Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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493
FXUS63 KDVN 240011
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
711 PM CDT Mon Oct 23 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 320 PM CDT Mon Oct 23 2017

As of 300 PM, a deepening 999mb sfc low was positioned along the
Michigan/Indiana border. For E Iowa/NW Illinois, breezy NW winds
were developing behind a cold front, and there was a broken band
of light rain and sprinkles working from west to east through the
region.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 320 PM CDT Mon Oct 23 2017

This Evening through Tuesday

Wind Advisory in effect for the counties roughly along and NW of
a line from Cedar Rapids to Dubuque from this evening through
Tuesday afternoon for peak NW gusts of 40-45 mph. Main impact is
difficult driving conditions for high profile vehicles

Upper low being carved out by a +145 kt jet streak is forecast to
pivot right through E Iowa/NW Illinois. A TROWAL feature is
apparent on model 850-600mb theta-e plots and overlaid temp
contours. Associated deep layer WAA, low-level convergence, and
frontogenetic forcing will cause a rainband to slowly pivot from
NC Illinois and S Wisconsin to the south into NW Illinois late
tonight into Tuesday morning. Further west, outside of this
deformation zone, isolated light showers are possible.

Tuesday`s high temps in the 40s will be the coldest so far this
season. And the windy conditions will make it feel like the 30s,
even during the afternoon.

Winds:

Tightening pressure gradient and boundary layer isentropic downglide
via CAA will lead to increasing NW winds this evening and tonight.
Convective overturning and momentum mix down of 35-45 kt winds
around 850mb should produce peak surface gusts of 35-45 mph.

Again the strongest winds, over 40 mph, are expected where the Wind
Advisory is in effect. In this area, there may be two periods of
strongest wind gusts: late this evening through about midnight, and
again from mid Tuesday morning into the early afternoon. Areas to
the E/SE of the advisory will likely not experience their highest
gusts until mid Tuesday morning into the early afternoon.

Confidence:

Current advisory is where confidence is highest and is well
collaborated with neighboring WFOs, but later shifts will have to
monitor for possible expansion to the SE. Also, since winds are
forecast to slowly decrease from the mid to late afternoon on,
there is potential the advisory could be dropped early. Uttech

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 320 PM CDT Mon Oct 23 2017

Tuesday night and Wednesday...Most precip to be exiting off to the
east of the CWA Tue evening, with clearing skies and decreasing wind
speeds with low amplitude bout of ridging bumping it`s way through
overnight. But still feel winds will maintain at least 5 to 10+ MPH
speed after midnight into early Wed morning, along with a potentail
mid level cloud deck skirting acrs the northeastern half of the fcst
area late Tue night to limit a more widespread frost formation event
and for now will advertise patchy in sheltered areas. But cold air
advection itself will still bring in widespread lows in the mid to
lower 30s, and if it were going to be clear and calm, a widespread
frost advisory would be needed for Tue night with these kind of
lows.

There are two model "camps" for Wed morning in handling track and
precip shield off a clipper-like upper level wave digging down and
east of the upper MS RVR valley late Tue night and especially Wed
morning. One that keeps all associated precip that would include a
rain-snow mix to the northeast of the fcst area, and the other(which
includes the 12z ECMWF) that clips the northeastern third or so of
the CWA with WAA showers Wed morning. For now will side with the
drier blend and watch for model trends toward one camp or the other.
Some post-wave Wed afternoon recovery back up in the 50s with even
some lower 60s possible in the southwest, as long as we get some
sunshine by afternoon. Non-diurnal temp trends Wed night with lows
occurring the first half of the night, before pref-frontal return
flow commences and increases into early Thu morning.

Thursday and Friday...Increasingly active pattern to usher the next
digging vigorous short wave trof acrs the northern and central
plains/MO RVR valley Thu into Thu night. The DVN CWA will look to
lay in this system`s upstream organizing cold front and sfc wave/low
system/s warm sector for a good chunk of the day. Breezy south to
southwest winds helping Highs make it into the upper 50s in the
northwest, to the mid 60s in the southeast, if the warm sector can
linger long enough before afternoon cold FROPA sweeps through the
area. Latest run medium range model solutions generally suggest the
FROPA process to come through dry, with a post frontal isallobaric
pressure rise surge in lingering tight cyclonic flow that may drive
winds close to Advisory criteria again late Thu afternoon and into
the night, especially if the sfc low acrs WI deepens below 1000 MB.

This system passage to commence a high amplitude cold dump down the
upper midwest Friday into Sat. Stout cold advection in string llvl
wind fields to crash temps well down into the 30s by Fri morning,
with Friday highs held in the 40s. Will have to watch this system`s
developing def zone precip shield wrapping back around and possibly
skirting acrs the northern CWA late Thu night into Fri morning with
precip type issues/rain-snow mix possible. This idea continuing
along with the 12z GFS, with clear out and sfc wind decouple for
temps plunging down into the 20s Fri night...first hard/killing
freeze for the season. The new 12z ECMWF is an outlier here, with
it`s upper trof placement and phasing rotating clouds and a precip
deck over the area Fri night into Sat morning. Although this would
limit Fri night lows to the 30s, the Euro is cold enough just aloft
for mainly a wet snow event late Fri night into Sat morning. Many
details to be worked out here obviously in later model runs for a
better handle.

Saturday through next Monday...The 12z run GFS continues to be cold-
below normal for much of the weekend, with moderating temps into
early next week ahead of the next upper level trof dumping down the
Rockies. Same with the latest ECMWF, but getting there in somewhat
different ways than the GFS.  Low confidence WAA type precip
possible late sunday night into Monday morning which again may be
accompanied by precip type issues if it occurs during that time.
 ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 707 PM CDT Mon Oct 23 2017

A slow moving upper level low will impact the terminals the next 24
hours with cloudy to mostly cloudy skies and blustery northwest winds
of 15 to 30+ mph. Ceilings will tend to be low VFR with periods of
MVFR mainly overnight and Tuesday with a chance of light rain. The
precipitation chances are handled as VCSH at this time.

&&

.FIRE WEATHER...
Issued at 320 PM CDT Mon Oct 23 2017

Tuesday

Sustained winds of 20-30 mph with gusts of 35-45 mph will result
in elevated fire weather conditions for dry, cured agricultural
fields. The main concern is that if a fire were to start it would
spread rapidly. Locations west of the Mississippi River, where it
is not raining, are most susceptible. Uttech

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Wind Advisory until 6 PM CDT Tuesday for Benton-Buchanan-
     Delaware-Dubuque-Jones-Linn.
IL...NONE.
MO...NONE.

&&

$$

SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...DLF
AVIATION...Nichols
FIRE WEATHER...Uttech



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