410 
fxus63 kmpx 212100 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
300 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 transtion 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.../18z taf issuance/ 


Latest observation south of mpx County Warning Area has numerous ceilings/visibility in the LIFR 
area with MVFR ceilings/visibility in Kansas/NE moving N/NE. This will be 
the source region for later this evening/overnight across most of 
mpx County Warning Area with LIFR or IFR ceilings/visibility a good bet for most of taf 
sites. Early term remains problematic with eau as MVFR ceilings 
moving northward across eastern Iowa...which may keep eau MVFR this 
afternoon...with decreasing visibility/ceilings overnight. Latest GFS/NAM has 
strong isentropic lift this evening below 90h which means lower 
ceilings/visibility developing. Drizzle also a good bet as lower 
ceilings and subtle lift in the boundary layer should help to 
generate some light precipitation. These LIFR/IFR ceilings/visibility 
will likely continue through 15z...then slowly rise...especially for 
axn as the frontal boundary and subsidence should begin to erode 
lower ceilings. Ceilings/visibility could be lower than expected as per 
earlier observation in Kansas source region. However...will keep conditions 
just above minimums with confidence level not extreme for this 
type of scenario. ..jlt.. 


Cwsu discussion... 


Just thin high clouds currently over msp. Do not expect lower clouds 
until this evening. Parts of Iowa still fighting dense fog and low 
clouds... expect that moisture to advect into msp vicinity this 
evening. At least IFR ceilings expected... possible LIFR ceilings and fog 
toward morning. Some improvement during the day Sunday... afternoon 
ceilings should rebound to the 015-020 range. 


South winds increasing...a gust or two of 20 kts possible this 
afternoon. More southeast this evening, and not quite as breezy 
Sunday...around 10 kts. - Kfm 


&& 


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


$$ 


Bap/jlt