Area forecast discussion...updated aviation
National Weather Service St Louis MO
1141 PM CDT Wednesday may 22 2013
Update...
issued at 841 PM CDT Wednesday may 22 2013
Isolated showers...mainly light can still be expected across northestern
MO and west central Illinois for the remainder of the night as a weak shortwave
over eastern Nebraska drops southeastward through northestern MO and west central Illinois late
tgt. More significant showers just ahead of a cold front extending
from a surface low near Ord SW through sar and familiar should remain east-southeast
of our forecast area as the front continues to move slowly southeastward.
Although much of the cumulus and stratocumulus clouds have dissipated
across southeastern MO and southwestern Illinois with loss of daytime heating...low-mid
level clouds will continue to rotate southeastward through at least the
northern half of our forecast area for the rest of tgt...behind the
upper level low/trough and associated surface low over the Great Lakes
region. Cooler low temperatures are forecast for tgt compared to
the previous night...and slightly below normal for late may due to
weak low level cold air advection behind the cold front and lowering surface dew
points. The 00z Thursday NAM model run drops the 8 degree c 850 mb
isotherm southeastward into southeastern MO and southern Illinois by 12z Thursday.
Gks
&&
Short term...(through late tonight)
issued at 314 PM CDT Wednesday may 22 2013
A few showers that popped up along and ahead of a reinforcing cold
front will continue to gradually move eastward...and any lingering
showers should taper off quickly after sunset this evening with a
loss of diurnal heating. The large low continuing to spin over the
upper Midwest/Great Lakes will act to keep much of the region
under partly to mostly cloudy skies tonight...thus have not gone too
far below guidance on tonight's lows...which will generally be in
the low to middle 50s across the area. Observation today over eastern and
southeastern Nebraska have indicated some pockets of light
rain/drizzle occurring on the back side of the low...thus cannot
rule out some light precipitation over the northern tier of the County Warning Area
as the low begins to finally lift northeast...mainly during the late
overnight hours to just before daybreak.
Phillipson
Long term...(thursday through next wednesday)
issued at 314 PM CDT Wednesday may 22 2013
Thursday through Friday night...vorticity maxes moving across the area tomorrow
may support isolated showers however the timing of the vorticity maxes
are currently forecast to be temporally out of sync with diurnal heating
which would tend to limit precipitation coverage. Some cloud cover should
persist tomorrow within cyclonic flow aloft in the wake of a
departing low pressure system. A strong surface high then builds into
the Midwest and brings cooler air to MO/IL...effectively pushing a
frontal boundary in southern MO/northern Arkansas southward as a cold front. The coolest overnight
lows out of the next several days will probably occur late
tomorrow night/early Friday morning. Temperatures should remain
seasonably cool on Friday under the influence of cool Ely surface flow.
Generally dry conditions are expected through Friday night however
nocturnal convection driven by the low level jet may clip the northwestern County Warning Area on
late Friday night.
Sat through Tuesday...surface winds will gradually become southerly across the County Warning Area
around the back side of the surface high once it shifts farther eastward. A
developing low over the plains will reorient a baroclinic zone such that
it stretches through eastern Kansas and western MO as a warm front. Temperatures will
warm up over the weekend as this boundary lifts into central MO with the
temperature increase aided by the strong sun angle at this time of
year. Models are hinting at a few ill-defined vorticity maxes moving
across the area over the weekend which may support scattered
thunderstorms. Additionally...upstream nocturnal mesoscale convective system development may also
affect our area this weekend...either as decaying remnants moving
into the County Warning Area or by generating an mesoscale convective vortex which focuses thunderstorms and rain development
during the following afternoon. Pop12 climatology for this time of year
is around 30 percent and that looks reasonable given the lack of
well-defined features to focus precipitation development and the uncertainty
regarding the effects of upstream mesoscale convective system activity. The upper air
pattn over the central part of the country will shift from ridging
to SW flow by the middle of the week after a shortwave moves into
the southwestern Continental U.S..
Kanofsky
&&
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1130 PM CDT Wednesday may 22 2013
Trough currently over Iowa will move slowly south...reaching KUIN
12-14z and kcou and the St. Louis metropolitan tafs 15-18z. MVFR clouds
currently over Iowa will move south with the trough...and have
gone with 1500ft ceilings at KUIN and 2000ft at kcou and the St.
Louis metropolitan tafs. There are some IFR ceiling in Iowa...so couldn't
rule out these lower ceilings...particularly at KUIN. Isolated
-shra is also possible...with the best chances at KUIN...so have
maintained vcsh there. West winds will veer northerly behind
trough...and then northeasterly by tomorrow evening as skies clear.
Specifics for kstl...expect trough to pass through the terminal
around 18z causing winds to veer from the north. Ceilings will
lower into the 2000-3000ft range by middle-morning before improving
back to VFR late in the day.
Britt
&&
Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&
$$
Weather forecast office lsx
