Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 200352

Area Forecast Discussion
National Weather Service Sioux Falls SD
1052 PM CDT Fri May 19 2017

.SHORT TERM...(This evening through Saturday)
Issued at 401 PM CDT Fri May 19 2017

Upper level low pressure beginning to lift north this afternoon. The
dry slot aloft also shifting north and helping drive the rain and
thunderstorms over north central and northeast Kansas. As the wave
lifts north the 850mb to 750mb front will intensify and should bring
some decent rainfall amounts to much of the area. Soundings do
indicate a little bit of instability so will include the mention of
isolated thunderstorms over mainly northwest Iowa. Widespread
rainfall amounts of a half an inch to an inch are expected with the
heavier amounts likely closer to the Missouri River along the
Nebraska border.

As the dry slot works north into the area on Saturday morning there
is a chance that much of the precipitation could trend more towards
drizzle. But at this time believe that with just a bit of
instability above the low level moist layer will see showery
activity. While snow is definitely not likely, it is not a non zero
chance. Temperatures aloft are pretty darn cold, especially north of
I-90 and west of I-29. Regardless, will be a very dreary day for
this late in the season with a wet ground and highs in the mid to
upper 40s.

.LONG TERM...(Saturday night through Friday)
Issued at 401 PM CDT Fri May 19 2017

Persistence to precipitation looks in order at least into early
Saturday evening, with trowal-like flow remaining back toward east
central SD. Even with the fairly strong dry punch aloft through
southwest MN and northwest IA to east of upper low centered near
KFSD around 00z, should at a minimum have a continuation of more
scattered showers or even drizzle with the shallow moist profile.
Gradually the passage of negative tilt trough axis will diminish the
precipitation threat from southwest to northeast, with stronger
northwest winds gradually taking hold through the night.

Sunday should be a breezy day with moderation to temps, especially
west of I-29 where sunshine will become a greater likelihood by
midday. Clouds cycling around deepening low pressure toward the
western Great Lakes could prove difficult to shake in parts of
southwest MN and Iowa Great Lakes area even toward evening. As a
result, highs will likely vary from some mid to upper 50s east of I-
29, to upper 60s from the James River valley westward.

The next period of active weather will develop Monday as a strong
lobe wraps around the upper wave and swings through the Dakotas
during the afternoon and early evening.  Convergence looks to be a
bit weak along the boundary with mainly west to southwest winds
ahead and north to northwest behind the front, but still should be
good enough to pool some near 50 dew point readings despite small
prospect for meaningful moisture return. With cold temps aloft,
still expect to see perhaps 700-1000 J/kg surface-based instability.
Shear is probably most questionable, but mainly linear with west to
northwest flow aloft.  If boundary can time out close enough to the
diurnal cycle, would not totally rule out the threat for perhaps an
isolated severe storm in a small window Monday afternoon toward the
lower Missouri valley and into northwest Iowa.

Tuesday remains under influence of cold temps aloft and perhaps
another lobe wrapping around the upper low, suggesting chances
for scattered showers. Temps in profile do not appear cold enough
to warrant an isolated thunder mention.

Wednesday and Thursday at the time look to remain dry, with temps
moderating considerably as upper ridge displaces trough enough to
allow low level winds to shift around to south/west.  Raw model
temps are much warmer than initial blends, which fail to even reach
isothermal values from 925 hPa other than for colder Canadian
global.  Therefore, have worked in some warmer temps, but perhaps
not as warm as needed for Thursday.  Differences in models grow
drastically on Friday, with ECMWF exhibiting strong trough across
Minnesota with GFS a broad ridge. Ensembles are fairly tight and
suggest ECMWF may be a bit aggressive both timing and amplitude.
Therefore, have blended in a little heavier weight to warmer subset
of solutions, and kept in the small chance for precipitation.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1045 PM CDT Fri May 19 2017

Rain showers will continue to lift northward through the region,
spreading across the entire forecast area through 12z. MVFR
ceilings will likewise continue to spread northward, with some
ceilings below 1000 ft agl likely developing late tonight through
much of the day Saturday. Visibility will also be reduced,
dropping to 1 to 2 miles at times in rain. Rain showers will last
through the TAF period, but there will be a gradual decrease from
the south Saturday afternoon and evening.




LONG TERM...Chapman
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