Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Duluth Minnesota
1016 am CST Monday Dec 22 2014
issued at 1016 am CST Monday Dec 22 2014
Have extended the Winter Weather Advisory for The Arrowhead
through noon today as moderate to locally heavy snow bands continue to
track northward through St. Louis...lake and Cook counties. Will see the
snow taper off after noon. No other significant changes made to
the forecast. As of this morning...still expecting the next
system to produce accumulating snow over much of northwest WI beginning
early Tuesday morning into Tuesday night.
Update issued at 555 am CST Monday Dec 22 2014
Updated aviation section below...
Short term...(today and tonight)
issued at 517 am CST Monday Dec 22 2014
A complex winter weather event through the first half of the week
will bring a mix of rain...snow...drizzle...and more to the region.
There will be two rounds of precipitation...the first a rain/snow mixed
type event this morning/afternoon...and the second mainly snow event
focused primarily across northwest Wisconsin. Common themes across
both events will be overcast skies...temperatures near freezing with
little diurnal change...and intermittent fog/drizzle.
On the synoptic scale we have a clipper system which will weaken as
a stronger longwave trough deepens across the central U.S. Monday
night into Tuesday. This will result in the low from the clipper
dropping south from the northern plains this morning into the middle
Mississippi Valley tonight...lifting northeast across Michigan
Tuesday into Wednesday. As the low lifts north the low/middle level
flow will become out of the north/northwest resulting in colder air
being advected into the region...but still with temperatures well
above normal for late December. At inl 850mb temperatures are in the 90th
percentile according to the observed sounding climatology.
Early this morning...the short term guidance performed well
overnight in depicting the change from mostly rain to mostly snow as
a band of precipitation moving from north to south. At this point /4 am
CST/ all of northern Minnesota was experiencing light to moderate
snowfall. Had a period of nice large flakes here at the offices with
a coating of wet snow accumulating on most surfaces. Decided to
continue the Winter Weather Advisory for The Arrowhead through 10 am
CST as an inch or two of snowfall accumulates where freezing drizzle
may have fallen overnight. In northwest Wisconsin we have seen a mix
near the lake with mainly snow elsewhere. Elsewhere...areas of fog
with occasional drizzle or flurries through the morning hours.
Temperatures remaining steady or gradually rising.
This afternoon...a light wintry mix across the region. As
temperatures rise snow may transition to a rain/snow mix...but in
general the predominant precipitation type should remain snow. Areas of
drizzle/fog will persist due to the abundant low level
moisture...and locally dense fog may develop where temperatures rise
into the middle 30s or warmer due to snow cover. Snow amounts for
the afternoon will be limited due to low snow to liquid
ratios...generally a coating to a half inch not counting the morning
accumulation across The Arrowhead previously mentioned. Highs low to
Tonight...cold air returns as an 850mb low over Iowa lifts northeast
towards the Great Lakes resulting in northerly flow over the
Northland. As the surface low deepens and makes it jog north expect
drier air aloft associated with the colder air intruding in. This
drier air will result in warmer cloud temperatures and a lack of ice
crystals in the column to support snow. Thus...drizzle mixed with
light snow at times is expected across much of northern Minnesota
overnight. Over northwest Wisconsin the story will be much different
as southerly flow results in the column saturating and excellent
large-scale lift due to warm air advection at low/middle levels and
middle-level positive vorticity advection. Snowfall will begin in the evening with the most
intense snow rates around Tuesday morning. Lows near freezing.
Tuesday...widespread accumulating snowfall event will be ongoing
across northwest Wisconsin on Tuesday. Snowfall rates will be most
intense in the morning...gradually diminishing towards the evening.
Snowfall totals from Monday night and Tuesday will be in the 3 to 5
inch range. Current forecast is on the conservative side due to
confidence issues discussed below. In northern Minnesota
precipitation will be much less intense with drizzle and some light
snow/flurries at times throughout the day. The twin ports region
will be somewhere in the middle...but at this point am leaning
towards the twin ports being in more of the drizzle/light snow than
the accumulating snowfall expected farther east. Highs in the low
There is average confidence with this northwest Wisconsin snowfall
event. The current forecast is a shift from the previous few forecasts
which had highlighted the tip of The Arrowhead as the most likely
location for the heaviest accumulations. /The previously issued
Winter Storm Watch has been cancelled./ We have done our best to
articulate the low confidence in this forecast over the past few
days through various legacy and social media products...and at this
point we have enough confidence to issue a Winter Weather Advisory
to pinpoint the best region for snowfall. There is still some
concern with this as forcing/surface low could be west or east from
current expectations which would result in a dramatic change in the
forecast for some...but for now the advisory reflects our best
forecast for accumulating snowfall.
Long term...(tuesday through sunday)
issued at 517 am CST Monday Dec 22 2014
Tuesday night and Wednesday are the tail end of the strong storm in
the earlier time frames of the forecast...with snow tapering off
over the area Tuesday night...though expect lake effects will keep
snow going for most of the night for Bayfield...Ashland and Iron
counties. It will not be true lake effect as there will not be
quite enough instability and the lake surface to 850mb difference
will only be about 10c. But the Warm Lake will be putting moisture
and warmth up into the atmosphere to boost our snowfall amounts. We
may be able to cancel the advisory for Sawyer and price early...but
expect we will need the northern counties the whole night...if not
into Wednesday morning. Temperatures to remain mild with lows
Tuesday night still in the low 30s. A weak ridge moves across the area
for Wednesday...bringing a period of drier and colder conditions.
However...expect this ridge will be dirty without a good surge of
cold air to clean things out...and we will probably have clouds and
flurries around the area. Highs still mild around freezing.
Another clipper to move through the area Wednesday night and early
Thursday...bringing some small probability of precipitation to mainly the northern County Warning Area.
However...this clipper to finally escort in some colder air and min
temperatures Thursday night to finally fall into the teens and lower 20s.
Another storm system we have been watching out in the longer ranges
is expected to move through the Midwest Friday...continuing to keep
temperatures relatively mild...but not as warm as the last day or
two. This storm has the potential to bring significant snows to the
area...but it is too far out to put too much stock in these model
By the weekend we finally get into colder than seasonable
temperatures behind the Friday system...with high temperatures on
Saturday and Sunday in the single digits and teens...and lows zero
to 10 below zero.
Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 555 am CST Monday Dec 22 2014
Another 24 hours of mainly IFR to LIFR ceilings with variable
visibilities is expected as a surface low swoops from eastern
South Dakota dips south to northern Missouri tonight and then
begins to move northeast and should be up into northeast Iowa by
12z Tuesday. With temperatures near freezing through the
period...periods of snow will be interspersed with drizzle/freezing
drizzle depending on the surface temperature. Snow will bring
visibilities IFR or even LIFR at times...with visibilities
generally IFR in fog and drizzle otherwise. Confidence in timing
of periods of snow with LIFR ceilings is low.
Preliminary point temps/pops...
dlh 34 32 34 30 / 90 70 60 50
inl 35 31 33 28 / 70 60 30 30
brd 36 32 33 27 / 80 60 40 40
hyr 35 33 34 30 / 50 80 80 50
asx 37 33 34 31 / 50 80 100 60
Minnesota...Winter Weather Advisory until noon CST today for mnz011-012-
WI...Winter Weather Advisory from 9 PM this evening to 6 am CST
Wednesday for wiz002>004-008-009.