669 
FXUS63 KFSD 232055
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
355 PM CDT Thu Mar 23 2017

.SHORT TERM...(This evening through Friday)
Issued at 354 PM CDT Thu Mar 23 2017

A couple of elevated waves have generated small complexes of 
thunderstorms across far southeast SD and northwest IA today, the 
first of which produced some isolated severe hail as it tracked from 
near Yankton into areas south of the Iowa Great Lakes. The second, 
weaker complex is lifting northeast into northwest Iowa as of 20Z. 
Movement on both waves has been quite fast, on the order of 50-60kt.

For tonight, watching a line of enhancement developing on IR and 
water vapor satellite imagery from west of KONL into far northwest 
Kansas late this afternoon. As upper trough over the Rockies begins 
to kick eastward and interact with this feature, expect thunderstorm 
development in western Nebraska, expanding northeast into southeast 
South Dakota through the early-mid evening as a 40-50kt low level 
jet develops in eastern Nebraska and enhances convergence along an 
inverted trough, progged to lie from central Nebraska, toward KYKN 
and KFSD, and into southwest MN by 03Z. Unlike activity earlier 
today, for which the most high-res models were playing catch up, the 
HRRR/ARW/NAMNest, and even lower-res GFS/CMCreg are similar in their 
depiction of development through the evening. Given the increasing 
elevated instability ahead of the wave, and increased support from 
the low level jet, cannot rule out another isolated strong-severe 
storm. However, with deeper moisture becoming available, locally 
heavy rain may be a greater concern. 

Thunder threat expected to wane after 06Z as column becomes more 
moist-adiabatic, but widespread showers should continue with deep 
moisture feeding into what becomes a nearly stationary low-mid level 
front across the forecast area. Surface front does eventually push 
southeast of the area by 12Z-15Z, with 850mb front lingering near 
KSUX-KSLB line into the afternoon. This will keep potential for a 
few thunderstorms over the far southeast part of the forecast area 
on Friday, with widespread rain across at least the southeast half 
of the area as deep moisture continues to rotate northward around 
the slowing system shifting east through the Plains. With rain band 
likely to persist over the same area, certainly potential for some 
rainfall amounts in excess of an inch southeast of Lake Andes-Sioux 
Falls-Windom line just tonight and Friday. That combined with the 
more localized rainfall from today's activity could result in some 
river rises for the Lower Big Sioux and our rivers across northwest 
Iowa.


.LONG TERM...(Friday night through Thursday)
Issued at 354 PM CDT Thu Mar 23 2017

Primarily continued to follow a blend of the GFS and ECMWF for the 
track of the surface and upper low, and their corresponding 
precipitation trends for Friday night and Saturday. High pops are 
still warranted Friday night generally along and southeast of a Lake 
Andes SD to Windom MN line as a deep trowal centered in the 290-310K 
layer becomes the dominant player to the north of the wrapped up 
upper low. That said, the QPF trend on the NAM looks too heavy near 
the I 90 corridor given the degree of dry air which is beginning to 
nudge into the mid levels in that area. Therefore trended closer to 
GFS/ECMWF/WPC values for Friday night rain amounts. The 
aforementioned trowal still hangs around in northwest IA on 
Saturday. However with ever increasing dry air advecting in, pops 
will will slowly wind down in that area. All told for the rain 
event, looking at a one inch to inch and a half band throughout the 
southeast half of our forecast area, lets call it along and south of 
Lake Andes SD to Windom MN. Amounts then rapidly taper off north of 
there to just very minimal amounts in our northwest around Huron. 
This is because the track of the low across the southern and central 
plains is not friendly to that area, too much dry air in the mid 
levels cutoff from the deep moisture supply. 

By Sunday and through the rest of the forecast, the upper flow is 
very wavy. One wave moves through Sunday and Sunday night but will 
only give minimal chances for measurable rainfall. Then another 
strong upper low digs into the desert southwest by Tuesday. After 
that some moderate discrepancies still exist in the track of it 
similar to yesterdays model runs. In the large scale, the 
deterministic ECMWF and GFS are not horribly dissimilar at 500mb. But 
by mid week the ECMWF is more cutoff with the low placing the 
northern plains in a dominant northern jet. The GFS is also wrapped 
up but does bring up a greater influence of moisture into our area 
from the Gulf. Interestingly, both models bring in another strong 
upper trough on its heels along the Pacific coast by Day 7 Thursday. 
Chance pops for mainly rain brought on by warm air advection ahead 
of the aforementioned upper low are still warranted Tuesday night 
and Wednesday. Chance pops are continued to be warranted into 
Thursday as the low gets closer. But taken literally the ECMWF would 
be dry by then. At any rate, a typical spring like active pattern. 
Because of this, temperatures will be above normal but not greatly 
above normal, as the periodic waves continually knock back daytime 
highs. Highs in the mid 40s and 50s will dominate Saturday through 
next Thursday.

&&

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

$$

SHORT TERM...
LONG TERM...MJ