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fxus63 kfsd 191559 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
1000 am CST Wednesday Nov 19 2008 


Discussion... 
cold air advection stratus has moved as far S as i90 as of 16z and will continue to push 
southward this afternoon reaching sux by middle afternoon. High temperatures in the stratus 
have pbly already been reached so will tend to hold temperatures steady north of 
i90. Further S...highs will pbly occur by middle afternoon and then slowly 
fall after stratus moves in. Should be a wndy day with gusts to 30 to 
35 miles per hour out of the north. 


&& 


Aviation... 
widespread MVFR ceilings along at north of i90 at 16z will spread S to sux by 21z. 
Should then generally remain MVFR ceilings through 12z Thursday. 


&& 


Previous discussion... 
complex forecast this go around...starting right away in the near term. 
Stratus is coming down like a ton of bricks very rapidly with the 
cold front...and is currently already to the ND/South Dakota border at this time. See 
nothing to stop it as cold air advection pours in today...however am banking on 
some of it mixing out as it heads southward. Relative humidity time sections are 
extremely dry above h9-h85. So it is plausible that many locations 
could eventually see some breaks. If that does not happen...our County warning forecast area 
will just be mostly cloudy to cloudy nearly all day with maximum temperatures 
then in jeopardy. As it is...there is enough cold air advection that many locations 
may see a late morning to midday maximum temperature before falling. Most of 
the County warning forecast area mixes to h9 today...and relied heavily on the nam40 h9 
temperatures for temperature readings through the day. H9 temperatures at Marshall Minnesota begins 
to tank right away. Hopefully they will spike up to the lower 40s 
early this morning after daybreak. Because if they do not...they may 
just slowly fall through much of the day. Dayshift will really have to 
watch the clouds and temperatures. It is also quite windy off the surface at 
h9...giving what should be another breezy to windy day for this forecast area. 


Chilly Canadian high pressure begins to really takeover tonight and 
Thursday. Relative humidity time sections show all of the moisture continuing to be 
bottled at or below 850 mb...with very dry air above it. Am banking on a partly 
to mostly cloudy sky...and hope that the high relative humidity values are not just 
an artifact of cold air. In addition...both the NAM and GFS continue to 
be in good agreement in bringing down a vorticity filament late tonight 
and Thursday in this area which should keep things stirred up. 
Therefore left the mention of flurries in the forecast with very chilly 
temperatures off the surface and llv steep lapse rates. Our going lows tonight 
and maximum temperatures on Thursday still look good and tweaked very little. 
Thursday most locations should once again mix to around h9. 


Surface ridge begins to slide off to our east Thursday night...greatly 
decreasing our winds. Any remaining stratocu should rapidly dry up 
promising our coldest night of the season so far. 


However return flow begins right away later Thursday night in 
advance of the next upper low. GFS...Gem and European model (ecmwf) have finally come 
around in pretty decent agreement with the placement of this feature 
as it tracks eastward Friday and Friday night. The NAM is off on its own 
with its southerly track and was ignored. The bulk of the main portion of 
the wave appears to move through our forecast area at this time...with a strong left exit 
region of the jet present...especially on Friday. GFS moisture profile is 
interesting...in that a very deep moisture layer comes in very quickly 
and sharply. Therefore early in the day...our SW corner should be 
mostly cloudy...with stone clear skies in our east. As the llv southeast 
flow increases on Friday...isentropic lift becomes quite strong and 
deep along the advancing surface warm front...with pretty strong 
frontogenesis around 800 mb-h75 per the GFS. All things being 
considered...began to raise probability of precipitation through most of the fsd forecast area on Friday... 
then tapering them off from west to east Friday night as the upper low 
departs. Maximum temperatures are tricky on Friday. Believe that many locations 
may not reach their daytime high until early evening. It will take a 
while for locations to warm up coming off of the cold min temperatures 
early Friday...especially with some snow anticipated and at the least 
rapidly increasing clouds. Because of this...cooled off some maximum 
temperatures especially in the favored areas such as the James River Valley and SW 
Minnesota...where southeast winds never do those locations any favors. For snow 
amounts...would not rule out a quick 1 to 3 inch event for many 
areas of the County warning forecast area. If the event would last longer...amounts would be 
heavier but it looks to be a rapid mover. 


&& 


Fsd watches/warnings/advisories... 
South Dakota...none. 
Minnesota...none. 
Iowa...none. 
NE...none. 


&& 


$$