775 
fxus63 kmpx 212349 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
549 PM CST Sat Nov 21 2009 


Discussion... 


Low level moisture has been advancing north with dewpoints across west Iowa 
into east Nebraska now into the lower 40s. Strong southerly flow will 
continue their nwrd expansion. Pockets of stratus to our south will 
expand under cover of darkness as low levels moisten. Clouds will 
likely thicken enough late tonight for some drizzle. Should be enough wind 
to keep visibility from being significant impact...but did introduce 
patchy fog into forecast for late tonight and Sunday morning. 
Combination of clouds...wind..and increasing dewpoints will yield 
min temperatures about 10 degrees warmer than this morning. 


Some concern with tomorrows temperatures with expected clouds and 
possible light precipitation. Trimmmed them a bit..but middle shift 
will have to take another look at this. 


Upstream trough no moving across west Montana into the SW U.S. Will become a 
bit less defined as it moves east and stronger trough barrels off 
Pacific behind it. Troffiness...increasing moisture and weak surface 
front moving into area will bring scattered light precipitation into 
area Sunday and Monday. 


Upped probability of precipitation for Monday night and Tuesday mainly across southern County Warning Area 
as this next system drops out of the northern rockies then rather 
slowly moves across east sodak and Iowa. Temperature profiles would 
keep precipitation as all rain until a transition beginning Tuesday night. 
Position of upper jet coming around base of trough would place S Minnesota in 
left exit region of upper jet late Monday into early Tuesday. 


European model (ecmwf) now leaning more toward GFS solution of second trough diving out 
of Canada and across SW Minnesota late Wednesday...and becoming quite 
aggressive on quantitative precipitation forecast output. Feel quantitative precipitation forecast is probably overdone in that 
upper trough will be fighting cold advection...but upped probability of precipitation somewhat 
for that period. 


&& 


Aviation.../00z taf issuance/ 


Conditions for pilots expected to deteriorate overnight 
tonight...with IFR conditions most likely at taf sites Sunday 
morning between 12z and 18z. A surface trough across the central 
Dakotas is pumping moisture from the south into the region 
tonight. It is a favorable setup for saturation overnight with low 
level moisture...thermal...and wind profiles favoring stratus. 
Model guidance continues to advertise this as well...with timing 
of onset and lowest heights in the morning being the challenge. 
All taf sites outside of kaxn should have 500-1500 feet stratus by 
daybreak. Drizzle looks most likely as well during the morning 
with the possibility of that or light shower activity during the 
afternoon. These areas of drizzle in the morning combined with the 
low level saturation will offer restrictions of visbys possibly 
into the IFR category. Improvement in visbys is expected in the 
afternoon while very gradual lifting of the ceilings. Srly winds will 
slightly drop tonight and remain fairly steady Sunday with 
sporadic gusts of 15-18 kts possible in WI. As the trough shifts 
into western Minnesota it will shift the winds to the SW or west-southwest at kaxn and 
krwf during Sunday afternoon. 


&& 


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


$$ 


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