Weather

636 
fxus63 kfsd 102045 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
330 PM CDT Friday Oct 10 2008 


Discussion... 


Strong thermal contrast across the County Warning Area today with areas along the 
northern tier stuck in an east northeast flow. This has kept 
temperatures from rising much...while south of this front winds have 
swung around to the south and temperatures have popped up into the 
70s. Expect this front to continue to play a roll into tonight with 
cooler and cloudier conditions behind and very mild conditions 
ahead. Will aim for lows of 40 to 45 behind the front...mainly from 
the James Valley west with lows in the lower to middle 50s ahead of 
the front. 


Rain chances not looking too good for tonight as we are between 
systems for the first half of the night. It looks like some upper 
level support...which is currently over western Colorado...could spread 
northeast and spark some middle level shower activity. Expect this to 
remain west of the James River and will carry a chance out there. 


The surface boundary/inverted trough will continue to be the focus 
of weather through the weekend. Rather difficult to nail down exact 
timing of best precipitation with weak impulses interacting with the 
front through the period...but may see a break in the showers in our 
west early on Saturday morning before Theta-E increases over the 
area in the afternoon. Still anticipating a tight thermal gradient 
across the County Warning Area...with middle 50s in the far west to middle 70s in our 
southeast. Better chance of showers and thunderstorms will come in 
on Saturday night...with isentropic lift/Theta-E increasing under a 
strengthening low level jet as another shortwave lifts out of 
Colorado. With this process...boundary actually seems to push back 
to the west with increasing southerly/southeasterly low level flow 
in response to strengthening low pressure over Colorado. With this 
process and increasing winds on Saturday night...looks to be a 
pretty mild night for this time of year...with readings in the west 
remaining close to saturdays highs...and temperatures in the east 
only falling to around 60. 


With the upper level low finally moving out of The Rockies on 
Sunday...will finally begin to see the surface front pushing 
eastward. Temperatures are of course tricky...highly dependent on 
position of front at that time. Because of this...guidance differs 
by some 10 to 20 degrees on Sunday afternoon...anywhere from the 60s 
to the 80s...but compromised and went for the 60s and 70s. With a 50 
knots low level jet over our County Warning Area on Sunday...a lot of moisture will be 
advecting into the region out ahead of the front...and almost a 
certainty that the area will see rainfall. May see some heavy 
rainfall with the system as precipitable water amounts will be nearing 2 inches over 
the Central Plains early on Sunday...and it is this moisture that 
will be pulled northward. Remains to be seen where exactly the heavy 
rain will fall. With a tight pressure gradient over the region...and 
the aforementioned strong winds aloft...will be a pretty windy day. 


Front only moves very slowly eastward however...not exiting our 
southeastern zones until Monday afternoon. Much cooler air will be 
coming in behind the system...with highs on Monday in the 50s across 
the County Warning Area. Models begin to differ on the upper level pattern after 
this...with GFS taking the upper level low into Canada by 
Tuesday...with precipitation ending over our area on Monday night. 
The Canadian and European model (ecmwf) hang southern stream energy back to our 
southwest...which brings additional precipitation to our eastern 
areas on Tuesday into Wednesday. For now...did not jump on this 
wholeheartedly...but did keep small probability of precipitation in our southeast for 
Tuesday. 


In the extended...Wednesday through Friday. Will see a slow warm 
up...to about close to normal for this time of year. Models hinting 
at the possibility of another system coming in for the Thursday time 
frame...though left dry for now with uncertainty. 




&& 


Aviation... 


Hon will be the trickiest location with low end VFR and 
high end MVFR ceilings likely behind the front. Hon should stay 
behind this front tonight...so plan on some ceilings of 1500-2500 
feet after 6z. May also see a few showers late in the period. 
Otherwise...expect occasional VFR ceilings at both fsd and sux. 


&& 




Fsd watches/warnings/advisories... 


South Dakota...none. 
Minnesota...none. 
Iowa...none. 
NE...none. 


&& 


$$ 


Public...jm 
aviation...08