Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 231743
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1243 PM CDT TUE AUG 23 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 336 AM CDT Tue Aug 23 2016

High pressure was located over the Ohio Valley, but still remains
in control of our weather for the time being thus the tranquil
start early this morning. Low pressure was over North Dakota, and
the resultant pressure gradient is maintaining southerly winds of
5 to 10 mph leading to a milder morning, with temperatures in the
upper 50s and lower 60s. Aloft, a vigorous shortwave trough was
noted just east of the Canadian Rockies. Meanwhile, a compact and
convectively aided shortwave was lifting across Nebraska. Dynamically
augmented low level jet in conjunction with the shortwave is aiding
strong moisture advection, resulting in a cluster of nocturnal
convection over portions of southern Nebraska.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 336 AM CDT Tue Aug 23 2016

The shortwave over Nebraska will track east-northeast into the Upper
Mississippi Valley by 12z Wednesday. Ahead of the approaching wave
strengthening and deepening southerly flow will lead to a dramatic
increase in moisture, especially this afternoon and tonight with
precipitable water values surging to 1.5 to 2 inches (175 percent of
normal) by 12z Wednesday. This moisture coupled with lift from both
the wave, and warm advection attendant to augmented low level jet,
will result in increasing coverage of showers and some storms from
southwest to northeast this afternoon and evening, lingering overnight.
Severe threat appears to be pretty low, with weak mid to upper level
winds resulting in deep layer shear only around 20 kts. With NAM and
GFS bufr soundings depicting complete lack of erosion of surface based
CIN, believe hail would be the threat and confined to a few of the
stronger cores early in evolution before moistening of atmospheric
column. Fairly skinny CAPE and weak H7-H5 lapse rates coupled with
weaker shear though looks to preclude any severe hail. Locally heavy
rain likely the main concern, with potential for swaths of 1-2 inches
given such deep tropospheric moisture and slower MBE velocities of
around 10-15 kts, aided by any cell training with veered southwesterly
low level jet.

As for temps, highs today will be somewhat challenging modulated by
amount of solar insolation prior to increasing cloudiness. Overall,
atmosphere is fairly unchanged thermally, and so expect most areas to be
around 80 or in the lower 80s once again. Tonight, with continued
southerly flow and moisture advection will see considerably warmer lows
well into the 60s to near 70 degrees.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 336 AM CDT Tue Aug 23 2016

Wednesday...Will walk lingering convective clusters/MCS east-
northeast out of the CWA by mid morning. 00z run models flare up
deeper shear profiles Wed morning and combined with diurnal
processes, may help storms re-strengthen as they exit out of the
local area and toward the CHI/MKE areas. Some locally heavy rain
still possible Wed morning before storms move out with lingering
saturated profiles. Then the main llvl boundary and convective
outflow will look to lay out from west-to-east acrs northern MO into
central IL by afternoon. After a early to mid afternoon precip lull,
the next approaching southwestern plains wave in broad
southwesterlies will start to act upon the frontal zone to the
south. Another round of convergent southerly llvl flow full of high
PWATs of 1.8 to over 2 inches will focus on the front Wed evening
and into the night.

Still some model discrepancy on how far north or south the main
convective axis will blossom, but the current ensemble mean targets
most storms from central into northeastern KS, the northern third of
MO and just north of the IA/MO border, and acrs central IL. This
latest thinking placement would then just make the southern quarter
to third of the CWA at risk of storms Wed night, unless there is
some sfc wave development along the front to lee of approaching
vigorous vort max aloft spread some elevated showers and storms
further to the north of I80 by late Wed night. Will adjust POP
chances accordingly. Deeper shear profiles in the vicinity of the llvl
boundary and CAPE potentail of over 2K J/KG may allow for some
strong to severe storms to affect portions of the southern CWA Wed
evening and night...mainly damaging wind the main threat. Locally
heavy rain again a continuing concern as well, with up to 2 inches
possible under re-occurring storm clusters. Further to the north
convective debris earlier in the day Wed may limit sfc based CAPES.
Still some worry advertised highs for Wed may be a bit high because
of storm outflow/lingering clouds.

Thursday and Friday...Will walk out lingering overrunning showers
and a few storms in the southern CWA mainly Thu morning into early
afternoon, before a bubble of high pressure slips acrs the region
from the northern plains. This will make for dry and cooler
conditions for Thu night and Friday. Some lows well down in the 50s
by early Fri AM. The latest medium range model ensembles then
suggest upstream southwesterlies to reload acrs the plains by late
Fri. Some elevated showers and a few storms possible into the
western CWA late Fri night into early Sat morning to the lee of
approaching short wave trof west of the MO RVR Valley.

Saturday through next Monday...Will continue to propagate showers
and some storms along with the passing wave Sat and Sat night. Cloud
cover and precip to limit sat warm up potential despite warming
profiles. Less cloud cover and precip coverage on Sunday could
allow for some low to mid 80s. Re-enforcing sfc and upper ridging
acrs the GRT LKS, as well as teleconnections to a possible tropical
system near FL may make it tough for upstream southwesterlies and
embedded additional vorts acrs the plains to push east and bring more
precip by Monday. But it will try, like the latest 00z run ECMWF
suggests, and will have to have POPs for more overrunning showers
Mon into Mon night for now.    ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1230 PM CDT Tue Aug 23 2016

Deteriorating conditions through this TAF period as increasing
moisture advection leads to lowering ceilings to MVFR during the
afternoon/evening. Shower chances are low through the day, so
kept out of TAFs at all sites but KBRL. Low-level jet forecast to
ignite sct showers and storms tonight - most likely to affect KMLI
and KBRL. Periods of IFR ceilings are possible.

Forecast uncertainty increases into early Wednesday
morning when a weakening MCS may move in from the W/NW. To cover
for this potential, included PROB30 groups. Greatest threat from
storms is torrential rainfall and VFR visibilities/ceilings. Stay
tuned to updates this evening and tonight. Uttech

&&

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

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...12
AVIATION...Uttech



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