Area forecast discussion...updated aviation
National Weather Service St Louis MO
104 am CDT Monday may 20 2013
Short term...(through late tonight)
issued at 331 PM CDT sun may 19 2013
Focus for storms early this evening is back over eastern Kansas/western
MO...then have this complex of storms move east into
Central/Northeast MO by 03z. Still some uncertainty on exact
placement and strength of storms as they move east into forecast
area. 12z models all over the place with some focusing main area of
storms along and south of I-70...while others have a long line of
storms move across entire forecast area. For now have area of storms
move across region...gradually weakening/diminishing towards
daybreak...going from likely probability of precipitation down to just chance probability of precipitation by 11z.
Best chances will be over western half of forecast area. As for
severe weather chances...decent CAPES/pws...low level jet...and
shortwave sliding through area tonight. So western portions of
forecast area still in a slight risk overnight...with main threat
being damaging winds.
Otherwise...gusty southeast to south winds to diminish after sunset.
Mild weather to persist with lows only in the middle to upper
60s...with low 70s in stl metropolitan area.
Byrd
Long term...(monday through next sunday)
issued at 331 PM CDT sun may 19 2013
Current indications based on the deterministic models and convection
allowing models is that any thunderstorms remaining from the overnight
mesoscale convective system should be in a drastically weakened state at daybreak. Given that the
primary short wave trough will have already rotated northeastward into Iowa
and a veered west-southwesterly low level jet...any remaining showers and thunderstorms
will most likely be located from southwest/south central Illinois across
southeast MO. These should diminish by middle morning as large scale subsidence
overspreads the region. In the wake of this activity and given the
tendency towards cumuliform clouds...good heating will commence.
This heating combined with a moist boundary layer and steep middle
level lapse rates will contribute to moderate-strong instability
and weak convective inhibition across the entire area by middle
afternoon. Southwesterly deep layer shear at or above 40 kts would favor
discrete to semi-discrete supercells as the dominate storm Mode
initially. At this we are expecting a favored west-southwest-east-northeast corridor
for storm development after 21z from around Jefferson City to
Bowling Green...although this axis could be a bit further south
depending on any residual boundaries. Mergers and additional
development within this zone and upstream should result in a mix
of storm modes by late afternoon and evening with potential for
supercells and bowing linear segments. The overall coverage of
storms should increase during the evening as the next upstream
short wave spreads large scale ascent into the region...also
contributing to upscale storm growth. There eventually could be a
heavy rain threat from central through east central MO due to
persistent and training convection...but the exact location is too
difficult to pinpoint at this point.
The convective details become less defined on Tuesday due to the
potential for residual showers/storms from Monday night and the
presence of mesoscale boundaries. The overall synoptic pattern
featuring the upper trough progressing eastward with the attendant
cold front moving through the County Warning Area during the late afternoon/evening
would favor high thunderstorm chances...especially the southeast half of
the County Warning Area. Deep layer shear of 30-40 kts and weak-moderate instability
would continue to favor organized-mixed Mode severe storms.
The boundary finally looks to pass south of the area by late
Wednesday with another reinforcing boundary on Thursday. The pattern
then is dominated by weak northwest flow on the backside of the upper trough
and looks dry Thursday night-Sat morning. Thereafter return flow and
weak disturbances passing through the plains upper ridge and into the
middle/upper MS valley will bring a re-newed chance of
thunderstorms....especially the northern half of the County Warning Area.
Glass
&&
Aviation...(for the 06z tafs through 06z Monday night)
issued at 105 am CDT Monday may 20 2013
Line of thunderstorms and rain will take much of the night to work its way through the
forecast area and should affect all taf sites before sunrise. Unclear whether
there will be a break between this and what develops upstream from
it later on Monday...but for now...have forecasted the tafs as if
there will be. The second...stronger round...should get going by
early afternoon and slowly expand southeastward. Not entirely certain where
this will hit without a clear feature to follow and thus have
gone thunderstorms in the vicinity for now but will likely have to ramp up the forecast at
some of the terminals. S surface winds will continue through the period
becoming gusty especially during the day on Monday.
Specifics for kstl...VFR conditions expected outside of thunderstorms and rain...one
round of thunderstorms and rain for late tonight...another round of thunderstorms and rain for later
on Monday. Right now it appears the second round of thunderstorms and rain will not
work into the terminal area until early evening after affecting
areas just to the northwest and then stay for a while.
Tes
&&
Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&
$$
Weather forecast office lsx
