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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
634 am CDT Friday Aug 22 2014

issued at 328 am CDT Friday Aug 22 2014

Aloft...upper ridge persists over the Mississippi Valley. Surface
low near klse this morning with a stationary front extending to its
southwest into Colorado and also to its east into the Great Lakes.
Thunderstorms this morning fueled by low level jet...warm sector dew points in
the 70s...and approaching mesoscale convective vortex.


Short term...(today and tonight)
issued at 328 am CDT Friday Aug 22 2014

Area of convection over south central Iowa should persist through
sunrise and affect southeast Iowa and west central Illinois. Short range
models including the hrrr and RUC weaken the convection after
sunrise...which makes sense given the diurnal trend of the low level jet.
However...models have typically been too quick to squelch
convection...and thus believe it will linger a bit longer than
prognosticated and will hang on to probability of precipitation in the southern half of the County warning forecast area
longer than mesoscale models would suggest.

Another round of storms expected this afternoon as the surface low
continues to sag ever so slightly farther south and the front
remains stalled over northern MO/southern Iowa. Of course exact positioning of
storms remains particular with so many boundaries
around. Current thinking is that favored area is along and just
south of i80 where the 850 mb front is prognosticated to set up.
Regardless of exact location...expect intense rainfall rates due to
high precipitable waters at or above 2 inches.

Active weather continues through tonight with boundaries lingering
and potential for upper waves coming out of the west-southwest.

Long term...(saturday through thursday)
issued at 328 am CDT Friday Aug 22 2014

The persistent ring of fire pattern continues through the weekend
presenting a threat for hot and humid conditions outside the
occasional mesoscale convective complexes likely to impact parts of
the region. The upper level ridge is then expected to break down and
shift eastward by the middle part of next week. This will allow
Canadian high pressure to build into the area...returning
temperatures closer to late August normals and providing a period of
drier weather.

Saturday and Sunday...low pressure lifting northeast through the
northern plains will lift the low level boundary/warm front
northward through the forecast area Saturday. The associated warm
advection and strengthening middle level cap will limit thunderstorm
chances to the northeast half of the forecast area. With dew points
easily in the lower to middle 70s...very muggy conditions will
continue. Maximum temperatures will continue to be a challenge due to
uncertainty in convective trends and associated cloud cover. With
surface winds more southeasterly...will bias toward the lower end of
guidance with highs from the middle 80s northeast to lower 90s south.
This would still result in heat index readings near to just above
100 south of I-80 in the afternoon hours. Saturday night through
Sunday...the area will fall into the more deeply mixed but capped
warm sector with 850 mb temperatures supportive of widespread highs
in the upper 80s to lower 90s and possibly warmer depending on the
amount of cloud cover. This would result in possibly another day of
100 plus heat index values and may require heat headlines over at
least the south.

Monday through Thursday...model solutions continue to differ in the
timing of the both the initial early week frontal passage and the
stronger cold front around Wednesday and Thursday. The European model (ecmwf) and Canadian have
the initial front pushing through into central Illinois and MO
Monday...while the GFS holds it well to the northwest. Our forecast will
continue a low confidence blended approach with thunderstorm chances
returning late Monday and continuing through Thursday. The past
couple runs were trending toward a greater likelihood of a dry
Thursday as high pressure builds in. Warm to very warm and continued
high humidity suggest a possible need for heat headlines at least in
the afternoon hours for Monday and Tuesday where highs are
maintained in the upper 80s to lower 90s with overnight lows holding
in the 70s for much of the area. Temperatures are trending a bit
cooler...for Wednesday and Thursday as the continuity in successive model runs
back the timing of the pattern change and placement of the in-coming


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 627 am CDT Friday Aug 22 2014

Patchy dense fog affecting kcid and kdbq will lift by middle morning.
Meanwhile...thunderstorms will affect kbrl this morning and
showers will move into kmli. Later today...another round of storms is
possible this afternoon and evening at all area taf sites...but
the greatest chance is for areas mainly south of I 80.
Otherwise...prevailing winds will be light and variable with
gusts near thunderstorms.


Dvn watches/warnings/advisories...


short term...dmd
long term...sheets

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