Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Duluth Minnesota
907 PM CST Thursday Nov 20 2014
issued at 900 PM CST Thursday Nov 20 2014
Have lowered min temperatures overnight as latest observations show
temperatures quickly crashing into the negative values under the
ridge axis. The coldest readings will only last for a few hours
before southerly winds develop and temperatures begin a gradual
climb through daybreak.
As of 900 PM...low temperatures already observed this evening
include kinl at -11f, khib at -9f, khyr -7f, and kdlh at 4f.
Short term...(this evening through Friday night)
issued at 346 PM CST Thursday Nov 20 2014
At 330 PM...skies were mostly clear across the County Warning Area. Any scattered
snow showers still lingering across the South Shore of Lake
Superior were quickly falling apart. Temperatures ranged from the
single digits in The Arrowhead to the teens elsewhere.
The main focus for tonight will be very cold temperatures across
the Northland. Have cut temperatures several degrees for overnight lows
based on clear skies and decreasing wind. Think temperatures have the
potential to fall into the teens below zero...especially in northwest WI
where they will be nearer the surface high over the Midwest. Warm air advection
will already push into the County Warning Area as the night wears on. This could
result in a bit of an increase in mainly high clouds later in the
night. As a result...have generally gone with temperatures in the single
digits below zero in the NE Minnesota side. Will have to watch temperatures
closely though as we may drop even further than that in spots.
Clouds will increase and thicken throughout the day Friday...as
strong warm air advection pushes across the upper Midwest and south central Canada.
High temperatures will generally be in the 20s for daytime highs.
The warm air advection could result in some spotty mixed precipitation Friday
night...especially in northwest WI. Will maintain small probability of precipitation across this
Long term...(saturday through thursday)
issued at 346 PM CST Thursday Nov 20 2014
Through the period we are watching the phasing of the north and
southern stream...and the resultant longwave trough that will affect
the region this weekend and early next week.
On Saturday the retreating surface high will allow a return flow of
very warm air with 800 mb temperatures temperature forecast to rise into the single
digits by Sunday morning. This warm air advection in addition to a
strong shortwave moving across the region.
Very warm temperature profiles will keep precipitation as rain
Sunday afternoon in eastern sections....The Arrowhead and
WI...but...as the system nears late Saturday night and Sunday
morning surface temperatures will be below zero which will result in freezing
rain. The freezing rain will change to all rain during the day
Sunday as surface temperatures rise above freezing. Bufr soundings indicate
definite ice in the column across the northwest area from about
Walker to inl...where precipitation type will remain snow over the forecast
By Sunday evening the surface low will be moving east...and very cold
air will be filtering in behind the low...and will quickly change
the rain into snow.
Both the GFS and the European model (ecmwf) have been trending east with the surface
low...the GFS much farther east than the Euro. This system will
still bear watching.
Much cold air comes in behind this system on north and northwest
winds...meaning the lake effect snow machine will kick in and
continue for the rest of the week.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 536 PM CST Thursday Nov 20 2014
An axis of high pressure will slide over the region
tonight...allowing VFR conditions to prevail through Friday
morning. Gusty south winds and strong warm air advection Friday
will bring increasing clouds and moisture to the region. Latest
NAM bufr soundings suggest low clouds move into the region from
the west through the morning....becoming widespread after 18z.
Have introduced a scattered/broken layer below 3 kft to convey this trend.
Based on latest guidance there is also a small threat for very
light freezing drizzle in the kbrd area. Have left out of
terminals at this time and will re-asses the threat for the next
Preliminary point temps/pops...
dlh -4 21 20 36 / 0 0 10 10
inl -12 24 21 35 / 0 0 10 10
brd -3 25 24 35 / 0 0 10 10
hyr -14 24 21 37 / 0 0 10 10
asx -4 25 22 39 / 30 0 10 10
Ls...Small Craft Advisory from 10 am Friday to 9 am CST Saturday for