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Area forecast discussion 
National Weather Service Lincoln Illinois
1229 PM CDT sun Apr 19 2015

Update...
issued at 1114 am CDT sun Apr 19 2015

Surface low lifting northward into the region and pushing plenty of
warm air advection rain ahead of it across the forecast area. Plenty of precipitation expected
today and into tonight, but more scattered in nature in the
overnight hours. Some dry air working around the low and eroding
some of the rainfall may bring a break in the rainfall
briefly...but not enough to pull precipitation anywhere for long. Have
made a few adjustments to the forecast, but no major updates are
anticipated at this time.

&&

Short term...(today and tonight)
issued at 328 am CDT sun Apr 19 2015

Latest water vapor imagery continues to show closed upper low over
eastern Colorado, with lead short-wave rotating around this feature
across Arkansas/Louisiana. As this wave lifts northward, precipitation
will eventually spread into central Illinois today. 07z/2am radar
mosaic shows dry conditions across the entire kilx cwa: however,
showers are beginning to develop and become more widespread further
south across western Kentucky and far southern Illinois. Based on
radar timing tools and latest hrrr forecast, think scattered showers
will arrive south of I-70 over the next couple of hours, then will
spread northward toward the I-74 corridor by midday. Have adjusted
probability of precipitation to account for the slower arrival of precipitation during the morning,
then have gone with categorical probability of precipitation across the board this
afternoon. Aside from some sbcapes of around 1000j/kg across the
far southeast cwa, forecast soundings remain fairly stable today. As a
result, am expecting mainly showers with just a few embedded
thunderstorms. Due to cloud cover and precip, high temperatures
will be several degrees cooler than in recent days, with readings
mainly in the 60s. Warmest temperatures of around 70 will be focused
along/west of the Illinois River where precipitation will be slowest to
arrive.

Long term...(monday through saturday)
issued at 328 am CDT sun Apr 19 2015

Lead short-wave will lift into northern Illinois/Indiana by early
evening, likely leading to a temporary lull in the showers.
Meanwhile, the main upper low will get a solid push eastward and
will arrive across Illinois later tonight into Monday morning.
Showers and perhaps a thunderstorm will accompany this feature, so
will continue likely probability of precipitation tonight through Monday morning. Once the
500mb vorticity maximum and the associated surface cold front pass to the
east, rain chances will come to an end by Monday afternoon. Thanks
to a tight pressure gradient behind the departing front, strong west/northwest
winds gusting to between 25 and 30 miles per hour will develop on Monday. The
winds will subside for a time Monday night, but will once again
increase markedly during the day Tuesday. High temperatures both
days will remain in the lower 60s, while overnight lows dip into the
upper 30s and lower 40s.

00z Apr 19 models have come into much better agreement concerning
the extended forecast, with consensus featuring a chilly and largely
dry week ahead. Both the GFS and European model (ecmwf) indicate a weak cold front
will pass through central Illinois Tuesday night into wednesday:
however, they disagree on how much precipitation it will generate. The GFS
is slightly wetter and faster with fropa, while the European model (ecmwf) is drier
and about 6 hours slower with the front. Due to the strong
northwesterly upper flow pattern in place across the Midwest, think
the faster GFS is the way to go with timing, but think the drier
European model (ecmwf) is better with quantitative precipitation forecast as deep moisture will be lacking with this
feature. As a result, have opted to carry low chance probability of precipitation
everywhere Tuesday night, then only across the southeast County Warning Area on Wednesday.
Once the front passes, a cool/Canadian airmass will settle into the
region for the middle and end of the week. High temperatures will
struggle to reach the 60 degree mark on both Wednesday and Thursday,
while lows drop into the 30s. Coldest morning may end up being
Friday morning, when ridge of high pressure is overhead and winds
will be lightest. Will need to keep an eye on temps, as frost
advisories will be possible across parts of central/southeast
Illinois later this week. After that, another system will approach
from the southwest by the end of the week: however, its influence
likely will not be felt until Friday night/Saturday at the earliest.

&&

Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1226 PM CDT sun Apr 19 2015
models bringing the surface low up and through the area within the taf
period. Two major concerns...visible drop and low ceilings associated with the
prolonged rain. Have kept the lower visible/ceilings on the eastern
terminals. Concern on the west side is the model hint at a
secondary line of precipitation showing up with the 500mb trough later as
the low pulls out to the east. Guidance not really reflecting that
well...and will be in conflict with some of the drier air being
pulled into the west side of the system. Confidence lower for pia
and spi than the other sites.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

Update...hjs
short term...Barnes
long term...Barnes
aviation...hjs

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