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1 2 3 4 Area Forecast Discussion
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fxus63 klsx 242056
afdlsx
area forecast discussion
national weather service st louis mo
356 pm cdt fri may 24 2013
. short term...(through late tonight)
issued at 353 pm cdt fri may 24 2013
cool canadian surface ridge holding tough late this afternoon from
lake michigan to se mo. ridge will loosen its grip over the region
overnight as it continues to drift se ... allowing se flow that has
developed over mid mo today to develop/strengthen across the
remainder of the cwa. primary question for tonight is if/when
convection will begin to threaten area. consensus of 12z guidance
is a bit slower with intensification of low level jet into the
mississippi valley ... and a bit further n with the 850mb theta - e
bulls - eye ... than indicated by earlier runs. this would suggest pops
bulls - eye would primarily be to our n across iowa ... with some of
this elevated shower and isolated thunderstorm activity possibly
dropping south during the predawn hours. i`ve delayed the onset of
the precip in our n counties by an hour or so ... but do allow
chance pops to drop as far s as a cou - ppq line by 6 am. this may
be too far s ... but trying to leave some leeway as 850mb waa does
show a subtle increase from se ia into n ozarks during the predawn
hours.
temperature - wise ... have attempted to depict impact of retreating
surface ridge over se part of the cwa with mins in the 40s ... while
increasing winds and clouds should mean lows in the l - m50s over nw
part of the cwa.
truett
. long term...(saturday through next friday)
issued at 353 pm cdt fri may 24 2013
sfc high pressure center over the grtlks will shift ewd on
saturday while a persistent lee side low over the plains pushes a
baroclinic zone newd as a wmfnt. this will cause winds to become
sely to sly across the lsx cwa with the wmfnt stretching along the
mo/il border through sunday before the bdry lifts farther nwd. a
general warming trend is expected through next week however there
will probably be a couple of cooler days mixed in due to the
effects of nocturnal mesoscale convective systems /either upstream
or overhead/. these effects may include lingering shra ... thick
cloud cover ... an mcv which focuses sct aftn tsra ... and/or outflow
bdrys which push the effective wmfnt farther south than was
previously fcst. temperature trends in the previous fcst look
reasonable and few changes were required.
as for pcpn chcs ... models continue to show a couple of vort maxes
which may support sct aftn shra/tsra as they move across the area
over the next several days. a persistent and redeveloping llj
interacting with a baroclinic zone will also support nocturnal
thunderstorm dvlpmt across parts of the central conus over the next
couple of nights. some of the tsra clusters will probably congeal
into mesoscale convective systems and could move into the lsx cwa
/based on corfidi vector fcsts/ depending on where they initially
form ... and where they initially form each night will depend on the
position of the effective wmfnt which may end up being pushed
farther south by outflow bdrys. these mesoscale details cannot be
accurately fcst very far in advance. in other words ... we expect to
see unsettled weather through early next week before the warm front
lifts far enough north to limit the mcs potential.
by the middle of next week ... the upper air pattn over the central
conus will shift from ridging to sw flow after a trof becomes
established over the wrn half of the country. gfs/ecmwf disagree on
the amplitude of the trof and on the position of a strong vort max
within it. the vort max may bring a chance of pcpn to mo/il when it
lifts through the plains late next week however there is
considerable uncertainty attm due to model disagreement.
kanofsky
&&
. aviation...(for the 18z tafs through 18z saturday afternoon)
issued at 1252 pm cdt fri may 24 2013
surface ridge axis extending from e wi to se mo will continue to
slide east this afternoon and tonight. this will mean that vfr
conditions will prevail through 06z ... with clouds limited to a bit
of ci and east - se surface winds primarily aob 10 kts. attention
then turns to threat of nocturnal convection. there seems to be
some consensus in the latest short range that theta - e advection on
nose of low level jet will be well to our n ... causing the
development and centroid of the mcs to track across iowa and then
either advect or attempt to develop a bit south into n sections of
the cwa during the predawn hours. based on this trend have
introduced vcts in uin by 12z.. but elsewhere have held off
mentioning thunder attm as solutions are literally all over the
place with convective trends during the day on saturday. details
for saturday should become a bit more clear once tonights
convective trends become established.
specifics for kstl ... vfr conditions will prevail through 15z
saturday ... with ne winds aob 8 kts this afternoon becoming
easterly tonight and se on saturday. should see an increase in mid
and high level clouds late tonight and saturday morning as cloud
debris streams downstream from iowa/n mo convection ... but these
should be aoa 10kft.
truett
&&
. lsx watches/warnings/advisories...
mo ... none.
il ... none.
&&
$$
wfo lsx