Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 150333

Area Forecast Discussion
National Weather Service Sioux Falls SD
1033 PM CDT Mon May 14 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 347 PM CDT Mon May 14 2018

At this time, 700mb short wave is swinging through our eastern
zones, extending from south central MN to east central NE by 00Z.
Associated with this wave is an 850mb wind shift. The two items are
helping to create widespread showers at this time in southwest MN
which will slowly usher eastward along the short wave. Many other
locations along and east of I 29 are warranted only small pops
through the evening hours as the low level southerly flow shifts
eastward. In addition in our far western zones in central SD,
isolated pops for TSRA are warranted late this afternoon as their
temperatures are very close to their convective temperatures.
Overall, clouds will begin to clear out overnight except there is
still quite a bit of moisture bottled up in the 850-700mb layer in
our far southern zones around Sioux City and Storm Lake through the
night. Would not even rule out a small, isolated light shower around
Sioux City late tonight as the high resolution models are showing a
very weak wave in the mid level streamlines in that area moving
rapidly southeastward. Finally, Tuesday looks like a rain free and
pleasant day as a surface ridge of high pressure extends into our
area from the Great Lakes region. Clouds should clear out of
northwest Iowa in the morning hours, leaving a mostly sunny sky at
all locations by afternoon. Given model 850mb temperatures, trended
toward warmer bias corrected readings for Tuesday producing high in
the mid to upper 70s, perhaps even 80 at Sioux City. Tonight`s lows
should be cooler then past nights with cloud cover beginning to
trend downward except again for our southern zones.

.LONG TERM...(Tuesday night through Monday)
Issued at 347 PM CDT Mon May 14 2018

It appears the forecast area will continue to be dry Tuesday night
and Wednesday. There is a subtle upper ridge of high pressure moving
slowly eastward across the plains, with winds becoming southerly by
Wednesday as the surface high moves off to the east. Wednesday
should see highs in the 80 to 85 degree range.

Wednesday night and Thursday things change a bit. The various
deterministic models are showing a short wave moving eastward across
North Dakota. The low level jet is not very strong feeding into this
wave in our area, but a few showers and thunderstorms may form
southward into the southerly flow and move across the CWA from west
to east over a subtle instability axis. Certainly no washout is
involved anywhere, and highs once again will be in the 80 to 85
degree range.

Late this week still looks quite unsettled. A large upper trough of
low pressure continues to press eastward through the intermountain
west and the first leading short wave moves northeastward late
Thursday night. This wave may impact our western zones more than our
east given its current track, with showers and storms then moving
into the central portions of our forecast area Friday morning. A
second and stronger short wave then moves eastward Friday night
probably producing a soggy night for much of this area. On its heels
is a pattern shift in which a northwest flow aloft develops and
moves southward from Canada. This will usher through a wind shift to
the north late Friday night and Saturday, blending the ECMWF and GFS
for timing as the GFS is faster when compared to the ECMWF. Only
chance pops are warranted at this time for Saturday and we will have
to watch the highs on Saturday as currently they may be
substantially too warm. Would not be surprised if they corrected
cooler as the days progress coming up.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1027 PM CDT Mon May 14 2018

Winds will be nearly calm overnight, and cannot rule out patchy
fog in areas mainly east of Interstate 29. Confidence is low so
did not include in TAFs at this time. Guidance is also suggesting
possible stratus development later tonight over parts of
northwestern IA, which could affect KSUX early Tuesday morning.




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