Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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738
FXUS63 KDVN 190835
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
335 AM CDT Tue Sep 19 2017

.SYNOPSIS...
Issued at 330 AM CDT Tue Sep 19 2017

Upper level shortwave and attendant showers will be exiting
northwest IL counties prior to daybreak. System brought
showers to a fair amount of the cwa yesterday afternoon
through evening, though rain amounts were unfortunately
rather light (less than 0.1 inch) but some isolated moderate
amounts (0.25-0.6 inch) attendant to storms in portions of
west central into northwest IL. Clouds continue to decrease
from west to east in the wake of the shortwave, and
combined with light winds and low level moisture enhanced
by recent rain is aiding widespread dense fog and low clouds
mostly south/west of Quad Cities.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Tue Sep 19 2017

Dense fog looks to burn off within an hour or two after sunrise
per GOES cloud thickness technique. Stratus may persist beyond
for a while, but increasing mid/upper level heights should aid in
decreasing clouds this afternoon. Banking on this amount of
solar insolation to push highs into the upper 70s and lower 80s.
Surface warm front is shown to bisect the cwa today, but
absence of forcing with heights building aloft, and weak low level
convergence precludes from any precip mention today. Precip chcs
are not zero however, as pretty decent 850 mb theta-e advection
is progged to develop by mid afternoon through this evening from
sw to ne with strengthening LLJ, but soundings show fairly shallow
moisture depth resulting in confidence too low for any mention.
Did hang on to some small PoPs late tonight over northeast IA for
potential of some elevated convection developing with veering LLJ
and attendant advection, and can`t rule out some activity into
east central IA near/sw of Quad Cities as well but far from coherent
signal in CAMs. Lows tonight in strengthening southerly flow
will remain mild and generally in the 60s, although a few sites
could only drop into the lower 70s in west/southwest cwa.

.LONG TERM...(Wednesday through next Monday)
ISSUED AT 330 AM CDT Tue Sep 19 2017

Wednesday...a challenging fcst day with mixed signals from the
latest available 00z run models. Cyclonic southwesterly steering
flow adjusts acrs the mid to upper MS RVR Valley, while embedded
wave shears out acrs MN into the western LK Superior Basin by
evening. Associated sfc front will look to get shunted acrs the
central CWA by Wed evening and then stall as it aligns from NE-to-
SW parallel to the steering flow. Just a low chance for some
lingering convective debris or showers sagging acrs the CWA during
the day left over from stronger activity earlier to the
northwest, and for now will keep the slight CHC pops loaded in the
grids. But with FCST soundings suggesting building cap/EML as the
day progresses and loss of convergent lift, feel the dry 00z
ECMWF and even the NAM may be more on target through 00z anyways.
If precip doesn`t materialize and debris decays early, extent of
warm air advection and mixing southwest winds could boost temps
into the upper 80s to lower 90s acrs much of the area and be not
all that far off record highs for Sep 20th. The models are
probably still overdoing sfc dpts near 70, and ongoing dry sfc
layer/mixing may translate to values more in the mid 60s. If DPTs
manage to make it in the upper 60s to around 70, heat index
readings will range in the low to mid 90s Wed afternoon.

Wednesday night may be the main precip window opportunity for the
rest of the week. Southwesterly 20-25 KT LLJ flow starts to impinge
on the lingering LLVL boundary, and as it tries to retreat back
north some as a type of warm front, that`s when sctrd showers and
storms may develop nocturnally along and north/northwest of where
even the boundary adjusts. More optimum shear profiles, southern
flank of upper jet dynamics, and LLJ convergence look to occur
further to the north acrs WI. But if storms get going locally, enough
support there for at least an isolated strong to severe storm, even
if elevated in nature. rainfall amounts to be localized again, with
those that manage to get under a storm or shower cluster possibly
getting up to a half inch by Thu morning. Many other areas to get
little rain at all. Seasonably mild overnight lows in the 60s.

Thursday and Friday...After a low chance of some lingering precip
Thu morning out of what ever Wed activity can occur, the latest suite
of medium range model runs all suggest a high amplitude-blocked up
pattern taking grip acrs the CONUS between active western Atlantic
tropical systems and western CONUS L/W Trof. The net result locally
would be dry and very unseasonably warm conditions to end the week. A
lot of upper 80s to low 90s look to be on tap, especially with a
southerly flow recharge and deeper mix. Summer won`t want to end on
Friday.

Saturday into early next week...longer range indications/upper jet
trends suggest the blocked pattern to continue acrs the region
maintaining unseasonable warmth and dry conditions through at least
Sunday locally, compounding the drought conditions. Incoming lee
side long wave transition zone, where western gulf northward
moisture conveyor shuttles up along to fuel an elongated precip
swath, now looks to edge east acrs the area later Mon into Tue. But
this timing still very suspect at this juncture and depends on
ongoing interaction with subsidence fields off/to the west of the
Atlantic tropical system/s.   ..12..

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1137 PM CDT Mon Sep 18 2017

Areas of fog and low clouds will increase overnight into the mid
morning hours with extended periods of MVFR to LIFR conditions and
possibly VLIFR conditions at all the terminals. Skies will clear
by late morning with VFR conditions into the Tuesday evening.
Winds will be light into mid morning and then become southerly at
5 to 10 mph.

&&

.CLIMATE...
ISSUED AT 317 AM CDT Tue Sep 19 2017

Record Highs for Wed September 20...

Moline.........92 in 1931
Cedar Rapids...93 in 1931
Dubuque........92 in 1895
Burlington.....93 in 1940

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Dense Fog Advisory until 10 AM CDT this morning for Benton-Cedar-
     Clinton-Des Moines-Henry IA-Iowa-Jackson-Jefferson-Johnson-
     Jones-Keokuk-Lee-Linn-Louisa-Muscatine-Scott-Van Buren-
     Washington.

IL...Dense Fog Advisory until 10 AM CDT this morning for Hancock-
     Henderson-McDonough-Mercer-Rock Island-Warren.

MO...Dense Fog Advisory until 10 AM CDT this morning for Clark-
     Scotland.

&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...12
AVIATION...Nichols
CLIMATE...12



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