Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 241051
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
551 AM CDT Thu May 24 2018

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 233 AM CDT Thu May 24 2018

Tranquil conditions abound as the area is under the influence of
high pressure over the Great Lakes. Drier light easterly flow is
drawing down dew points into the 50s to near 60 degrees and
making for a rather comfortable early morning, while temperatures
are mostly in the 60s to near 70 degrees beneath mainly clear
skies. A few convective clusters were noted across the Plains
occurring within zone of elevated moisture transport and assisted
by weak shortwaves on backside of mid level ridge over the central
CONUS.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 233 AM CDT Thu May 24 2018

Rain chances are non-zero, but overall expect mostly dry and
summery conditions to characterize the next 24 hours.

Great Lakes high pressure will continue to gradually retreat
during the period. This will allow our winds to turn from
the south today ushering in a warmer and more moist airmass.
The result will be highs topping out well into the 80s to
possibly near 90 degrees in a few locations... roughly 10-15+
degrees above normal. Expect to see a moist axis along and
especially west of the Mississippi River this afternoon
featuring dew points in the mid 60s, so expect the humidity
to be more noticeable if not even a bit uncomfortable in these
areas while a bit lower but perhaps still somewhat noticeable
east. Strong boundary layer heating of this moist axis is expected
to aid buoyancy and make certain convective temperatures are
breached. Therefore, I can`t rule out isolated weak convection
developing late this afternoon mainly west of the Mississippi
River. However, no apparent additional trigger noted upstream in
GOES-16 early morning satellite data or depicted within
deterministic models thus feeling any coverage extremely low for
any mention.

Tonight, any isolated weak convection should dissipate prior to
sunset leaving behind mainly clear to partly cloudy skies.
Late tonight there is a low chance of some showers and possibly
a few storms sneaking into western CWA as a mid level shortwave
and 850 mb moisture advection encroach on the area. Otherwise,
a milder night is on tap with southerly winds yielding widespread
lows in the mid to possibly a few upper 60s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 233 AM CDT Thu May 24 2018

Overall little in the way of changes to the overall pattern that has
been discussed in previous discussion.  Weak H5 flow with largescale
ridge across most of the central and eastern CONUS through the
weekend.  This will result in summer-like weather for the area.
Memorial day looks to be warmest of all days this weekend.

First, Friday, a wave in the flow will pull north of the border into
Canada.  Convection will fire in association with a weak confluence
zone associated with this wave.  Overall the wave is weak and thus
shear is weak as well.  This will limit overall updraft organization
and thunderstorms strength. Looking closely at the environment, raw
plane field data suggests that CAPE will be high across the area
Friday. The GFS has 5000 J/kg SBCAPE over DMX. This is likely
overdone due to unrealistically  high dewpoint temperatures in the
models.  In fact, when looking at model soundings, the CAPE is
almost half of this and that CAPE that does exist, is long and
skinny.  Dewpoints in the model soundings are in the mid to upper
60s, much more realistic. With the deft of shear and the skinny
CAPE, overall thunderstorm strength will be low as a parcel will
likely cool before the total CAPE is realized. Cannot totally rule
out isolated severe hail or wind, however, the threat for severe
weather is quite low.

What does seem to be a larger threat is for isolated heavy rain from
any showers or storms that develop.  With weak flow and cold pool
driven storms, expect areas that have storms to see decent rainfall.
Overall coverage will likely be limited in nature.

There is a contingent severe risk that is hinted at in the NAMnest.
If nocturnal convection can leave a remnant MCV, and there is
enough clearing for heating then the MCV may increase shear locally.
There are a lot of ifs in this case.  If there is nocturnal
convection Friday AM, will we be able to clear out soon enough to
build CAPE? This scenario, while contingent on a MCV, would likely
be the best chance for any severe weather on Friday across the area.

Past Friday, chances for rain and thunder will be tied to diurnal
processes and any waves in the flow.  While thunder chances are low
in the extended, this could change with any mesoscale feature, such
as a MCV, that could make its way into the area.  The overall
forecast skill for these is difficult, as such the best skill will
not be realized until the day of the event.  Overall, expect the
chances for rain to change as we know the mesoscale features better.

The rest of the long term will feel like summer.  There are some
indications that we may cool down for next weekend.  However,
confidence in this occurring is quite low.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 544 AM CDT Thu May 24 2018

VFR conditions expected to dominate the TAF cycle, with mainly
some high level clouds throughout along with a period of diurnal
cumulus. Can`t rule out an isolated late afternoon shower, mainly
west of the Mississippi River. Another low chance of showers will
arrive late tonight toward 12z. Neither were mentioned into the
TAFs due to low coverage owing to low confidence on occurrence at
the terminals. Easterly winds will turn southerly today at 10-15
kts with some locally higher gusts then diminish below 10 kts from
SSE tonight.

&&

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

$$

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


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