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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
707 am CDT Wednesday Aug 27 2014

Update...
issued at 706 am CDT Wednesday Aug 27 2014

An mesoscale convective system moving east across northwest MO and extreme south central Iowa was
occurring along the edge of the higher elevated cape and thetae
gradient across northern MO...which extends east into central Illinois.
Another area of scattered thunderstorms over SW and west central Iowa
was occurring in an area of broad thetae advection at 850 mb...and
was also drifting east to slightly southeast. Have updated to
likely probability of precipitation over the far SW to account for showers and isolated
thunderstorms advancing eastward over the next several hours.
However...both areas of showers and thunderstorms should continue
slow down and weaken along their eastern and northeast edge as
they move into the more nwrly flow over eastern Iowa...as indicated
at 850 mb on the VAD wind profiles at both kdvn and kdmx. The northwest
winds indicated around 15 kts...was poorly handled by short term
models that generally depicted a light westerly flow over the
region.

&&

Synopsis...
issued at 331 am CDT Wednesday Aug 27 2014

At 3 am...msas surface pressure fields indicated high pressure over
northern Minnesota...with the surface front well south along the I-70
corridor in Illinois and MO. Area radars showed scattered...elevated
weak showers streaming east along the I-80 corridor from dsm to
the quadrant cities with a isolated showers over southeast Iowa and west central
Illinois. A more significant...and so far slow moving...mesoscale convective system was along
the Iowa/NE/MO border area...in an axis of more significant 850
thetae convergence. Very light north to northeast winds out of the
Minnesota high was pulling in cooler and drier air at the low
levels...with widespread temperatures in the middle to upper 60s and
a few readings near 70 in the far south.

&&

Short term...(today and tonight)
issued at 331 am CDT Wednesday Aug 27 2014

In the near term...elevated thetae convergence fields in the
rap...which had a good correlation with the storms in SW Iowa...would
support the storm cluster slowly drifting east through
sunrise...reaching the far southwest and south before dissipating by
middle morning. Elsewhere...there is not much support or middle level
instability to suggest the elevated showers and isolated
thunderstorms over the central and south will ramp up like previous
mornings and will maintain low chance probability of precipitation. Higher chance probability of precipitation are
maintained mainly south of the Highway 34 corridor in southeast Iowa...where
weak moisture convergence at 850 mb continues this morning.
Beyond...rain chances have been removed over all but the far south
from late morning through afternoon as a low level easterly flow
continues to advect in drier air under a weak middle level ridge.
Temperatures will be similar to a bit cooler than yesterday due to
the easterly flow and likely increased cloud cover.

Tonight...all models have the next mesoscale convective system developing over western or northwest
Iowa around midnight...expanding east toward morning. Have adjusted
probability of precipitation accordingly...with much slower timing resulting in a dry night
in the east and later onset central and west. Heavy rainfall does
not look to be a major threat as mesoscale convective system generation and maintenance
tools point toward the best forcing not advancing much past northwest or
possibly north central Iowa by 12z.

Long term...(thursday through tuesday)
issued at 331 am CDT Wednesday Aug 27 2014

There should be a respectable thunderstorm complex across northern
Iowa Thursday morning with a Wing of convection moving across the
area. The northwest half of the area has the better chances for
rain. Boundaries left over from the morning storm complex will
provide the focus for scattered convection in the afternoon and
evening.

Although the signal is not as clear...another organized thunderstorm
complex should develop west of the area Thursday evening and move
east northeast late Thursday night into Friday morning. The
northwest third to half of the area has the better chances for rain.

Boundaries from the Friday morning storm complex would again provide
the focus for scattered convection that develops Friday afternoon
and evening.

Late Friday night another front or boundary is forecast to begin
moving into the area. The combination of moisture and forcing should
result in scattered convection persisting through sunrise Saturday.

Saturday on...
the overall weather pattern is supportive of nocturnal thunderstorm
complexes across the Midwest. Where each develops and moves affects
subsequent development. As a result...there will be periods of dry
weather that may be 6-12 hours in duration.

Temperatures Saturday through Tuesday should be near normal.

The model consensus has chance to likely probability of precipitation for Saturday and
slight chance to chance probability of precipitation Saturday night.

The model consensus has slight chance probability of precipitation for the area
Sunday/Sunday night. Several models are suggesting high pressure
moving through the area on Sunday which may result in dry conditions.

Monday through Tuesday the model consensus has chance probability of precipitation for each
12 hour period.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 706 am CDT Wednesday Aug 27 2014

Very light rain showers may impact the Cid and mli terminals
early this morning...otherwise VFR conditions are expected today.
High pressure advancing from Minnesota into the Great Lakes will provide
light northeast surface winds. Late tonight...a thunderstorm
complex is expected to develop over northwest Iowa and may advance
eastward to affect the Cid...dbq and mli terminals toward sunrise.
Confidence is low in the timing of this feature...thus only prob30
groups were used.

&&

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

$$

Update...sheets
synopsis...sheets
short term...sheets
long term...08
aviation...sheets

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