Area forecast discussion...updated aviation
National Weather Service St Louis MO
1131 am CDT Wednesday Jun 19 2013
Short term...(through late this afternoon)
issued at 303 am CDT Wednesday Jun 19 2013
Early this morning...upper level ridge exists over the hi plains
with northwest flow downstream from it over our region. A ridge-runner
shortwave is over western Kansas and Nebraska generating clusters of thunderstorms and rain
with a weaker upper level disturbance over southeastern Kansas helping to
maintain some thunderstorms and rain activity near ict. At the surface...an ill-defined
boundary snakes from southern Indiana through southern Illinois and southern MO and curves
northward near the Kansas-MO border. To the north of this boundary...a light NE
surface flow has built in. Surface temperatures have fallen into the 60s with a
few spots threatening to dip into the upper 50s...a real treat for
late June.
It seems we cannot escape discussing rain chances each day...and this
day seems to be no exception.
Northwest upper level flow is expected to weaken today...flatten overhead
with rising 500 mb heights. This will tend to not result in much push
for surface fronts...and so will probably see the weak surface boundary
linger near its present position through the day...though questionable
in what shape it will be in by middle-late afternoon. In any event...
all models show relatively modest sbcapes of 500-1000 j/kg with zero
cinh during middle-late this afternoon over an area that normally
inclines towards precipitation more than other areas given its intangibles
such as topography...in southeastern MO and southern Illinois. GFS overdoes precipitation
development with surface dewpoints of 70f...but even WRF model and its more
realistic middle 60s dewpoints should result in isolated shra/tsra. Have
introduced slight chance probability of precipitation over much of the southern and eastern forecast area...including
the stl metropolitan area...for middle-late afternoon for what should be
short-lived single cell convection with the very weak deep layer
shear and modest Cape. Ridge-runner shortwave is expected to still
be too far west to have any impact by early this evening.
H850 temperatures and comparison to persistence support maximum temperatures near or
just above the warmest MOS values...or middle 80s for most locations
with upper 80s expected for stl metropolitan.
Tes
Long term...(tonight through tuesday)
issued at 400 am CDT Wednesday Jun 19 2013
May still have isolated showers and storms into the early evening
across parts of southeastern MO and southwestern Illinois. A weak shortwave will move eastward
into Iowa and western MO late tgt. This coupled with a southwesterly low level jet
bringing low level warm air advection and increasing low level moisture into northwestern
MO may lead to some convection across parts of northestern and central MO
late tgt into early Thursday morning. The better threat of convection
should be on Thursday as low level moisture increases over the entire
area...although the shortwave should weaken as it gets further east.
NAM model appears a little deficient in its quantitative precipitation forecast on Thursday. The upper
level ridge over the Southern Plains will build slowly northeastward into MO Thursday
night and Friday. The NAM model is a little lower with its middle-upper
level heights compared to the GFS as it continues to forecast
shortwaves moving through our area and just north of our area. May
still have convection across mainly northestern MO and west central Illinois during
this period. By Friday night and Sat the upper level ridge should build
over our region with most of the convection remaining north of our forecast
area. With the upper level ridge over our area...persistent
S-southwesterly surface/low level winds...and plenty of daytime sunshine a prolonged
period of above normal temperatures is expected for the weekend
into next week. The GFS model flattens the upper level ridge on
Monday and Tuesday which may lead to a better chance of convection...
especially over the northern portion of our forecast area.
Gks
&&
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1118 am CDT Wednesday Jun 19 2013
Isolated thunderstorms are possible this afternoon near a weak frontal
boundary however sparse coverage precludes a mention in the tafs
at this time. VFR conditions are expected to prevail outside of any
thunderstorms which develop. Light Ely winds will gradually turn southeasterly
then southerly late in the taf period.
Specifics for kstl...isolated thunderstorms are possible this afternoon
near a weak frontal boundary however coverage will be sparse. Light
winds will gradually turn southeasterly then become southerly late in the taf period.
Kanofsky
&&
Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&
$$
Weather forecast office lsx
