Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service quadrant cities Iowa Illinois
616 am CDT Friday Jul 31 2015

issued at 346 am CDT Friday Jul 31 2015

High pressure was located across MO this am as light westerly
winds were reported across the area. Northwest 500 mb flow continued across
the area and as leading to slightly drier air across the area. A
850 mb jet was moving into the area from the northwest. A weak surface trough was
located from Duluth to just north of Aberdeen South Dakota. This surface trough
and 850 mb jet will be the dominate weather players in the short term


Short term...(today and tonight)
issued at 346 am CDT Friday Jul 31 2015

Main forecast concern for the short term are the chances for probability of precipitation
across far southern zones today into this evening. Weak forcing
looks to limit overall coverage of precipitation and leads to low
confidence in precipitation occurring.

Surface trough...weak 850 mb convergence and day time heating looks to be
the main forcings for precipitation later today. Large scale models pop
quantitative precipitation forecast across SW and S portions of Iowa from 18z through 06z today. As the
southward moving surface trough moves through the area...our chances for
probability of precipitation will leave with it. Hires cams also pop quantitative precipitation forecast across the area
from 21z to 03z. Without strong forcing...will keep probability of precipitation in the
schc realm.

850 mb jet advecting into the area will lead to winds near 20 knots
and gusts to 30 knots across our NE. These winds will likely
result in drier air being mixed to the surface and thus a difficult
dewpoint forecast for the day today. Regardless...with highs in
the 80s and dewpoint temperatures in the 50s with moderate
should be an overall beautiful sensible weather day.

Long term...(saturday through thursday)
issued at 346 am CDT Friday Jul 31 2015

Active/unsettled northwest flow to result in periodic precipitation
chances... and eventual cooler temperatures next week.

Saturday and Saturday night...anticipate at least some rain chances
developing especially by Saturday evening into the overnight
attendant to moist transport and convergence with veering low level
jet. Confidence is low on extent of storm coverage as NAM/GFS
deeper by 2-4+ mb with northern plains surface low and sharper on
definition of warm frontal structure and stronger with low level
wind fields and attendant convergence... while ecm weaker and more
diffuse. Storm Prediction Center has nearly the entire County Warning Area in slight risk of severe
storms...and cannot discount at least isolated severe storm potential
especially west of the Mississippi River where models generally
depict environment with MUCAPE around 1000-1500 j/kg and 25-30+ kts
of shear 0-6km above ground level. Expect more humid conditions to go along with
very warm/hot temperatures well into the 80s most areas with some locations
possibly 90 or lower 90s especially southwest 1/2 of County Warning Area depending
on amount of sunshine.

Sunday and Sunday night...maintained chance probability of precipitation for slow decaying of
lingering precipitation processes Sunday am and potential redevelopment on
any residual outflow boundaries by middle to late afternoon into
evening. However...lower confidence with precipitation chances here as some
potential for eml to advect into area and cap things
off...especially if more robust convection /MCS/ occurs early Sunday
am. High temperatures will be challenging due to potential convective
debris... but banking on at least partial sunshine to boost temperatures
into the 80s during the afternoon to go along with humid conditions.

Monday through Thursday...through midweek it appears County Warning Area will reside
near the Battle Ground between heat dome over rockies into plains
and upper low and cooler temperatures around the Great Lakes. This will
result in surface front near the region with periodic rain chances
as upper level disturbances propagate down across the region in
northwest flow. Due to timing challenges aided by model smoothing of
low amplitude waves unfortunately have to carry daily rain chances.
The week looks to start off seasonal on temperatures but with time do
anticipate a downward trend to below normal with influx of cooler
air in wake of passing Great Lakes system.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 611 am CDT Friday Jul 31 2015

VFR conditions are forecast for the taf sites through the period.
Main concern for aviation are the winds and gusts this afternoon.
Some gusts near 30 kts are possible. These winds will be out of
northwest. These winds could lead to some crosswind issues on Landing at
airports without runways into the wind. Brl has a very slight
chance of showers and thunderstorms this afternoon. At this not have enough confidence to add into the taf for brl.


Dvn watches/warnings/advisories...


short term...Gibbs
long term...05

National Weather Service Glossary of Abbreviations