AFOS product AFDFSD
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Displaying AFOS PIL: AFDFSD
Product Timestamp: 2017-10-03 11:01 UTC

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931 
FXUS63 KFSD 031101
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
601 AM CDT Tue Oct 3 2017

.SHORT TERM...(Today and Tonight)
Issued at 418 AM CDT Tue Oct 3 2017

Impressive upper level jet lifting north through the Western High 
Plains with a broad area of showers and thunderstorms to the east. 
While there were a few severe storms late yesterday afternoon, the 
main focus of this event was heavy rainfall. The exception was a 
small cluster of storms that moved quickly enough to overtake the 
surface front around Sibley and Bigelow around 230 am. A few shallow 
vortices, a couple pretty strong, developed but then weakened 
pretty quickly. Interestingly on the water vapor and IR loops a 
small area of subsidence developed near the Big Sioux River 
between FSD and SUX and shifted east about 15 minutes before the 
stronger updraft developed and the better wind signatures showed 
up.

As this strong upper level jet lifts north the showers and 
thunderstorms will continue to weaken and shift east. Residual mid 
level moisture may allow a few showers to continue into the morning 
hours but coverage will quickly dwindle by late morning. Model 
soundings suggest that cloud cover will quickly erode through the 
day so that partly cloudy skies are expected by afternoon. However 
with a cool air mass in place highs will still only be in the 60s.

High pressure will settle down the Missouri River Valley late 
tonight and allow light winds to develop in south central SD. While 
widespread frost is not expected, patchy frost in low lying areas is 
possible. No advisory at this time but something to keep an eye out 
on. Lows should vary from the mid 30s in central SD to the mid 40s 
in northwest IA.

.LONG TERM...(Wednesday through Monday)
Issued at 418 AM CDT Tue Oct 3 2017

Tail of upper jet pulls away on Wednesday through the northern Great 
Lakes on Wednesday, allowing ridging aloft to become reestablished 
across the region. Surface ridge drifting across the area will 
provide a dry and pleasant day, just a bit cooler than normal. 
Gradually through Wednesday night, elevated warm advection will 
strengthen and will likely see scattered showers build northeastward 
across the Missouri River in the later night hours. Indications are 
there would be several hundred J/kg of elevated instability, so 
perhaps even a few thunderstorms as far north as I-90, but much more 
coverage potential toward northeast Nebraska and far southern 
portions of northwest Iowa.  Threat for showers and storms will 
continue Thursday, more prevalent further south of I-90, in zone of 
persistent isentropic lift.  Main warm front at surface will be tied 
up closer to I-80, and this will leave a largely cool, cloudy and 
dreary day to the north, with temps at best into the lower 60s.

A little more agreement today on handling of the hangback energy 
across the western U.S. from early this week, that begins to pull 
eastward as a sharp upper trough Friday into early Saturday. High 
precipitation probabilities remain favored with persistence of 
moisture transport and the increasing large scale lift ahead of 
trough through Friday evening.  Will have to watch for some areas of 
heavy rainfall again for Thursday into Friday, as moisture content 
of the airmass will be fairly high and sets up an efficient 
overrunning pattern with main low-level front hanging up to the 
south.  

Precipitation should end fairly quickly Friday night into early Sat. 
from west to east with sharp nature of lift forcing with the short 
wavelength trough. Saturday looks like the warmest day of the next 
seven, with southwest flow quickly rebounding with increasing 
sunshine during the day.  The turn to west/southwest flow is a 
result of the next upstream large-scale trough which is forecast to 
dig into the northern Plains through early next week. Models have 
some differences in when the more significant cooling occurs with 
various energy swinging through the large scale trough. For now, 
have settled on the blended guidance which falls in line with a 
secondary system dropping in later Sunday night or early Monday, 
with just a small chance for a shower along trough axis. Some of the 
models suggest colder air would bring along risk of first more 
widespread frost threat by the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 558 AM CDT Tue Oct 3 2017

MVFR and IFR ceilings will shift east this morning along with the
rainfall chances. A small chance for thunderstorms will be in
place through about 14z in parts of northwest IA. Otherwise after
about 18z some diurnal cumulus clouds mostly from 3000 feet to
5000 feet are expected, then clearing overnight.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...08
LONG TERM...Chapman
AVIATION...08