391 
fxus63 kmpx 070320 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
1020 PM CDT Monday Oct 6 2008 


Update...for 06z aviation discussion below 


&& 


Discussion.../issued 233 PM CDT Monday Oct 6 2008/ 


Forecast concerns remain centered on precipitation chances and 
temperatures surrounding approach of upper trough/upper jet and 
associated cold frontal passage. 


The forecast area is currently largely precipitation free...with 
the largest batch of precipitation associated with the cold front 
in the far eastern Dakotas..and upper support in the right 
entrance region of an upper jetlet. 12z radiosonde observations continue to show the 
presence of an abnormally moist atmosphere...with precipitable waters  from 175 
to 225 percent of normal measured at bis/abr/mpx/inl. The forecast 
area has been bounded on the north and west by low clouds...light 
fog...and rain...with primarily high clouds and warmer 
temperatures prevailing across southern and central Minnesota...as 
well as Iowa and much of southern and western Wisconsin. In the 
short term...the forecast scenario is largely unchanged from the 
past 24 hours or so. 


GFS...NAM and European model (ecmwf) continue to agree quite nicely through 48 hours 
or so. Cold front nears the Minnesota/Dakota border by 00z...as 
support from the aforementioned jetlet continues. Showers should 
overspread the west during the evening...the central during the 
overnight and early morning...and eastern sections of the area 
near and just after the noon hour. The bulk of the showers should 
exit the west central Wisconsin counties between 06z and 12z Wednesday. 
Rainfall amounts could exceed an inch in isolated spots...but most 
should Register between a quarter and three quarters of an 
inch...as well above normal precipitable waters  will continue across the 
prefrontal region. The front moves quickly eastward into the 
Great Lakes region...leaving dry conditions for a couple of days. 
Afternoon temperatures in the wake of the front should not 
decrease appreciably...as a quick return of warmer air will occur 
on Wednesday in advance of a secondary boundary. The cooler air 
/0-4c 850 mb temperatures/ will invade the region behind this 
front. Low temperatures Tuesday night will...of course...be much 
cooler than the last couple of nights...due to clearing skies and 
a drier airmass. Tuesday night should also feature some patchy 
fog...with residual surface moisture from the plentiful 
rains...and winds dropping off as a surface ridge pokes into the 
area. 


The real questions enter the forecast toward the end of the work 
week and into the weekend...with divergent Middle Range model 
solutions. The European model (ecmwf) has been the most consistent...favoring a 
longwave trough in the western United States...and a less 
progressive precipitation arrival. The GFS has been all over the 
place through the last few runs...although the 12z run has trended 
more toward the European model (ecmwf) solution. Following the spirit of the 
European model (ecmwf)...shower and thunderstorm chances should begin to increase 
from Friday into the weekend...with the upper flow sending a 
series of short waves into western...central...and northeastern 
Minnesota. A front will be parked across Minnesota and into 
northwestern Wisconsin...leading to the greatest precipitation 
chances being located from southwest Minnesota...toward Saint 
Cloud...and Duluth. Sunday looks to be the most likely day to see 
widespread showers and thunderstorms...as a cold front sweeps 
through the area. The uncertainty in the various model solutions 
has lead to some uncertainty in temperatures for the upcoming 
weekend...although at this time...it appears that some parts of 
the area could see highs in the 70s for a time ahead of the cold 
front. 


&& 


Aviation.../06z taf issuance/ 
the main aviation concerns continue to revolve around 
ceilings/vsbys/precipitation associated with the frontal boundary 
moving across western/central Minnesota. Rain showers will become more 
numerous across Minnesota taf sites overnight...and WI sites Tuesday 
morning. Restrictions should mainly fall into the MVFR category 
once the showers arrive. Precipitation should end across western 
sites /kaxn and krwf/ shortly after daybreak Tuesday...and at the 
remaining Minnesota sites during the late morning hours. Showers are 
expected to linger at krnh into the early afternoon...and at Keau 
until late evening. Gusty northwest winds will also occur across 
west central Minnesota on Tuesday in the wake of the front. 


&& 


Mpx watches/warnings/advisories... 
Minnesota...none. 
WI...none. 
&& 


$$