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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
636 PM CDT Sat Apr 18 2015

Short term...(this evening through sunday)
issued at 253 PM CDT Sat Apr 18 2015

Corridor of moderate isentropic lift continues to lift northward
through the area...producing a narrow corridor of slow
moving...rainfall. Several weak convective driven shortwaves also
appear to be tied to this convection...with the strongest wave now
beginning to lift northeast from northwest Missouri. This southern wave
seems to be driving a bit more convection over Iowa/MO that in
return could lead to lower quantitative precipitation forecast in the local area. At the
surface...broad warm sector beginning across western Nebraska and
extreme SW South Dakota. Fairly cool and stable air remains
settled over the eastern half of SD/NE.

Into the afternoon/evening...high-res models doing a good job
handling this event so far suggesting that the linear band of rain
continues to lift northeast and towards the northestern edge of the County Warning Area by
00z. Shortwave energy over northwest MO should force any precipitation associated
with it to the east of the area. However...rainfall intensities
continue to drop off...so have lowered quantitative precipitation forecast for the event.
In general the highest potential for any redevelopment would be
found in the warm sector southwest of the County Warning Area. Thus...will
continue to lower probability of precipitation for this evening.

Overnight...lower probability of precipitation during the early overnight hours begin to
increase slightly late this evening and towards midnight ahead of
850mb trough axis. Models indicating MUCAPE upwards of 500-800
j/kg advecting into the areas south of I-90 late tonight. Thin
nature of cape and weak shear would not support severe
weather...but a few scattered storms or showers could be
possible. With the passage of the surface trough...would not rule out
a bit of drizzle.

Sunday...low-lvl and surface troughs will swing quickly through the
area on Sunday...with strong isentropic downglide ending any
precipitation chances quickly. Considerable cloud cover will hang
around through the day. It will also be quite windy with downward
mixing pulling wind gusts at or above 30 knots in the late morning and
afternoon.

Long term...(sunday night through saturday)
issued at 253 PM CDT Sat Apr 18 2015

Cool pattern for the upcoming week as northwest flow remains much of
the week as Hudson Bay low remains through much of the week. Breezy
northwest flow overnight Sunday night will keep temperatures from
radiating too much Sunday night. Winds will increase during the day
Monday as momentum from aloft is brought down to the surface. With
dry air mixing down from aloft...near red flag conditions return to
the region especially across the west. Will likely need to consider
Fire Weather Watch for Monday and Tuesday for portions of the
region. Across the east on Monday...could see some diurnally driven
instability showers...though models have reduced instability aloft
slightly.

Monday night and Tuesday night...temperatures get cool enough both
nights could see some front/freeze concerns across the area. With
dry dew points...am not sure how much frost there will be...so left
mention out of the forecast for now.

Winds are lighter on Wednesday...though the GFS continues to suggest
a secondary dropping south across the area during the afternoon
hours. Hard to southeast...but the European model (ecmwf) hints at something similar though
the cold air is much weaker behind the front. As such....kept
increasing winds in the cons all for the later half of Wednesday.
Certainly doesn/T look like enough moisture is available for
showers.

Dry conditions continue into late in the week. Though the winds are
are expected to fall into the 10-20 range...rhs will still be quite
low keeping the fire danger elevated through much of the week.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 629 PM CDT Sat Apr 18 2015

Ceilings are the main problematic element for the rest of tonight
and Sunday morning. Rainfall is lifting to the north as expected
and likely will not be a serious player for the rest of the taf
period. Drier air is trying to ooze northward into our area ahead
of a closed upper low near the Kansas and Colorado border. Looking
at observations upstream in eastern Nebraska and western Iowa...it
appears that conditions could go solidly VFR at least for a while
this evening despite what the humidity time sections and model
soundings are showing off of the NAM and GFS. The models would
keep our taf sites sopped in all night. The one exception to this
is khon...who could have conditions lingering in the MVFR category
for the night...and possibly even some upper end IFR this evening.
At any rate...will have to monitor all of these trends and see if
VFR does advect northward...or if the models are right and lowers
ceilings as the night progresses. On Sunday behind a cold
front...it will become quite windy with directions from the north
and northwest and any ceilings should go VFR with a very well
mixed atmosphere.

&&

Fire weather...
issued at 355 am CDT Sat Apr 18 2015

Rather light precipitation amounts west of the James River will not
help ongoing fire concerns on Sunday. Strong winds 20 to 30 miles per hour
will reach the area through the day...with relative humidity values falling near 30
percent. Will maintain a very high fire danger risk over western
fire weather zones. Further east...slightly more rain will
fall...and will lessen fire danger a bit.

Near red flag conditions expected across central South Dakota Monday
and along and east of I-29 Tuesday. Strong northwest winds of 20-30
miles per hour expected both days. With dry air mixing down from
aloft...relative humidity values are expected to fall into the 15 to
25 percent range both days.

Elevated fire weather concerns continue late into the week. While
winds are expected to be slightly less...a dry airmass across the
area will lead to minimum relative humidity values of 20 to 30
percent.

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...dux
long term...
aviation...mj
fire weather...

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