Area forecast discussion...updated aviation
National Weather Service St Louis MO
608 PM CDT Thursday may 23 2013
Short term...(through late tonight)
issued at 325 PM CDT Thursday may 23 2013
Secondary shortwave dropping down back side of Great Lakes trough has
maintained a few spotty showers over the area this afternoon. Think
most of this activity will either advect out of our area or
dissipate by 00z...but will watch radar trends to determine if any
of this activity will persist into the early evening. If it
does...it shouldn't last much past sunset.
Rather extensive and persistent SC deck is also holding tough across
area. However ceilings have been increasing and visible satellite
imagery suggests clouds are becoming a bit more cumuliform with
time....so believe clearing is still in the offing during the early
evening hours.
Since we're still leaning towards a decreasing cloud trend
tonight...i've remained on the cool side of guidance for mins.
Temperatures will begin the evening on the chilly side...and with
the southward push of the surface ridge into the area winds should be
rather light and dewpoints should be fairly low during time of maximum
radiational cooling.
Truett
Long term...(friday through next thursday)
issued at 325 PM CDT Thursday may 23 2013
The main forecast issues continue to be temperature trends and precipitation chances.
A strong surface high will continue building into the western Great Lakes on Friday
with the ridge axis extending southward into MO/IL. Ely surface flow around
the high will keep temperatures seasonably cool on Friday/Friday night
in addition to reinforcing a baroclinic zone across the plains.
Meanwhile...a developing low pressure system over the plains will
reorient the aforementioned baroclinic zone and lift it northeastward as a
warm front. Temperatures will warm up quickly on Sat across central MO
due to both the warm front and the late may sun angle. The extent of
warming across western/southwestern Illinois for the weekend is more in question
because of uncertainties regarding the location of nocturnal
mesoscale convective systems and the effect of their outflows on
the position of the effective front. Temperatures across western/southwestern
Illinois will warm up once the front lifts farther north...but that may
not happen until Monday. Temperatures across the area will also
depend on the extent of remnant cloud cover from overnight
convection that occurs upstream.
Generally dry conditions are expected through Friday night however
nocturnal convection driven by the low level jet may reach the northwestern County Warning Area on
late Friday night/early Sat morning. A few vorticity maxes may try to
undercut the upper ridge that will be in place over the central
Continental U.S. Through early next week...and these features may support scattered
rain showers/thunderstorms and rain at times. Additionally...the forecast weather pattern will be
conducive for nightly mesoscale convective system development across various parts of the
central Continental U.S.. some of these thunderstorm complexes may move
across the lsx County Warning Area depending on the position of the effective
front each night and its orientation with respect to the low level jet axis.
Upstream convection could also produce an mesoscale convective vortex which then focuses
thunderstorms and rain development in our area on the following afternoon. These kinds of
mesoscale details cannot be forecast very far in advance therefore
this forecast package maintains chance probability of precipitation /higher values where models
seem to be in slightly better agreement/ for several days where
thunderstorms are possible but mesoscale details are unknown at this time.
A pattern shift will be underway by the middle of next week once a
closed low pressure system develops over the southwestern Continental U.S. And shifts the
upper air pattn over MO/Illinois from ridging to SW flow. GFS/European model (ecmwf) depict
very different scenarios for how the low lifts into the plains
therefore generally followed the recommended CR initialization for
Tuesday and beyond.
Kanofsky
&&
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 557 PM CDT Thursday may 23 2013
Light showers have moved south of the St. Metropolitan taf sites...so
expect dry conditions through the taf period. Back edge of clouds
will move south across the area...and expect skies to clear by 03z
at all of the taf sites. Northerly winds will slowly veer from the
east middle morning Friday.
Specifics for kstl...expect that ceilings at kstl will improve to
VFR by 00z. Skies clear early this evening with winds slowly
veering from north to east by 14z on Friday.
Britt
&&
Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&
$$
Weather forecast office lsx
