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Area forecast discussion 
National Weather Service Topeka Kansas
640 PM CDT Tue Sep 2 2014

..update to aviation forecast discussion...

Short term...(this evening through wednesday)
issued at 320 PM CDT Tuesday Sep 2 2014

Fairly zonal mid-level flow was in place across much of the
northern and central U.S. Today, oriented from northwest to
southeast. At the surface, high pressure was in place across much
of the forecast area with low pressure centered over southern New
Mexico and western Texas. As of 19z, surface observations showed
the boundary that had tracked south of the forecast area yesterday
had lifted northward into the area again as a warm front,
stretching roughly from Council Grove toward Topeka. Visible
satellite imagery showed scattered low- level clouds from this
morning continuing to linger along and south of this boundary
across east central Kansas, limiting the diurnal heating and
keeping temperatures generally in the upper 70s to mid 80s.

Main focus for tonight into Wednesday is on the potential for
isolated to scattered thunderstorms to develop. The frontal boundary
may sink a bit further south again this evening before lifting once
again northward as a warm front later tonight through the overnight
hours. Models also show a couple of weak embedded shortwaves within
the mid-level flow that should lift northward toward the region.
The combination of these shortwaves and the warm front along with
support from an increasing low-level jet veering from south to
southwest overnight should help to spawn the development of
scattered convection. Soundings suggest that these storms should be
elevated, with a modest amount of instability aloft for these storms
to tap into (upwards of 1500-2500j/kg of mucape). Shear values may
be a bit weaker than originally projected, with approximately
25-35kts of 0-6km bulk shear. While widespread severe weather is not
anticipated, cannot rule out some marginally severe hail and even
some gusty winds. The best chance for this hail looks to be focused
across portions of central and east central Kansas, where the better
instability is expected to be located. Short-range models have been
slowing the timing of the initial development of this scattered
activity, with a few isolated storms possible this evening and
better chances for scattered storms during the overnight hours into
Wednesday morning. These storms should quickly exit from west to
east through mid morning with clearing skies by the afternoon. A
30kt low-level jet should persist through much of the day Wednesday
with breezy southwesterly surface winds gusting upwards of 25-35mph,
helping to advect warmer temperatures and higher dewpoints into the
region. As long as the mid-level clouds sufficiently clear out
during the day, temperatures should warm into the low/mid 90s with
dewpoints reaching into the low 70s. As a result, expect afternoon
heat indices to rise into the 98 to 103 degree range.

Long term...(wednesday night through tuesday)
issued at 320 PM CDT Tuesday Sep 2 2014

Wednesday night and the first part of Thursday should be quiet
before a frontal boundary begins moving into the forecast area.
This frontal system is expected to linger over the area for a
couple days as the mean westerlies remain mainly north of the
forecast area. Therefore there is no real big push from the north
to the frontal boundary. However the European model (ecmwf) continues to trend a
little more progressive with the front. For now have continued the
better chances for precip from Thursday night through Friday night
and adjusted pops down a little for Saturday because of the European model (ecmwf)
trend. Chances for severe weather will be conditional on whether
storms are able to develop ahead of the boundary within the more
unstable airmass. Since there is not much forcing, models show
much of the quantitative precipitation forecast occurring Post frontal once the lift from the
front moves through. Additionally the deep layer shear within the
warm sector is rather modest with only 15 to 20 kts of 0-6km
shear. So if storms were to develop ahead of the front, they may
tend to be more pulse type or multicellular in nature. Think highs
Thursday will be quite warm ahead of the front due to 850mb temps
around 24c and good mixing of the boundary layer. With much of
the guidance showing the front moving into north central Kansas late
in the day, have kept highs in the lower 90s there with mid 90s
possible elsewhere. The European model (ecmwf) and GFS suggest there should be some
decent cold air advection by Friday. With clouds and potential
rainfall expected, have trended temps cooler with highs ranging
from the lower 70s north to the mid 80s over east central Kansas.

Precip should come to an end by Saturday as ridging continues to
build into the area with no obvious shortwave progged by the
models. This is expected to lead to a cool and generally dry
weekend. Lows are forecast to be in the 50s and highs in the 70s
with the center of the ridge over the forecast area.

Chances for precip return to the forecast for the beginning of the
work week. Models indicate a southwesterly mid level flow
developing as heights fall across the western U.S. However
confidence in precip chances is lower than normal due to the
models generating precip based on possible mesoscale waves within
the flow. These features tend to be more transient from model run
to run. With this in mind have remained a little conservative with
pops for Monday and Tuesday and keep chances between 20 and 40
percent. Temps should begin trending warmer for the work week as
well with southerly return flow developing. Although 850mb temps
show only modest warming so highs are forecast to be in the 80s
with lows in the 60s.


Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 632 PM CDT Tuesday Sep 2 2014

The latest models are in good agreement that scattered elevated
showers and thunderstorms are forecast to lift across the area
overnight. Not certain what the coverage will be therefore did not
add a new group to the taf. There may be a period of vis/cig
restrictions during and shortly after the storms, which may need
to be added at the next issuance.


Top watches/warnings/advisories...


Short term...hennecke
long term...wolters

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