Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 180500
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1200 AM CDT Fri May 18 2018

...06Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 244 PM CDT Thu May 17 2018

High pressure north of Lake Superior ushered in drier air across
the Great Lakes region. This afternoon, the flow was leading to
cooler and drier conditions across our area. To the south, there
is a closed off upper level low that continues to fire showers and
weak thunderstorms south of the area. This high pressure and upper
level low will serve as the main weather drivers in the short term
period.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 244 PM CDT Thu May 17 2018

At the surface high pressure will drive most of the sensible
weather in the short term period.  Overall H5 flow remains ridged
to SW flow across the area. A wave approaches the area from the
west and ejects the closed low to the NE. The low rotates to the
north and east, there will be low chances for showers as it moves
east of the area. Believe that the dry in place will fight with
any precipitation. As a result, decided to keep schc pops. This
seems consistent with the CAMs and synoptic models. One of the
larger questions is do we see any thunder. No SBCAPE exists and
the SREF thunder probability is below 10 for most of the area.
Model soundings suggest just showers. As a result, have left
thunder out of the forecast tomorrow.

As far as sensible weather goes, as the western wave moves in,
moisture return will occur bringing higher dewpoints than what we
have seen most of the week into the area. This will lead to a
slight increase in the mugginess across the area.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 244 PM CDT Thu May 17 2018

Pattern remains active through the beginning of the period before
quiet weather returns for next week. Towards the end of the
period, chances for rain and thunder return to the area.

Friday evening, departing upper level low will move to the east.
Llvl moisture return will occur. Guidance is consist on the
development of rain showers, mainly across the IL zones. Little to
no instability exists for thunderstorms. As this low moves to the
east another closed H5 low will swing into the area. With a more
negatively tilted nature of this low, shear will be conducive for
organized convection. Saturday, the warm front is expected to lie
south of I80. Convection is expected to fire across western IA
and move east through the time period. At this time, this
convection will likely arrive between 00z and 06z in a decaying
mode. Regardless, shear, especially in the low levels will be
conducive for mesovortex development and a subsequent severe wind
threat. Very low level shear may lead to an isolated tornado
threat across the area.

Sunday, the weakening H5 flow and H85 advection will push the
effective boundary slightly north of I80. Areas along and south of
the boundary could see another round of possibly severe storms.
CAPE will be lower than Saturday, however overall shear will be
better and timing of convection will favor our area. As with most
of these cases, ongoing convection in the AM may limit overall
thunderstorm chances in the afternoon. Into Monday, overall quiet
period is expected with warming temperatures expected.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1158 PM CDT Thu May 17 2018

VFR conditions expected to largely dominate the TAF sites owing to
easterly drier flow from Great Lakes high pressure. That said,
an upper low over southern Missouri located in between high
pressure over the Great Lakes and Central Plains will be drawn
northward while devolving. This system although weakening may still
generate a few showers at times mainly near and east of the Mississippi
River.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Gibbs
SHORT TERM...Gibbs
LONG TERM...Gibbs
AVIATION...McClure



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