496 
fxus63 kdlh 231655 
afddlh 


Area forecast discussion 
National Weather Service Duluth Minnesota 
1055 am CST Monday Nov 23 2009 


Update...have updated to extend the duration of the dense fog 
advisory through 10 am Tuesday. While rain and daytime heating is 
expected to bring an improvement in the dense fog for the 
afternoon...we expect the dense fog to quickly re-establish itself 
during the early part of the evening. Conditions should then 
improve on Tuesday. Rather than cancel the advisory and then 
reissue...we decided to not an improving trend for a time...before 
conditions deteriorate once again early this evening. Feel fairly 
strongly that dense fog will again be a problem tonight...and the 
dense fog reported last night was very hazardous...with virtually 
no driving visibility. As a result...we will extend the advisory 
through 10 am Tuesday. Elsewhere...we should see a decrease in 
rain from southeast to northwest across northwest WI. Much of NE Minnesota should see rain 
continuing...if not decreasing in areal coverage to some extent. 


&& 


Previous discussion... /issued 642 am CST Monday Nov 23 2009/ 


Aviation.../12z taf issuance/ 
areas of light rain will affect much of the forecast area through 
tonight. Some of the fog this morning and again tonight may be 
dense...although guidance has had a difficult time in forecasting 
the onset and end of the dense fog. Therefore confidence is low 
with respect to to LIFR visibilities. Ceilings will also vary from LIFR to VFR today 
through tonight. 


Previous discussion... /issued 358 am CST Monday Nov 23 2009/ 


Discussion... 
east-west bands of low level warm advection...associated with a 
dissipated surface trough...are spreading north across our area. 
At this time...bands are associated with light rain and fog 
formation more rapid than rain can rinse out. Between bands... 
compensatory low level downward motion briefly exposes a middle deck 
and causes temporary improvement. A band now along our southern 
edge is increasing in width and moisture as it spreads north. 


Low pressure over the central/Southern Plains will establish an 
inverted trough northward along or immediately east of the Red 
River valley by noon today. A weak but digging trough aloft will 
anchor the inverted trough along our western edge through tonight 
and Tuesday. We anticipate fog and light rain to continue...with 
the back edge not apt to reach our western areas either tonight or 
Tuesday. Again...continued warm advection along and east of the 
inverted trough will keep the column unseasonably warm. 


Extended...Tuesday night through Sunday. 
The medium range models show a complex scenario setting up for the 
beginning of the extended forecast period...with two distinct 
shortwave troughs affecting our County Warning Area. A southern wave located over the 
central Midwest will bring rain to our southern zones Tuesday night and 
Wednesday...while a stronger system digs southeastward out of 
Canada...bringing a chance of rain and snow to our northern zones. The 
models show that these two waves will eventually merge over the 
Great Lakes region on Wednesday and Wednesday night. Lift associated 
with these systems will provide lift which will tap ample 
moisture...continuing the chance of precipitation across our entire 
County Warning Area...with the best chance for precipitation across our eastern zones. During 
this time frame...the rain will mix with snow...and eventually 
change to all snow Wednesday night as colder air advects south from 
Canada on the west side of the now departing low. A weaker elongated 
vortmax will follow and affect the Northland on 
Thursday...continuing the chance of snow showers across the eastern half 
of our County Warning Area. The snow will end for most locations Thursday 
night...except across the snowbelt of northwestern WI where lake effect snow 
showers may linger. High pressure will move over the western Great Lakes 
by Friday...resulting in drier conditions. At this time...next weekend 
appears dry...although the European model (ecmwf) does show another shortwave digging 
southeastward out of Canada and over the upper Midwest. However most of the 
precipitation associated with this disturbance shouldnt affect the forecast 
area until Sunday and Sunday night. 


&& 


Point temps/pops... 
dlh 49 39 46 33 / 70 50 40 40 
inl 48 35 43 31 / 70 70 50 40 
brd 51 39 47 32 / 60 60 40 40 
hyr 53 41 48 35 / 60 10 40 50 
asx 51 41 47 38 / 30 10 30 50 


&& 


Dlh watches/warnings/advisories... 
Minnesota...dense fog advisory until 10 am CST Tuesday for mnz012-019>021- 
026-037. 


WI...dense fog advisory until 10 am CST Tuesday for wiz001. 


Ls...none. 
&& 


$$ 


06/Cannon