Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Duluth Minnesota
413 am CST Sat Dec 20 2014
Short term...(today and tonight)
issued at 413 am CST Sat Dec 20 2014
Long-duration light intensity snow/freezing drizzle continues
through the weekend due to warm advection ahead of the next weather
system. Temperatures will rise gradually to near-freezing by Sunday
afternoon...with highs around 10 degrees above normal and lows
around 25 degrees above normal. Forecast low temperatures this weekend will
rank in the top ten record warm lows at dlh and inl.
On the synoptic scale...somewhat of a transitional pattern aloft
keeping the Northland in a persistent southwest flow with two
significant middle-level shortwave troughs moving across...one this
morning through the early afternoon and then another wave late
tonight into tomorrow. Warm air advection at low/middle levels will
continue through the weekend...with the best push of warmer air
aloft late Saturday night into Sunday as the second middle-level
shortwave trough depends and moves east across the international
border region...warm enough to possibly cause sleet to mix in in a
few spots in central Minnesota.
Today...overnight the Winter Weather Advisory seemed to be working
out well with light freezing drizzle/freezing fog causing icy Road
conditions according to a number of area emergency dispatch centers.
No surface station reports of fzdz specifically...but the automated
weather sensors typically do not do well differentiating mist/fog
and drizzle. These conditions will continue through the
afternoon...with drizzle turning more to snow showers this afternoon
as the middle-level moisture increases and we have better ice Crystal
generation aloft. Temperatures mild...warming up to around 30.
Tonight...early in the evening some freezing drizzle will be
possible as we experience drying at middle-levels and warming at cloud
top level...quickly changing to all snow after midnight as a strong
middle-level disturbance moves across the region. The best large scale
forcing will be across kooching/Itasca/northern Saint Louis counties
where some spots could see a quick inch after midnight. Some sleet
may mix in around the Brainerd lakes region due to a nose of warm
air aloft...but the window of opportunity for this is fairly limited
on spatial and temporal scales. The area of snow showers will
gradually move east towards middle-day Sunday. Lows holding steady in
the upper 20s.
Sunday...snow showers moving from west to east with flurries
possible everywhere due to the large-scale lift in place. While
there will be some clearing aloft in the far western parts of the
County Warning Area...low level inversion means the stratus deck will persist. Highs
Total snowfall through the period will be a coating to an inch in
most spots...with the Iron Range and points north possibly
receiving just over an inch due to a period of heavier snow showers
on Sunday. No significant ice accretion is expected this morning
with the freezing drizzle...but untreated surfaces could develop a
thin layer of ice.
Long term...(sunday through friday)
issued at 413 am CST Sat Dec 20 2014
This period will be dominated by a digging trough that will close off
in the upper Midwest. A 100+ knots upper level jet will help create
areas of widespread upward vertical velocity. The system will become
vertically stacked and the subsequent surface low will deepen
considerably as the system meanders across the Midwest through
This weather scheme will bring widespread and long lasting light
snow to areas of the Northland. And there could be some areas of
heavier bands of snow but where these will be is still uncertain.
By Sunday night the surface low will be over the Dakotas with a strong
baroclinic zone over central Minnesota and WI...where an area of strong
fgen will develop...with Northland possibly in the area of greatest
lift generated by the fgen process. This area remains throughout
most of Monday...so we'll see an extended period of light snow.
However...as Monday evening begins with drier air aloft...there
could be freezing drizzle...but as the atmosphere saturates...there
will be a quick changeover over to all snow Monday morning. Snow
amounts during the day could be a few inches..and will refine
amounts through the weekend.
The system will continue to affect the Northland through
Tuesday...then it will pull out of the area. Snow amounts are hard
to pin down as the track of the low solution is not clear...but
much of the Northland could see more accumulating snow on Monday
night and Tuesday.
The cyclonic flow and cold air advection behind the system could
generate snow showers on Wednesday. A stiff northwest wind and 800 mb
temperatures forecast to dip to -10c cold generate lake effect snow showers
over northwest WI on Christmas day.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1144 PM CST Friday Dec 19 2014
There is very little change in the forecast reasoning for the 06z
tafs from the previous issuance. Generally IFR conditions are
expected to persist most of this valid taf period as weak but
persistent low level warm/moist advection persists into Saturday
evening as very slow moving middle level trough axis moves east. The
result should be a persistence of low ceilings/fog and freezing
drizzle and/or very light snow/flurries. Most of the significant
visibility reductions should be resultant more from fog than from
precipitation. Some improvement into MVFR flight category is
expected the last 9-12 hours of the taf period.
Preliminary point temps/pops...
dlh 29 28 32 30 / 30 40 40 40
inl 30 27 31 28 / 20 40 30 20
brd 30 27 33 29 / 10 30 20 50
hyr 30 27 31 31 / 20 20 40 40
asx 32 26 34 32 / 20 20 30 30
Minnesota...Winter Weather Advisory until noon CST today for mnz010>012-