Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...corrected aviation section 
National Weather Service quadrant cities Iowa Illinois
730 PM CDT Friday Jul 11 2014

Synopsis...
issued at 250 PM CDT Friday Jul 11 2014

Moisture continues to increase into the County Warning Area with precipitable
water ranging from 1 to 1.5 inches. However...forcing is weak and
sbcapes are very minimal due to plenty of middle/high level clouds.
Doppler radar shows scattered returns across our western and
northern County Warning Area but at most locations only sprinkles are reaching the
ground. Current temperatures ranged from the lower 70s to lower
80s.

Elsewhere...temperatures were around 90 from Kansas into the Southern
Plains.

&&

Short term...(this evening through saturday)
issued at 250 PM CDT Friday Jul 11 2014

Forecast focus on thunderstorm potential and temperatures.

Tonight...scattered showers and a few thunderstorms are possible
this evening but should become more numerous after midnight. Most
operational models support this thinking as stronger forcing
arrives as a strengthening low level jet veers into the County Warning Area. There
may be locally heavy rainfall but not looking at any flooding
issues as there has not been any significant rain since June 30.
Will go with chance probability of precipitation this evening then likely after midnight.
Operational models seem to want to paint the highest quantitative precipitation forecast near and
along I-80 but this will depend on where the warm front sets up.
Overnight low temperatures will be warmer than the past several
nights...in the upper 60s to lower 70s.

Saturday...tricky forecast because it will all depend on if the
mesoscale convective system lingers into Saturday morning and debris clouds. This may impact
temperatures and eventual re-development of thunderstorms during
the afternoon. Deep layer shear will be increasing during the
afternoon as upper level trough dives southeast into the Midwest
which should support supercells. Middle level winds will be increasing
to at least 40 knots. Storm Prediction Center has the entire County Warning Area in a slight risk for
mainly large hail and damaging winds...but an isolated tornado is
possible. For now the thinking is that scattered thunderstorms may
fester in our northern County Warning Area possibly most of the day and then
intensify across our north half late in the afternoon while spreading
southeast during the evening...as a cold front pushes across the
County Warning Area. Precipitable water increases to 2 inches which will support
locally heavy rains of 1 to 2 inches. Maximum temperatures will range
from the lower 80s north to lower 90s south.

Long term...(saturday night through friday)
issued at 250 PM CDT Friday Jul 11 2014

Active stormy weather will continue ahead of the passage of the
upper low moving south from high latitudes. Saturday evening will
see the final strong thunderstorm threat occur...as the main short
wave in advance of the strong pattern shift moves along the cold
front. This should provide deep layer shear supportive of organized
storms and some severe weather. The mesoscale details are a bit less
confident. The amount of ongoing daytime storms Saturday will
greatly impact the available cape for evening frontal convection.
Thus...I am leaving severe and heavy rain wording out of the
forecast for now. Another 0.5 to 1 inch of rain is expected Saturday
night...which should not pose any specific river flood or flash
flood problems.

A rather dirty frontal passage is expected into Monday...with a prolonged
period of chance probability of precipitation due to additional energy arriving aloft as the
upper low builds southward. With such cold air aloft...we run the
risk of showers and diurnal storms in the cold advection. No heavy
rain is expected...but it certainly does not appear to be a clear
Blue Sky behind the front Sunday morning.

Monday night through Wednesday appear seasonally very cool...with
lows around 50 to 53 each night...and highs in the upper 60s to
lower 70s. Any rain or dense clouds would hold highs in the low 60s
during this period. The energy savings compared to normal on this
event on a National level might be newsworthy.

By the end of the week...moderation is in effect...but I have left
the forecast dry due to poor confidence on surface and upper air
features.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 626 PM CDT Friday Jul 11 2014

Area of light rain showers moving east of area taf sites this
evening. Next round of rain expected to develop toward midnight
and expand across northern two-thirds of County warning forecast area through the early
morning hours...affecting all taf sites. With increasing low
level jet...should see embedded thunderstorms with this next round.
Yet another round of precipitation likely late in this taf period as the
main cold front approaches from the west Saturday afternoon. All in
all...a wet and messy forecast with variable ceilings and periods of
thunderstorms.

&&

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

$$

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

National Weather Service Glossary of Abbreviations