Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Marquette Michigan
653 PM EST Friday Nov 28 2014

Short term...(this evening through saturday)
issued at 248 PM EST Friday Nov 28 2014

Complex short term...as is normally the case during transitions from
snow to mixed precipitation and freezing rain/drizzle.

A fast moving area of snow has been tracking across the southern County Warning Area
today and is now moving into the southeastern County Warning Area. The snow is ahead of a
weak shortwave currently over Minnesota and in an area of warm air advection. Generally up
to 1 inch of snow has been observed with the system snow. Additional
more isolated snow showers are located west/west-southwest of the County Warning Area more toward
the shortwave...which will mainly move along and S of the WI border
through this afternoon.

Later this evening into the overnight hours attention turns to areas
near Lake Michigan as southerly winds bring an les band now arching to the
Mackinac Bridge into the area. Additionally...upslope/onshore S-south-southeast
flow will bring snow showers to much of the area mainly east of a line
from Sawyer to Menominee. Do not this this band will drop as much
snow in any one area as previously thought due to models showing the
band being more transient. This makes sense given that low level
flow will veer with height and also winds will veer with time. Have
around 2 inches of snow for these areas from now through tonight.

Things become more complicated late tonight as an 800-900mb warm
nose with above freezing temperatures moves in from the SW. Precipitation at this
point will be mainly confined to downstream of Lake Michigan...but
light/isolated precipitation is also possible elsewhere as warm air advection continues.
Additionally...models show a narrow area of precipitation at or S of
Menominee associated with another weak shortwave currently over ND
right around the time of ptype transition. Naturally lots of
uncertainty how much and where this precipitation will occur. Precipitation may
initially be sleet during the transition to freezing rain and
eventually freezing drizzle as the dgz dries out. If that band does
set up over Menominee...greater amounts of initially snow...then
possibly sleet and freezing rain would occur. Main area of concern
with freezing precipitation is downstream of Lake Michigan...mainly near
and east of a line from Manistique to Newberry...where flow off Lake
Michigan will keep precipitation going as lake effect precipitation comes to an
end. Transition will occur closer to 12z over the eastern u.P. Even with
high temperatures expected to be in the middle 30s Sat...Road surface temperatures in the
low to middle 20s will lead to any liquid precipitation freezing on
contact with untreated roadways...especially bare roads and roads
covered in hard packed snow. Therefore...main threat from freezing
precipitation is on Road/sidewalks...with no significant threat to elevated
surfaces. Am not very confident on amount of freezing precipitation
accumulations. With fresh snow falling tonight /hopefully helping to
make a crusty cover on the roads when the freezing precipitation
falls...thus keeping the roads from becoming as slick/...and the
potential impacts from freezing precipitation being very dependent on Road
surface treatment and clearing of the snow off the roads...will not
issue any headlines for the freezing precipitation. However...will issue an
Special Weather Statement highlighting the threat over the eastern areas. Another area that
may see better chances of freezing precipitation is the Keweenaw peninsula
as south-southeast winds upslope into northern portions of the peninsula...but am
less certain in this area and think amounts will be lower than over
the Eastern Upper Peninsula. Precipitation should diminish some over the eastern
u.P. And the northern Keweenaw Sat afternoon...but not completely end.

Long term...(saturday night through friday)
issued at 341 PM EST Friday Nov 28 2014

Sat night into sun...low pressure near Lake Superior lifting to the NE
to James Bay will drag a cold front across Lake Superior. Although
there may be some leftover light rain over the far eastern County Warning Area...expect
dry conditions through most of Sat night. Models suggest 850-600 mb
fgen will increase late into western Upper Michigan and into the rest of the
County Warning Area Sun morning. As 850 mb temperatures drop from near -12c over the west
by 12z/sun to -18c by 00z/Mon...lake enhanced/effect snow will also
increase for northwest flow favored locations. However...850-700 mb drying
in the afternoon will limit accumulations to only light amounts of
an inch or two. Over the rest of the County Warning Area...the fgen dynamics could
also squeeze out some light snow with accumulations less than an inch.

Sun night into Monday...very cold air will plunge into the northern lakes
with 850 mb temperatures dropping to around -25c by 12z-18z/Mon. Even with
strong over lake instability (lake induced convective available potential energy above 750 j/kg) the
dry airmass and very shallow dgz will support mainly just moderate
snow amounts for west-northwest flow snow belts. The les should taper off by
late Monday into Monday night as winds back to SW.

Tue-Wed...the models suggest that a middle level and surface trough will
slide through the area Tuesday into Tuesday night. Only chance probability of precipitation for
light snow was included as the deep layer qvector conv will have
little moisture to work with. Some west-northwest flow les may develop behind
this system...per colder European model (ecmwf) solution...with 850 mb temperatures dropping
to around -16c on Wednesday.

Thu-Fri...model differences between the European model (ecmwf) and GFS/gefs were
larger as the GFS brings a shortwave through the Ohio Valley while the
European model (ecmwf) also pushes a northern stream shortwave through the Western Lake that could
bring some light snow to Upper Michigan.
&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 649 PM EST Friday Nov 28 2014

As more low level moisture is advected into the area through the night in a low level
southeast veering south-southwest wind...expect conditions to deteriorate. Downslope
nature of this flow at iwd will slow the lowering ceilings...but even
there some MVFR ceilings are likely late at night. The best chance for lower
IFR and even LIFR ceilings later on will be at saw...where the low level wind
will present an upslope component. This upslope flow will also bring
about the chance for some -sn and even some -fzdz later on with a developing
elevated warm layer. This -fzdz could impact cmx as well on Sat...but
rising temperatures above 32 in the continued southerly flow will bring about a
change to just -dz later on as ceilings rise into the MVFR range at saw
with a veering flow to a less favorable SW direction.
&&

Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 248 PM EST Friday Nov 28 2014

A developing low pressure system over the plains will continue to
move toward the upper Great Lakes into Saturday. This will allow for
winds to gradually turn south later today into tonight...but they
should stay below 20-25 knots. The front moves though Sunday...while
strong Arctic high pressure builds into the plains. This will allow
northwest gales to develop later Sunday and continue into Monday. The high
rapidly shifts over the lake Monday afternoon...then moves into
Quebec by Tuesday. High will allow for a brief respite of gales Monday
afternoon into Monday night...with southerly gales possible again on
Tuesday on the back side of the high.
&&

MQT watches/warnings/advisories...
Upper Michigan...
none.
Lake Superior...
none.
Lake Michigan...
none.
&&

$$

Short term...Titus
long term...jlb
aviation...kc
marine...Titus

National Weather Service Glossary of Abbreviations