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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1143 PM CDT Thursday Sep 3 2015

..updated aviation discussion...

Synopsis...
issued at 326 PM CDT Thursday Sep 3 2015

Latest surface analysis was indicating a weak front sagging southward
across the eastern Iowa/Minnesota border region into southern WI. Some marginal
convergent low level flow along this feature...with currently more
pronounced cumulus field across southwestern WI into northeastern Illinois. More
sunshine and southwest winds of generally 7-10 miles per hour producing ambient
temperatures across the County Warning Area in the upper 80s to lower 90s with more areas at
least 90 as opposed to 80s. This coupled with low 70s dewpoints making
for low to middle 90 heat index readings with a few upper 90 readings.
Aloft...a large bulging upper ridge/heat dome across much of the
central Continental U.S.. but water vapor imagery and this morning/S upper air
analysis were indicating an embedded upper low across northern
Michigan...and a secondary vorticity spoke swirling south-southeastward across
northern WI.

&&

Short term...(this evening through friday)
issued at 326 PM CDT Thursday Sep 3 2015

Tonight...with the surface front pushing into the far northern and
northeastern County Warning Area this evening and overnight...along with the vorticity
spoke rolling down across southern WI there will be a chance fro at
least an isolated shower or storm into the far northern and
northeastern County Warning Area late this afternoon and well into the evening. It
currently appears a better chance in heart of the current cumulus field just
to the north and east of the local area...but the evening shift will
have to be on the watch for development further south and west. Will
keep and fine tune the low chance/isolated probability of precipitation in the north and
northeast with a lean toward the latest run hires/hrrr-CR/arw-east
which seem to have a handle. If a few showers/storms manage to
develop in or make it into the County Warning Area they may linger well into the
overnight before decreasing late with support from the approaching
vorticity spoke. Post-frontal cloud deck currently across northeast WI will
also look to try and push southwest toward the County Warning Area...but will bank
on most of them falling short. They could hold temperatures up in the
northeastern County Warning Area higher than forecast values. Otherwise will be going
with lows similar to the past few nights of middle 60s to lower 70s.
Light low level convergent flow area in the vicinity of the front may Foster
some fog in the northeastern County Warning Area late tonight...but confidence not
there currently to place in the grids.

Friday...a day similar to today with like thermal profiles...
possibly a bit warmer profiles than today. But forecast soundings
suggest somewhat weaker mixing and the possibility or more clouds
especially in the northeastern third of the County Warning Area....thus for now will
go with highs similar to or a few degrees cooler than current temperatures
out there now. With lingering frontal zone draped across the
northeastern/eastern County Warning Area and vorticity maximum trapped across Lake Michigan into lower
Michigan by blocking upper pattern...will go with low chance/isolated probability of precipitation
mainly Friday afternoon in the far eastern/northeastern County Warning Area with a
watch for a need to expand them westward toward the MS river depending
on capping inversion and westward lift impact of the western Great Lakes
wave aloft. ..12..

Long term...(friday night through next thursday)
issued at 326 PM CDT Thursday Sep 3 2015

Very warm and humid conditions will continue across the area Friday
night through Saturday night. Lows will generally be in the 66 to 71
degree range and highs will be in the 87 to 92 degree range.

The chances for rain are not very good but there is a potential some
for diurnally driven convection in the far northeast and east areas
Friday evening and again Saturday afternoon. Saturday night
currently looks to be dry.

Sunday will be the last day of very warm and humid conditions. A
cold front will be slowly moving across Iowa so cloud cover may keep
temperatures in the 85 to 90 degree range. Parts of Benton and
Buchanan counties might see some isolated showers or thunderstorms
by late afternoon.

Sunday night on...

The extended will be marked with a pattern change with a good
potential of below normal temperatures developing. Additionally...
rain chances will be on the increase for the first half of the week.

Late Sunday night and Monday the cold front moves through the area.
The overall forcing does weaken with time...especially on Monday so
there are questions regarding how extensive the rain chances will
actually be. Right now the model consensus has chance to likely probability of precipitation
Sunday night with chance probability of precipitation on Monday.

The cold front will then stall out either over the area or across
northern Missouri and into central Illinois Monday afternoon. The
front is then expected to vacillate across the area Tuesday through
Wednesday. Conceptually...the scenario of an east west frontal
boundary across the area raises the question regarding heavy rain
potential. Internally the models have some subtle signals suggesting
heavy rain but they are quite weak. These signals will have to be
watched over the next 72 hours in order to see if they trend
stronger.

As a result...the model consensus has chance probability of precipitation Monday night
through Tuesday night. These probability of precipitation may trend higher over the next
several days.

A large cool Canadian high will push the front out of the area
either on Wednesday or Wednesday night. The model consensus has
slight chance to chance probability of precipitation on Wednesday and slight chance probability of precipitation
Wednesday night.

The models are indicating the Canadian high will be across the area
on Thursday. As such the model consensus has dry conditions with
cooler than normal temperatures. ..08..

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1138 PM CDT Thursday Sep 3 2015

Ridge of high pressure aloft will keep VFR conditions going
through the taf period. Minor patchy fog possible late
tonight...best chances for thicker/more widespread fog is at kdbq
with light east/southeast surface flow. Dropped visibilities as low as 3sm at
kdbq...but could briefly be lower between 10-14z/Fri.

Friday...slight chance for a pulse shower or thunderstorm but did
not mention in tafs due to very low probability. Uttech



&&

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

$$

Synopsis...12
short term...12
long term...08
aviation...uttech

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