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Area forecast discussion 
National Weather Service Lincoln Illinois
1046 am CDT Wednesday Jul 27 2016

issued at 1046 am CDT Wed Jul 27 2016

15z/10am surface analysis shows stationary frontal boundary just
south of the Ohio River, with a few clusters of showers/storms
along the boundary from the Ozarks northeastward to northern
Kentucky. For the time being, all this activity remains just S/SW
of the kilx County Warning Area. Meanwhile further north, latest satellite/radar
is showing isolated showers developing from near Beardstown to
Jacksonville in advance of a weak short-wave trough noted on water
vapor imagery over western Iowa. 12z NAM is not picking up on the
isolated convection at all, while the latest hrrr and the 00z
WRF-arw are at least hinting at it. Will update the forecast to
bring slight chance pops further north into the County Warning Area to account for
the current showers. Other than that, the going forecast looks
fine and am not anticipating any other major changes.


Short term...(today and tonight)
issued at 307 am CDT Wed Jul 27 2016

The stationary front will remain just southeast of IL, roughly along
the Ohio River valley. A relatively weak pressure gradient north of
the front under a weak surface high will set the stage for patchy
fog to develop, especially in low lying areas. Locally dense fog has
already begun to form from Salem to Robinson, and those conditions
will linger through an hour or so after sunrise. Once the fog
clears, skies will be partly cloudy with diurnal cumulus forming in
much of the area. A plume of moisture streaming north of the
stationary front will keep rain and storm chances going for our
counties along and south of I-70 today. Storm chances will expand in
coverage to include the remainder of our counties later tonight,
with slight chance pops north of I-70 and chance pops along and S of I-
70. The potential for severe wind and/or hail remains low.

Long term...(thursday through tuesday)
issued at 307 am CDT Wed Jul 27 2016

On Thursday, another wave ripples through the nwrly flow and dives
into the Midwest, interacting with what remains of the boundary,
spreading showers and thunderstorms through Friday. Once the system
moves to the east a bit, showers will become more widely spread, but
likely linger through Saturday. High pressure ridge builds into the
Midwest and have continued to trend back on the pops from the
blended forecasts as well, but Monday starting to show some
consistency with small disturbance moving into the region with
another round of precip, particularly to the south. Will need to
watch that trend.

Temps trending slightly cooler through the first half of the weekend
with the more northwesterly flow and the precip influence. 850mb
temps not moderating quite as much, and holes/breaks in the cloud
cover for the next couple days could result in some isolated warmer
temps. After the first half of the weekend, the building heat in the
western half of the Continental U.S. Begins to shift, putting another warming
trend in place for central Illinois into the first of next week.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 640 am CDT Wed Jul 27 2016

The humid airmass is supporting patchy fog across central
Illinois, but the terminal sites have remained VFR through 12z and
should stay that way before daytime heating creates enough mixing
to clear out the residual fog by mid-morning. A weak convergence
line extending from near St Louis toward Effingham and Flora is
becoming active with showers already this morning. That convection
should remain south of the taf sites this morning, with spi having
the best chance of seeing a shower approach thunderstorms in the vicinity range. For now,
have left out any daytime storms from the tafs, and just indicated
a cumulus layer developing across the board in the 5k feet layer.

Better chances of showers and storms is expected to advance
northward toward I-72 this evening and overnight, as a weak
shortwave moves from SW to NE across south-central Illinois. We included
a thunderstorms in the vicinity in spi and Dec after 06z, while continuing VFR conditions.
The models are continuing to show MVFR fog potential later
tonight, but will leave it out of the tafs for now.


Ilx watches/warnings/advisories...


short term...shimon
long term...hjs

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