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fxus63 kdvn 190846 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
346 am CDT Mon Aug 19 2019

Synopsis...
issued at 330 am CDT Mon Aug 19 2019

High pressure was largely in place over the upper Midwest. The
surface high was centered northwest of the local area, extending
from northwest Wisconsin into Minnesota and down into eastern Nebraska.
The Storm Prediction Center mesoanalysis displayed a ribbon of enhanced moisture and
subtle convergent flow in the 925-850mb layer over central to
southern Iowa. And we've had very isolated showers at times
through the night in this area.

Collocated with the region of higher lower tropospheric moisture,
through central Iowa into northwest Illinois, have been patches of
stratus clouds at around 5000 ft above ground level. Otherwise, it has been a warm
and humid night with temps and dewpoints in the mid 60s to low
70s.

&&

Short term...(today and tonight)
issued at 330 am CDT Mon Aug 19 2019

Today

Warm and humid with a slight chance for isolated showers and
possibly a few weak thunderstorms. Highs will reach into the low
80s north to mid/upper 80s far south. Combining the warm
conditions with dewpoints in the low 70s will yield peak heat
indices in the mid 90s along and south of Highway 34 (west of
galesburg).

A very moist and weakly convergent boundary layer up to 850mb may
provide enough forcing for isolated showers and possibly a few
weak storms today. Appears the best chance for isolated activity
is across the central cwa, near the axis of highest 925-850mb
dewpoints/mixing ratios. Surface-based cape will increase into
the 1500-2500 j/kg range by the afternoon with deep layer shear
staying under 30 kts.

Synoptic and hi-res model guidance are all painting a few bands of
quantitative precipitation forecast across the central section of the County Warning Area from the mid morning
into the evening. Most areas won't receive much in the way of
rainfall (less than 0.10"), but there could be localized spots
that get heavy downpours and amounts over 0.50 inches.

Tonight

A new batch of convection is likely to form over central to
northwest Iowa within the convergent axis of a strengthening
nocturnal low-level jet late tonight. Mean 850-300mb flow, the
orientation of the low- level instability gradient and 1000-500mb
thickness contours support a storm motion to the east-southeast. Have 30-40%
chances for showers and thunderstorms late in this period across
the west, as an mesoscale convective system may be approaching by this time. Various cam
solutions are showing this to be more of an early to mid morning
event on Tuesday, so the details and potential for severe weather
are discussed in the following section of this afd. Uttech

Long term...(tuesday through sunday)
issued at 330 am CDT Mon Aug 19 2019

Potential exists for evolution or upscale growth of convection
into an mesoscale convective system impacting portions of cwa Tuesday am. This is
attributed to shortwave observed in early morning water vapor
imagery over Idaho, which is shuttled down across the region
within modest mid/upper level steering flow, and aids robust
augmentation of low level jet owing to substantial increase in
warm advection/isentropic ascent. Still some uncertainty on the
where the potential mesoscale convective system may develop or track, and therefore have
capped pops in high chance category for now. That being said,
seemingly favored track right now appears to be across the
southwest half or so of County Warning Area per orientation of favored 850/700 mb
thermal gradients, axis or pooling of 850 mb moisture, and 500/300
mb diffluence. NAM models shows MUCAPE in excess of 5000 j/kg
which seems awfully aggressive, but even half that (2500-3000
j/kg) in presence of progged modest shear and mid level flow would
be sufficient for a strong wind threat. As with any qlcs have to
monitor also for mesovortex generation. Model data this morning
doesn't look as favorable for qlcs tornadoes with notable weaker
winds near 1 km of only 20 kts or so. However, still good
directional change (se sfc to SW at 1 km) owing to effective srh
greater than 200 m2/s2 with notable sickle shaped hodographs, and
therefore can't be ruled out. With the idea of convection in
the area during Tuesday morning, I have lowered Tuesday highs by
a few degrees with widespread mid 80s. However, if mesoscale convective system with cold
pool occurs then potential of needing to be even further lowered.

Midweek, southern portions of the area will remain in close
proximity to a front and edge of ring of fire /heat dome/ and
will have chances for showers and storms. In time though it
appears this battle zone will shift further to the South/West as
influx of cooler/drier air invades region with carving out of
large broad eastern Continental U.S. Trough. So, heading into the latter
half of the week expect drier and pleasant conditions to dominate
with high pressure building down into the Great Lakes leading to
near/slightly below normal temperatures.

This weekend the high will shift east. Ensuing return flow will
lead to climbing temperatures and humidity, and storm chances
re-entering the picture especially over the latter portion of the
weekend and early next week.

&&

Aviation...(for the 06z tafs through 06z Monday night)
issued at 1102 PM CDT sun Aug 18 2019

Light northeast winds may allow for some fog and MVFR cigs/vis
late tonight into Monday morning, then followed by VFR conds for
most of the day on Monday. North to northeast winds less than 10
knots.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

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