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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1136 PM CDT Thursday Apr 24 2014

issued at 232 PM CDT Thursday Apr 24 2014

12z upper air analysis depicted strong shortwave over the
Oklahoma Panhandle with another located across eastern Montana.
18z surface map showed two low pressure centers near the region.
The first one was over central Iowa with a warm front extending
southeast into southern Illinois. This boundary along with Theta-E
advection and marginal MUCAPE values was responsible for the
first wave of showers and isolated thunderstorms that tracked
through the area. Light amounts under a quarter of an inch were
common with this first wave especially across the northwest third
of the County Warning Area. The second area of low pressure was located just south
of Kansas City with some strong thunderstorms developing out ahead
of it in Missouri and eastern Oklahoma.

Temperature gradient evident across the County Warning Area as of 2 PM with
readings only in the low 50s over the northwest to the low 60s in
the far southeast portions. Dewpoints were in the upper 40s/low


Short term...(this evening through friday)
issued at 232 PM CDT Thursday Apr 24 2014

Main surface low currently near Kansas City to track near St.
Louis this evening as strong shortwave over 0oklahoma heads towards
southern Illinois. Latest 12z model suite and hi-res models all
show strong forcing arriving late afternoon over the southwest and
spreading northeast across the area by early evening. This results
mainly in rain showers moving across the County Warning Area ending quickly from
west to east in the middle to late evening hours as the system moves
east. Steep middle level lapse rates although marginal may be enough
for a few rumbles of thunder across the south half and have
maintained isolated thunder wording this evening. Better
instability remains well to our south where the severe threat will
remain. Feel that the severe storms that develop south across
Missouri and Arkansas may limit the amount of moisture transport
into our area thus have lowered quantitative precipitation forecast amounts to that additional
amounts between a 0.25 to 0.50 inches seem more reasonable.

Tonight...increasing subsidence behind the system will allow clouds
to quickly clear from west to east with skies becoming clear by
early morning. This in addition to light northwest winds will
allow temperatures to drop into the upper 30s to middle 40s.

Friday...pleasant and dry conditions expected as high pressure
builds into the area. Deep mixing will allow high temperatures to top
out in the upper 60s to lower 70s under sunny skies.

Long term...(friday night through thursday)
issued at 232 PM CDT Thursday Apr 24 2014

The region is still in line for a prolonged period of rain as an
upper low forms over the plains Sunday and moves slowly east
reaching the Mississippi Valley by Tuesday. This solution is
presented by all of the operational models...which lends more
confidence to the wet forecast next week. The prolonged rainfall is
expected to produce a substantial amount of rain over a period of 2
to 3 days which could result in significant rises on area tributaries
and the Mississippi River.

The only cry day during the Middle Range and extended forecast will be
Saturday as the western trough moves into The Rockies...pushing an
upper ridge into the Mississippi Valley. Surface low pressure over
the Central Plains...developing ahead of the upper trough will have a
warm front extending east through Missouri. Easterly flow north of
the front should keep temperatures on the cool side especially north
where highs should only be around 60 while closer to the front in
the south middle 70s are expected.

Gulf moisture will be surging north ahead of the western trough
Saturday and will pool along the surface and 800 mb fronts. With the
moisture in place and low level winds expected to
strengthen...showers and thunderstorms should develop over the area
during the evening and continue overnight. At this time the best
forcing based on convergence associated with the low level jet should be
located to our west near the Missouri the severe threat
looks low for Saturday night. The easterly low level flow north of
the warm front should strengthen pulling in cooler air off Lake
Michigan. Went with lows around 40 north to the middle 50s south for
now. Some guidance though was showing lows north as cold as the middle
and upper 30s.

Sunday through Tuesday have probability of precipitation in the likely to categorical range
as the upper low moves slowly east into Iowa. Expect thunderstorm
chances will be the greatest Sunday and possibly Sunday night with
the better forcing ahead of the upper low. As the low moves closer
Monday and over the area Tuesday the the precipitation should be
mainly showers with some isolated thunder possible. The GFS and
European model (ecmwf) are showing potential rainfall amounts of several inches /in a
48 hour period/ over all or part of the forecast area by Tuesday.
Temperatures should be below normal during this period given the
extensive clouds and precipitation expected to be over the area.

The long range models show the upper low remaining over the area
through Thursday and possibly into Friday. While the threat for
organized rains will be low...the cold pool of air associated with
the upper system will create a good environment for at least
scattered showers. While thunder has not been mentioned for the middle
and late week period...any afternoon sun will increase the potential
for an isolated storm. Temperatures should remain below normal
through the rest of the week.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1118 PM CDT Thursday Apr 24 2014

Band of low clouds with IFR to MVFR ceilings near Mississippi River
will gradually shift east of terminals overnight as weak high
pressure builds in. Northwest winds around 10 kts and locally
gusty will become light westerly toward daybreak. The diminishing
wind and wet ground will bring risk of some fog with visibilities possibly
quite variable from 1-5sm due to shallow steep low level inversion.
After early morning fog...VFR conditions expected for the rest of
the taf cycle with mainly some middle and high clouds. Winds will
increase above 10 kts by late morning from westerly direction with
occasional gusts 15-20+ kts during the afternoon with deep mixing.
Frontal boundary to settle over the area Friday night...with winds
becoming light and variable. Potential of a few showers developing
late Friday evening with elevated warm advection above the front but
probability appears too low for inclusion at this time... but will need to be
monitored in later taf issuances.


the substantial rains expected over the area from Saturday night
into Tuesday will likely cause significant rises on area tributaries
and will also have some impact on the Mississippi River. The effect
of the rain on the area rivers will lessened some by the fact that
the rain will be falling over a several day period...allowing the
initial rainfall to soak in. Once the ground saturates then runoff
will increase. While the bulk of the rain should occur by
Tuesday...showers are expected to occur over the area through
Thursday and possibly into Friday.


Dvn watches/warnings/advisories...


short term...gross
long term...dlf