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Area forecast discussion 
National Weather Service Topeka Kansas 
530 PM CST Sat Nov 21 2009 


Update... 
update for 00z aviation. 


&& 


Discussion... 
see previous discussion. 


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Aviation... 
tough forecast cloud/visby wise overnight. Southeasterly flow 
continues at all taf sites...as does a stream of clouds out of the 
south southwest currently over ctrl Kansas and bringing MVFR ceilings to 
the area. Models and satellite trends indicate some decreasing 
dewpoints in the eastern portions. However all models suggesting 
some kind of inversion to develop around 1500ft. At this time 
think trapping of moisture and clouds under this inversion will 
keep MVFR ceilings going with some reductions to visby as temperatures 
slowly fall. Have kept sites clearing up 15z and beyond. At this 
time atmosphere seems too mixed for fog potential but saturated 
enough for haze. 67 


&& 


Previous discussion... /issued 302 PM CST Sat Nov 21 2009/ 


Discussion... 


Short term (through sunday)... 


Pressure gradient has tightened up over Kansas this afternoon in 
response to a Lee trough. Despite cloud cover...southerly winds and 
some warm advection has allowed temperatures to rise into the upper 
50s and lower 60s. While low level moisture is in place and 
producing the cloud cover...deep moisture and lift are quite limited 
and no precipitation is anticipated. 


It appears that low level moisture will hang on into tomorrow 
morning while the middle and upper levels of the atmosphere remain 
relatively dry. It is not the greatest fog setup...but won't be 
surprised to see some patchy morning fog and perhaps a bit of 
drizzle as well. Low temperatures should stay warmer than last night 
with the slightly warmer airmass and likely cloud cover. 


Short wave trough energy will swing across the plains on Sunday with 
some enhanced middle level lift due to positive vorticity advection and jet divergence...but it 
appears that deep moisture will remain limited. Rain chances will be 
slightly better to the north over Nebraska while Kansas should stay 
primarily dry with a chance for some morning drizzle. High temperatures 
will be similar to today but possibly a degree or two warmer as 
there should be a bit more sunshine. 


Barjenbruch 


Long term (sunday night through Tuesday night)... 


Sunday night through Tuesday night...an upper level trough will dig 
southeast from the Pacific northwest across the Central Plains on 
Monday night and Tuesday. Both the NAM and ec dig the upper level 
trough farther west across the Central High plains then across 
northern Kansas into southern Iowa Monday night and Tuesday. While the 
GFS has a more northern track...digging the 500 mb trough southeast 
across the Central Plains into central Iowa. At this time...i'm leaning more 
towards the NAM and ec track...this will provide much of the County Warning Area a 
chance for light rain developing along the Pacific cold front late 
Monday afternoon and with enough ascent ahead of the upper trough 
to keep light rain chances through Tuesday. It may get cold enough 
aloft and at the surface for some of the rain across the northern 
counties to become mixed with or change over to snow late Monday 
night into Tuesday morning. The best area for heavier snowfall 
will be across central and eastern NE along the deformation axis 
on the northwest side of the upper low where frontogenetical 
forcing will be maximized...along with the better trowal 
formation. I did not place in any snow accumulations across north 
central Kansas at this time...but if the transition over to snow is 
quick enough Monday night there may be the potential for a inch or 
two of wet snow...but surface temperatures should remain at or above 
freezing Monday night. 


As the 500 mb trough lifts east and northeast across the Midwest Tuesday 
afternoon...we should see the wrap around precipitation end from southwest 
to northeast across the County Warning Area through the afternoon hours. Low-level 
cold air advection...cloud cover and periods of showers on Tuesday will cause 
temperatures to be much cooler with highs in the 40s. 


Wednesday through Friday...a longer wave-length upper level trough 
will develop across the east central Continental U.S.. this will keep eastern 
Kansas under northwest flow aloft with most of the precipitation remaining well 
north and east of the County Warning Area. Highs will continue to be cool with middle 
40s to lower 50s. Overnight lows will be in the middle 20s to lower 
30s. 


Saturday...temperatures may warm up again as a downstream upper 
ridge amplifies over the plains and low-level winds become 
southerly. Highs Saturday will reach the middle 50s to lower 60s...may 
be a bit warmer is skies are mostly to partly sunny. 


Gargan 


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Top watches/warnings/advisories...none. 


&& 


$$