527 
fxus63 kmpx 072149 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
349 PM CST Wednesday Jan 7 2009 


Discussion... 


High pressure will build southward across the eastern Dakotas and 
Minnesota overnight with mainly clear skies...diminishing wind 
and temperatures dropping below zero across much of the Minnesota County Warning Area. 
Thursday will get off to a nice start...but then deteriorate from 
west to east Thursday night as a short wave and low pressure system 
approach from the west. Plenty of concerns with this system 
Thursday night and Friday. The trend from todays model runs was 
for a slower...stronger and farther south solution. This has really 
diminished the elevated warm layer with only the far SW and south 
central indicated as having the potential for freezing rain/sleet. 


In the end...the 15z sref is a good compromise between the 
NAM/GFS/ECMWF and Canadian. This would have a surface low tracking 
southeast across the Dakotas Thursday night and across Iowa and northern Illinois 
on Friday. Strong low/middle level warm air advection would precede the low Thursday 
night with snow developing rather quickly in the west and 
spreading east and south overnight. On Friday...a strong but open 
wave at 700 mb would track southeast across the County Warning Area. This coupled with 
middle level frontogenesis...near negative epv and Omega maximized 
near preferred snow growth temperatures is leading US into heavier 
snow amounts for this system. Therefore...increased probability of precipitation into the 
categorical range for late Thursday night and Friday morning for 
much of the County Warning Area. In fact...we now have a 4 to 5 inch snow 
accumulation forecast by late in the day Friday along and just 
south of the I-94 corridor. Sref plumes would suggest a mean of 
35 inches of quantitative precipitation forecast for kmsp. If one took away a few of the low/high 
members...there is a pretty good clustering in the 0.45 range. 
This amount coupled snow ratios that average 14:1 would put US 
over 6 inches. Confidence not high enough for a watch as the NAM 
led the way on being the deepest along with the most quantitative precipitation forecast. The 18z 
NAM is already backing away from its 12z solution. 


In the wake of this system...ridging aloft will build over western 
North America with troughing for the east. 500mb heights by early 
next week 2 Standard deviations above normal in the west with 
heights nearly 300m above normal. Anomalous flow from the positive 
center in the west and the negative center in the east has flow 
coming almost due south from the North Pole. A clipper is still 
shown to pass through during the latter half of the weekend. Kept 
small chance for snow in Saturday through Sunday with Saturday 
night looking the best at this time. The trend for next week is for 
substantial high pressure to build slowly south into the northern 
Continental U.S. For the week. Bitterly cold temperatures in store with 
several days in a row staying below zero becoming more and more likely. 


&& 


Aviation... /18z taf issuance/ 
conditions beginning to improve across the area...especially over Minnesota. 
Snow is still lingering across Wisconsin with eau and rnh still 
reporting occasional snow...as they are still within the cyclonic 
flow associated with a low moving across the eastern Great Lakes. 
Cold air is pushing into the area and as it comes in from the 
Dakotas skies are clearing out...as has occurred already in axn 
and rwf. High pressure will slowly nose in from the Dakotas 
through tomorrow...allowing winds to remain 10 kts or less across 
the area. Once the snow moves out of west central Wisconsin this 
afternoon...not expecting any more precipitation until after the 
valid taf period. Visibilities and ceilings should also remain VFR 
from 00z tonight on...with most cloud cover holding off until 
after 18z Thursday...even for the western terminals. Feel models 
are holding on to low level moisture for too long and based on 
current trends decided to clean things up much earlier than models 
would like. 


&& 


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


$$ 


Rah/mg/trh