Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 251615
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1115 AM CDT THU AUG 25 2016

...Update to include Hydrology Section...

.UPDATE...
Issued at 1031 AM CDT Thu Aug 25 2016

The overall trend with the mcv and associated precip shield is
becoming more clear. As a result, a significant revamp has been
done to the overall forecast; pops/clouds have be increased and
temperatures have been lowered a little.

UPDATE Issued at 926 AM CDT Thu Aug 25 2016

The induced mcv from convection in the Plains last night continues
to slowly push an area of rain with some embedded thunderstorms to
the east northeast. RAP trends are starting to catch on to the
mcv and moves it east northeast across the south third of the area
later today.

As such the pops have been increased yet again with an emphasis on
timing and probable areal coverage. The overall support for the
thunderstorms is slowly weakening thus the thunderstorm threat
should be confined to the south and southeast edges of the
precipitation shield.

Pops may get increased further during the day as the overall trend
and timing becomes better defined.

UPDATE Issued at 740 AM CDT Thu Aug 25 2016

Latest runs of HRRR and RAP continue earlier concerns of being
more aggressive with precipitation toward midday through
afternoon with convectively aided shortwave and attendant
isentropic lift. Have begun to raise pops with latest update
but will need to be re-evaluated, with the best chances looking
south of Highway 34 but perhaps light rain and sprinkles in
stratiform as far north as Highway 30. Have also tweaked down
highs 1-2+ degs south to account for more clouds and increased
rain chances, but if trends persist then could be cooler by still
a couple more degrees.

&&

.SYNOPSIS...
Issued at 332 AM CDT Thu Aug 25 2016

Cold front extends just south of Dubuque to Cedar Rapids line at
08z, with some pockets of showers and isolated storms occurring
near and ahead of the boundary. Main corridor of convection
is occurring further south from portions of eastern Illinois back
through Kansas attendant to upper level shortwaves and low level
jet and moisture transport.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 332 AM CDT Thu Aug 25 2016

Post-frontal pressure rises of 1-2 mb are supportive of boundary
sliding through rest of cwa today. Developing and deepening
northerly winds through 850 mb will usher in slight drying,
leading to decaying precipitation chances from north to south
through midday. Forecast confidence is lower for this afternoon
and tonight, as frontal boundary stalls just to our south. Models
depict some isentropic lift and moisture transport developing
back into southwest cwa by mid afternoon and continuing tonight
near to south of I-80. These processes appear to be tied to
convection and attendant wave lifting northeast across Kansas
early this morning. Drier air deepens but only 6-8kft agl, which
can still easily be overcome by lift for light showers and
sprinkles up to I-80 and possibly Highway 30 if further north NAM
would verify. For now, have maintained or expanded low pops south
of I-80 later today and tonight, but will continue to assess
trends in radar and other observational data and update if needed.

As for temps, highs today will be modulated by amount of solar
insolation. Given weak cool advection, and anticipation of skies
becoming at least partly sunny, if not mostly sunny especially
north, highs should manage to get around 80 or in the lower 80s.
Lows tonight anticipated from the upper 50s north to mid/upper 60s
south, based on obs and progged low level thickness and verification
of temperatures early this morning.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 332 AM CDT Thu Aug 25 2016

Friday...Broad low to mid level ridging acrs the western GRT LKS to
the mid and upper MS RVR Valley, while southwesterlies re-organize
acrs the plains. Still some signs of elevated return flow/isentropic
lift up acrs northern MO into IA and will keep some low CHC POPs
acrs the south and west at times for higher based showers and a few
storms during the day, but may be more in the way of just over-
running cloud cover in most areas. Temps held down in the 70s to
around 80. Then southwestern plains short wave trof will look to
eject out acrs the MO RVR and the upper MS RVR Valleys thru Sat
morning. Associated broad lift and increased south/southwesterly LLJ-
warm moist conveyor up to the lee of the wave, should induce areas
of storm clusters up acrs the DVN CWA as Friday night progresses.
Marginal at best support to produce strong storms Fri night, but a
few model solutions indicating another round of seasonably high THTA-
E feed/PWATs of 2 inches or more into Sat morning. Thus locally
heavy rainfall should be the main concern, if this extent of column
saturation verifies.

Saturday and Sunday...With the 00z run models depicting the mean
ridge axis still to the west/upstream of the CWA until it passes by
mid Sat evening, expect occasional rounds of showers and some
embedded thunderstorms on Sat. Despite the cloud cover, BL saturation
and areas of precip, rather robust pre-wave warm air advection and
breezy south/southwest sfc winds still to drive high temps into the
upper 70s to lower 80s. Post-wave ridging will look to end the
precip from west-to-east later sat night into Sunday morning. If we
get a clear out of sky cover, could be a foggy early Sunday morning.
Most of Sunday to probably be dry, but the latest medium range
models suggest re-organizing return flow acrs into MO may allow for
some elevated showers to drift into he south and west later Sunday
afternoon. This activity may then become more isolated into Sunday
night if nocturnal LLJ takes more of a focus back further to the
west like the latest 00z run ECMWF suggests.

Monday through next Wednesday...longer range indications suggest
mean westerlies to tighten back further to the north along the U.S.-
Canadian border next week...while seasonably warm conditions
infiltrate the region.  While the various medium range solutions
break out almost daily areas of precip in and near the local fcst
area, see no real organized focus and would think most of the early
to mid week period would have plenty of dry hours. Will also have to
watch for teleconnections as the week progresses to what ever
tropical system that can impact the southeastern CONUS.   ..12..

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 641 AM CDT Thu Aug 25 2016

Cold front will exit the area and pull up stationary to the south.
Lift over the front will maintain bouts of vfr clouds through the
taf cycle, with the potential for some sprinkles and showers
mainly south of Highway 30 this afternoon and evening. Have handled
this potential with vcsh wording at BRL. Winds will be northerly
at 5-10 kts.

&&

.HYDROLOGY...
Issued at 1105 AM CDT Thu Aug 25 2016

Recent heavy rains across the Upper Mississippi Valley have led
to rises on area rivers. On the Mississippi River, Gladstone LD18
(GLDI2) and Burlington (BRLI4) are currently forecast to reach
minor flood stage by early next week. Since these river level
forecasts are approximately 5 or more days away, confidence on
reaching minor flood stage is low and a Flood Watch has not been
issued.

If significant changes to the forecast occur, we will express our
confidence in this section of the AFD. Please continue to monitor
for updates into next week. Uttech

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

UPDATE...08
SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...12
AVIATION...McClure
HYDROLOGY...Uttech



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