Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
FXUS63 KDVN 261116 AAA
Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
616 AM CDT MON SEP 26 2016
Issued at 336 AM CDT Mon Sep 26 2016
Early this morning, a much more seasonable airmass surged into the
area. Dewpoints in the low 40s to upper 30s were found across NW
Iowa and SW MN. Temperatures in this area were in the low 50s to
upper 40s. High clouds were slowly moving out of the area as the
cold front surges east into Indiana and KY. A strong vort max
aloft will lead to windy conditions today across the area.
.SHORT TERM...(Today and Tonight)
ISSUED AT 336 AM CDT Mon Sep 26 2016
Main forecast concern in the short term is the dewpoint and wind
forecasts as fire danger for field fires could be very high today.
Rather quiet and cooler short term forecast is the main sensible
High pressure will further entrench across the area today as upper
level closed low slowly slides to the east. Shortwaves through
this flow will lead to winds in the 15 to 20 kt range this
afternoon with possible gusts to 30 kts. NAM and GFS soundings
suggest mixing to 825 hPa. H85 winds are near 40 kts, so some of
this flow will translate into gusty winds. With the deep mixing,
think that dewpoints will be lower than what many of the spectral
and regional models have. Looking at the CAMs, it appears that
dewpoints across the southern CWA will likely result in afternoon
min RH values near 25. While most of the native grasses have not
cured much, many fields are near 90 percent cured. With those
values and the wind and RH, it appears that field fires could be a
concern today. Will be issuing a SPS to discuss this threat.
.LONG TERM...(Tuesday through Sunday)
ISSUED AT 336 AM CDT Mon Sep 26 2016
The upper trough in the vicinity of Lake Superior on Tuesday is
shown to deepen into a closed low while shifting slowly southward
along Lake Michigan through Wednesday. This will maintain deep
northerly flow through mid-week ushering in the coolest air of the
early fall season.
Tuesday will start off with considerable sunshine but during the
afternoon expect increasing clouds over northeast Iowa into
northwest Illinois, as a PV anomaly rotates down backside of sagging
upper low. With the increase in clouds may come a chance of showers
late in the day, but better chances look to occur Tuesday night over
the northeast third to half of the cwa as the PV anomaly sweeps
down across the region. Any rainfall amounts look to be very light
and mainly a trace to a few hundredths of an inch. Prior to the
arrival of the clouds Tuesday PM, deep mixing will fuel more gusty
northwest winds 10-20+ mph, while thermal parameters support a
general range from the lower 60s far north to the lower 70s south.
Clouds and spotty light precipitation Tuesday night may aid in
warmer lows in the upper 40s to near 50 degrees over the northeast
while mainly mid to some lower 40s elsewhere.
Wednesday looks to be trending toward a cloudy and rather cool day
as the core of the cold air aloft traverses the region. Will also
have a chance at some light showers or sprinkles again mainly over
the eastern half of the cwa. Highs in some areas of far northeast
Iowa and northern Illinois could struggle to hit 60 degrees if skies
were to stay overcast, with 850 mb temperatures generally around 4C
to 5C supporting lower 60s with a few mid 60s possible southwest with
any length of solar insolation.
Late week into the weekend there remains uncertainty with the
overall pattern and eventual track of the upper low. The consensus
favors the region becoming more under the influence of surface and
upper level ridging Thursday into Friday, with temperatures
moderating closer to normal. As the upper ridge builds in the upper
low will become cutoff and blocked with developing rex block over
the Great Lakes. Over the weekend, as a trough comes ashore in the
west the ridging breaks down and the ECMWF shows the upper low
retrograding back toward Lake Michigan on Saturday. It has been
consistent with this idea, but remains a western outlier. Should
this occur then would likely see more clouds along with cooler
temperatures and even a chance of showers for our eastern counties
mainly late Friday through Saturday. However, despite the ECMWF
consistent westerly track of the retrograding low this weekend, it
remains west of it`s ensemble mean and all other guidance.
Therefore, the forecast for Friday through the weekend is toward the
consensus further east track with less influence resulting in dry
conditions and near normal temperatures of mostly 70s for highs and
50s for lows.
.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
ISSUED AT 612 AM CDT Mon Sep 26 2016
VFR conditions are expected throughout the period with main
concern being gusty winds this afternoon. Any general aviation
airport with only north/south runways will have crosswinds today.
Issued at 336 AM CDT Mon Sep 26 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 is above 21 feet early
this morning (second highest level on record unofficially), but
appears to be quickly nearing crest.
Cedar Rapids has eclipsed major flood stage and continues to rise
rapidly. The crest at Cedar Rapids is for 23.0 feet Tuesday morning.
Confidence in the crest level is moderate due to uncertainty with
effects of attenuation. Either way, well above major flood stage is
likely at Cedar Rapids into the middle of the week. Major flood stage
is also forecast at Conesville by the middle to end of the week.
Confidence there remains moderate as well due to uncertainty with
effects of attenuation as the high water routs downstream.
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.