Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 302023

323 PM CDT Thu Apr 30 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 314 PM CDT Thu Apr 30 2015

A vigorous upper level LOW is currently spinning over central
Indiana with a strong disturbance rotating around into eastern IL
on its backside. Unfortunately for the disturbance, it is working
on very dry and stable air thru the column and should only be able
to muster flat diurnal cumulus clouds across portions of eastern
and central IL where the lift is strongest. Areas further to the
west are clear. At the surface, even though the main cold front
has been south of MO for a few hours now, another more subtle
boundary is still working its way thru southern MO and far
southern IL, facilitating the final push of dry air into our
region with dewpoints in the low-mid 30s. The northerly winds
behind the front have hardly made a difference thanks to full
sunshine, with readings in the upper 60s and lower 70s currently.

The upper level support from the LOW to our east is expected to
exit by late this afternoon, leaving the remainder of the flat
cumulus field in terminal decline, accelerating as we head towards
sunset. This will give us clear skies for all shortly after

A RIDGE of high pressure will then build in to near a
Jacksonville, IL (IJX) to Rolla, MO (VIH) line by late tonight,
with temps expected to bottom out in the upper 30s and lower 40s,
supporting the cooler MOS temps. These values not expected to
present any issues regarding frost formation other than isolated
potential in only the most protected areas.


.LONG TERM:  (Friday through Next Thursday)
Issued at 314 PM CDT Thu Apr 30 2015

Once the aforementioned surface ridge axis shifts eastward
tomorrow, winds will take on much more of a southerly component
around the back side of the surface high. This transition from
predominantly northerly flow to predominantly southerly flow will
occur across the western CWA on Friday and then across the rest of
the CWA on Saturday after the ridge axis has moved farther to the
east. Southerly flow, strong May sunshine, and rising heights
aloft will keep the recent warming trend in place through the
weekend and into early next week. Temperatures could reach the 80s
across most of the area as early as Sunday, which would be around
5-10 degrees above average for early May.

The CWA remains on the eastern periphery of the H5 ridge on Friday
and Friday night until the flow aloft becomes quasizonal on
Saturday. Within that flow pattern, models do show a few vorticity
maxima passing to the north which could support isolated to
scattered SHRA/TSRA, mainly across the northern CWA sometime
between Friday night and Saturday night. The active frontal
boundary should be well to the north on Sunday, therefore slight
chance PoPs have been removed from the forecast. Higher precip
chances for the rest of the area appear to hold off until the
early or middle part of next week when the pattern shifts to one
with southwest flow aloft with a low pressure system moving from
near Baja California into the central CONUS.



.AVIATION:  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1155 AM CDT Thu Apr 30 2015

VFR conditions and dry wx will prevail at the TAF sites thru the
valid period. Otherwise, gusty N-NE winds will diminish and veer
NE-E after sunset and continue into Friday.

Specifics for KSTL: VFR and dry thru the valid period. Gusty N-NE
winds should remain in the 360-020 range today before
significantly diminishing around sunset where they will then veer
more of a true NE (040-060) and continue thru Friday.





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