Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Topeka Kansas
603 am CDT sun Apr 20 2014

..aviation update...

Short term...(today and tonight)
issued at 248 am CDT sun Apr 20 2014

07z water vapor imagery shows the main shortwave still over
southwest nm with bits of vorticity lifting out across the Texas and OK
panhandles into western Kansas. Surface obs show an inverted trough of
low pressure extending from southeastern Colorado into eastern Nebraska. Low
level moisture return has been less than impressive and even now
with a good low level jet higher dewpoints seem to be stuck along
the Texas Gulf Coast. Models forecast the upper shortwave to move out
across OK and Kansas today and tonight. This wave should bring some
cooler mid level temps and steepening lapse rates that is expected
to remove any inhibition to convection. However models show the
magnitude of the large scale forcing to be weak. Additionally the
main surface feature for focusing low level convergence remains
mainly to the northwest of the forecast area today. So with
instability driven mainly by day time heating, think convection will
be scattered in nature and may be more hit or miss due to the
relative lack of a dominate feature to focus convection. Cape values
are expected to be in the 1000 to 1500 j/km range but deep layer
shear continues to be unimpressive. This suggests chances for severe
weather remains low. With some insolation and southerly low level
winds persisting through the day, highs are forecast to warm into
the mid and upper 70s.

The main question for tonight is whether convection falls apart with
the loss of day time heating or if the mid level deformation and
weak forcing of the upper wave will allow precip to fester
overnight. Think the lessening of instability overnight may cause
coverage to lessen, so have shown pops to trend lower overnight but
will keep a chance for precip as the GFS and European model (ecmwf) continue to
generate some light quantitative precipitation forecast. Lows tonight should remain mild since the
boundary doesn't make much of a push until Monday morning. The
forecast shows low generally in the upper 50s.

Long term...(monday through saturday)
issued at 248 am CDT sun Apr 20 2014

By 12z Monday morning, consensus guidance progs the cold front to be
entering far north central Kansas. Due to forcing along the boundary
combined with maximum lift from the upper trough axis, have
maintained chances for thunderstorms, highest being across
east central and far northeast areas through mid afternoon. Elevated
instability increases during this time while shear profiles remain
weak below 20 kts therefore severe storms are not expected. Main
concerns on Monday will be the heavy rain potential as deep moisture
raises precipitable water values peak between 1.25 and 1.5 inches. Dry air works
its way southeast behind the front by late afternoon with precip
chances ending early Monday evening. Upper ridge on Tuesday will
spell quiet and warm conditions across the area with highs
remaining in the low 70s.

A negatively tilted trough deepens and lifts northeast over the
inter-mountain west late Tuesday evening, ejecting a leading
shortwave trough into the northern and Central Plains. An aiding low
level jet will develop showers and thunderstorms over north central
Kansas. The GFS and European model (ecmwf) are fairly consistent in timing with the
GFS being a tad slower. The 00z NAM carries less moisture
availability and so will maintain chance pops from previous

A warm and moist air mass builds in the Central Plains Wednesday
afternoon with the dry line and cold front set up across western
Kansas and Nebraska. As the upper trough lifts northeast, showers
and thunderstorms are possible along and ahead of the aforementioned
boundaries late Wednesday afternoon. Latest guidance has been
consistent with this activity developing west of the County Warning Area and
progressing eastward with the cold front Wednesday evening into
Thursday. Precip chances were increased to likely for Wednesday
evening. While the capping inversion holds through the day at cnk,
elevated severe storms would be possible (especially over north
central kansas) with instability near 1000 j/kg and effective shear
(0-6km) in excess of 50 kts. The European model (ecmwf) is the slightly faster
solution than the GFS, however both clear precip out of the area
Thursday afternoon. Will continue to monitor this system as changes
are likely in the depth of instability and timing. Highs during
this time peak in the upper 70s Wednesday and lower 70s Thursday.

Next system looks to impact the area Saturday with chances for
showers and thunderstorms during the day. European model (ecmwf)/GFS are trending a
cool Canadian airmass further south behind a cold front with highs
Saturday in the 60s.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 603 am CDT sun Apr 20 2014

Confidence in timing precip at the terminals is low since there is
no good feature to focus convection. Most of the guidance is
pointing to daytime heating destabilizing the atmosphere and weak
forcing from the upper wave sparking convection by the late
afternoon. Think convection is likely to be of a scattered nature.
Because of this will keep the forecast VFR with only a thunderstorms in the vicinity at
this time. If a thunderstorm moves into the terminal, temporary IFR
visibility is likely.

The potential for low level wind shear will persist until about
14z when the rap forecast soundings show the boundary layer mixing


Top watches/warnings/advisories...none.



Short term...wolters
long term...Bowen