Area forecast discussion
National Weather Service Topeka Kansas
303 PM CDT Wednesday Jun 19 2013
Short term...(this evening through thursday)
issued at 301 PM CDT Wednesday Jun 19 2013
19z water vapor imagery shows a closed upper level low over the
Pacific northwest with a shortwave rotating through the trough over
the Great Salt Lake. Downstream there was a broad upper level ridge
over the plains with a weak disturbance near the middle MO River
Valley moving east. At the surface...a trough of low pressure was
gradually deepening along the Lee of the central rockies. This has
allowed for southerly winds to increase. Any remnant outflow
boundaries from early this morning have become ill-defined.
For late this afternoon and this evening...laps data and rap
analysis shows a conditionally unstable airmass over the forecast
area with cape values around 2000 j/kg...and very limited inhibition
left. Really the only thing needed for convection is some sort of
lift to get parcels moving up to become positively buoyant. Low level
convergence appears to be relatively weak with rap forecasts not showing
much increase in low level convergence through sunset. With no real
large scale forcing to speak of...think convection is likely to be
isolated if it does develop. There is some signs of vertical
development in the cumulus field across southeast Nebraska. If a storm is able
to develop an outflow...the gust front could be enough lift for
further development. Otherwise think the better chances for precipitation
will be late tonight and through the morning Thursday. Most guidance
shows decent middle level Theta-E advection with the low level jet
increasing over central Kansas. Forecast soundings show increasing
moisture along this gradient as middle level lapse rates steepen to
around 7 c/km. Therefore there could be some elevated storms develop
overnight and move across eastern Kansas through the morning Thursday.
Low confidence in location of the elevated development and where it
might track preclude increasing probability of precipitation from the previous forecast. So have
continued with 40 to 50 percent chances into Thursday morning. Think
if elevated storms form...that the resulting mesoscale convective system should be moving
off to the southeast or diminishing with the weakening of the low
level jet by the afternoon and the pop forecast reflects a downward
trend in chances through the afternoon.
Southerly winds and some modest mixing of the boundary layer should
keep lows tonight in the upper 60s to around 70. Highs Thursday may
be a little more tricky as the models show weak mixing of the
boundary layer due to cold pool put down by the nocturnal
convection. Even if there are storms...do not think they will
persist for the whole day and we should still see some good
insolation in the afternoon with south winds increasing. Therefore
have highs for Thursday in the middle 80s across east central Kansas where
clouds and precipitation could potentially hang on longer in the
morning...to around 90 in north central Kansas where sunshine should
break out earlier in the day.
Wolters
Long term...(thursday night through wednesday)
issued at 301 PM CDT Wednesday Jun 19 2013
Thursday night and Friday...some concern as to convection
redeveloping late Thursday night/early Friday morning. Thursday
afternoon thunderstorm complex expected to develop along surface warm
front draped over central Nebraska and western Iowa. NAM forecasted
convectively generated cold pool may push frontal boundary south
potentially over southern Nebraska/northeast Kansas by Friday
morning. 305k-320k isentropic lift...55kt low level jet and some middle-level
frontogenetical forcing could be enough to promote redevelopment of
convection mainly over the far northeastern sections of the state.
Upper level forcing is lacking however...leaving reduced
confidence. Left Friday afternoon dry at this time. However...if
convection develops during the early morning hours...outflow
boundaries may still be present during the afternoon across the
County Warning Area. With a 500 mb shortwave prognosticated to enter the state Friday
afternoon...this may be enough to refire convection during the
afternoon hours. Temperatures will be on the increase over the
coming week as large upper level ridge begins to build into the
central U.S. Heat indices could reach over 100 Friday afternoon.
Friday night through the rest of the week...ridge continues to
broaden across the plains on Saturday with the ridge axis extending
from eastern Colorado/western Kansas through northeast Kansas and
into the upper Midwest. Slight chances for thunderstorms will be
possible along the northern side of the ridge on Sunday. Chances
increase for locations north of i70 Sunday night as an 500 mb shortwave
travels northeast along the northern periphery of the ridge. Cold
front tries to push southeast into Kansas on Tuesday...but upper
level support for the front moves into Canada by Monday afternoon.
Otherwise...Central Plains ridge broadens and covers much of the
Continental U.S. By Tuesday. Ridge begins to amplify over the western U.S. By
Wednesday afternoon setting up the Summer time pattern of northwest
flow over the Central Plains. Highs will be in the low to middle
90's...and lows will be in the 60's and 70's.
Byrne
&&
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1240 PM CDT Wednesday Jun 19 2013
Because there is no forcing or surface feature for convection to
form...think any diurnally driven storms will be isolated in
coverage and have removed the thunderstorms in the vicinity from this afternoon since
predictability is very low at this point. There does appear to be
some Theta-E advection overnight with middle level lapse rates around
7 c/km. This may be enough for elevated storms to develop after
06z. Confidence is marginal...but with all the guidance showing
some precipitation...will include a thunderstorms in the vicinity mention through the morning
Thursday. Otherwise anticipate conditions to remain VFR with cumulus
field forming around 4 kft.
&&
Top watches/warnings/advisories...
none.
&&
$$
Short term...wolters
long term...Byrne
aviation...wolters
