Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
628 PM CDT Wednesday Jul 30 2014

issued at 317 PM CDT Wednesday Jul 30 2014

12z upper air analysis continues to have an upper ridge from the plains to
the Gulf Coast. An 850mb low as in southeast Colorado with several
weak troughs from the Ohio Valley into the upper Midwest. Satellite
trends through middle afternoon show an extensive cloud shield from
Colorado into Arkansas with diurnal clouds from the Ohio Valley into
the northern plains.

18z surface analysis has weak lows in the Oklahoma Panhandle area with a
warm front extending east into Arkansas. A cold front ran from near Keau. Dew points were in the 60s
across the Southern Plains and lower Mississippi Valley with mainly
50s across the remainder of the plains and Great Lakes. Dew points
in the low 60s were just ahead of the Great Lakes cold front from
eastern Iowa into western Ohio.


Short term...(this evening through thursday)
issued at 317 PM CDT Wednesday Jul 30 2014

Satellite trends show vertical development in the clouds from kiib
to kikk which is along the back edge of the lower 60 dew points.
Radar does show weak diurnal convection has developed in eastern
Illinois in the slightly stronger forcing.

Based on satellite trends some weak diurnal convection will probably
occur over the next several hours across eastern Iowa but the rap
trends indicate downward motion developing prior to sunset across
the area.

Weak disturbances aloft will pass through the area overnight which
is expected to develop some middle clouds that persist through sunrise.

Quiet and dry conditions are expected Thursday morning. New diurnal
clouds should begin developing by middle day as new thermals develop.
During the afternoon another disturbance arrives from the plains. As
forcing from this disturbance increases...isolated to low end
scattered convection is expected to develop that should last until

Long term...(thursday night through wednesday)
issued at 317 PM CDT Wednesday Jul 30 2014

Main forecast focus is on precipitation chances through the period.

Thursday night through Sunday...deep cyclonic northwest flow
continues over the upper Midwest through the weekend. Precipitation
chances will hinge on strength and timing of periodic short waves
traveling through the flow. Timing of the initial short wave during
the day Friday suggests chance for thunder.

Main energy now on the verge of dropping into the Dakotas will drop
into the base of the upper trough over the Ohio River valley during
the weekend. Models in good agreement that with this evolution...
the upper low over the Great Lakes will kick out and mark the
beginning of a pattern shift. Low level ridging late Saturday into
Monday will return dry weather for that time frame.

Forecast confidence decreases significantly going into next week.
Flow is prognosticated to become more zonal...albeit weak. Lack complete
confidence in the timing of the initial pattern shift and then have
the usual concerns about the model handling of timing of waves in
quasi-zonal flow. End result will be a rather wet looking forecast
with chances of rain from Tuesday on until the timing can be better
defined. ...


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 614 PM CDT Wednesday Jul 30 2014

Rather quiet forecast with only few-scattered diurnally driven
cumulus clouds and light winds expected. There is a possibility
of fog around sunrise given the light winds and high humidity that
time of morning...but if it does will be short-lived
and not too restrictive. Wolf


Dvn watches/warnings/advisories...


short term...08
long term...dmd

National Weather Service Glossary of Abbreviations