Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 212010

Area Forecast Discussion
National Weather Service Quad Cities IA IL
310 PM CDT THU JUL 21 2016

Issued at 308 PM CDT Thu Jul 21 2016

18z surface data has a frontal boundary from western Lake Superior
to the South Dakota/Nebraska border. Dew points were in the 70s
across the Midwest with pockets of dew points in the low 80s.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 308 PM CDT Thu Jul 21 2016

The excessive heat warning will continue through Friday.

Very hot and humid conditions will continue through sunset with no
rain expected.

After sunset, the forecast becomes a conditional IF...THEN
situation. IF a thunderstorm complex develops along the IA/MN border
THEN thunderstorms will likely overspread at least the eastern two
thirds of the area. IF thunderstorms occur THEN overnight lows will
be lower than forecast.

IF no thunderstorm complex develops THEN very warm and humid
conditions will be seen through sunrise Friday with low temperatures
potentially higher than forecast.

Right now the current forecast is for isolated to low end scattered
convection developing based on an old rule of thumb about morning
accas over the area.

What happens tonight will influence Friday. IF no thunderstorms
occur Thursday night THEN very hot and humid conditions will be seen
Friday with high temperatures potentially warmer than forecast.

IF thunderstorms occur Thursday night into Friday THEN clouds and
convection may persist keeping temperatures much cooler than

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 308 PM CDT Thu Jul 21 2016

The period of excessive heat will continue synoptically through
Saturday, if not Sunday. However, as we get past Friday, the
probability of MCS contamination seems to become more likely and I
will not yet extend the headline through Sunday. Over all, our
situation remains very much steady state as it is tonight, we are
playing with fire.  The warm side of the nearby boundary has every
seasonal variable supporting exceptional heat, from duration to crop
transpiration, to frontal convergence just north of deep
southwesterly flow, we are in the hot zone. Along the edge of the
heat, like today, both progressive MCS and flash flood producing
back building MCS are likely each day. The potential for any of
these to back build into the CWA are strong, and if they do, a short
respite from heat may occur. We will need to continue with the most
likely hazard of heat, through Saturday, and if now storms occur
Saturday night, they Sunday as well. Highs in the lower to mid 90s
are expected both Saturday and Sunday, though dewpoints Sunday may
be a few degrees lower than now, in the lower to mid 70s.

Monday onward, the models build high pressure into the upper
Midwest, and with northwest flow aloft, this should bring dewpoints
back to the 60s for much of next week. The dry weather should begin
to get active again by Tuesday night again, as a mid week short wave
crosses the plains. The GFS  brings another prolonged period of MCS
with this return flow, while the ECMWF has a much deeper trof and
cooler air mass in place beyond Wednesday.  Given the active
monsoonal flow, and weaker synoptic July pattern, it seems the GFS
may be most accurate unfortunately.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1233 PM CDT Thu Jul 21 2016

VFR conditions will continue through 03z/22 with density altitudes
at or above 3 kft. After 03z/22 visibilities will slowly decay to
MVFR due to the high moisture levels in the lower atmosphere. The
thunderstorm chances become conditional. IF a thunderstorm
complex develops along the IA/MN border THEN TSRA with IFR
conditions may affect KCID/KDBQ/KMLI and possibly KBRL. 18z TAFs
have included VCTS due to accas over eastern Iowa which sometimes
suggests the potential of nocturnal convection.


.DVN Watches/Warnings/Advisories...
IA...Excessive Heat Warning until 7 PM CDT Saturday for Benton-
     Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry IA-
     Muscatine-Scott-Van Buren-Washington.

IL...Excessive Heat Warning until 7 PM CDT Saturday for Bureau-
     Carroll-Hancock-Henderson-Henry IL-Jo Daviess-McDonough-
     Mercer-Putnam-Rock Island-Stephenson-Warren-Whiteside.

MO...Excessive Heat Warning until 7 PM CDT Saturday for Clark-



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