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Area forecast discussion
National Weather Service Sioux Falls South Dakota
638 PM CDT Wednesday Apr 23 2014
Short term...(this evening through thursday)
issued at 406 PM CDT Wednesday Apr 23 2014
Active forecast in the short term with warm and windy conditions
ahead of surface trough working east through the forecast area
tonight. Short term hi-res models suggest storms trying to develop
late this afternoon across north central Nebraska as short wave
energy increases in the middle levels and upper level divergence q increases
as a series of jet impulses move across the area. Cumulus field
already developing further to the south across south central
Nebraska where moisture is more prevalent. Expect this area of
convection to expand and lift northeast overnight into eastern
portions of the forecast area. With slow moving boundary...could
see some training of storms especially along and east of Highway
60. This could result in some good rainfall amounts as
precipitable water values surge above one inch...which is above
two Standard deviations above normal.
Front works east Thursday morning and mixy northwest flow is
expected to develop. With dry conditions as of late and limited
moisture expected across South Dakota...have opted to issue a red
flag warning for locations currently under Fire Weather Watch.
Considered adding east central South Dakota zone...but opted to hold
off for now as mixing is not as strong there. Also considered
adding Sioux City zone...but held off for now as rainfall amounts
will likely have an impact on relative humidity values Thursday afternoon. Still
looks like a very mixy day across the west with unidirectional flow
and strong heating mixing to near 700 mb. Have kept dew points
below guidance values to account for dry nature of air mixing down
from aloft...which is expected to produce relative humidity values of 15 to 20
percent along and west of I-29 tomorrow afternoon. With upper level
low lingering in Minnesota much of the day Thursday...expect clouds
to reduce mixing some and thus kept highs in the lower 60s there.
Long term...(thursday night through wednesday)
issued at 406 PM CDT Wednesday Apr 23 2014
Models showing much better agreement in a bringing a mild day to the
area for Friday. With the exiting trough quickly shifting into the
Great Lakes and the next trough digging over the West
Coast...ridging builds over the forecast area. Skies will be mostly
sunny to partly cloudy with northwest winds generally less than 15
miles per hour. Warmed highs into the middle 60s to middle 70. While warm and dry
conditions are expected...fire danger will not be as high as
Thursday given lighter winds and slightly higher dewpoints.
Saturday will be dominated by strong southwest upper level flow with
the Pacific trough moving into The Four Corners region and the ridge
nudging eastward. Moisture and clouds will be on the increase
through the day while east southeast winds low level winds increase.
Temperatures do look milder than previous model runs...but will be
capped some with increased cloud coverage and easterly surface
winds. Highs should still manage to reach the upper 50s in southwest
Minnesota to near 70 in northwest Iowa.
Unsettled weather pattern sets up for the first half of next week as
the Pacific trough emerges into the plains and slowly wobbles
eastward. Long range models are actually coming into better
agreement with the track and timing of this feature...although there
remains some minor differences. An upper level cut off low moves
into western Kansas by Sunday afternoon then tracks in a generally
eastward motion into Missouri by Monday night. The European model (ecmwf) is a bit
slower than the GFS in kicking this low into the Great Lakes/Ohio
Valley which could keep unsettled weather in the picture well into
Wednesday night or Thursday...however did follow more of a GFS
timing solution for now. Moisture plume with warm air advection will
bring scattered to likely showers and thunderstorms Saturday
night...becoming likely area-wide Sunday into Sunday night. Surface
low center passes south of the forecast area Sunday night and
Monday...which will tap into some cooler temperatures moving into
the start of the work week...but persistent moisture and lift with
this system will keep clouds and occasional rain in the picture.
Highs will only top out in the middle 40s into the 50s Monday and
Tuesday. Following the GFS...have tapered off the precipitation by
Tuesday. Temperature profiles remain warm enough for entirely
rainfall at this point.
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 638 PM CDT Wednesday Apr 23 2014
Thunderstorms developing across northeast Nebraska this evening.
Based on current timing expect them to reach ksux around 01z.
Expect MVFR conditions to develop as rain expected to persist for
a few hours as storms continue to develop near the surface
boundary. For kfsd...weak convection trying to develop near the South Dakota
and NE border would reach kfsd between 02z and 03z. Not confident
this will organize. Instead...rain and storms may wait until the
boundary is closer. Current thinking is closer to 04z. Instability
is much less but enough for thunderstorms for a couple of hours
prior to 06z. After that light rain likely to continue through
late tonight. For both kfsd and ksux...expect precipitation to end by 12z
with VFR conditions developing. No precipitation expect at khon at this
time. As for winds...front moving through will result in
decreasing winds this evening with a switch to northwest overnight.
Tomorrow northwest winds will really pick up again with sustained
winds near 20 kts and gusts approaching 30 kts.
South Dakota...red flag warning from 1 PM to 7 PM CDT Thursday for sdz255-256-
Wind Advisory until 8 PM CDT this evening for sdz040-055-056-062-
Minnesota...Wind Advisory until 8 PM CDT this evening for mnz071-072-080-081-
Iowa...Wind Advisory until 8 PM CDT this evening for iaz001>003-012>014-
NE...red flag warning from 1 PM to 7 PM CDT Thursday for nez249.
Wind Advisory until 8 PM CDT this evening for nez013-014.