717 
fxus63 kmpx 202317 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
617 PM CDT Sat Mar 20 2010 


Discussion... 


Another quiet weather period lies ahead with main challenge being 
temperatures next week with frontal boundaries forecast to be 
sitting around the area Tuesday through Saturday. Precipitation chances 
will be minimal despite the fronts hanging out in the area thanks 
to split flow regime. 


Currently...WV imagery shows a sharp short wave sitting from Nebraska 
into the Twin Cities...this is in the process merging into the 
upper low that is currently cutting off over OK. Over the next 
few days...upper ridge currently over The Rockies will be building 
into the upper Midwest while flattening out. This will continue 
the much needed run in dry weather into next week. At the 
surface...ridge is ovhd currently and will be slowly sagging south 
through the night. Central Minnesota will be getting back into return 
flow tonight...with ridge still sitting across Iowa border. Will 
result in a S to north temperature gradient across the state...with teens 
possible in the south while central Minnesota stays in the 20s...as 
depicted by the European model (ecmwf). For Sunday into Monday night region will be 
in warm air advection and brisk srly winds...will allow temperatures to warm 
nicely...with most of the area back into the 50s by Monday...with 
lows staying mostly above freezing. 


Issues begin creeping into the forecast Tuesday as another front 
is forecast to slip through the area. A weak short wave is 
forecast to ripple across the international border...while a second and 
more pronounced through slowly moves through The Rockies. The northern 
wave will send a weak cold front into the area Tuesday...with the 
front stretching back into a Lee side low over eastern Colorado. This front 
is forecast by even the slowest model /ECMWF in this case/ to be 
basically through the County Warning Area by 18z Tuesday. Based on this...cooled 
highs some Tuesday...but with cold air advection getting under way and 850 mb temperatures 
still mainly above zero...should only see temperatures only 5 to 10 
degrees cooler than Monday. High pressure will slip ovhd for 
Wednesday...with temperatures falling back closer to normal. For Thursday 
on there is very little confidence in temperature forecast. This is due 
the arrival of a more significant Arctic front across the area. 
Upper flow over the area will be wrly and parallel to the 
front...with northwest flow and best southern upper push of cold heading into 
the eastern Great Lakes. This means the Arctic front looks to get hung 
up near the area. Will likely see a fairly tight temperature gradient 
along this feature...which is forecast by the 12z European model (ecmwf)/Gem to be 
south of the area while the GFS keeps the front out of here until 
Thursday night. The resultant high forecasts Thursday vary by a 
good 20 to 30 degrees...with the GFS painting another day of 50s 
across the County Warning Area for Thursday...with the Gem/European model (ecmwf) holding highs 
down into the 20s/30s in the Arctic airmass. At this 
point...stayed close to the HPC and mean GFS ensemble guidance 
numbers...which has highs in the 40s. This is likely 10 degrees 
off in one way or the other. As stated earlier...parallel upper 
flow with respect to the front leads ME to question just how far 
south this front will be able to run. Beyond that 500 mb heights are 
forecast by the GFS/European model (ecmwf) to be around 546 dm...so a near normal 
end to the forecast looks good. 


For precipitation there are two possibilities out there...though neither 
looks all that impressive at the moment. The first is with the 
front/inverted through slipping through on Tuesday. This system is 
looking similar to the front that passed through Thursday night in 
the sense that it will be lacking much in the way of low level 
moisture. Best upper forcing will be passing across the international 
border with that weak wave...with a stream of moisture coming out 
of The Rockies low toward Minnesota. Neither of these features look to 
really impact the area with much more than cloud cover...with not 
much more then a few spits of rain expected during the day. The 
other possibility would be in the Friday/Saturday time frame as 
the GFS and European model (ecmwf) both bring a rather broad and diffuse wave 
across the region and the Arctic front. Given recent dry trend 
with the last system and the expected middle week front...have left 
forecast dry until a little more consistent trend comes about. 


&& 


Aviation.../00z taf issuance/ 
surface ridge continues to build over the taf sites during the period. 
VFR conds expected through the period. 


Kmsp... no aviation weather concerns anticipated through Monday. 
Generally clear sky. 


&& 


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


$$ 


Mpg/jm