Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 192327

Area Forecast Discussion
National Weather Service Sioux Falls SD
527 PM CST Sun Nov 19 2017

.SHORT TERM...(This evening through Monday)
Issued at 343 PM CST Sun Nov 19 2017

The upper flow will be fairly zonal both tonight and Monday. With
surface high pressure extending throughout the Gulf Coast states,
and a large area of low pressure moving eastward across southern
Canada, the surface winds will continue out of a southwesterly
direction. Conditions will be dry with only passing high clouds, and
with the southwesterly flow of air, temperatures will be mild for
this time of year. Lows tonight will be substantially warmer than
Saturday night`s temperatures, with 925-900mb temperatures mixing to
a balmy lower 50s to lower 60s across the forecast area.

.LONG TERM...(Monday night through Sunday)
Issued at 343 PM CST Sun Nov 19 2017

Strong upper low is still on track to move southeastward Monday
night and Tuesday into the Great Lakes region. 1030-1035mb high
pressure will be following in its wake pushing a cold front
southward. Due to increasing northwest winds, consensus lows looked
pretty good Monday night in not allowing temperatures to fall too
much due to mixing. Therefore lows will vary from around 20 in our
northern zones, to near 30 close to Sioux City. However cold air
advection will continue to pour in through midday Tuesday before
stabilizing. So we are looking at temperatures only rebounding
around 5 degrees off of the lows for afternoon highs. Increased
surface winds above superblend values by blending in mos values.
Tuesday will be a windy day, with 25 to 35 mph speeds common east of
I 29, and a bit less along and west of I 29. With the surface ridge
passing across the plains Tuesday night, the winds will dramatically
decrease helping to produce the chilliest temperatures for the
upcoming week. Used a blend of bias corrected mos and raw model
values to cool off superblend lows which looked a little too warm.
The one exception is in our far southwest across south central SD,
where a return flow of southerly air should keep their temperatures
from falling much after midnight.

On Wednesday and early Wednesday evening, a jet streak coupled with
a warm front will move eastward. Moisture is a little starved in the
lowest 2km, so that should keep much of our forecast area free of
precipitation. The one exception is in our far northeast zones
around Brookings and Marshall where moisture depth is a little
deeper along the warm air advection. So low pops are warranted for
those locations Wednesday afternoon for very light snow or a light
rain/snow mix.

Building heights will then be in store as an upper ridge of high
pressure strengthens over the southwest United States. 925mb
temperatures in particular are very warm on Friday as a short wave
moves into locations north of our CWA in the afternoon. Just south
of this short wave, 925mb temperatures of +9C to +14C are very
common in our forecast area. Therefore continued the trend of
raising superblend highs by blending in raw model values and some
bias corrected ECMWF. The one exception is in southwest MN and
around the Brookings area, where cloud cover late in the day with
moisture between 850 and 700mb may hinder highs there a bit. But
still, even our northeast zones will likely have highs in the mid
50s, with upper 50s and lower 60s elsewhere. After this short wave
moves eastward, temperatures will cool again for the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 527 PM CST Sun Nov 19 2017

Surface winds quickly decrease this evening. Above the surface
inversion at about 1000 ft AGL, west-southwest winds of 20 to 25 kts
could bring a bit of low-level wind shear (WS010/24025KT) through
20/1200z. This is below thresholds for inclusion in TAFs, but worth
a brief mention. Some high clouds will move through overnight and
Monday, but minimal weather impacts are expected for aviation
operations over the next 24 hours.




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