Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 241538

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1038 AM CDT WED AUG 24 2016

Issued at 1032 AM CDT Wed Aug 24 2016

The early morning storms dropped 1 to 3 inches of rain roughly
along Interstate 80 counties, and up into Whiteside county.
Additional small heavy rain showers are expected today until the
MCV exits our cwa. This rain has saturated counties, and this puts
them at threat for flash flooding with additional heavy rainfall
tonight. Looking at current conditions, satellite, and the latest
CAMS, the next round of thunderstorms may move up over top of the
same counties roughly along I-80 tonight. A easily visible vort
max is lifting northeast through Kansas this morning, and with
clearing ahead of the wave in Iowa, the HRRR depiction of new
convection forming in Iowa looks reasonable. This should then move
east northeast along the boundary, over our CWA this evening. For
these reasons, the Flash Flood Watch has been expanded to cover
locations along I-80 in our central and eastern CWA, and also
Whiteside county, where amounts near 3 inches fell today.


Issued at 351 AM CDT Wed Aug 24 2016

Widespread showers and storms ongoing early this morning, as
upper level shortwave and dynamically augmented strong low level
jet and moisture transport converge into cwa. Anomalously
high moisture content, strong forcing and southwest flow parallel
to cold front (currently moving into northwest Iowa) resulted in
significant rains and flash flooding over portions of far
northeast Iowa into southwest Wisconsin where amounts of 2 to 5
inches have been reported from around Charles City, Iowa to
Decorah and just northeast.


.SHORT TERM...(Today and Tonight)
ISSUED AT 351 AM CDT Wed Aug 24 2016

Showers and storms anticipated to gradually diminish from west
to east this morning with passage of the upper level wave, and
waning of low level jet and attendant moisture advection. This
will likely lead to a lull in precipitation by midday into
early afternoon. Showers and storms are then likely to redevelop
and/or spread into the area from the southwest possibly later
this afternoon and especially this evening and tonight, as renewed
bout of decent forcing with next upper level wave (currently over
Colorado) and right entrance region of upper jet overspread the
the cold front roughly bisecting the area. Risk of strong to
severe storms exists ahead of the front roughly near to south of
I-80, as wind fields overall strengthen with impressive bulk
shear 0-6km of 35-45+ kts. The wild card is amount of heating and
destabilization, which will play role in determining magnitude of
storms. Given such high atmospheric moisture, the main threat
would be strong wind gusts. Otherwise, main concern is with heavy
rain and potential for flash flooding. Favorable ingredients in
place to support potential widespread heavy rainfall including
anomalously moist environment (precipitable water values of 1.5 to
2 standard deviations above the mean), strong forcing aided by
enhanced upper diffluence attendant to approaching Rockies wave
and southwesterly flow parallel to boundary supportive of training
or repeated storm activity near the front. Environment very
similar to that of far northeast Iowa and southwest Wisconsin,
which has received 2-5+ inches and reports of flash flooding early
this morning. Unforeseen mesoscale interactions and slightly
stronger/faster front than many models adds uncertainty as to
exactly where the axis of heavy rain will occur. Overall though,
most guidance is suggesting south of I-80 being most favored for
heavy rainfall and potential flash flooding, thus have issued a
flash flood watch from 00z to 12z Thursday for much of the area
south of I-80 where 1-4+ inches of rain is possible. Some of the
more recent solutions suggest this could be a bit further north
near the I-80 corridor, and again this axis still difficult to
pin down and may shift depending on the frontal timing/placement.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 351 AM CDT Wed Aug 24 2016

Thursday and Friday...Latest 00z run progs suggest slowing main sfc
frontal boundary sagging south and southeast of the DVN CWA by
midday, aligning parallel under broad west-southwest flow acrs
KS/MO/central IL. Thus will walk out overrunning showers and a few
storms acrs the southern 2/3`s of the fcst area by early afternoon.
Do not see the potentail of any strong storms even closer to the
passing boundary in the southern CWA Thu morning, and heavy rain
threat to shift south/southwest. Advertised post-frontal high temps
may still be a bit too warm if overrunning cloud cover hangs on for
much of the day. Thu night dry with sfc high pressure building down
acrs IA out of the northern plains. Could be a range of low temps in
the low to mid 50s in the far northwestern CWA where skies clear
out, to the lower 60s under continuing cloud shield in the south. If
post-frontal sfc winds can decouple, there may be some fog issues
under the clear areas toward Fri morning. Fri continued dry and
somewhat below normal temp-wise, with increasing high cloud cover
ahead of the next approaching S/W trof acrs the plains that will
have to battle both sfc and upper ridging lingering acrs the western
GRT LKS. Increased and hastened elevated moisture return flow on the
00z runs for showers and some embedded thunder spreading in acrs the
area from the west/southwest later Fri night.

Saturday and Sunday...May be a rather wet period with digging
seasonably strong wave acrs MN and the northwestern GRT LKS
interacting with ongoing southerly flow/increased warm moist
conveyor. Highest POPs Sat into Sunday morning. Will keep lower POPs
for later Sunday into Sunday night, but think the more progressive
00z ECMWF is more on track and would be basically dry by late Sunday
and Sunday night. Depending on cloud cover and precip trends, high
temps for the weekend may have to be eventually adjusted down from
what will be in the grids.

Next Monday and Tuesday...Two camps this period with the 00z ECMWF
advertising dry subsidence acrs the upper midwest and local temps
warming in the 80s, while a hurricane churns in the Gulf with eyes
on LA. The 00z GFS meanwhile has daily warm air advection showers
and storms this period, and thus biases the POP blend with low
chances through mid next week. It will probably be in between with
plenty of dry and seasonably mild periods early to mid next week.


.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
ISSUED AT 638 AM CDT Wed Aug 24 2016

Scattered showers will linger this morning with the passage of an
upper level shortwave and surface warm front. Conditions will
vary from vfr to mvfr with localized ifr this morning, with winds
turning southerly and perhaps gusting for a time especially at
BRL and MLI. There is a chance of showers and storms by mid
afternoon into this evening ahead of a cold front. The coverage
of precipitation is expected to increase tonight near to south
of I-80, with conditions lowering to mvfr and ifr in storms with
heavy rain. Rain chances should taper off at CID and DBQ gradually
later tonight with deepening northerly winds.


.DVN Watches/Warnings/Advisories...
IA...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Cedar-Des Moines-Henry IA-Jefferson-Johnson-
     Keokuk-Lee-Louisa-Muscatine-Scott-Van Buren-Washington.

IL...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Bureau-Hancock-Henderson-Henry IL-McDonough-
     Mercer-Putnam-Rock Island-Warren-Whiteside.

MO...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Clark-Scotland.



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