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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
646 am CDT Sat Apr 18 2015

Synopsis...
issued at 330 am CDT Sat Apr 18 2015

A quiet night over the County Warning Area with mainly thin cirrus clouds and
current temperatures ranging from the lower 50s to lower 60s.
Regional Doppler radar data indicated a few showers and isolated
thunderstorms in central Iowa in an area of weak warm air advection/
850 mb transport. However...these showers were moving north.

Elsewhere...high pressure was situated just north of Minnesota and in the
upper Ohio Valley. Water vapor loops showed a filling upper low in
extreme southern Colorado moving slowly east.

&&

Short term...(today and tonight)
issued at 330 am CDT Sat Apr 18 2015

Forecast focus on shower chances...clouds and temperatures.

Today...operational models struggling with the dry easterly feed
from high pressure to our north and east. The models are now
keeping our eastern County Warning Area dry while bringing some showers into our
western counties mainly this afternoon. Forcing looks weak and the
airmass is stable so models may still be generating too much quantitative precipitation forecast.
Therefore have confined chance probability of precipitation to west of the MS river today.
Models seem to also develop too much cloudiness especially the
farther east you go into the County Warning Area. Temperatures will be a challenge
with an east to southeast wind but probably not as much cloud
cover as guidance suggests. The result should be afternoon highs
in the 70s...several degrees lower than yesterday. Rainfall
amounts in our far west will be up to a tenth of an inch.

Tonight...filling upper low in Colorado becomes an open wave as it lifts
into the central/Southern Plains...and begins phasing with a
northern stream trough. Better forcing and increasing moisture
transport should lead to likely probability of precipitation after midnight in our western
counties. However...east of the MS river the dry air should continue
to win out and I will keep that area rain-free. The airmass still
looks too stable to mention thunder. Rainfall amounts will range
from 1/4 to 1/2 inch west to little if any east. Minimum temperatures
should bottom out mainly in the lower to middle 50s.

Long term...(sunday through friday)
issued at 330 am CDT Sat Apr 18 2015

Period of rain likely through Sunday night...then cooler and mainly dry
through mid-week.

Models remain in good agreement that the closed upper low emerging
into the Central Plains on Sunday will deamplify into open wave
while lifting through the middle-Mississippi Valley Sunday night.
This energy will phase with southern Canada shortwave to form
slow moving closed low over the western Great Lakes early next week.

The main challenges will be probability of precipitation... and quantitative precipitation forecast amounts Sunday and
Sunday night. The remnants of southern stream cutoff low
emerging into the plains on Sunday look to be the primary forcing
mechanism for precipitation while lifting through the middle-Mississippi Valley.
Positive vorticity advection at 500 mb and some middle level
frontogenetical forcing and moisture appear sufficient for likelihood
of a period of rain over much of County Warning Area. However... drier low level
easterly flow initially on Sunday should slow or may inhibit arrival
of any measurable rain over northwest Illinois and possibly far northeast
to east central Iowa until late Sunday and Sunday evening when the
better forcing arrives. Highest rainfall amounts through Sunday night
(generally 0.2 inch to 0.5 inch) favor western and southern sections
of County Warning Area given close proximity to better lift and 850 mb Theta-E axis.
Amounts of generally up to 0.2 inch look reasonable across the
rest of the County Warning Area. Marginal lapse rates and limited MUCAPE should
preclude much in the way of thunder with precipitation mostly rain or showers.
Highs on Sunday will be challenging due to clouds and some precipitation
around... and cooler with mainly 60s. Warmest readings may be
over portions of east central into northeast Iowa and far northwest Illinois
where drier conditions anticipated for much of Sunday.

The middle-Mississippi Valley shortwave is expected to phase with southern
Canada shortwave to form large nearly cutoff upper low over the western
Great Lakes early next week. This system will be slow moving and thus
have influence on our weather for much of next week with flow aloft
generally northwesterly ushering in cooler temperatures (highs in the 50s/60s
and lows in the 30s/40s). Some patchy frost may be possible on one
or two nights from Monday through Wednesday if skies clear and winds go
light. Outside of some quick passing light rain showers Monday and Tuesday
mainly northern County Warning Area... expect generally dry conditions through mid-week.
Still quite a bit of variability in models over the latter half of week
tied to movement of upper low. Trimmed probability of precipitation to slight chances much of the
period from Wednesday night through Friday... as trends suggest slower
movement of upper low and thus more continuation of drier northwest flow
with much if not all of precipitation focusing over portions of the central/Southern
Plains into lower Mississippi Valley in line with pattern of late.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 643 am CDT Sat Apr 18 2015

Mainly VFR conds through this taf cycle. A storm system in the
plains may spread rain showers into portions of eastern Iowa...but
should only bring rain chances to kcid by this evening. East to
southeast winds 5 to 15 knots through the period.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Synopsis...haase
short term...haase
long term...05
aviation...haase

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