Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 132313

Area Forecast Discussion
National Weather Service Quad Cities IA IL
613 PM CDT Sun May 13 2018


Issued at 330 PM CDT Sun May 13 2018

Storm clusters with northern stratiform rain shield moving acrs the
CWA currently, should be out of the area before 00z. Until this
passes, isolated svr storms possible as well as wake-low gusty
winds gushing northwestward out of the rain shield. The main sfc
boundary contiunes to be quasi-stationary from northeastern KS,
acrs far northern MO and central IL. With western CONUS Rex block
maintaining partial ring of fire-like pattern around periphery of
thermal ridge from the deep southern plains, to the southern GRT
LKS/eastern OH RVR weather to continue acrs or
near the local area through at least Tuesday with occasional
rounds of thunderstorms.


.SHORT TERM...(This Evening through Monday)
ISSUED AT 330 PM CDT Sun May 13 2018

Tonight...the current activity may affect what happens later tonight,
as well as CAPE/Instability gradient laying out from west to east
south of I80 for a more southerly focus, but bulk of latest model
runs and HiRes/CAM parameters suggest new convective activity to
develop along and north of Hwy 30 and especially west of the MS RVR
after 9-10 PM this evening. This in a zone of renewed nocturnal
southwesterly LLJ convergent zone and to lee of ridge-riding vort
max. Enough bulk shear to combine with elevated MUCAPE plume of 2000-
3000+ MUCAPEs for an elevated hail threat with these storms, and as
these storms congeal into more of a west-to-east line, they may try
to sag south and southeastward toward better CAPE gradient and
toward the main LLVL boundary after 1-2 AM. Thus a possible severe
risk as well as heavy rain swath could migrate to along and just
south of the I80 corridor from the Quad Cities on eastward by early
Monday morning. If it get`s too shallow rooted, a damaging wind
threat may develop late tonight in these areas. Localized swaths of
1+ inch rainfall may occur from north of Hwy 30, to the eastern I80
corridor by 12z Monday. Although there may be ponding of water,
these northern areas have missed out on the heavier rainfall of the
south and far east during the past 24 hrs and should be able to take
the additional rainfall without a widespread flash flood threat. Will
not put it in the grids, but where the rain wanes or stops for
awhile, there may be some pockets of overnight fog developing. Will
undercut guidance lows acrs the northern 2/3`s of the CWA.

Monday...After morning convective debris/outflow decays, some signs
of the main sfc boundary retreating northward some with vicinity
lighter sfc flow. The warmer sfc temps and 60 DPTs will allow for
afternoon CAPE build ups of 2000 to 3500+ acrs the southern half of
the fcst area. Flattening steering flow(with split developing to the
north), will still look to shuttle a vort max/wave up from the west-
southwest toward the area by late afternoon. With this increasing
lift and signs of weakening CAP aloft combined with better sfc
heating, storms may fire by late afternoon and early evening along
the front or sfc thermal gradient-discontinuity along and just south
of I80. Other more elevated storms will look to develop further
north as well and later into the evening and overnight. All modes of
severe weather possible with near sfc rooted or sfc rooted storms
that can fire by late afternoon in the more southerly areas. Hail
threat further north later in the evening with elevated natured
storms. One fly in the ointment may be if a storm cluster can take
off more in prime THTA-E convergence zone from acrs northeast KS/NW
MO/SW IA/SE NEB region by mid afternoon, and progress eastward acrs
MO robbing some energy from a more northward advance. But not enough
confidence in this scenario and will have to advertise high POPS for
convection again from late Monday afternoon and into Monday night.
more heavy rain possible, that by then may start to have some
influence on some tributary rivers and creeks that get impacted.

.LONG TERM...(Tuesday through next Sunday)
ISSUED AT 330 PM CDT Sun May 13 2018

Storms lingering Tuesday morning in the south, then diurnal decay.
Upper jet and mid level mean steering flow pattern on the medium
range models suggest that the main llvl boundary and storm action
zone may then finally settle south of the area/region for a break
during the mid and late week period. Then an approaching trof could
bring about the next chance for precip sometime over next weekend.
Seasonable to above normal temps for the extended range.


.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 608 PM CDT Sun May 13 2018

Mainly MVFR conditions will be seen through 12z/14. After 06z/14
the models suggest another thunderstorm complex will develop and move
across eastern Iowa and northern Illinois producing IFR
conditions in the stronger storms. After 12z/14 MVFR/IFR
conditions are forecast to improve to VFR/MVFR with another round
of TSRA developing after 18z/14.


Issued at 1146 AM CDT Sun May 13 2018

On the Mississippi...the crest appears to be progressing south of LD
16 IL City and through Muscatine, New Boston, Keithsburg, Gladstone,
and on the doorstep of Burlington today. New Boston looks to be
cresting out just under the Major flood stage, while Burlington is
nearing crest at a little above Major flood stage. The last site to
experience the crest still appears to be Gregory Landing on Tuesday.
Sites from the Quad Cites on north are continuing to fall, with the
next site projected to fall below flood stage being LD 11 at Dubuque
later tonight.

Concerning the tributaries...flood warnings continue for just a few
sites along portions of the lower ends of the Iowa and Wapsipinicon
Rivers, as rainfall runoff continues to route through these
tributary systems. Depending on the extent of rainfall falling on
the various tributary basins over the next several days, other sites
may experience withing bank rises or even approach flood stage. The
rivers already in flood will also have to be watched for slowed post-
crest recessions or secondary crests developing. But on the larger
watershed of the mainstem Mississippi River, the rounds of rainfall
with the passing storm occurrences over the next several days, are
still only expected to delay or slow the river level recessions
after the crests occur.   ..12..




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