Severe Thunderstorm Warning 121, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
357 AM CDT Sun Aug 18 2019

.SYNOPSIS...
Issued at 349 AM CDT Sun Aug 18 2019

Linear MCS is currently approaching northwest CWA, while additional
stronger storms have developed over southern IA into northern MO.
MCS driven by cold pool dynamics is diving E/SE while southern
convection lifting northeastward with the two converging and set
to bring much needed rain to a good portion of the area this
morning. The convection is occurring ahead of a cold front
extending from MN through southeast NE, which will pass through
the area later today and evening.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 349 AM CDT Sun Aug 18 2019

The cold pool driven linear MCS, and broad warm advection/isentropic
ascent in advance should result in good coverage of showers and
storms this morning. Despite some favorable severe parameters
including 30-40+ kts of effective bulk shear and 2000-3000 j/kg
MUCAPE, the time of day /overnight-morning arrival/ will likely
limit the severe weather threat. But, that being said isolated
severe weather is possible, especially with any mesoscale
augmentation via mergers or splits, and terminus of LLJ ahead of
line etc.

The cold front will move across the CWA this afternoon through
early evening, and will be accompanied by at least low chances
for additional storms. However, much uncertainty exists with
this potential and is tied to how much recovery of airmass occurs
in wake of morning activity. This will also make for a very
tricky high temperature forecast today. Forecast is staying close
to previous days allowing for more PM cloud breaks getting highs
back to around 80F or generally range of 80-85F, and low chances
for PM/early eve storm. If storms persist longer today then
anticipate reduction in both temps and chances for redevelopment
ahead of front. If storms quickly diminish, then potential to see
increase in highs and better prospects for PM redevelopment. More
solar insolation coupled with southwest flow and compressional
heating would likely push temps in some areas into the upper 80s
to possibly near 90F ahead of the front. This amount of
instability in presence of progged 20-30 kts of bulk shear would
support an isolated severe storm threat. Have kept low PoPs
for much of evening tapering off north to south after midnight.
Will have to monitor potential for higher PoPs south if LLJ
doesn't veer and remains focused into front as suggested by a
couple of models.

Cooler and drier air begins to filter in overnight, with lows
dipping into the mid/upper 50s northwest CWA. Meanwhile, still
hanging onto the warm and humid mid/upper 60s south.

.LONG TERM...(Monday through Saturday)
ISSUED AT 349 AM CDT Sun Aug 18 2019

Next cold front is slated to move through on Tuesday. Will be
closely monitoring potential for strong/severe storms ahead of
front possibly as early as Monday night then into Tuesday, with
models depicting moderate instability and seasonably strong mid
level winds. The convective trends will loom large on the high
temperature forecast Tuesday. Currently have highs in the upper
80s to lower 90s with heat index readings well into the 90s to
possibly near 100F. However, trends of the models past several
days showing better agreement on storm potential for Tuesday,
thus any delta on temperatures would be lower from the looks of
it right now.

Once this cold front passes, some very nice pleasant weather is
anticipated mid into late week as cool Canadian high pressure
builds down through the Great Lakes. This will provide low
humidity and near to slightly below normal temperatures.
Warmer temperatures are then anticipated heading into next
weekend, as the high settles over the eastern US and southerly
return flow increases on the backside. This will likely lead
to a gradual increase in humidity and eventual return of rain
chances.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1253 AM CDT Sun Aug 18 2019

Potentially several rounds of showers and thunderstorms are
possible at all TAFs sites overnight into Sunday morning. MVFR
ceilings and visibilities are expected with these showers and
storms with periods of IFR conditions. Heavy rain and strong
winds will be possible with the strongest storms. Conditions are
forecast to improve to VFR conds on Sunday. A cold front will
arrive Sunday evening with winds becoming northwest with the
passage of the front.

&&

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

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...McClure
AVIATION...Haase

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