Weather

128 
fxus63 kmpx 060833 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
233 am CST Tuesday Jan 6 2009 


Discussion... 


The primary forecast challenges are temperatures today and then precipitation 
timing and type on Thursday night and Friday. 


GOES WV loop showing split energy moving from the Lee of The 
Rockies into ctrl North America. WV along with upper level pv 
anomalies and height falls showing stronger wave being the southern one 
evolving into the Southern Plains. Northern energy over south ctrl Canada 
into ND is fairly weak and moving due east. So in between we are 
caught in an area of scant moisture and somewhat limited Omega. As 
County Warning Area is under system warm sector through today...isentropic ascent 
does little to saturate. So just a slight chance for some flurries 
or light fzdz over northern forecast area /ctrl Minnesota/ is about it. High clouds 
should prevail in the morning with some stratus development as the 
afternoon wares on. Despite this...temperatures should still reach the lower 
30s across southern Minnesota and up to the I-94 corridor of eastern Minnesota and western WI 
given MOS trend and high starting value this morning. 


Initial cold front to work through the area this evening with a 
reinforcing backdoor front Wednesday morning. Both will help to 
promote steeper lower tropopause lapse rates and offer snow 
shower/flurries potential along and behind them. Snow shower 
potential on Wednesday is greatest in western WI where middle-level positive vorticity advection 
appears maximized. All in all...a few tenths at most may be seen 
late tonight into Wednesday over eastern Minnesota and western WI. 


Slightly colder air...with temperatures at or just below normal...will 
prevail Wednesday night and Thursday as weak Canadian high moves in. Next 
Pacific system also split...however northern stream system has more of 
an identity. The trend in the guidance has been northerly with the 
path of key features...meaning a greater lower tropopause thermal 
return. For Thursday night...good isentropic ascent and saturation 
prognosticated along and ahead of elevated warm front across ctrl Minnesota. 
Mref plume diagrams for ctrl Minnesota have trended towards a strong 
signal for Thursday night...mainly from 03z to 12z Friday for precipitation 
accums. Have boosted probability of precipitation accordingly. With the strength of the 
low level jet increasing through the night...preserved the chance 
for freezing rain to mix in to southern Minnesota precipitation after midnight. The mix 
potential will last into Friday morning with elevated warm sector 
aloft. However...guidance signal and consistentcy for Friday is much 
weaker than on Thursday night. This is also revealed on the ensemble 
measure of predictability charts. Right now have leaned towards 
the 00z European model (ecmwf) which drops the 800 mb low southeast across the area under 
favorable right entrance region. Have bumped up probability of precipitation slightly. 
Appears there could be at least some minimal snow accums in ctrl 
Minnesota and western WI during that time. 


This system appears to be the beginning of a push for Arctic 
air which likely will move into the eastern half of the US in several 
phases through the middle of the week. Could be quite cold given 
prognosticated mslp and 800 mb temperatures by Wednesday and Thursday of next week. Given that 
pattern...precipitation chances next week appear to be confined to 
clippers. 


&& 


Aviation.../06z taf issuance/ 


VFR conditions expected all sites until early afternoon. Low 
pressure developing into the eastern Dakotas and western Minnesota 
by morning with frontal boundary extending through central Minnesota. 
Generally dry column moisture except for middle and high levels as 
short wave trough enters the area. Little chance of precipitation 
until cold front moved into western Minnesota behind the low 
pressure area. MVFR ceilings will likely develop in the cold advection 
pattern over northwest part of forecast area in the afternoon and then 
spreading southeast during the evening. Sharpening upper trough may help 
to generate snow showers or flurries toward the end of the 
period...mainly over north and east taf sites. Visby restrictions are 
not anticipated at this time. 


&& 


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


$$ 


Mtf/jpr