Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdvn 182304 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
604 PM CDT Wed Sep 18 2019

..00z aviation update...

issued at 345 PM CDT Wed Sep 18 2019

18z surface data has a weak boundary running from north central Iowa
into southeast Missouri. A stronger cold front ran from northwest
Minnesota into western Kansas. Dew points were in the 70s ahead of
the cold front and in the vicinity of the weak boundary. Dew points
in the 50s were behind the cold in the plains.


Short term...(this evening through thursday)
issued at 345 PM CDT Wed Sep 18 2019

Persistent convection across central Iowa has moved into eastern
Iowa. Extrapolation takes the current storms generally east toward
Dubuque with a slow dissipation through sunset. Other storms in
southeast Iowa and northeast Missouri will dissipate with sunset as

The evening hours should be relatively quiet after sunset.

After midnight new storms will develop across central Iowa into
Minnesota. Individual storms in the line will move northeast but the
overall line will slowly move southeast. Thus rain will move in from
the northwest with it generally reaching a Freeport, Illinois to
Sigourney, Iowa line by sunrise Thursday. Given the high moisture
levels in the atmosphere locally heavy rainfall is possible.

On Thursday the band of rain will slowly move southeast during the
day with areal coverage slowly decreasing. The best chances for rain
look to be across the northwest half of the area.

Long term...(thursday night through wednesday)
issued at 345 PM CDT Wed Sep 18 2019

Warmer than normal and humid through the end of the work week then a
cool down to around normal. Moisture from the remnants of Imelda
poses a heavy rain risk.

Thursday night
assessment...medium confidence

The daytime convection from Thursday will decrease in areal coverage
after sunset. An approaching upper level disturbance is expected to
allow isolated showers and storms to persist through the night.

Friday through Saturday
assessment...medium confidence

The upper level disturbance approaching Thursday night will move
through the area on Friday and Friday evening. This disturbance will
allow new showers and storms to develop rather quickly during the
day along the approaching cold front and allow storms to persist
through Friday night.

The model consensus has chance pops for Friday and Friday night.

As for Saturday the slowly moving cold front will start entering the
area. Moisture already in place combined with moisture coming from
the remnants of Imelda will allow showers and storms to quickly
develop during the day. The potential for heavy rainfall is a given
and the overall situation will need to be watched carefully for
possible headlines.

The model consensus has chance to likely pops for the area on

Saturday night on...

Saturday night through Sunday night
assessment...high confidence on rain occurring. Low confidence on

Moisture from the remnants of Imelda and moisture already in place
will interact with the slow moving cold front across the area. The
overall large scale set up is very favorable for rain and the
potential for heavy rainfall.

Saturday night into Sunday looks to see the more widespread rainfall
with rain ending from north to south Sunday night. The highest rain
chances are generally south of I-80.

The model consensus reflects this by having chance to categorical
pops Saturday night, chance to likely pops Sunday and chance pops
Sunday night.

assessment...high confidence

The global models have a wedge of high pressure moving through the
area behind the cold front which should allow for a dry day. The
model consensus concurs with dry conditions.

Monday night through Wednesday
assessment...low confidence

The global models disagree on what will happen but do agree that
there will be several upper level disturbances moving through in the
flow aloft.

The European model (ecmwf) has dry conditions Monday night through Tuesday night with
rain chances with the upper level disturbance on Wednesday. The CMC
global has dry conditions Monday night, rain with a passing
disturbance Tuesday/Tuesday night and dry conditions Wednesday.

The GFS has a fairly significant rain event with a warm front across
the far south with another cold front moving through the area late
Tuesday. The GFS solution may be overdone if the cold front late in
the weekend gets far enough south of the area. However if the front
stalls out across northern Missouri and central Illinois then there
may be credence to the GFS solution.

The model consensus is thus biased toward the GFS solution with
slight chance to chance pops Monday night and chance pops Tuesday
through Wednesday.


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 694 PM CDT Wed Sep 18 2019

Widely scattered thunderstorms occurring ahead of a slow moving
warm front may impact the brl site early in the evening.
Elsewhere, only light showers with VFR conditions are expected.
Some light fog is possible toward morning with restrictions
expected to be MVFR or better. Thursday, another round of
thunderstorms is expected to move into the area. Forecast
confidence is low with the timing and duration of these storms and
thus only prob30 groups were utilized. Outside of the rain and
storms, conditions are expected to be VFR.


Dvn watches/warnings/advisories...


National Weather Service Glossary of Abbreviations