Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 252259
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
459 PM CST Sun Feb 25 2018

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 325 PM CST Sun Feb 25 2018

A few high clouds drifted across the area during the afternoon
hours. A west to southwest breeze was gusting around 30 mph. Early
afternoon temperatures ranged from the upper 30s along Highway 20,
to the 40s to the south.

&&

.SHORT TERM...(This Evening through Monday)
ISSUED AT 325 PM CST Sun Feb 25 2018

Quiet weather will continue through the short term period. Surface
high pressure will spread across the area tonight, allowing for a
light wind and mostly clear sky. Have favored the cooler end of
temperature guidance with significant radiational cooling, despite
the lack of snow cover. Lows should be mainly in the 20s. Cannot
rule out some patchy fog late tonight, especially where winds become
calm overnight, but this would only be an impact to aviation and
will not carry in forecast grids.

For Monday, have favored warmer temp guidance with late February
insolation and southwest surface flow. Afternoon highs are expected
to reach the upper 40s along Highway 20, and possibly as warm as the
upper 50s in the far south.

.LONG TERM...(Monday Night through next Sunday)
ISSUED AT 325 PM CST Sun Feb 25 2018

Monday night and Tuesday...Increasing south winds to make for non-
diurnal temp trends Monday night, lows held up in the 30s. Then as a
digging closed upper low carves out troffiness acrs southern CA and
toward the desert southwest, broad southwesterly steering flow still
on track to organize from those regions, northeastward through the
eastern GRT LKS. Warming LLVL return flow to boost temps to around
50 in the far northwest Tuesday, to the low 60s south of I80.

A sfc boundary sagging in from the northwest will align under the
steering flow and slow just to the northwest of the DVN CWA through
late Tue afternoon. But as this feature continues to sag south
toward the I80 corridor Tue night, some LLVL convergence lift
noticed in the vertical profiles along the boundary. The fcst
soundings also show building inversion and associated dry layer
aloft, thus moisture depth to fuel much of any precip in these
convergent fields somewhat at question, even sub-inversion llvl
moisture layer drizzle. But there are some signs of moisture depth
deepening for the south toward Wed morning in the southern CWA, and
possibly north of the front. Will keep low POPs for light precip
chances in these areas going for now, and if precip manages to form
in the north there may be some precip type issues toward Wed morning
if sfc temps can cool toward freezing in post-frontal northerly flow.

Wednesday through Thursday...Still much uncertainty with respect to
the mid to late week potential storm system the models have been
showing for a few days now, but they are holding on to it in various
forms of phasing and are generally quite ominous, especially the 12z
GFS and ECMWF. Both models have a seasonably mild day Wed with
increasing clouds and light rain during the day, with the main show
then taking place Wed night into Thu. It`s probably not worth going
through the details at this point with plenty of time to change with
pending phasing issues, but in general the 12z GFS has a southern
plains pan-handle hook low track with the sfc low deepening under 990
MB acrs the east-central CWA by late Thu morning.

This GFS solution sweeps unneeded heavy rain acrs the area Wed night
into early Thu, followed then with a dynamical cooled def zone wet
heavy snow acrs the north half of the area on Thu morning and into
the afternoon, as 20 to 30 KT sustained northerly sfc winds blast
the landscape. The 12z ECMWF is not quite as wet initially with the
Wed night rains(both the GFS and ECMWF even have some thunder in the
south Wed night), but then has cooler profiles in a more hastened
mode from late Wed night into Thu, switching over to more widespread
heavy accumulating snows by Thu around a convergent inverted trof
axis off an east central IL main low. Both models have the precip
winding down by late Thu afternoon or early evening in the east as
the cyclone pulls away, with sfc winds diminishing greatly Thu
night. Again, all this very subject to change at this point, and a
more unphased system or one that phases more off to the east of the
area would be much less impactful for the local area. But the focus
will be on additional model runs, especially 24 to 72 hours from now.

Friday through next Sunday...Much will depend on whatever occurs
with the Wed into Thu potential storm system, but most of the medium
range models suggest dry ridging in the wake of the cyclone for
Friday into Saturday with slow moderating temp trends(depending on
potentail snow cover). Both the 12z GFS and ECMWF sweep a banded
precip event from west to east acrs the area ahead of the next wave,
sometime late Sunday into Monday. The GFS is milder and more
progressive suggesting passing mainly light to moderate rain, while
the cooler Euro produces accumulating wet snow again late Sunday
night into Monday.   ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 450 PM CST Sun Feb 25 2018

VFR conditions are expected to dominate the TAF cycle. However,
as W/SW winds diminish tonight and become light southerly there
is a low chance of patchy fog with MVFR/IFR visibilities toward
daybreak at CID and DBQ. Confidence is too low for mention, but
will continue to monitor for later forecasts. Winds should
once again shift from W/SW on Monday and increase to around 10 kts.

&&

.HYDROLOGY...
Issued at 1035 AM CST Sun Feb 25 2018

Wapsipinicon River

Minor flooding is occurring this morning at Dewitt this morning
due to runoff from rainfall on top of already saturated grounds.
The river level is expected to crest in minor flood stage this
evening, and begin falling overnight.

Rock River

Runoff from Saturday evening rainfall has hindered progress of
receding river levels along portions of the Rock River this
morning. At Como, the river level has risen slightly back above
flood stage, and is expected to crest at minor flooding Monday
evening. Further downstream, major flooding remains ongoing at
Joslin and Moline. While recent observations continue to show
river levels decreasing, this will need to be monitored as runoff
from upstream reaches these locations.

Pecatonica River

Major flooding was observed this morning at Freeport, with the
river expected to reach crest in major flooding tonight. Yellow
Creek has risen, but remained within it`s banks this morning.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...RP Kinney
SHORT TERM...RP Kinney
LONG TERM...12
AVIATION...McClure
HYDROLOGY...Speck


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