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Area forecast discussion 
National Weather Service Hastings NE
100 am CDT Sat Aug 30 2014

Short term...(this evening through saturday)
issued at 318 PM CDT Friday Aug 29 2014

Current radar shows the thunderstorm activity in the eastern part of
the forecast area is finally about to move out of the forecast area.
There is another batch of thunderstorms moving in from the north.
Satellite has clouds clearing out of the western part of the
forecast area this afternoon. Surface analysis has a cold front in
the eastern part of the forecast area slowly pushing to the east
this afternoon.

The cold front and an upper level wave is expected to continue to
push to the east this afternoon and evening. Models are fairly
consistent with these thunderstorms moving through the area by early
evening. The main question is whether there will be any additional
thunderstorms as the secondary wave moves into the area during the
evening hours. There are already a few cumulus moving through the
Panhandle this afternoon. When this gets closer to the moisture
further east there could be a few thunderstorms develop. These
should be mainly in the northeast part of the forecast area during
the evening.

Expect thunderstorms to exit the forecast area during the evening
hours and clouds gradually diminish as well. With the recent
rainfall and humid conditions expected to continue the
clouds clear out there could be some patchy fog around mainly across
Nebraska in the early morning hours. Winds will be light as a
surface high settles into the area.

The surface high will move to the east on Saturday and expect mostly
sunny skies for the day. As the high moves east...winds will turn to
the south and gradually increase in the afternoon.

Long term...(saturday night through friday)
issued at 318 PM CDT Friday Aug 29 2014

Guidance suggests zonal upper tropospheric flow will be noted over
the central Continental U.S. To start the long term forecast period...with an
upper tropospheric short wave expected over the northwestern Continental U.S..
the short wave is expected to move east over the Central Plains on
Sunday and then off to our east on Monday. With the passage of this
short wave...enhanced upper tropospheric zonal jet energy is
expected to overtake our area on Monday...with this jet energy then
expected to lift to our north as upper tropospheric ridging builds
into the region from the southeastern Continental U.S. Tuesday Onward. Boundary
layer flow is expected to remain from the south/southeast to start
the long term forecast period. The passage of the aforementioned
upper tropospheric short wave on Sunday however should allow an area
of low barometric pressure at the surface to move east/northeast
across South Dakota during the day Sunday...thus allowing a lower
tropospheric baroclinic zone to clear our area Sunday afternoon into
Sunday night. Boundary layer flow from the north/northeast should
then present itself Monday and Tuesday before lower tropospheric
return flow infiltrates the area Wednesday Onward.

Starting with Saturday night and early Sunday morning...guidance
suggests the axis of a 40-45kt jet streak just above the boundary
layer will develop from western Kansas into central and northeastern
Nebraska. At this time it appears thermal advection along this axis
will be sufficient for at least isolated precipitation production
across the area...a solution supported by the NAM and operational
GFS...and to a much lesser extent the ec. Given this...went ahead
with ~20% probability of precipitation across much of the County Warning Area Saturday night into early
Sunday morning.

Any lingering precipitation Post-sunrise on Sunday should quickly
dissipate and move off to the east/northeast as the lower
tropospheric jet axis does the same. This could lead to a period of
dry weather between late morning and early afternoon on Sunday. By
late Sunday afternoon and really into Sunday evening
however...thermal advection ahead of the approaching upper
tropospheric short wave should promote enough Omega for convection
across the area. In addition to the increasing synoptic-scale
Omega...lower tropospheric convergence along the passing baroclinic
zone will also provide a zone of enhanced lift where convection will
likely initiate. This is a solution supported by quantitative precipitation forecast fields from the
NAM...operational GFS and ec. Given all this...went ahead with 30-
50% probability of precipitation across the County Warning Area beginning late Sunday afternoon...with probability of precipitation
increasing to as high as 70% Sunday evening. Precipitation should
then move off to the east of our area Sunday night into Monday
morning as the upper tropospheric short wave and lower tropospheric
baroclinic zone do the same. An overall lack in Omega should then
provide dry conditions to the area for the most part Monday
Onward...but the passage of an upper tropospheric perturbation could
bring some precipitation to the area Monday night...and again
Thursday night into Friday...and allblend responded by providing
~20% probability of precipitation to these forecast periods. These probability of precipitation were left unchanged
for the most part.

Guidance suggests ascending parcels in association with convection
Saturday night into early Sunday morning will only have a 100-
300j/kg to work with. Given this...will hold off from any mention of
severe weather Saturday night into early Sunday morning. Rich
boundary layer moisture...with surface dew point readings in the middle-
60s for most locations...working in concert with increasing upper
tropospheric lapse rates due to the approaching short wave...will
likely promote potential energy values of around 2000j/kg...a
solution supported by the NAM...operational GFS and ec. Perhaps more the fact multiple models suggest deep-layer bulk
shear in excess of 40kts...and perhaps approaching 50kts...will also
be in existence across the area Sunday afternoon and evening.
Although deep convection will likely become quasi-linear along the
advancing lower tropospheric baroclinic zone...if deep convection
can be realized ahead of the baroclinic zone...then 0-1km srh values
in excess of 100m^2/s^2 and perhaps approaching 200m^2/s^2 suggest
tornadic activity also cannot be ruled out. Given all this...the
inherited severe weather potential statement...which includes Golf Ball size hail...thunderstorm
wind gusts to around 70 miles per hour and tornadic activity...seems right on
and this same message will be maintained with the afternoon


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1259 am CDT Sat Aug 30 2014

Some lower visibility possible from light wind and recent
saturation of soil. Any precipitation should hold off until just
after the valid time of the forecast.


Gid watches/warnings/advisories...


long term...Bryant

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