Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 200352
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1052 PM CDT Wed Apr 19 2017

.SHORT TERM...(This evening through Thursday)
Issued at 353 PM CDT Wed Apr 19 2017

Strong forcing along the 800-750mb boundary today has allowed
showers and thunderstorms to develop and push off to the northeast.
The axis of instability in that layer is shifting east and the
better precipitation is now across southwest MN. Th precipitation
shield is running out of instability a bit as well and lightning is
weakening. Earlier today a few slightly stronger updrafts interacted
with what was likely about 500-1000 J/kg to produce some pea to
possibly dime hail.

As the main wave continues to push through SD and Nebraska the
larger precipitation shield should continue to weaken and push off
to the northeast. However as this cooling/drying aloft pushes into
eastern Nebraska and moves across the fairly strong surface to 850mb
boundary this will likely allow some strong updrafts to develop,
however at this time the strongest updraft should be across parts of
eastern Nebraska, closer to the surface front. The latest SPC Meso
Analysis does indicate that the 850mb front runs from about SUX to
SLB so there is still a good shot for some strong updrafts as the
CAPE lifting from that boundary would still be around 1000 J/kg or a
little more with substantial shear. The main threat here would be
from about 4 pm to 9 pm.

Lower confidence on the more general rain and thunderstorm potential
across southeast SD so will need to maintain some chances through
the night as wave moves through.

Thursday will see cloud cover slow to decrease, but they should
gradually diminish in the afternoon. Highs in the 50s with a few 60s
along the Missouri River Valley.

.LONG TERM...(Thursday night through Wednesday)
Issued at 353 PM CDT Wed Apr 19 2017

Sharp upper ridge will push into the Northern plains Thursday night
with surface ridge progressively nosing in through the eastern
Dakotas, with the upper ridge gradually undercut by a strong trough
pushing through the central/southern Plains from later Friday
through Saturday. A cooler period likely with temps near normal
through Friday night. Would not be impossible to see a bit of frost
in low lying areas toward Highway 14 as temps dip toward the mid 30s
each night.

Ridge elongates and settles southward through the weekend, and trend
toward more zonal flow aloft by Sunday could allow a weak boundary
to settle toward the northern CWA.  Will be room for mixing of
slightly stronger winds in 925-850 hPa layer across northwest IA on
Saturday, but likely not more than a diurnally supported 10-20 mph.
A gradual warming trend in order, and could see a few readings into
the lower 70s by Sunday toward the Missouri River. There is at least
a low probability that temps could be somewhat warmer and humidity
lower on Sunday through the Missouri River corridor, along with a
bit stronger wind if the boundary does not settle quite as far
south. If so, fire danger could be a category or two higher,
especially if winds could increase to 20-25 mph toward south central
SD.

With flow becoming more progressive early next week, weather will
also work from the quiet mid-range to a more active extended range.
The first wave will push out of the Rockies and into the northern
Plains on Monday. Surface wave likely to develop across South Dakota
and translate to northern MN Monday night, dragging a cold frontal
boundary eastward across the area. Quite breezy from the south ahead
of system on Sunday night into Monday. As Monday progresses, fairly
strong dynamics with wave which sharpens translating eastward, but
moisture somewhat limited working southward.  Have a bit of an
afternoon and evening thunder threat, but coverage of any storms
would be quite limited.

Behind system, continued breezy northwest wind into Tuesday with a
quick dropoff in weak ridging Tuesday night in fairly good model
agreement.  Next system in zonal pattern moves quickly into the
plains by later Tuesday, on a track further southward than the
Monday system, and with main instability gradient shoved well south
closer to I-80. Increasing threat of showers heading through Tuesday
night into early Wednesday, but have left thunder out for the time.
Southward shift to features with cooler high pressure settling in
from the north suggests a period of below normal temps by Tuesday,
and especially Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1047 PM CDT Wed Apr 19 2017

Spotty drizzle has developed across portions of the area north of
Interstate 90 and may continue into the late night hours with MVFR
and IFR visibilities. Otherwise, MVFR/IFR ceilings will persist
into the late morning or early afternoon on Thursday. In addition,
northwesterly winds will increase through the morning, gusting 20
to 25 kts into the afternoon.

&&

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

$$

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


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