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FXUS63 KLOT 231125

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
625 AM CDT Sun Sep 23 2018

239 AM CDT

Through tonight...

High pressure over the Great Lakes will provide fair weather and a 
light east wind through the day today.  Temperatures are expected to 
top out in the low to mid 70s today, though areas near the lake will 
be held in the 60s with onshore flow. Outside of a couple passing 
high clouds today, should see plenty of sunshine. Clear skies 
continue into tonight and overnight lows will bottom out in the 50s 
for most areas, but a few of the typically cooler spots may drop 
into the 40s.



301 AM CDT

Monday through Saturday...

First item of interest in the long term is a subtle southern
stream disturbance (which has origins from TD 19E) progged to 
move into the lower Ohio Valley region Monday. Guidance continues
to suggest the vast majority of the forcing and resultant precip
with this wave will pass south of our CWA. However, increasing
southerly flow should transport moisture back north into our area
and with the glancing blow from the shortwave trough likely
supporting at least a chance of scattered showers Monday afternoon
and night, mainly southeast half of the CWA. Lapse rates and
instability are progged to be quite weak and given the weak 
forcing have pulled the thunderstorm chances from the forecast Mon
afternoon and night. 

Low and mid level flow is progged to veer in the wake of this
southern stream wave, which should slow the northward transport of
moisture into the area ahead of a stronger cold front progged to
move across the region Tuesday afternoon and evening. Plume of
somewhat steeper lapse rates are progged to advect east into the
area ahead of this next system and should support moderate
instability ahead of the cold front. Stronger frontal forcing and
respectable height falls should support QLCS development
along the front Tuesday afternoon and evening. Moderate
instability and seasonably strong winds aloft, albeit
unidirectional, could allow for some threat of locally damaging
winds with the QLCS. 

Quick hitting shot of seasonably chilly air will filter into the
region behind the front midweek, but pattern for the time being
looks to remain progressive with another northern stream shortwave
progged to track across southern Canada later in the week.
Southerly winds will allow for a moderation in temps ahead of the
next cold front, however the first front should push the deeper,
quality moisture well to our south. Return flow duration looks
limited and so precip chances with the front Thursday night look

Forecast uncertainty grows heading into the weekend with some
indications that Thursday front won't make it terribly far south
before stalling out as another shortwave trough ripples through
the zonal flow into the region. Precip, thunder chances, and temps
will all hinge on where the front ends up next weekend and at this
distance there is just too much uncertainty to justify making any
changes to the blended model guidance solution which has
increasing rain chances. If front remains to our south and we're
raining, then high temps could struggle to get out of the 50s, so
there should probably be an asterisk next to Saturday's high 
temps forecast in the upper 60s/lower 70s noting the potential for
much cooler conditions depending on how things evolve. 

- Izzi


For the 12Z TAFs...

Continued quiet and steady state weather on tap for today under
the influence of high pressure. Expect VFR conditions and east to 
southeast winds through the day. On Monday, moisture will return 
to the region. Ceilings currently in place over the Ohio River 
valley are progged to lift north across the terminals by around 
midday. There will also be a chance for showers, mainly in the 
afternoon beyond the current TAF period.






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