Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 261800

Area Forecast Discussion
National Weather Service Marquette MI
200 PM EDT Wed Apr 26 2017

.SHORT TERM...(Today and tonight)
Issued at 524 AM EDT WED APR 26 2017

...Freezing rain and icing potential tonight is main focus...

Rain has spread over much of Upper Michigan. So far the rain has
generally fell at a light to moderate clip. Some areas have seen
around 0.5 inch though since late Tue evening. Low pressure leading
to the rain is lifting across eastern IA but there is a lead sfc
trough extending to scntrl Lk Superior. Temperature gradient across
the trough is sharp already with low 30s far west forecast area and
upper 40s south and east. Since temps over far west interior are
near freezing there could be freezing rain in isolated locations.
Law enforcement reports slushy roads near Wakefield but otherwise
seems impacts are limited thus far. Area of rain is supported by
lead shortwave and moisture transport along with divergence aloft
from upper jet over Ontario. Forcing diminishes this aftn so expect
rain to diminish as well. Temps aloft are quite warm and once the
rain diminishes, high temps this aftn should reach lower 60s over
cntrl and east but on the cold side of the trough, readings will
stay in the upper 30s far west.

Forecast tonight was challenging as there are various ideas on how
secondary shortwave/sfc low and upstream convection modulate the
overall precipitation coverage and intensity. Favored idea showing
heaviest rain over eastern forecast area as that will be closest to
strong h85-h7 moisture transport and along northwest edge of
elevated instability. Even so though the negatively tilted shortwave
lifting through the region should support some rain spreading over
the west and central forecast area and that is where the ptype
issues begin as temps over west will be falling to around freezing
if not a little lower. Max wet bulb aloft will be 3-5C if not warmer
so looking at a freezing rain setup. Expecting ice accumulations up
to 0.25 inch over west third with isolated higher amounts in the
favored higher terrain that will likely end up colder. Values match
up decently with latest WPC freezing rain/ice progs. Main issue is
how much qpf will be around. Used something near the average value
but there is some guidance pumping out much higher qpf over west
which could enhance the icing potential. Enough confidence in seeing
at least advy level icing up to 0.25 to issue a winter weather
advisory for west third of Upper Michigan tonight and on into Thu
morning. Colder air gradually works in late so could see some sleet
or snow mix in as max wet bulb zero temps fall blo 1c toward 12z.

Farther east, appears that sfc temps will remain in the mid to upper
30s inland Marquette county to Dickinson county so despite heavier
rain forecast there do not expect much freezing rain until possibly
Thu morning for a time. Finally, will have to continue to watch how
heavier rain materializes as due to very saturated soils from recent
wet spell and ongoing rain, could see some runoff issues with at
least higher stream/river levels and ponding of water. Continue to
mention in the Hazardous Weather Outlook. Should note though river
ensembles using higher qpf amounts did indicate that if the higher
qpf materialized we could see some flooding on some of our primary
larger rivers.

.LONG TERM...(Thursday through Tuesday)
Issued at 406 AM EDT WED APR 26 2017

Nam shows a negative tilted 500 mb trough and closed low over the
upper Mississippi River Valley 12z Thu. The closed low and 500 mb
trough slowly move northeast to James Bay by 00z Sat with more
troughing in the upper Great Lakes Fri night. Nam shows some deeper
moisture and 850-500 mb q-vector convergence on Thu. For this
forecast, used a blend of the NAM and ECMWF along with a bit of the
Canadian for Thu. This will mean a wintry mix of pcpn for Thu
morning over the western 1/3 of the cwa and will continue the
advisory through 16Z for that area with ice accumulations being the
main threat. The pcpn will pull out Thu afternoon and temperatures
will also warm enough that fzra should not be a threat. Overall, did
not make too many changes to the going forecast.

In the extended, the GFS and ECMWF show a deep 500 mb trough across
the Rockies with a closed 500 mb low near the 4 corners region 12z
Sat. The trough and upper low move into the southern plains 12z Sun
and then bring both up to the upper Great Lakes 12z Mon. ECMWF is
slower with the progression of the trough over the Great Lakes
region 12z Tue while GFS has it further northeast to the lower Great
Lakes and western Quebec area then. Upper troughing remains over the
area into Wed. Sun night into Mon could be a mix of rain and snow
with this next system and will still have to watch it as there could
some accumulating snow with this one depending on the track of it
and also the cold air.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 200 PM EDT WED APR 26 2017

A sfc trof over Upper Michigan will result in poor conditions at
KIWD/KCMX/KSAW through this fcst period under periods of showers and
considerable low-level moisture in the vcnty of the trof. IWD/CMX
will be down to IFR with periods of LIFR. Dense fog at SAW with
conditions below site minimums should improved this afternoon to
LIFR as light to moderate rain moves in. LIFR conditions should
continue at SAW through tonight with some improvement as winds
become nnw with a more downslope component. Shallow cold air will
filter into western Upper MI for-fzra at KIWD and KCMX tonight.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 524 AM EDT WED APR 26 2017

Northeast gales to 45 knots continue over west and central Lake
Superior into this evening. By late tonight into Thursday morning
winds will begin to subside to 20 to 30 knots as winds become
northerly. Late Thursday through Friday, winds will further decrease
to 10 to 20 knots as winds become westerly. Winds of 10 to 20 knots
are expected through the weekend but could see much stronger winds
to at least 30 kts next Monday as strong low pressure system lifts
across the Great Lakes.

Upper Michigan...
  Winter Weather Advisory from 7 PM EDT /6 PM CDT/ this evening to
     1 PM EDT /noon CDT/ Thursday for MIZ001>004-009-010-084.

Lake Superior...
  Gale Warning until 11 PM EDT /10 PM CDT/ this evening for LSZ162.

  Gale Warning until 3 AM EDT Thursday for LSZ264.

  Gale Warning until 2 AM EDT Thursday for LSZ263.

Lake Michigan...


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