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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
310 am CDT Monday Apr 21 2014

Synopsis...
issued at 309 am CDT Monday Apr 21 2014

06z surface analysis has a weak low near kfsd with a frontal boundary
running roughly along the Minnesota/Iowa border into southern Wisconsin. A
cold front ran from the low into eastern Colorado while the main
Canadian cold front ran from northwest Minnesota into northeast
Colorado. Dew points were in the 40s and 50s from the western Great
Lakes into the Southern Plains with 20s and 30s behind the Canadian
cold front.

&&

Short term...(today and tonight)
issued at 309 am CDT Monday Apr 21 2014

Convection overnight has been mainly confined to the frontal zone
north of the area. However...new convection has developed in the
unstable air across Iowa and Missouri where dew points were in the
50s. Radar does show considerable virga across southeast Iowa into
western Illinois.

Based on the overall synoptic set up...new convection that has
developed west of a kiib to kotm line should become more widespread
in coverage through sunrise. So areas west of a kdbq to Kirk line
have the best chance at seeing some rain by sunrise.

Daytime heating is expected to allow the convection to persist and
become more widespread during the morning hours. The extreme eastern
parts of the County warning forecast area may remain dry through middle day.

When the cold front sweeps through the area this afternoon...
convection should be the most prominent along with thunderstorms. A
somewhat broken line of convection should develop along the cold
front with more scattered convection ahead of it. Convection should
shut down fairly quickly from west to east during the afternoon once
the main cold front moves through.

Some lingering convection should persist over roughly the eastern
third of the County warning forecast area during the early evening before ending. The late
evening and overnight hours look to be dry as Canadian high pressure
builds into the Midwest.

Long term...(tuesday through sunday)
issued at 309 am CDT Monday Apr 21 2014

The long term forecast will begin with cool and dry weather Tuesday
through early Wednesday...followed by a rather dynamic cold frontal
passage/low passage Thursday.

With sun Tuesday...we should climb back to the upper 50s north to
middle 60s south...all in all not a bad day but none the less cooler
than the past few days. Tuesday night...short wave ridging should
allow for a radiational cooling night of lows in the middle 30s
northeast to lower 40s southwest. An increase in middle and high clouds
is likely toward early Wednesday as the next system spreads moisture
across the plains. Models now bring the front across the County Warning Area during
the middle morning to early afternoon hours with strong forcing. It
seems likely that we will not have a break between any Wednesday
night convection/dissipating convection and any new development
Thursday. Thus...it seems our threat for severe weather is low due
to a lack of lower level instability. Rainfall continues to look
light to moderate...generally a half inch or less given the
progressive nature of the system and less than ideal diurnal timing.
Coverage does look high enough Thursday to continue with likely
probability of precipitation.

In the wake of the system Thursday...we will continue to have lower
probability of precipitation in for Thursday evening. The GFS has some more energy on the
back side of the cold front for potential showers...while the European model (ecmwf)
is dry. These probability of precipitation could easily be removed on the next shift if the
GFS loses this feature.

Friday into Saturday morning appears dry...and from there on...the
extended computer models vary incredibly. While frontal positions
and quantitative precipitation forecast certainly draw ones attention to the differences between the
00z GFS and 00z European model (ecmwf)...that is not the source of the variation. It
all comes down to how each model handles the energy on the system
Thursday as it moves towards the East Coast. All models have a
closed low moving over southeast Canada from Friday through the
weekend. However...the GFS continues to produce a very strong cut
off low from this process. An upper low so strong is places the
Continental U.S. Into a full Omega block...with strong subsidence through day
10 over the upper Midwest. It also keeps very cold air circulating
around that low...resulting in dry...cold...mostly sunny skies. The
Gem and European model (ecmwf) do not produce such a Deep Cut off low. Thus...without
a strong cut off...they show a more progressive synoptic flow...with
a deep upper trough emerging into the plains by next weekend. From
that point on...the European model (ecmwf) creates very wet scenario...which would be
likely should its handling of the East Coast whopper upper low...or
more properly...lack there of...be correct. For now...we have a
cool forecast Saturday through Sunday...with moderate chance probability of precipitation
for rain and some thunder south.
Ervin

&&

Aviation...(for the 06z tafs through 06z Monday night)
issued at 1101 PM CDT sun Apr 20 2014

VFR conds through 21/15z with scattered showers developing later
tonight into Monday morning. Coverage of precipitation should
increase late Monday morning into the afternoon as a cold front
advances across the area. Occasional MVFR ceilings in showers and a few
thunderstorms. South to southwest winds less than 10 knots the
remainder of tonight then becoming northwest 10 to 15 knots behind
the cold front on Monday afternoon. VFR conds with sky clear Monday night
as high pressure begins to build into the area from the northern
plains. Northwest to north winds 10 to 15 knots Monday night.



&&

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

$$

Synopsis...08
short term...08
long term...Ervin
aviation...haase