Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 181943

Area Forecast Discussion
National Weather Service Quad Cities IA IL
243 PM CDT Mon Sep 18 2017

Issued at 241 PM CDT Mon Sep 18 2017

Warm moist air has gradually worked north over the CWA today, and
has set up a warm front through the middle of our area, generally
from Cedar Rapids to Sterling Illinois. The main axis of showers and
thunderstorms has moved east into Minnesota through Missouri,
stretching over central Iowa. An MVC is located near northwest
Missouri, and can be seen in the radar composite imagery, but
otherwise is not strongly represented in the weak wind flow.


.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 241 PM CDT Mon Sep 18 2017

Though the over all forcing for the front will weaken tonight, the
area appears set to be in a favorable lift zone of the MCV working
northeast. That MCV will likely interact with the subtle warm front
to bring a period of moderate intensity showers and thunderstorms to
the area through about midnight. Initial movement will be northeast,
but cell growth on the south and east edge should bring this area
eastward with time, through the Quad Cities around 9 PM. Short term
guidance reflects this thought, as does all high resolution
convective allowing models. The global solutions are showing light
rain, which generally should also be possible even if storms do not
grow in intensity. There is plenty of CAPE around as temperatures
warmed to the lower 80s today already, and dewpoints are in the mid
60s. Both are warmer than forecast.   Rainfall tonight, while
generally light, will support a slow movement of storms that could
have a swath of 0.50 to 1 inch.

The clouds and convergent flow will hold temperatures up tonight, in
the lower to mid 60s, while also allowing for some fog potential and
lower cloud certainty. By morning, the low clouds and any remaining
showers will end early in the east, with warm air spreading back
over the region. Highs in the lower to mid 80s should occur, even
with only full sun in the afternoon.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 241 PM CDT Mon Sep 18 2017

While there are rain chances through mid-week, the prospects of a
widespread rain are low. Above normal temperatures and dry
conditions will end the week and the weekend.

Dry conditions will be seen across the area Tuesday evening.
Attention then turns to the mid-week system.

Late Tuesday night the models generate rain in the northwest quarter
of the area. However, the models look overly moist. Thus the
potential does exist that late Tuesday night may remain dry for the
entire area.

Wed/Wed night the WRF/GFS are bringing 70 dew points back into the
area ahead of the next front. The CMC global/ECMWF have upper 60s
dew points which look more realistic but may still be a bit high.
How much moisture that is available for the front will be important
regarding areal coverage of precipitation and rainfall amounts.

Currently the model consensus has slight chance to chance pops on
Wednesday with chance pops Wednesday night. Interestingly, the
models bring the front into the area mid to late Wednesday afternoon
and then dissipate the front across the area Wednesday night. If
convergence along the front is weak and moisture is lower than what
the models are projecting, then rainfall would end up being very

If the front dissipates across the area as suggested by the models
Wednesday night, then any weak convergence may be enough to generate
precip Thursday morning before ending in the afternoon. Again, if
the models are too moist then areal coverage and rainfall amounts
would be less. Right now the model consensus has slight chance to
chance pops across the area Thursday morning with slight chance pops
across the northern half of the area Thursday afternoon.

Thursday night on...

The model consensus has very warm and dry conditions Thursday night
through Sunday evening as an upper level high develops over the
Midwest. Temperatures will average well above normal. The very dry
conditions raises the potential that highs may be warmer than
guidance and lows may be cooler than guidance.

Late Sunday night and into Monday the upper level high starts to
break down as another front moves toward the area. However, the
models disagree on how quickly the upper level high breaks down and
how quickly the front will arrive. The models appear to have a loose
agreement in that the better forcing for any precipitation will be
behind the front. The CMC global and ECMWF have a risk of rain no
earlier than Monday afternoon while the GFS develops pre-frontal
rain late Sunday night and into Monday.

As a result of these differences, the current model consensus has
slight chance to chance pops late Sunday night and Monday.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1230 PM CDT Mon Sep 18 2017

VFR conditions will be seen through 23z/18 as an upper level
disturbance moves into eastern Iowa. After 23z/18, conditions will
deteriorate to MVFR with SHRA and possibly some isolated TSRA. Any
SHRA/TSRA that impacts a TAF site is expected to result in a
period of IFR conditions. After 06z/19, the rain will end with
MVFR conditions deteriorating to near IFR with fog. Although not
included in the 18z TAFs, the potential exists for LIFR conditions
developing with the fog.




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