Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200425
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1125 PM CDT TUE JUL 19 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 314 PM CDT Tue Jul 19 2016

Similar to the majority of convective events this summer, the sfc
theta-e and MLCAPE gradient is bisecting eastern Iowa and
northwestern Illinois. A severe complex of storms, with a history
of producing damaging winds and a few brief tornadoes, is
currently moving eastward out of south-central Iowa and north-
central Missouri. The greatest risk for severe weather late this
aftn and evening will be in the counties along and south of
highway 34.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 314 PM CDT Tue Jul 19 2016

This Afternoon into this Evening...Complex of light to moderate
stratiform rain shield with embedded convective elements to
gradually work its way to the ESE along the northern periphery of
the MLCAPE gradient, affecting roughly the southeast two-thirds
of the forecast area. The severe risk remains across the southern
portion of the CWA.

Severe storm potential: There is a slight risk for severe
thunderstorms along and southwest of a Marshalltown, Iowa to
Muscatine, Iowa to Macomb, Illinois line. Here instability will be
on the order of 2000-3000 J/kg MLCAPE (DCAPE over 1000 J/kg) and
0-6 km shear between 30-40 kts. Consequently, the environmental
ingredients are sufficient for a few strong or severe
thunderstorms. The strongest storms would be capable of producing
wind gusts over 60 mph, torrential rainfall rates given PWATs up
near 2 inches, and possibly an isolated brief tornado. Tropical-
like vertical moisture/temp profiles are not supportive of large
hail.

Timing: The dominant storm complex will move from west to east
through roughly the southern two tiers of counties through 6
or 7 PM.

Tonight into Wednesday...Nocturnal low-level jet forecast to veer
late tonight, increasing chances for elevated showers and storms,
probably well after midnight. This wave of convection will most
likely linger into Wednesday morning and even the aftn over at
least the eastern half of the CWA. Very heavy rainfall rates,
lightning strikes, and localized strong wind gusts are the
primary threats.

Aforementioned instability gradient is not expected to make
significant progress to the east, which keeps the chances for
showers and thunderstorms across majority of the of the forecast
area. The exception is over the far southwest where a Excessive
Heat Watch is now in effect Wednesday afternoon.

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 344 PM CDT Tue Jul 19 2016

Wednesday Night...Models finally dry out the local area as
impressive heat dome/elevated warm layer advects into the Upper
Midwest and Western Great Lakes. Expect warm and muggy conditions
with lows in the mid 70s.

Thursday Through Saturday...

Excessive Heat Watch is in effect through Saturday except in the
counties along highway 20 where it is in effect through Friday.
Oppressive heat indices of 100 to 110 F will greatly increase the
risk for heat exhaustion. It is best to avoid outdoor activities
during the late morning and afternoon hours.

Models are projecting up to 586 dam 1000-500mb thicknesses and
596 dam 500mb heights. Elevated mixed layer advecting out of the
Central Rockies and Plains to push 850mb temps into the middle
20s C. NAEFS 850mb temperature standardized anomalies are 2-2.5
standard deviations above the mean for this time of year which is
impressive.

Aside from the heat, the trend will be toward drier conditions,
but cannot ignore threat for scattered storms if a boundary sags
south out of Minnesota and Wisconsin. The time period to watch for
this is probably Friday into Saturday morning. Any storms would
provide brief relief from the excessive heat.

Sunday through Tuesday...Consensus blend brings a cold front
through, knocking temps back to near normal conditions and giving
us some relief from the extreme heat indices. At this time, slight
chances for storms accompany the front, although it is too early
to determine the risk for severe storms. Uttech

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1123 PM CDT Tue Jul 19 2016

Generally VFR conditions expected with episodes of mostly MVFR visibilities
due to patchy fog later tonight and also isolated to scattered showers
and storms later arriving from the north by mid morning Wednesday which
is handled as a VCTS wording due to low confidence. Winds generally
light and tending south to southeasterly.

&&

.DVN Watches/Warnings/Advisories...
IA...Excessive Heat Watch from Thursday morning through Saturday
     evening for Benton-Cedar-Clinton-Des Moines-Henry IA-Iowa-
     Jackson-Johnson-Jones-Linn-Louisa-Muscatine-Scott-
     Washington.

     Excessive Heat Watch from Wednesday afternoon through Saturday
     evening for Jefferson-Keokuk-Lee-Van Buren.

     Excessive Heat Watch from Thursday morning through Friday
     evening for Buchanan-Delaware-Dubuque.

IL...Excessive Heat Watch from Thursday morning through Saturday
     evening for Bureau-Carroll-Henderson-Henry IL-McDonough-
     Mercer-Putnam-Rock Island-Warren-Whiteside.

     Excessive Heat Watch from Wednesday afternoon through Saturday
     evening for Hancock.

     Excessive Heat Watch from Thursday morning through Friday
     evening for Jo Daviess-Stephenson.

MO...Excessive Heat Watch from Wednesday afternoon through Saturday
     evening for Clark-Scotland.

&&

$$

SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...Uttech
AVIATION...Nichols


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