Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 201421

Area Forecast Discussion
National Weather Service Quad Cities IA IL
921 AM CDT Wed Sep 20 2017

Issued at 916 AM CDT Wed Sep 20 2017

Morning balloon data shows multiple caps aloft. These caps
combined with weak forcing/convergence, relatively dry air down
low and rising heights aloft does not support the development of
any precipitation during the morning hours.

An assessment regarding precipitation potential and overall timing
for this afternoon is currently underway.


Issued at 338 AM CDT Wed Sep 20 2017

QLCS continues passing across E MN and into W WI early this am
attendant to mid/upper forcing for large scale ascent sweeping
across Upper Midwest ahead of deepening western CONUS trough.
Tail end of this activity extends through NW IA and continues to
constrict in coverage as it move into increasing MLCIN
further downstream across IA. However, veering 40-50 kt LLJ and
attendant warm/moist advection may result in some development
of elevated convection across portions of the cwa mainly along
and north of I-80 this am. Otherwise, main window for shower and
storm chances is mid to late pm and especially tonight as a cold
front sags into the region.


.SHORT TERM...(Today and Tonight)
ISSUED AT 338 AM CDT Wed Sep 20 2017

Have lower PoPs this am for areas along/north of I-80 for the
potential of isolated to low end scattered coverage of showers
and storms with veering 40-50 kt LLJ and attendant warm/moist
advection. Then general suggestion is for a building cap/EML to
limit any convective development mostly until late pm along and
just ahead of cold front from possibly far NW IL back through
NE IA. Strong post-frontal rises in the central Plains
early this am offers some concern of earlier arrival of front
NW cwa. Should this occur it could reduce or eliminate rain
chances and lead to cooler highs in areas NW of CID-DBQ line.
Due to cap/EML concerns and weak forcing I have kept PoPs in
slight chance to lower chance for late pm. Otherwise, low level
thermal ridge and strong warm advection on gusty southerly winds
with trends of likelihood of ample solar insolation support
going at or above warm side of guidance for highs today ahead
of the front from much of east central/southeast IA... northeast
MO through N IL. Bufr soundings show deep mixing to around or
above 850 mb where progged temps around 20C support widespread
upper 80s to lower 90s in these areas. A few sites will look to
be near record highs including MLI (please see climate section
below). With dewpts in the upper 60s to around 70, this will
translate to heat index readings in the lower to middle 90s in
the aforementioned areas. At least winds to be gusty and temper at
times the very warm to hot conditions.

Tonight, looks to be the main window for shower and storm chances
as SW nocturnal LLJ 20-25+ kts impinges on frontal zone. Much
of this activity likely to focus along and further NW of surface
boundary, and this could have impact on PoPs being too low NW cwa
and too high SE cwa. Signal of retreating height falls and
diminishing wind fields/deep layer shear still present. However,
more than sufficient instability still supportive of potential
for a few stronger storms and isolated marginal severe hail/wind
risk. Rainfall amounts to be spotty and variable but do anticipate
potential for localized 0.5-1+ inch amounts with PWATs surging
over 1.5-1.6 inches, and favorable orientation of LLJ for repeated
activity in some areas. Lows could dip down into the 50s and
lower 60s post-frontal across NW cwa. Elsewhere, seasonably warm
night with lows mid 60s to around 70.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 338 AM CDT Wed Sep 20 2017

Thursday...Will just have some spotty slight CHC POPs in the west in
the morning for decaying convection lingering out of Wed night.
Patchy fog possible through mid morning in VCNTY of the boundary
especially in northwest IL, but with cloud cover concerns will not
mention it for now. Then amplifying southwesterlies along and west
of the region along with associated southerly flow push, should
allow the previously stalled out LLVL boundary to retreat northward
warm frontal style as the day progresses. warm surge and re-building
EML aloft will translate into a very warm and capped atmosphere acrs
the area for Thu afternoon. Lingering clouds in the morning decay
for afternoon insolation, and mixing south-southeast sfc flow in
warm air advection translate to another unseasonably warm afternoon
with highs in the upper 80s to low 90s. Sfc DPTs should mix down
into the mid to upper 60s during the afternoon but make for heat
index readings in the low to mid 90s. Ambient high temps may be
close or just a few degrees shy of records for Sep 21st in a few
spots and will advertise in climate section for reference. Overnight
lows in the 60s to continue unseasonably mild trend.

Friday through Sunday...The latest run medium range models show
little change for this period from runs last night, suggesting the
local area trapped under a unseasonably warm dome of the high
pressure portion of a blocked pattern acrs the CONUS into the
weekend. Western CONUS into western Rockies L/W trof temporarily
held at bay by eastern CONUS subsidence fields enhanced by active
Atlantic tropical system regime. Thus dry and unseasonably warm
conditions to continue through at least Sunday. Mixing south winds,
full insolation and projected low to mid level vertical thermal
profiles support widespread low to mid 90s on Friday, especially if
the sfc layer remains parched acrs much of the area. this would
translate to another day with high temps not all that far off of
record highs. Then most of the 00z run medium range models temper
back the H85 MB temps some for Saturday and Sunday, but not enough
to inhibit more upper 80s to around 90 degree readings especially on
Sat. Saturday sfc DPTS more in the realm of low to mid 60s for heat
index readings into the lower 90s.

Early next week...the main challenge continues to be timing the
incoming ridge-to-leeside of L/W trof transition zone for the next
precip chances. again the Atlantic tropical systems and west side
subsidence fields to be players, but current model run upper jet
energy ejecting out around trof base suggest it may have enough pull
eastward to bring llvl moisture convergence swath/front acrs the
local area by Tue. Increasing chances for mainly along and post-
frontal showers in this regime Tue into Tue night. Some danger that
the local area again to be in-between better forcing support to the
north and west, and moisture convergence to the south which may
translate into less precip as the front prop[gates eastward through
the region. But these kind of details not to dwell upon yet that far
out, and will carry at least moderate POPs for the pattern
transition window at the end of the extended period.     ..12..


.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
ISSUED AT 629 AM CDT Wed Sep 20 2017

VFR conditions expected to largely dominate the TAF period. DVN
VWP is showing around 30-35 kts near 2kft agl from swly
direction thus have expanded LLWS to include all terminals until
mid morning. Then expect gusty sfc winds from sly direction at
12-24 kts into the afternoon. A cold front will begin to move
into the region this afternoon and eventually stall out over the
region tonight. There will be a chance of showers and storms with
this front, and have continued to mention this threat for storms
in PROB30 groups. Overnight, KDBQ and KCID may see MVFR cigs
develop with boundary layer cooling on easterly flow and abundant


ISSUED AT 338 AM CDT Wed Sep 20 2017

Record Highs for September 20...

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

Record Highs for September 21...

Moline.........92 in 2007
Cedar Rapids...93 in 1920
Dubuque........94 in 1891
Burlington.....94 in 1908




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