203 
fxus63 kmpx 181752 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
1252 PM CDT Friday Jul 18 2008 


Update... 
updated for aviation discussion below. 


&& 


Discussion... 
/issued 300 am CDT Friday Jul 18 2008/ 


Forecast challenges revolve around how quickly to bring precipitation 
chances back to the forecast area tonight and tomorrow. 


Surface front has largely cleared the forecast area...leaving dry 
high pressure to sink into the area from the northwest. Patchy fog 
currently developing across portions of the area /mainly in the 
cleared area north of the cirrus shield from the mesoscale convective system in Iowa/ 
should be gone shortly after sunset. 


A dry...cool and largely cloudless day will prevail across the 
forecast area under the influence of the high pressure. Removed 
all mention of probability of precipitation until late tonight...with upper forcing for 
anything remaining near the front...well to the south of the area. 
Late tonight...the front begins to move northward as a warm 
front...approaching southern Minnesota by Saturday morning. NAM 
and GFS differ some on how quickly any precipitation would enter 
southwest and southern Minnesota. NAM seems unrealistic in its 
quicker return to southerly moist flow...so have sided with the 
slightly slower GFS solution...bringing the best probability of precipitation into the 
southwest after 12z. Highest rainfall totals should affect the 
southern part of the forecast area before 18z...due to proximity 
of the front...as well as upper support from a somewhat coupled 
jet structure. 305/310k moisture transport maximizes along and 
south of the Iowa border also. The greatest precipitation chances 
and quantitative precipitation forecast amounts then transition to east central Minnesota and west 
central Wisconsin during the afternoon on Saturday. 


Forecast becomes somewhat uncertain from Saturday night and into 
Sunday...with diverging model solutions. European model (ecmwf) keeps the front 
hanging around the area...with a couple of different short waves 
dropping southeastward into eastern Minnesota and western 
Wisconsin. NAM solution is similar. Have kept probability of precipitation going through 
Sunday night...with /in general/ the eastern half of the forecast 
area seeing the greater chance for storms. 


Monday and into Tuesday look to be dry...with upper ridging 
building into the region. 


&& 


Aviation.../18z taf issuance/ 


IFR clouds have finally scattered out at Keau while broken conditions 
around 2000-2500 feet have quickly filled in again with heating. 
Similar conditions extend into SC Minnesota but krwf and kmsp are north 
of this area...with only some scattered cumulus elsewhere. Winds will 
gradually shift around from north to east by Sat morning. Light 
winds and residual moisture could mean more fog at Keau late 
tonight and have included this in the taf. Significant difference 
between NAM and GFS re storm potential for Saturday. More on this 
in the afternoon discussion. For now have brought in middle clouds 
during the middle morning at most sites...and chance of precipitation at 
krwf. ... 


&& 


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


$$ 
Kat