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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1139 PM CDT Thursday Oct 23 2014

issued at 757 PM CDT Thursday Oct 23 2014

As if often the case...the fog developed at dense levels versus
gradually lowering to them. Thus...the dense fog advisory has been
started now rather than waiting until 1 am. This dense fog will
slowly expand east over the County Warning Area tonight...and a possible expansion
of the advisory is being considered.


issued at 325 PM CDT Thursday Oct 23 2014

12z upper air analysis has an 850mb low over the Great Lakes with an upper
level disturbance from Minnesota into northeast Kansas.
Radar/satellite trends through middle afternoon show showers across
northeast Iowa and northwest Illinois. Skies were slowly clearing
from the west across Iowa.

18z surface analysis has an implied front/boundary from near kjef to
kdlh with a cold front from near krst to kfnb. Dew points were in
the 40s across the Great Lakes with a tongue of 50 dew points from
the Southern Plains into southeast Minnesota.


Short term...(this evening through friday)
issued at 325 PM CDT Thursday Oct 23 2014

Based on radar trends...isolated to scattered showers will continue
through sunset with the best chances north of I-80 and generally
east of Highway 61.

After sunset...clearing will slowly move east toward the Mississippi
as high pressure builds into Iowa. Those areas that saw rain during
the day may see some patchy fog develop as the skies clear.

After midnight...skies will continue to clear and winds become
light. Fog will develop and become fairly widespread. As a result...
a dense fog advisory has been issued for much of the area. Depending
upon how the fog develops...the areal coverage of the advisory may
need to be expanded.

Dense fog should be seen across much of the area at sunrise Friday
with areas of fog elsewhere. The fog should begin lifting toward the
end of the morning commute and burn off by late morning.

Friday afternoon should be quiet and dry across the area. Maximum
temperatures on Friday will be dependent on when the fog and low
clouds burn off. If the low clouds hold on longer...then high
temperatures for Friday would need to be lowered.

Long term...(friday night through thursday)
issued at 325 PM CDT Thursday Oct 23 2014

Friday night...general suggestion from models of pseudo warm frontal
passage in the evening with strong low level Theta-E advection
conducive for low clouds and possibly areas of drizzle or patchy very
light rain and fog. Cool front to follow overnight sweeping low level
moisture out and thus clearing skies. Lows coolest northwest (upper 40s
to around 50) to warmest far south (mid 50s).

Saturday through Sunday...surface high pressure to dominate much of the
period with dry and continued above normal temperatures... with maxes in the
60s to lower 70s (southern cwa). The high will gradually shift to
the east during day on Sunday with increasing east/southeast winds 10-20+ miles per hour
ahead of developing warm front. Strong low level moisture gradient
develops across County Warning Area during Sunday PM... but fairly shallow depth coupled
with middle level ridging precludes any mention of precipitation Sunday PM at this time.
Sunday night...warm front looks to lift through the County Warning Area with continued
strong moisture transport on 40-45+ knots low level jet supportive of chance
of showers across the northern County Warning Area Sunday evening. Rest of Sunday night
will be dry and rather mild in warm sector with lows well into the 50s
to lower 60s on southerly wind around 10 kts and gusty.

Monday through Thursday...chances for showers and possibly a few storms
exists Monday through Tuesday as western trough moves east through the
region. Still considerable model run to run variances on strength...
timing and track of energy which will have big impacts on precipitation amounts
and timing. Hi-res European model (ecmwf) has shown the greatest changes over past several
runs shifting main trough 500-700 miles north from Southern Plains to
now over western Great Lakes by Tuesday evening closer to GFS runs past
few days. GFS has actually shown better run to run continuity with this
system although it too is showing some changes especially in strength.
Monday may be without much in way of precipitation and mild with County Warning Area in
capped pre-frontal warm sector with highs well above normal and Manly in
the lower to middle 70s. Rain chances would then look to increase
markedly Monday night into Tuesday with cold front and main dynamics with
trough... with widespread moderate rain amounts possible as it looks right
now but again this dependent on strength of forcing and moisture with
impacts to track/strength of energy. In wake of trough passage...indication
of quasi-zonal flow setting up favoring drier side with typical fall
roller coaster ride on temperatures middle to late next week. GFS and European model (ecmwf) are
suggesting potential for stronger cold front and much colder temperatures late next


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1123 PM CDT Thursday Oct 23 2014

A dense fog and very low IFR ceiling event will begin the period...and
last well into Friday morning. Confidence is low on when the
minimum fog/ceilings will lift...maybe as late as 17z Friday...but
will show some improvement beyond minimums/ 1/4sm fog vv001 after
15z. In the wake of the fog...some MVFR stratus is possible
through the day Friday...again low confidence on how this plays
out since models either don't have it at all or are hammering the
area with IFR through the entire 24 hour period now. Should status
linger...another fog event with stratus is possible Friday night.
Since is most likely in northern Iowa...I have introduced another
period of IFR weather to the dbq taf after 00z/25.


Dvn watches/warnings/advisories...
Iowa...dense fog advisory until 10 am CDT Friday for Benton-Buchanan-
Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry Iowa-Iowa-
Muscatine-Scott-Van Buren-Washington.

Illinois...dense fog advisory until 10 am CDT Friday for Hancock-Henderson-
Jo Daviess-Mercer-Rock Island.

MO...dense fog advisory until 10 am CDT Friday for Clark-Scotland.



short term...08
long term...05

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