Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
FXUS63 KDVN 251743
Area Forecast Discussion
National Weather Service Quad Cities IA IL
1243 PM CDT SUN SEP 25 2016
...AVIATION AND HYDROLOGY UPDATE...
Issued at 1056 AM CDT Sun Sep 25 2016
KDVN shows only a few isolated elevated showers developing in a
line roughly from Clinton north into SW WI at 1025 am. Otherwise,
the large area of rain over central IA from nocturnal complexes
early this morning has since dissipated with an upstream complex
further SW across NW MO into eastern KS also decreasing in
coverage and trending more eastward in time. A large area of
clearing over the forecast area has allowed temperatures to surge
into the mid 60s to around 80. Surface analysis shows the surface cold
front roughly from Decorah through Marshalltown to Osceola, still
west of the local forecast area.
Pops have been lowered considerably this morning, but still
expect surface-based showers and a few thunderstorms to develop
along and ahead of the front over eastern IA this afternoon,
spreading east into IL from mid to late afternoon. There may be a
potential for strong storms along and east of the MS River, where
the current clearing and insolation may lead to more
destabilization than previously expected. Significant rainfall
today still looks unlikely over the eastern IA tributary rivers
and thus not expecting any impacts to on-going flooding or
Issued at 331 AM CDT Sun Sep 25 2016
Early this morning, weakening convection and showers were on the
CWA`s doorstep. Overall motion of the cells have been to the north
with a very slow easterly propagation of the line. These showers
and isolated rumbles of thunder will slowly make its way into the
area through day break. The best forcing for these showers and
thunder will slide north of the CWA. To our west, a cold front was
just entering the state of Iowa. This cold front looks to be the
gateway for more fall like weather.
.SHORT TERM...(Today and Tonight)
ISSUED AT 331 AM CDT Sun Sep 25 2016
Main forecast concern for the short term are the chances for rain
and thunder and the QPF associated with them. At this time, it
appears that many of the areas with cresting rivers today, will
not see much total rainfall, as the better chance for organized
thunderstorms and heavy rain will be east of the Mississippi River
Llvl forcing for organized convection and rain is weakening this
morning. This means that showers will diminish in intensity and
coverage through the morning. Hires guidance and QPF suggests that
little to no rain should fall across western zones this morning.
Current forecast has less than 0.25 inches in Buchanan County.
This is likely overdone base on current radar trends. Think that
this rainfall will have little to do with current crest forecasts
Later this morning a cold front will roll across the state of
Iowa. This front looks to be crossing the Mississippi river
between 18z and 21z today. Sporadic clearing will limit overall
instability in front of the front. Deep layer shear of 20 to 30
kts will likely limit the chance of severe weather. Current
thinking from SPC is that a wet microburst is possible. Based on
CAMs and regional gridded and spectral models, it appears that the
best chances for thunderstorms will be just out of the CWA to the
east. Have kept chc pops for most of the area with the exception
of likelies in the afternoon close to our eastern border.
Tonight, the main focus turns to the strong H5 vort advection and
resultant strong CAA. This will likely keep the BL coupled and
lead to winds in the 10 kts with gusts near 20kts realm. Drier air
will rush into the area for Monday morning.
.LONG TERM...(Monday through Saturday)
ISSUED AT 331 AM CDT Sun Sep 25 2016
Little change to theme of forecast with mainly dry conditions and
near to below normal temperatures.
