897 
fxus63 kmpx 182016 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
316 PM CDT Thursday Mar 18 2010 


Discussion... 
the weather challenges in the forecast are precipitation chances 
on Friday and quantifying the degree of and longevity of the 
upcoming cool down. 


The GOES water vapor loop this afternoon reveals a well-defined 
disturbance moving east across Lake Winnipeg...with the surface 
observations indicating a trailing cold front southwest across 
North Dakota which is pushing southeast. Solid surface pressure 
rises along with air temperatures in the 20s are seen behind this 
front. Parallel middle-level moist flow ahead of the trough has been 
seen on satellite and the radar mosaic through the day in South Dakota and NE. 
Occasional sprinkles have been observed and feel comfortable with 
mention of that in western and southwestern Minnesota tonight. The 
surface cold front will move through the forecast area overnight. 
This will swing winds to the northwest and drop temperatures. Have 
adjusted the nighttime hourly temperature trend to account for 
this. 


The models have consistently trended south with the developing 
middle-level wave along the baroclinic zone. This has continued into 
today. Southern Minnesota will remain under favorable upper ascent...but 
the low-level dry and cool air advection undercutting this support 
and middle-level moisture warrants only a chance of light 
precipitation over south central Minnesota...with better support further 
south in Iowa. The column is cool enough to primarily support light 
snow across the Interstate 90 corridor where precipitation is able 
to fall...especially by later afternoon. 


The cooler air will reinforce itself through Friday. Surface 
temperatures on Friday will be 20 to 25 degrees cooler on Friday 
afternoon than this afternoon...with clouds helping as well. 
Saturday should see sunshine by afternoon and likely again on 
Sunday. Similar to the previous forecast shift...the models 
continue to trend north with the polar stream and activity along 
it. With westerly flow and ridging over the area...continue the 
trend to increase temperatures on Sunday into Monday. The flow 
remains somewhat split next week...with the upper Midwest 
primarily under west to west northwest flow. The GFS and European model (ecmwf) 
have come more into alignment with a system in this split flow 
during the Tuesday to Tuesday night period...although its impact 
appears to presently be minimal. Temperatures during the middle to 
latter part of next week should be somewhat flat-line and near 
normal. 


Hydrology... 
most points along area rivers continue to gradually rise. Snow 
across west central and far southwestern Minnesota has been depleted to 
mainly ditches from reports received...so large scale melt over 
inflow basins appears primarily done. Nighttime temperatures will 
drop below freezing across the hydrologic service area on Friday 
through Sunday nights. The coolest temperatures...to near the 
upper teens on Saturday and Sunday nights...are forecast over 
southern and southwest Minnesota. At least some minimal refreezing is 
likely. 


&& 


Aviation.../18z taf issuance/ 


Cold front moving across North Dakota this afternoon and drop into 
central Minnesota through central Minnesota through 06z. This will bring in middle 
level clouds into County Warning Area during the afternoon/evening and perhaps some 
sprinkles or brief light showers to kaxn/krwf 00z-06 period. Middle 
level clouds remain and drop farther south during the night. Colder 
air and perhaps MVFR ceilings dropping south with it along with the 
threat of a -rasn mix at krwf. Any precipitation threat should exit the 
region by 12z Friday. MVFR ceilings 2-3k feet should gradually lift in the 
afternoon from north to south. Could see some breaks developing 
into the west Friday afternoon...as surface ridge builds east. Light SW-west 
winds to become northwest and increase as the fnt moves through and 
gradient increases. 


Kmsp...west or brief SW winds should become northwest during the early 
afternoon with increase high/middle level clouds. Appears cold front to 
drop though kmsp through 06z and becoming gusty thereafter as the 
colder air moves in. Ceilings to lower to MVFR category after 13z then 
improving to VFR again Friday afternoon. 


&& 


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


$$ 


Mtf/dwe