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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 75 °
• Low: 55 °
• Clear

• Tuesday
• 
• High: 84 °
• Low: 63 °
• Partly Cloudy

• Wednesday
• 
• High: 82 °
• Low: 63 °
• T-Storms

• Thursday
• 
• High: 75 °
• Low: 55 °
• Chance of Rain

• Friday
• 
• High: 75 °
• Low: 59 °
• Partly Cloudy

Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
845 am CDT Monday may 21 2012 


Discussion... 
have updated forecast to increase middle level clouds associated with 
middle level warm air advection across County Warning Area today. Will generally be 
partly to mostly cloudy this afternoon. Did lower temperatures a 
degree or two due to the clouds. Also added a few spriknles across 
western County Warning Area this morning. 


&& 


Aviation.../for the 12z taf issuance/ 
VFR conditions will continue through the taf forecast period. A 
few altocumulus castellanus showers have developed West River but as they're moving 
east...they have weakened quite a bit. So may see a few middle level 
clouds drifting over taf locations as a result. South winds will be 
increasing after 20z as gradient begins to tight and high pushes off 
to the east. 


&& 


Discussion.../issued at 316 am CDT/ 
should be a quiet day with moderating temperatures as a southerly 
wind develops. High lapse rates aloft this morning may support some 
altocumulus castellanus in central South Dakota but better lapse rates remain west of 
the County Warning Area today so expect dry air below 750mb to keep any brief rain 
threat at Bay. Otherwise...partly cloudy conditions with winds 
becoming breezy in central South Dakota. Highs should mainly be in 
the 70s with a few lower 80s in south central South Dakota. 


Will maintain a low pop for tonight as lapse rates and instability 
increase a bit...possibly enough to spark off a shower or 
thunderstorm...nothing severe. With a strongly increasing southerly 
breeze did go ahead and raise lows a couple of degrees...something 
closer to the consraw output which does better under strong flow 
regimes. This means lows from the upper 50s to middle 60s. 


This will lead into a very warm Tuesday with very strong southerly 
winds. Will not issue a Wind Advisory at this time but will likely 
need to issue one this afternoon. Expect south winds of 20 to 40 miles per hour 
through most of the day. Decent mixing should also support highs 
from the middle 80s to lower 90s...and would not be surprised if we can 
warm a couple more degrees beyond this. 


Will see a chance for thunderstorms over mainly the northern and 
western County Warning Area on Tuesday night...but severe weather is not expected. 
Looks like the better instability will remain bottled up to the 
west. Very strong south winds will continue which should yield lows 
in the middle 60s for most locations. 


The best chance for thunderstorms will come late Wednesday afternoon 
into Wednesday night as a boundary sets up over the southeast County Warning Area. A 
fairly strong middle level wave will spread across the area on 
Wednesday night so a very good chance for rain and thunderstorms. 
Expect cape values of 1500 to 2000 j/kg over northwest Iowa on 
Wednesday night and with decent deep 40 knot or so bulk shear values 
some severe weather will be a threat. Also some potential for heavy 
rain with the boundary setting up parallel to the upper level flow 
and precipitable water values likely around an inch and a half or a little 
higher. 


Will see some threat for rain and thunderstorms linger into Thursday 
but not looking like a major threat. Expect cooler temperatures with 
highs from the upper 60s to middle 70s. 


In the latter periods(fri/sun)...some agreement during this time 
with the better agreement between the European model (ecmwf) and Gem. The main 
feature will be a digging trough of low pressure over the western 
United States and a strengthening ridge over the eastern United 
States. Friday night into Saturday morning the biggest difference 
with the GFS quite a bit cooler than the ec/Gem. Will side a bit 
towards the warmer models but have to temper that back a bit with 
some lack of confidence. Will be a decent threat for precipitation 
through this entire period...and may at some point in time need to 
increase probability of precipitation for Friday night if models continue to trend in the 
current direction. Basically looking at 70s on Friday with boundary 
to the south...then 80s Sat and sun as the boundary shoots 
northward. The ec/Gem support 90 to 95 degrees on Saturday in my 
southern County Warning Area so will need to watch for the trends in the models and 
may need to go warmer on Saturday. /08 




&& 


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


&& 


$$