Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 290447

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1147 PM CDT THU JUL 28 2016


Issued at 300 PM CDT Thu Jul 28 2016

Sfc trough that moved through eastern Iowa and northwestern
Illinois has turned winds from the south/southwest to the west-
northwest. Earlier today, areas of convection were restricted to
this zone of sfc convergence. Currently, an inverted trough builds
northwestward from north-central Illinois into extreme northwest
Illinois (into parts of eastern Jo Daviess and all of Stephenson
Counties). Isolated slow moving storms are likely to continue in
these areas. Presence of low-level vorticity and vertical
stretching by shower and thunderstorm updrafts means the risk for
a few funnel clouds or brief weak tornadoes are possible.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 300 PM CDT Thu Jul 28 2016

This Evening through Tonight...Isolated showers and thunderstorms
will decrease in coverage through the evening/nighttime period as
the mechanism for their development was mainly diurnal heating
along an inverted sfc trough.

Later on tonight, the 850-700mb inverted trough axis is
forecast to slowly sag southward into the northern and central
sections of the CWA. Hi-res models such as the HRRR/RAP have a
moist tongue wrapping up from the southeast into and on the
backside of the trough axis. The collocation of higher relative
humidity and positive 0-1 km convergence warrants the
continuation of low end chances for showers through tonight with
the best chances in the counties north of I-80.

Otherwise...areas of patchy dense fog are possible in favored
low-lying locations where clouds are able to clear out for
several hours. Thinking patchy fog formation has a higher
probability of occurrence along and south of I-80. Lows are
forecast in the lower to middle 60s.

Friday...Decreasing 850mb temps into the lower teens and a
northerly component to the sfc winds will make for a comfortable
day with highs in the mid to upper 70s. As mentioned earlier, the
850-700mb trough is characterized by increased moisture along the
trough axis. Thinking that with cooler temps aloft and
appreciable daytime heating by the late July sun angle, cumulus
formation will likely expand into a stratocumulus deck. If cloud
cover does become widespread, we can expect less convective
coverage during the aftn/evening. At this time, have 40% POPs for
sct coverage.

Thunderstorm Potential: The key mid-level feature tomorrow is a
500mb vorticity max progged to cross through the CWA. PVA
associated with the upper disturbance will provide some large-
scale ascent. One thing to watch for are breaks in the cloud cover
resulting in areas of differential heating and localized areas of
enhanced convergence. MLCAPE around 1000 J/kg or less and weak
shear should limit the thunderstorm risks to lightning and brief
gusty winds.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 300 PM CDT Thu Jul 28 2016

Friday Night through Sunday...Northwest mid-level flow dominates
through this time. The models are showing a few vorticity maxima
crossing through the Mid/Upper Mississippi Valley. However, this
occurs with a background environment of cooler or near normal
temps, light NE sfc winds, and dewpoints in the 60s...implying
less fuel for storms due to less instability.

A consist message I see from the models is for better storm
organization and coverage to remain south of the CWA...down across
Missouri eastward into the Ohio Valley. Most locations in the DVN
forecast area should stay dry.

Monday through Thursday...Yet another pattern change indicated by
the models. The culprit is a seasonally strong upper-low progged
to track through Saskatchewan and Manitoba. Low-level mass fields
responding to this synoptic area of low pressure would result in
a south-southwest flow from the sfc to 850mb and significant warm
air advection in the Central U.S. Latest Model-blend temps, beyond
Monday, are in the upper 80s/lower 90s as 1000-500mb thickness
values increase to levels comparable to the prolonged very muggy
period which ended this past Monday. The GFS/ECMWF are near
582 dam.

Examining the NAEFS, do not see a strong signal for 850mb temps
exceeding 24 C which is where this ensemble had values peaking at
during the last extremely humid period. At this time, 850mb temps
are not forecast to become excessively high.

The synoptic models are hinting at a favorable setup for MCS
development from Minnesota southeastward into Iowa/Illinois -
along the northeast periphery of the heat dome through at least
Tuesday. If this scenario plays out Model-blend temps may be too
warm for some areas. For now, there is higher confidence in the
potential for oppressive dewpoints in the mid to upper 70s,
possibly near 80 F, than there is in max temps. Uttech


.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1140 PM CDT Thu Jul 28 2016

Precipitation chances and ceilings the main challenges with the
taf cycle. Weak low pressure will remain near the area through
Friday evening and keep the threat for at least isolated to
scattered showers and a few storms, as spokes of energy rotate
around the low. Very difficult to determine any favored location
and timing, thus have continued to leave out any precipitation
mention with 06z and will just need to amend if/when radar and
short term trends necessitate. Otherwise, low clouds with mvfr
to ifr ceilings at CID and DBQ anticipated to build southward into
MLI as well overnight and linger through Friday morning. BRL is
lower confidence being south of the low but most guidance is
supportive of lower clouds and with radiational cooling and better
low level moisture I have gone with period of ifr to mvfr
conditions there as well. Some gusts in northerly winds Friday
afternoon will enhance influx of drier air and should allow any
ceilings to lift to vfr.


.DVN Watches/Warnings/Advisories...


LONG TERM...Uttech
AVIATION...McClure is the U.S. government's official web portal to all federal, state and local government web resources and services.