Scientific Forecaster Discussion

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Area forecast discussion...corrected 
National Weather Service Lincoln Illinois
1024 am CDT Wednesday Apr 16 2014

issued 1021 am CDT Wednesday Apr 16 2014

Low pressure in South Dakota will move east into Iowa and then
northeast toward Lake Huron. As it progresses, a warm front will
lift across IL, putting our forecast area in the warm sector by
this evening. During the day, southerly winds will increase as the
pressure gradient tightens between departing high pressure and the
South Dakota low. 12z rap forecast soundings show mixing heights up to
825-850 mb. That should allow momentum Transfer of wind speeds
around 25 miles per hour with some gusts to 35 miles per hour. We expect to remain below
Wind Advisory criteria of 30-39 miles per hour sustained winds for an hour or
more. Peak winds appear to be in the noon to 3 PM time frame.

Mixing of dry air from the middle levels will help the surface temperatures
climb about 10 to 15 degree warmer than yesterday. Lightly filtered
sunshine will also help boost high temps, with readings in the middle
to upper 50s by 3-4 PM.

We should remain dry until the cold front pushes across Illinois
sometime late Thursday/Thursday night. Still, limited moisture
will keep rain chances and amounts on the low side.

Our current forecast grids look on track over the next 12-24 hours,
especially temps, dewpoints, winds and sky. No formal update will
be needed this morning.


issued 556 am CDT Wednesday Apr 16 2014

Little change needed to previous taf set. Wind will be the main
concern through this afternoon. Southerly wind gusts around 30
knots are expected to develop near all taf sites by late morning,
and continue through the afternoon. May see some even higher at
kpia. We will lose the gusts with sunset, but sustained winds will
still average around 15 knots much of the night. Late in the
period, winds will start to shift more to the southwest, ahead of
a cold front which will move through the area later on Thursday.


Previous discussion...
issued 249 am CDT Wednesday Apr 16 2014

Short through Friday

Winds will increase markedly across central Illinois today as
gradient tightens between departing high pressure system and low
tracking from the Dakotas into southern Minnesota. Models are not
quite as strong with the winds as they were in previous runs, so
am not concerned about reaching Wind Advisory criteria. BUFKIT
momentum Transfer at kpia shows 33kt winds at the top of the mixed
layer this afternoon, as opposed to 43kt on the prior run just 24
hours ago. Despite this decrease in momentum, think S/southeast winds
will gust to between 30 and 35mph across the western half of the
kilx cwa, with gusts to around 25mph further east near the
Indiana border. This strong southerly flow will help bring much
warmer air into the region. Extent of warming will be mitigated
somewhat by an easterly component to the wind and mixing heights
lowering to less than 5000ft. Resulting afternoon highs will range
from the middle 50s east to around 60 far west.

As southern Minnesota low lifts toward Lake Superior, it will
drag a weak cold front into the Illinois River valley by dawn
Thursday. This boundary will become stationary along the I-55
corridor during the day Thursday, creating little in the way of
sensible weather. A middle-level short-wave will approach from the
southwest late in the day and will eventually interact with the
front to perhaps produce a few light showers. Current surface
analysis shows a very dry air mass has settled across the eastern
half of the Continental U.S. All the way to the Gulf of Mexico. In fact,
buoys in the northern Gulf are currently showing dew points as low
as the middle to upper 30s. With so much dry air to the south, do
not think front will have enough moisture to work with in order to
produce precipitation across the area on Thursday. GFS is the only model
that is holding on to quantitative precipitation forecast across the Illinois River valley
Thursday afternoon, but think this is overdone. Will therefore go
with a dry forecast across the board. There are even some
indications that dry conditions will continue Thursday night into
Friday as the upper wave arrives. At this point, will leave chance
probability of precipitation for showers in the forecast Thursday night into Friday
morning as synoptic lift associated with the wave will likely be
enough to squeeze a few light showers out of the dry air mass. Once
the wave passes, dry weather will return Friday afternoon and

Long term...Saturday through Tuesday

After a warm/dry day on Saturday, attention turns to next
approaching system for early next week. Models have been trending
slower with its approach, with most 00z Apr 16 guidance suggesting
Easter Sunday may remain largely dry. GFS is the most aggressive
model in driving precipitation eastward into the area, but even it has
backed off and keeps rain at Bay until Sunday afternoon at the
earliest. Gem focuses best rain chances Sunday night into Monday,
while European model (ecmwf) is even slower and advertises mainly a Monday rain
event. As a result of the distinct slowing trend, have trimmed
probability of precipitation accordingly. Will keep Saturday night and Sunday morning dry,
then will bring chance probability of precipitation into the picture across the western
County Warning Area Sunday afternoon. Will highlight the Sunday night/Monday time
frame with the highest pops, followed by a return to dry weather
on Tuesday. Aside from the early week rain chances, the extended
forecast will feature warmer weather, with model guidance
suggesting temperatures reaching the 70s by Tuesday.



Ilx watches/warnings/advisories...