Area forecast discussion
National Weather Service Sioux Falls South Dakota
340 am CDT Wednesday may 22 2013
Short term...(today and tonight)
issued at 259 am CDT Wednesday may 22 2013
Upper level low continues to spin across the area early this
morning...fairly close to kykn...but with some uncertainty given
what is hopefully a temporary loss of the GOES-east data due to
late evening malfunction /estimated return toward 18z today/.
Bulk of precipitation continuing to occur just on back side of the
middle level center where tendendy to focus a bit of lower to middle level
frontogenesis and isentropic lift in the 295-300k layer. Returns
have really varied overnight...sometimes nearly dissipating...only
to reform and become quite widespread just an hour later. At current
time...about the best coverage of the night so far along and west of
i29 as pulse in the isentropic lift works westward north of the
cyclone center. Treating like a classic high pop/low quantitative precipitation forecast event at
least through the early morning hours...with signs in several models
of a weakening of this trowal-like feature through the morning...
but perhaps a resurgence in coverage by early to middle afternoon near
and just east of i29 if solutions taken literally. Generally...expect a
day with occasional showers...starting to dwindle from the west. Not
expecting to see much in the way of clearing today...perhaps a
partial bit leaking into the far north/northwest. Thus with clouds
and expected precipitation...another chilly day with fairly limited
recovery from current readings...meaning highs 10 to 15 degrees
below normal.
Precipitation should wind down through the evening hours tonight
as isentropic down Glide increases across the area. Added mention
of patchy fog across central South Dakota where skies clear and
winds decrease. Considered expanding further east...but fog is
conditional on timing of clearing and wind potential.
Long term...(thursday through tuesday)
issued at 259 am CDT Wednesday may 22 2013
Relatively quiet weather is expected on Thursday with surface
ridge passing through the region to the north. Models suggest
return flow sets up fairly quickly Thursday afternoon into
Thursday night...though no direct tap to the Gulf is present so am
not expecting a substatial increase in moisture until Friday night
into Saturday when low level jet sets up across the Central
Plains. Models seem to sugges a fairly weak capping
inversion...with the potential for storms to develop as a leading
short wave breaks off upper low spinning across the northwest US. The
European model (ecmwf) suggests the upper wave may shear out to the north and west
of the County Warning Area as it tries to work east into the upper ridge across
the Central Plains...while the GFS suggests a series of phased
waves traveling across the area. The waves in the GFS solution
appear to be convective driven...and have therefore sided closer
to an European model (ecmwf) solution. With that said...was not that excited about
precipitation chances and lowered probability of precipitation slightly...especially
during the day on Friday. With better moisture return Friday
night...precipitation chances appear to be more significat with
little capping inversion from a lifting layer between 700-800 mb.
Off and on chances of precipitation continue to plague the
extended with dirty west to southwest flow aloft with waves
breaking off in a piecemeal fashion and moving through the plains.
With upper low remaining to the west...low level flouw remains
southeast to south through much of the extended. This will result
in an overall gradual warming trend...along with an increase in
moisture. With little agreement on timing of upper waves...left
guidance probability of precipitation as is with chances of thunderstorms throughout the
extended.
&&
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 1046 PM CDT Tuesday may 21 2013
Once again...MVFR conditions will likely dominate the weather
for the rest of tonight and Wednesday along and north of I
90...with MVFR to lower end VFR south of I 90. One challenge in
this forecast is that there will probably be patches of drizzle
moving through the area tonight and Wednesday. Drizzle will likely
lower the conditions into the IFR category for brief periods of
time. However...due to the intermittent and spotty nature of the
drizzle...it is extremely difficult to predict these episodes much
ahead of time. Therefore short term amendments to the tafs could
occur to account for these conditions.
&&
Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&
$$
Short term...Chapman
long term...
aviation...
