Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 182042
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
342 PM EST Sun Feb 18 2018

.SHORT TERM...(This evening through Monday)
Issued at 341 PM EST SUN FEB 18 2018

Considerable dry air was in place this morning across much of the
U.P. although with the approaching system to the west profiles began
to moisten aloft and lower ceilings by midday. Several locations are
still being stubborn to saturate which is having an impact on the
ongoing snowfall across the western U.P. and Kewennaw Peninsula.
Radar returns indicate another slug of steadier snow lifting
northeast this afternoon across the Keweenaw Peninsula, with
guidance indicating good lift within the dendritic growth zone. This
should help increase the snowfall totals closer to the current
advisory conditions through this evening to around 3-5 inches and
locally higher totals. Otherwise the focus then turns towards the
overnight into Monday periods.

Tonight the omega field decreases substantially acrosss the U.P.
which raises concerns with p-type. Model soundings indicate some dry
air lingering throughout the DGZ, with considerable moisture
becoming shallow or within the 0-1km layer. Winds will generally be
from the northeast/north, but with a lack of lift to grow moist
parcels to dendrites, expect freezing drizzle to develop across the
central/east U.P. The abundance of liquid doesn`t get too high until
later in the day Mon. Surface temps are progged to linger in the
mid/upr teens across the western U.P. with slightly warmer temps
further east where better warm air advection will occur.

Mon aftn/eve, there appears to be a brief lull between freezing
rain/drizzle events as drier air does try to work into the lower
levels based on latest forecast guidance. Winds will continue to be
northerly, then deeper moisture will begin to arrive aloft late Mon
ngt.

.LONG TERM...(Monday through Saturday)
Issued at 502 AM EST SUN FEB 18 2018

Potential for light to moderate snow and possibly significant
freezing drizzle/rain accumulations Mon and Tue, but details are
still being worked out.

The challenges of precipitation type forecasting are made worse by
model disagreement stemming from differing handling of merging upper
jets over the area. Smaller differences in handling of these
features are having much greater impacts on differences in
precipitation amounts and timing, as well as moisture levels in the
mid levels. All this to say that uncertainty is limiting confidence
in precip type, amount and timing. May need headlines for the event,
but feel the magnitude of uncertainty in so many areas is too great
to issue any headlines at this time. However, will issue a Special
Weather Statement to highlight potential.

In general, here are some thoughts for the main two items of concern
(snow and ice):

Snow: The most snow will fall on Mon, with the greatest amounts over
the NW half of Upper Michigan. Currently have 3-4 inches in the
forecast for these areas on Mon, but could see up to 6 inches if
higher QPF models (CMC and GFS) verify, or less than forecast if NAM
and WRFs verify. Mon amount over the SW half are forecast to be
under 2 inches, especially near Lake Michigan, but could be a little
more or less. Then Mon night into Tue night, have a gradual 1-2
inches over the NW half and little to nothing over the SW.

Ice: This comes in a couple waves, with light accumulations possible
between them. The first is Mon and Mon evening and is primarily
caused by lack of moisture in the dendritic growth zone and should
be primarily confined to the SE half. Currently have amounts of 0.10-
0.15 inches over the far south-central and eastern U.P. with no ice
over the NW portions of the area and under 0.10 inches in between.
The second wave occurs Tue and Tue evening and is more of a classic
freezing rain/drizzle event where temperatures aloft rise above
freezing with sub-freezing temps at the surface. However, there is a
lack of moisture in the DGZ causing this as well. Have 0.10-0.15
inches of ice over roughly the E half of Upper Michigan, decreasing
to just a glaze over the far W. With both waves, there remains
considerable uncertainty in the amounts. Depending on exact
temperatures, some of this could fall as sleet, but the better
signal is for freezing rain.

After a quiet period Wed into Thu, we move into a more active period
late in the week and weekend, but have no confidence in details at
this point.
&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 536 AM EST SUN FEB 18 2018

EIFR conds will be spotty throughout tonight across IWD/CMX with
slightly better conds for SAW where less moisture will be present in
the lower levels. The concern will turn towards freezing drizzle
overnight/early Mon as the moisture becomes shallow. CIGs will
remain around 1000-1500ft agl at TAF sites; however, could see SAW
going slightly lower with the moisture becoming trapped and lack of
mixing.

&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 341 PM EST SUN FEB 18 2018

South gales to 35 knots are expected over northern Lake Michigan
late through this evening. Otherwise, winds are expected to stay
below gales through the rest of the forecast period.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory from 11 AM EST /10 AM CST/ Monday to
     midnight EST /11 PM CST/ Tuesday night for MIZ006-007-
     012>014-085.

  Winter Weather Advisory from 4 AM EST /3 AM CST/ Monday to 7 PM
     EST /6 PM CST/ Tuesday for MIZ004-005-010-011.

  Winter Weather Advisory until 1 AM EST Monday for MIZ001-003.

Lake Superior...
None.
Lake Michigan...
  Gale Warning until 1 AM EST Monday for LMZ248-250.

&&

$$

SHORT TERM...Beachler
LONG TERM...Titus
AVIATION...07
MARINE...Beachler



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