Area forecast discussion
National Weather Service Lincoln Illinois
318 am CDT sun may 26 2013
Discussion...
issued 318 am CDT sun may 26 2013
Short term...today through Tuesday
Latest regional radar mosaic showed convection lighting up from northwest
Iowa southeast into west central Illinois. This was occurring well north
of a stationary surface boundary which bisected Missouri from northwest to
southeast...and focused along a strong thermal gradient at 850 mb. More
significant activity in Iowa was being fed by elevated instability
from a 35 knots low level jet...with coverage and intensity fading farther east
into central Illinois as this support diminished. However this may
increase over the western County Warning Area for the next few hours as the low level jet
veers. This convection has a history of training in eastern
Iowa and with observed rain rates up to 0.75 in/hour some localized
heavier amounts of 1-2 inches certainly possible...mainly west of
the Illinois River. Latest 4km NSSL WRF had best handle on this convection
and would favor best storm coverage over the western half of the
County Warning Area this morning...gradually lifting north and diminishing by
midday. Focus for new precipitation generation through afternoon would be
tied to another shortwave crossing into west central Illinois by 18z.
Temperatures today should be several degrees warmer than yesterday with
more of a southeast wind component. Have trended toward cooler mav
guidance with expected cloud cover for highs still several degrees
below normal in the upper 60s/lower 70s.
For tonight through Monday...the surface front currently to our
southwest will lift north into the County Warning Area. Thus will maintain a
continued chance of scattered storms as several middle level waves
are forecast to shift over the County Warning Area. Extent of column saturation
and p/west rising over 1.5 inches suggests locally heavy rain
possible primarily over the northwest County Warning Area where forcing is shown to be
strongest.
The front is forecast to lift into northern Illinois on Tuesday...and
this should focus most of the higher precipitation chances to our north.
However with uncertainty on how quickly the front lifts north
due to expected convection and outflow...will keep low chance probability of precipitation
for the north into Tuesday. Otherwise...brisk southerly flow will
bring a much warmer into central Illinois with highs getting well into
the 80s.
Long term...Wednesday through Saturday
By middle-week the upper air pattern will feature a sub-tropical
ridge strengthening over the Carolinas...while a low closes off
over the northern rockies. Resulting deep layer southwest flow
will continue to pump warm air into the region and with dewpoints
well into the 60s...a stretch of Summer-like weather will set up
over the Midwest for the end of may. The main question for the
extended forecast is how quickly the ridge over the East Coast
breaks down...allowing the large trough to the west to shift into
the upper Midwest. Current indications show an active setup from
the plains possibly as far east as Iowa and Missouri for Thursday
and Friday as a surface low lifts into the plains and an
associated cold front slowly works east into the warm and unstable
airmass. Will keep a low chance pop across the west Thursday/Friday to
account for any activity to our west that makes it this far east
in a decaying fashion. The best shot at more widespread storms
appears to be next weekend when the ridge finally shifts east
into the Atlantic and the upper trough and surface front can get into
the County Warning Area. Of course much uncertainty that far out with the ec
ensemble mean showing a much weaker trough by 192 hours. Temperatures will
remain well above normal until the cold front eventually passes.
25
&&
Aviation...
issued 1100 PM CDT Sat may 25 2013
Little change from earlier thinking...coverage of precipitation later
tonight and its affect on ceilings/visibilities the main challenge. Other
than some scattered rain showers occurring over parts of east
central Illinois late this evening...not a great deal going on. Starting
to see some light returns on radar over west central Illinois that was
pushing southeast and may affect spi and Dec with some light showers but
have not seen much...if any reports underneath those returns yet.
We have had some brief lowering of ceilings/visibilities to MVFR at times in
the heavier rains...but those have been brief and widely scattered.
Will continue with mainly VFR ceilings through the period and then try to
time the best coverage of rain and thunder into our area late tonight
and especially Sunday morning. After that...confidence on just where
and when additional showers and thunderstorms will occur is quite
low. Frontal boundary to our south is expected to remain there for
another day keeping US in an easterly flow through the period. East
winds of 10 to 15 kts tonight will become east-southeast at 10 to 15 kts on
Sunday.
Smith
&&
Ilx watches/warnings/advisories...
none.
&&
$$