Models forecast the upper trough over the Upper Mississippi Valley
on Monday to deepen into a closed low while dropping slowly south
across lower Michigan into midweek. This will keep the area under
deep cyclonic flow through Wednesday with west to northwest winds,
gusty at times early in the week, ushering in the coolest air of the
young fall season with highs in the 60s to lower 70s and lows in the
40s to lower 50s through Wednesday. Will have to watch for periodic
bouts of clouds and possibly sprinkles or a few brief light showers
by Tuesday into Wednesday over northeast cwa, but have maintained
dry forecast as forecast soundings show limited moisture depth. The
ECMWF is most aggressive and an outlier with very light QPF on
Wednesday, as it`s a bit further west with the low near Lake Michigan
and brushes cwa with a vort max. In addition the flow turns more
northeasterly especially over northern Illinois, which may aid in
bringing some lake-enhanced moisture. All this adds up to needing to
watch the Wednesday timeframe for possibly some introduction of
precipitation chances, and also increasing cloud cover and lowering
Late week into next weekend, have continued with a dry forecast and
moderating temperatures, as surface and upper level ridging build
in. The one potential fly in the ointment is the ECMWF for the past
couple of runs has remained consistent with retrograding the large
upper low back towards the Midwest by next weekend. This would
likely yield more clouds and cooler highs, but for now have kept
with consensus dry forecast and temperatures warming near to
slightly above normal.
.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1242 PM CDT Sun Sep 25 2016
A cold front moving through the region this afternoon will produce
scattered showers and thunderstorms. At noon, these were forming
along the MS River between the Quad Cities and Dubuque and will
push east out of the TAF sites at the start of the forecast
period. Light showers and pockets of MVFR ceilings, immediately
along the wind shift may impact the terminals until 2 pm. Gusty west
to northwest winds behind the front this afternoon will likely
diminish this evening, then resume gustyness Monday morning as
cooler and much drier air flows into the region.
Issued at 1242 PM CDT Sun Sep 25 2016
Flooding of several of the tributary systems across Iowa remains the
primary hydrologic problem for today, while flooding along the
Mississippi River continues to be forecast for the upcoming week.
Forecast for major flooding continues. Vinton has now surpassed 20
feet and is still rising, placing it at the second highest level on
record (unofficially). Confidence on the crest forecasts at Vinton,
and more so at Cedar Rapids and Conesville, are moderate due to
uncertainty with effects of attenuation as the high water routs
The crest at Cedar Rapids was lowered a half foot down to 23.0 feet,
but may be lowered further if Vinton crests below current forecast
and effects of attenuation become more apparent. Either way, well
above major flood stage is likely at Cedar Rapids from Monday
morning into the middle of the week. Major flood stage is forecast
at Conesville by the middle to end of the week.
Excessive amounts of water continue to rout downstream through the
Iowa and Cedar Rivers. There is high confidence on significant
flooding, especially during the middle to end of the week. Exact
timing varies by site.
Low to moderate confidence is associated with the crest forecasts,
or by how much a river level exceeds either moderate or major flood
stage due to attenuation of the routed flow. Please follow forecast
information closely throughout this event.
The Wapsipinicon River at Independence experienced a large flow
surge above the Major Flood stage last night, making for some
uncertainty on the associated local flow contributions. The crest
was adjusted upward, but recently the river level trends have slowed
possibly indicating the Wapsi may finally be near crest at IDPI4
around 19.3 or 19.4 feet. Routing this enhanced recent flow from
Independence downstream has produced increased crest forecasts of up
to 2 feet higher at Anamosa Shaw Road, and up to a half foot higher
near De Witt. Ranges at these two downstream sites may vary over the
next 24 hours because of unknown attenuation factors.
The Maquoketa River near Maquoketa also showed an overnight rise and
will reach the lower end of minor Flooding early this afternoon,
before dropping back down below flood stage tonight.
The Mississippi River forecasts continue to show only minor or
little adjustments in handling the large amounts of routed water
coming from upstream that will work though the main stem system.
Some locations will begin to see the river rise above flood stage
early this upcoming week, while others may not see flood stage until
the middle portion of the week. Crests on the Mississippi won`t
occur until late week or into next weekend. Just minor adjustments
of a slowed rise late in the week at Keokuk LD19 and Gregory Landing
due to flow cut back at the Red Rock Dam on the Des Moines River.