Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Quad Cities Iowa Illinois
618 PM CDT Sat Aug 27 2016

..aviation update...

issued at 336 PM CDT Sat Aug 27 2016

Quiet weather day so far. Temps have warmed into the mid
70s north to lower, even middle 80s central and south. Storm Prediction Center
mesoanalysis depicted high dewpoints in the upper 60s/lower 70s and
correspondingly high pwats near 1.75 inches over the lower portion
of the upper Mississippi Valley.


Short term...(this evening through sunday)
issued at 336 PM CDT Sat Aug 27 2016

This evening and tonight...a narrow zone of low-level convergence
and agitated cumulus is forecast to move out of south-central Iowa
bringing a chance for isolated showers and thunderstorms, which the
hrrr/rap insists will develop over the SW forecast area late this
afternoon, then move toward the Quad Cities area this evening. Feel
these solutions are overdone on the extent of convection but cannot
ignore them completely. Have 20-30% chances and anticipate low areal

Thunderstorm threats: although instability in the form of 1000-2000
j/kg of MUCAPE is forecast, shear will remain low, precluding a
severe threat. If storms do form, heavy rainfall rates and lightning
strikes are the primary threats.

Late tonight into Sunday morning...weak sfc high to build in behind
departing upper-level trough leading to periods of clear skies and
very light winds. Based on slightly longer nights this time of year,
dewpoints in the mid/upper 60s to near 70 f, and the aforementioned
sky and wind conditions, thinking shallow ground fog will form in
favored low-lying areas late tonight. The fog could become locally
dense and increase in areal coverage into early Sunday morning.
Future shifts may be able to enhance fog wording/intensity later

Sunday afternoon...a little warmer compared to today - mid 80s on
average for east Iowa/northwest Illinois and noticeably humid with dewpoints
in the lower 70s. Isolated to sct showers and storms are possible
approximately in the counties south of Highway 30. The better
chances are south of I-80. In this area, low values of 0-1 km
convergence are present where southerly and southeasterly winds
intersect. Overall chances are not that high - 20-30% most areas.
Many locations will probably make it through the day without
receiving measurable rain. Uttech

Long term...(sunday night through saturday)
issued at 336 PM CDT Sat Aug 27 2016

Main forecast challenge for the long term period is the difficulty
in pinning down favored periods and areas for showers and storms.
Model consensus is sorely lacking through Wednesday, and cannot
completely rule out rain during any particular period. Will
continue to carry the highest pops, in the 30 to 40 percent range,
from Monday into Tuesday. The American models, as well as the
Canadian and ECMWF, are all suggesting some potential for periods
of at least scattered coverage during this time frame. The
potential for an organized system with widespread heavy rain looks
low. However, with dewpoints still in the low 70s and weak wind
field, there will likely be some isolated heavy rains.

Looking ahead, Wednesday night into Friday looks mainly dry with a
somewhat drier and cooler airmass working into the region. The GFS
is suggesting potential for another system on Saturday.

Expect near to slightly above normal temperatures through
Wednesday, then slightly below normal from Thursday on.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 613 PM CDT Sat Aug 27 2016

Quiet weather is likely through Sunday, with only an isolated
shower or storm a remote possibility this evening and again Sunday
afternoon. What is likely under the light and variable flow
overnight will be fog formation. Shallow fog is expected over all
areas, and it could be dense in spots prior to 14z Sunday. All
sites are at risk for IFR/LIFR visibility and possible low cigs as
well. The conditions are expected to rapidly improve to VFR again
by 15z Sunday morning.


issued at 1140 am CDT Sat Aug 27 2016

Many area rivers are forecast to rise over the next week due to
recent heavy rainfall. The point with the main near term concern
is the Cedar River near Conesville. The new forecast has that
point rising above minor flood stage around midday Tuesday. The
river has yet to begin another rise, and would prefer to assess
trends before committing to a Flood Watch. We will be re-
evaluating tonight into Sunday. The Wapsipinicon River near DeWitt
is also forecast to rise above minor flood stage next Friday,
which is much too far out for a Flood Watch, especially given that
location's history of under performing crests.

On the Mississippi River, the main change with the morning
forecast guidance was somewhat higher crests at some points. Three
locations are now forecast to go over flood stage in the next four
to 5 days: Keithsburg, Gladstone, and Burlington. Confidence
remains low, with another complicating factor being the
considerable uncertainty in additional quantitative precipitation forecast over the next several
days. Will hold off with any flood watches again today.


Dvn watches/warnings/advisories...


short term...uttech
long term...rp Kinney
hydrology...rp Kinney

National Weather Service Glossary of Abbreviations