491 
fxus63 kmpx 091058 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
500 am CST Friday Jan 9 2009 


Updated for aviation discussion below... 


Discussion... 
snow has blossomed across the forecast area overnight...as 
depicted by the prognosticated isentropic lift from 285-295k ahead of the 
northern plains shortwave trough. Despite mixing ratios of 3-4 
g/kg...snowfall rates have not been overly impressive...largely 
due to the fact that the maximum Omega is not correlated with the 
temperatures favorable for dendrites. The best correlation has 
been found south of the Minnesota River Valley...where estimates of 
snowfall are in the 2 to 4 inch range overnight. Pv advection 
should drive snowfall across central/southern Minnesota into west central 
WI today...although the forcing wanes substantially this 
afternoon. Think the majority of measurable snowfall will occur 
this morning...with light accumulations after 18z. 09.00z model 
runs were much more progressive with this system than prior 
solutions...so have opted to end the advisory at 00z Saturday. 
There is still a threat for a period of freezing drizzle across 
south central Minnesota this morning as the dendritic layer experiences a 
loss of saturation. The deformation axis and attendant snowfall 
sets up to the south/east of the area this evening...so any 
accumulations after 00z should be minor. Generally expect 2-4 
amounts to be common in the advisory area...with the greatest 
amounts /up to 5/ along/south of the Minnesota River Valley. Areas 
along/north of Interstate 94 will see the lowest snowfall 
amounts...where generally expect one half inch to 2 inches. 
The surface ridge builds into the area tonight...with decreasing 
winds/clouds following suit. The next shortwave dives across the 
area on Sunday...when 20 probability of precipitation were maintained. 


An active weather pattern unfolds for next week...with multiple 
shortwaves bringing snowfall chances on Sunday night and 
Monday...and again on Tuesday and Tuesday night. Even more 
notable...is the Arctic outbreak that is shaping up for middle to 
late in the upcoming week. Although the snow cover is not as 
deep...according to research by Craven...this pattern is analogous to the 
Arctic outbreak of 18-20 January 1994. Highs between -10 and -20 
were noted across the County Warning Area during that episode...along with 
widespread lows of -25 to -30. While it is much to early to tell 
if this will be a record-breaking event...it is becoming 
increasingly likely that extremely cold conditions will occur. 


&& 


Aviation.../12z taf issuance/ 


Banded snow remains across much of the forecast area this morning. Northern 
fringes affecting taf sites though and will be a tough call this 
morning. Appears saturation has occurred at kmsp and points south. 
Isentropic lift and minus 15c Omega maximizes across mainly 
southwest metropolitan/into SC Minnesota through about 16z. Will continue trend 
of tempo IFR conds at kmsp. Kaxn/kstc will be on northern fringe of 
snow area...with perhaps brief IFR visibilities. Krnh and Keau will see 
some light snow too...but should be limited in scope through the 
morning. BUFKIT soundings then shut precipitation off quickly this 
afternoon. 70h trough does sag south of the area by late 
afternoon...and will gradually end snow and lift ceilings to VFR at 
all taf sites during the afternoon. Problem area will be southwest 
Minnesota/krwf area this morning. Radar showing rather showery radar 
returns with some -fzra/-fzdz/up reported over eastern sodak. Laps 
plan view showing favorable middle level thickness moving across this 
region...as do forecast models. Will have to mention -fzdz threat 
there for a few hours. Then gradually lifting ceilings visibilities here 
during the day as well. Will likely be the slowest region to 
clear...as surface trough lags to the northeast. Moderate easterly surface 
flow will become more northerly today as surface low to the south of the 
area moves east across Iowa/Missouri region. 


&& 


Mpx watches/warnings/advisories... 
Minnesota...Winter Weather Advisory until 6 PM CST this afternoon for Anoka- 
Blue Earth-Brown-Carver-Chippewa-Dakota-Douglas-Faribault- 
Freeborn-Goodhue-Hennepin-Kandiyohi-Lac Qui Parle-Le Sueur- 
Martin-McLeod-Meeker-Nicollet-Pope-Ramsey-Redwood-Renville- 
Rice-Scott-Sherburne-Sibley-Stearns-Steele-Stevens-swift- 
Waseca-Washington-Watonwan-Wright-Yellow Medicine. 


WI...Winter Weather Advisory until 6 PM CST this afternoon for Dunn- 
Eau Claire-Pepin-Pierce-St. Croix. 


&& 


$$ 
Ls/dwe