Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 281739 AAB
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1239 PM CDT THU JUL 28 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 340 AM CDT Thu Jul 28 2016

MSAS surface analysis at 07z suggested a weak surface boundary or
inverted trough, reaching from near St Louis north through eastern
Iowa to near La Crosse. Isolated showers and thunderstorms were
occurring along and east of this feature, mainly in two areas; one
south of Quincy and the other just east and southeast of the Quad
Cities. Weak low level convergence and dewpoints pooling in the
upper 60s to around 70 were resulting in a few areas of mainly
aviation/MVFR type fog. Aloft, a series of shortwaves was embedded
in the NW flow from IL to the rockies.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 340 AM CDT Thu Jul 28 2016

Main challenge is centered on chances for thunderstorms throughout
as convection continues to fire along and east of the weak surface
trough over the area. The bulk of short range models develop the
inverted trough into a NW to SE orientation across the forecast area
today, then shift it southward to focus convergence to mainly over
west central IL tonight. Building daytime instability, with perhaps
some assistance from the next upstream shortwave advancing out of
southern SD, should trigger scattered showers and thunderstorms from
late morning through afternoon, especially along and east of the MS
river, where higher chance pops are placed. Conditions do not appear
favorable for severe storms due to the weak forcing and lacking
shear. However, as seen the past couple days, the weak shear,
convergence along low level boundaries and sufficiently steep low
level lapse, may lead to isolated funnel clouds. The layer non-
supercell tornado parameter tool in both WRF/NAM and RAP models
suggest the highest potential of occurrence would be over NW IL or N
central IL around midday, then shifting eastward through the
afternoon.

With a lack of significant cloud cover in place, and little
contribution from upstream convection early this morning, skies
should be at least partly sunny, have boosted highs to the upper 70s
north to mid 80s in the south.

Tonight, the potential for thunderstorms along this southward
trending boundary will be more limited as the night progressed based
on lowering mid level lapse rates and marginal MUCAPE values. Thus
have slight to low end chance pops for showers and thunderstorms in
the evening, shifting southward with just showers mentioned toward
morning in the southeast. Low level moisture convergence and pooling
will also again be supportive of at least patchy fog and have added
mention over mainly west central IL toward morning. Kept mins a bit
cooler than previous nights, from the lower 60s north to mid and
possibly upper 60s south and southeast.

.LONG TERM...(Friday through next Wednesday)
ISSUED AT 340 AM CDT Thu Jul 28 2016

Friday...Several of the 00z run models now slow progression of mid
and upper level trof/low acrs the region this day. This combined
with a sfc wave and/or inverted trof reflection feature acrs the CWA
and diurnal instability, seems there will be increasing shower and
some thunderstorm activity as the day progresses and especially by
afternoon into the early evening acrs the fcst area. But not enough
instability or shear to produce strong or severe storms. Cloud cover
and boundary layer north to northeast fetch to limit highs in the mid
70s to around 80. As upper low moves east and loss of diurnal
support, showers should wane into the overnight. Some breaks in the
cloud cover could foster some low temps in the lower 60s or even
upper 50s, as well as areas of fog.

Saturday and Sunday...lingering broad upper trof and diurnal
instability may allow for more isolated to sctrd shower development
as Sat progresses(less coverage expected than on Friday), and
depending on the extent of cloud cover, llvl thermal profiles
support another seasonably below normal day with highs in the upper
70s to around 80. Clearing and seasonably cool Sat night with some
upper 50s possible again in some locations. Latest 00z run medium
range models such as the GFS and ECMWF in better agreement of
maintaining a dry Sunday with showers and storms to the south of the
area along organizing warm front acrs KS into MO. With more
sunshine, temps will moderate back into the low to mid 80s on
Sunday. Upstream thermal ridge will continue to build acrs the
plains Sunday into Sunday night. The models then start to diverge
some on how far north of the warm front can retreat Sunday night and
act as a convective focus for southerly LLJ. The 00z ECMWF is more
bullish with a further north push and breaks out elevated storm
clusters acrs at least the south half of the DVN CWA late Sun night
into Mon morning. The 00z GFS is further south and just clips the
southwestern CWA with some night time storms, and wonder if enough
debris and cool pools linger acrs MO from the earlier activity that
the GFS would be more in line.

Monday through next Wednesday...As the above mentioned thermal
ridge/heat dome out west tries to migrate eastward, Mon through Tue
and possibly even into Wed the local fcst area may lay under the
battle zone and be susceptible to occasional storm clusters or MCS`s
especially at night. LLVL southerly flow really starts to advect
warm and more humid air up acrs the region, but warm up potential
will depend on the amount of lingering convective debris and cool
pools for any storm episodes this period. Otherwise, without these
possible limitations highs will warm up at least into the upper 80s
to lower 90s by Tue and Wed and heat indices may breach 100 degrees
again.   ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1240 PM CDT Thu Jul 28 2016

MVFR conditions will give way to VFR before possible IFR cigs and
vsbys move in overnight across the area. Isolated showers and
thunderstorms are possible east of the Mississippi River today,
have included VCTS for this chance. Do not have high confidence on
vsbys late tonight so started to trend in a lower direction. A
north wind may limit the duration of the vsbys across the north.

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Hladik
AVIATION...Gibbs


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