold
air arrives from west to east switching the freezing rain/sleet over
to snow mid to late aftn. Overall isolated higher terrain areas of
Baraga and Marquette county could see significant icing into this

Temps cool sufficiently tonight for snow to be main ptype all areas.
Most snow tonight will be over Keweenaw with WSW winds to the south
of the departing low. H85 temps drop to -10c by late tonight so
there certainly could be an inch or two of snow late tonight into
Fri morning. Elsewhere, expect drying trend to develop as the night
goes on. Winds will stay gusty from the southwest, especially close
to Lk Superior.

.LONG TERM...(Friday through Wednesday)
Issued at 436 AM EDT THU APR 27 2017

Nam shows a closed 500 mb low between Hudson Bay and Lake Superior
12z Fri with another closed low in the central Rockies and another
in the Canadian Rockies. The closed low over the central Rockies
opens up and becomes an elongated trough on Fri. The southern end of
the trough becomes a closed low over the 4 corners region 06z Sat
and this closed low heads east into KS 12z Sun. Cannot believe that
there will be some lake effect pcpn, but there will be for the
Keweenaw Peninsula on Fri as 850 mb temperatures are down to -8C and
with Lake Superior temperatures around 4C, that is enough for lake
effect even at this time of year. Should be some disruption of it
though during the day with strong heating, but did put in chance
pops for westerly flow areas. More lake effect is possible for Fri
night into Sat morning and have some slight chance pops in for
northwest flow as temperatures again are cold enough. These are the
only major changes made to the going forecast made. Could be some
freezing rain early Fri morning in the Keweenaw and in parts of the
north central Fri night.

In the extended, GFS and ECMWF show a 500 mb closed low and trough
over the central plains 12z Sun that heads north into ne IA 12z Mon.
The upper low continues to the northeast to near James Bay 12z Tue
with colder air aloft over the area then. More upper troughing moves
into the area 12z Wed and remains into Thu. Temperatures will
continue to be below normal through this forecast period. Next
system comes in for Sun into Tue and there looks like there could be
a rain/snow mix with this one and could also be heavy precipitation
with this. Dry weather is then expected Wednesday into Thursday.

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 746 AM EDT THU APR 27 2017

Low pressure lifting northward across the region will result in snow
at IWD and CMX and rain changing to snow at SAW. Expect LIFR to IFR
conditions reduced most frequently by cigs. The snow may become
heavy this morning at CMX and that will result in a period of VLIFR
vsby. As the low lifts to the north of the region tonight, expect
conditions to improve to MVFR. Some snow will linger at CMX through
the night.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 457 AM EDT THU APR 27 2017

Winds have subsided to 20 to 30 knots as winds become northerly.
Winds will swing around to the southwest tonight into Friday. Winds
will diminish to 25 kts or less later Saturday into Sunday. NE winds
of 30 kts to gales to 35 kts are then expected Sunday night into
Monday as strong low pressure system lifts across the Great Lakes.
The strongest winds will be over western Lk Superior.

Upper Michigan...
  Winter Weather Advisory until 8 PM EDT /7 PM CDT/ this evening
     for MIZ001-003>005-010-084.

  Winter Weather Advisory until 1 PM EDT /noon CDT/ this afternoon
     for MIZ002-009.

Lake Superior...
Lake Michigan...


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