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Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
356 am CDT Tue Jul 16 2019

issued at 351 am CDT Tue Jul 16 2019

The latest water vapor loop was indicating lingering Barry
circulation acrs the Arkansas/MO border slowly moving toward the northern
MO bootheel region. The local area generally remain in between this
feature and active northerly storm track acrs the northern Continental U.S..
cloud debris off these two action zones and weaker mixing profiles
to make for some reprieve from the heat today, before it comes back
with a vengeance by the end of the week. Also, some occasional
thunderstorm chances will occur acrs portions of the area from today
through early Thu.


Short term...(today and tonight)
issued at 351 am CDT Tue Jul 16 2019

Today...with remnant Barry circulation/upper low on track to open
up and weaken as it drifts off to the east, sctrd light shower
chances will continue mainly along and east of the MS river through
mid afternoon before shifting off to the east. Should be mainly
showers, although some midday instability may allow for some
embedded thunder eventually before that activity associated with
Barry wanes.Eyes then turn to a much more substantial potential for
thunderstorms moving in from the west this afternoon in the form of
a convectively enhanced wave/mesoscale convective vortex associated with the ongoing storm
complex acrs central into eastern NE. Before then, will have to
watch sctrd remnant storm clusters now north of the Des Moines area
as they try to move east toward the northwestern County Warning Area this morning.
Most cams and hires solutions decay this convection as it moves east
toward the local area this morning, but can't totally trust those
ideas. Most of the models also diurnally decay the Nebraska strong
storms/mesoscale convective system as they move eastward acrs western Iowa this morning, but
again can't totally accept that idea and the day crew will have to
watch for storm maintenance.

Even if the complex decays, the associated mesoscale convective vortex will look to kick up
new storm clusters acrs central and northern Iowa by early to mid
afternoon. Will then walk sctrd storm clusters into the western and
northwest County Warning Area by mid to late afternoon. If some decay in cloud
debris allows for enough heating and sbcapes attaining at least 2000
j/kg, these storms may be marginally severe with damaging winds.
Still high freezing/wbz levels make large hail a secondary threat.
If a storm cluster can organize cold pool mechanics, more
significant wind gusts over 60 miles per hour will be possible. Convergent
pools of higher pwats will fuel locally heavy rain under the passing
storms, and can't rule out a localized flash flood threat for a less
progressive storm or areas that get hit more than once.

Cloud cover and associated heating/instability build up limits will
be a challenge today, with partly cloudy to mostly sunny swaths
possible in between clouds off Barry and convective debris form the
northwest. Will go with highs generally in the mid to upper 80s in
most areas, with lighter sfc winds/less mixing allowing sfc dpts to
maintain in the muggy upper 60s to lower 70s.

Tonight...most models that have the late afternoon into evening
storms in our west half then decay them as they propagate eastward
toward the MS river around 9-10 PM or so. They do so probably
encountering less unstable air and lingering subsidence behind
departing Barry circulation. But again can't totally trust these
trends but will decrease pops from west-to-east after midnight. Late
night mesoscale convective system generation grounds look to occur acrs South Dakota/NE and the
western Minnesota-Iowa areas, with just a low chance for some of this
activity making it down into the northwestern County Warning Area before 12z Wed.

Long term...(wednesday through monday)
issued at 351 am CDT Tue Jul 16 2019

Excessive heat watch remains in effect from Wed PM through Sat,
as prolonged/multi-day period of dangerous heat still on
track during this timeframe. Some uncertainty exists with
temperatures on Wed due to potential for a few storms and debris
cloudiness in some areas. Thermal parameters however, would
easily support highs in lower 90s with periods of sun, which
combined with dew points in the 70s would yield Max heat index
readings around 100. This heat will only intensify during Thu-Sat
period, as the low to mid level thermal ridge overspreads the
area. Associated 850 hpa temperatures are forecast around 25c by
GFS and ec, which should translate to widespread highs in the mid
to upper 90s with possibly a couple favored hot spots topping the
century mark. Forecast dew points in the mid 70s could be a bit
aggressive, as winds will be gusty both Thu-Fri with afternoon
mixing likely drawing them down a bit. All this may do though is
allow temps to nudge even higher in favorable modest low to mid
level SW flow. Bottom line, confidence continues to increase in
multiple days of excessive heat over the latter half of the week
into the upcoming weekend, with heat index values in the 100 to
110 degree range. In addition, it will remain very warm at night,
with heat index readings likely staying at or above 75 degrees not
allowing for much in the way of relief. If trends persist would
expect the excessive heat watch to be upgraded later today.

There is signs of a break in the dangerous heat by late in the
weekend into early next week, as the broad and anomalous upper
ridge /heat dome/ is flattened and re-amplifies out west as a
fairly strong trough ejects across the northern plains and upper
Midwest. This will push a cold front through the area bringing
relief in the form of cooler and drier air. There still remains
some timing differences in the GFS, ec and Canadian but the
general timeframe would appear to be Sat night or Sunday.

Aside from the heat there will be some storm chances, especially
Wed-Thu and mostly across the north as it appear now with
potential for development or propagation of convection into the
north with outflow of Minnesota/WI storms and proximity of low level jet.
Would have to monitor for strong gusty winds and locally heavy
rain with any storms. Additional storm chances will develop deeper
into the weekend attendant to the cold frontal passage.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1255 am CDT Tue Jul 16 2019

Lower MVFR cigs and some embedded fog will make it in the vicinity
of mli and already impacting the brl site. There will even be a
chance for IFR cigs at brl with lower level saturation profiles
on the northwest flank of Barry remnants. Will keep the showers
off to the southeast of brl in the taf for now. To the north, will
have to watch for portions of an mesoscale convective system along the Iowa/Minnesota border to
sag down toward dbq through sunrise if even in a diminishing
stage. Some chance for MVFR fog at most sites around sunrise this
morning, but better chances at brl. Light south to southwest sfc
wind regime, or even variable for much of the taf cycle in
between northern storm track and lingering Barry circulation. Will
not put them in the tafs for now, but chance for thunderstorms to
develop acrs central and north central Iowa this afternoon and move
into the vicinity of Cid and possibly dbq this evening. These may be
strong with passing bouts of MVFR to IFR conditions with heavy
rain and gusty winds.


Dvn watches/warnings/advisories...
Iowa...excessive heat watch from Wednesday afternoon through Saturday
evening for Benton-Buchanan-Cedar-Clinton-Delaware-Des
Moines-Dubuque-Henry Iowa-Iowa-Jackson-Jefferson-Johnson-
Jones-Keokuk-Lee-Linn-Louisa-Muscatine-Scott-Van Buren-

Illinois...excessive heat watch from Wednesday afternoon through Saturday
evening for Bureau-Carroll-Hancock-Henderson-Henry Illinois-Jo
Daviess-McDonough-Mercer-Putnam-Rock Island-Stephenson-

MO...excessive heat watch from Wednesday afternoon through Saturday
evening for Clark-Scotland.



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