Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 170452

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1152 PM CDT Tue May 16 2017


Issued at 952 PM CDT Tue May 16 2017

Area radars at 9 pm showed a large complex of strong to severe
thunderstorms over western and central Iowa moving E-NE. Over the
past hour, a wing of elevated weak showers and an isolated
thunderstorm had developed over southeast IA. These were spreading
north to northeast.

The surface-based convection over central IA will likely weaken as
it moves away from the higher CAPEs and shear that is expected to
remain over central and western IA through the most of tonight.
Also supporting this trend will be the northeastward movement of
the associated upper level shortwave and better forcing in the
southwest flow aloft. Convective allowing models have depicted
this tendency this evening, showing overall weakening as storms
approach late tonight, then possible redevelopment along
potential outflow boundaries in eastern IA into northeast MO
toward 12z. The exception will be portions of Benton and Buchanan
counties that will likely see some remnants of the complex
currently just north of Des Moines moving through between 11 pm
and midnight. These may have some strong gusty winds, but not
anticipating severe weather at this time.

Have updated the forecast to include possible weak showers and
thunderstorms in the west early, then chance pops for thunderstorms
moving into eastern IA around 09z to 12z. The rest of the
forecast area will have a mild night with south breezes and a high
overcast from upstream storms.


Issued at 330 PM CDT Tue May 16 2017

Strong upper wave seen on latest water vapor imagery digging east
acrs the 4-corners region, will be the weather maker across the
plains tonight, and for our local area Wed afternoon and evening
as it ejects out northeastward up the MO River valley and into MN
by the Wed overnight period. Then, another large upper low to
bring about a wet end to the week and start to the weekend.


.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 330 PM CDT Tue May 16 2017

Tonight... Little subtle vort wing and mid level steeper lapse rate
plume currently inducing elevated isolated to scattered showers
and storms across northeastern IA into SE MN, should continue to
move away from the CWA. Will have to watch isolated enhanced CU
field in northeast MO over the next few hours for the same type of
elevated development moving into the southern CWA. Otherwise the
local fcst area looks to remain largely dry, warm and capped
through at least midnight, as the latest layout of prime deep
convective indices overlaid by incoming lift from the TX
panhandle, arching northeastward acrs the MO River valley and
into north central IA, and into southeastern MN, show the areas
that will be convectively active this evening. Several linear
MCS`s and LEWP-type evolution indicated by several HiRes
models/CAMs in these areas tonight. Then with some veer to robust
southerly 40-50 KT H85 nocturnal jet, do expect some of the
western into central IA overnight convective systems to push
eastward into the western half of the DVN CWA after midnight. But
many signals and strengthening elevated warm wedge aloft suggest
this activity to come in mainly in a weakening or even decaying
mode, with only a low chance for some strong storms in the far
western CWA as they arrive out of central IA. Some convective
debris to probably make it just east of the MS River around and
just after sunrise Wed morning. Only see a higher severe storm
risk late tonight if an upstream system can get surface rooted
and chug east aided by cold pool propagation, then damaging winds
would be likely. Mild overnight lows in the mid to upper 60s.

Wednesday...Morning showers and some storms will look to start to
decrease and move out northeast of the CWA by late morning, and may
have to watch for some diurnal storm enhancement capable of
producing some hail before they exit or decay. Then some clearing to
make for atmospheric recovery...maybe.  Closed upper low nearing 550
MB depth, expected to roll northeastward in negatively tilted
fashion up the MO River Valley by Wed evening. This feature to
spill diffluent southwesterly flow with embedded vort max to the
lee of it across northern MO and much of IA, and NW IL.
allowing models continue to depict these storms weakening as they
move into the less favorable environment over eastern IA
Embedded mid level jet rounding the bend of 70-90 KTS, 40-50 KT
southerly H85 jet, and other prime shear parameters combined with
building CAPES of at least 1000-1800+ J/KG are starting to point
toward a potentially strong episode of storms later Wed afternoon
and into evening. Bulk shear profiles increase to a very high 60 to
75+ KTs across the local area toward 00z Thu, while 0-3 KM SRH
values increase to 250-350+ M2/S2...0-1KM 25-30 KTS. These type of
shear profiles combined with LCL`s of 2800 to around 3000 FT
suggest a definite tornado potential as well as strong rotating
updraft producing large hail. All modes of severe in fact look to
be possible. Current accepted timing of the strong to severe
storms spreading in from the west and southwest after 3 pm, with
some solutions not til after 5 PM. Will increase and adjust
afternoon POPS accordingly. See the potential for SPC to upgrade
the current slight risk for tomorrow to at least enhanced if the
morning convective debris can clear off in time for a
heating/recovery window before the "wing" of high shear approaches
from the southwest. ..12..Convective
allowing models continue to depict these storms weakening as they
move into the less favorable environment over eastern IA

.LONG TERM...(Wednesday Night through next Tuesday)
ISSUED AT 330 PM CDT Tue May 16 2017

Forecast focus on an active and wet pattern in the long term.

Wednesday night:  Thunderstorms, possibly severe, will be pushing
across the dvn cwa during the evening. Tornadoes are certainly
possible with a curved hodograph, 40-60+ knot shear, sfc-3km SRH of
300-500 m2/s2, CAPE 2000-3000 J/kg, SWEAT of 400-500, and LCL height
of 2500-3000 ft agl. There is a 70-90 kt jet streak at 500 mb and
diffluence aloft, along with a 987 mb cyclone tracking into nw IA by
evening and strong omega noted on time height sections. This looks
to be a potent situation during the evening.  The cold front will be
arriving after midnight ending the thunderstorm activity.

Thursday: Cyclone will be tracking into the Great Lakes region
ushering less humid air on a brisk northwest wind. No rain expected
as we will be between storm systems. Temperatures should still be
warm in our se cwa with highs ranging from the mid 60s at
Independence to 82 at Macomb.  Cooler air will be filtering into the
cwa by Thursday night.

Thursday night and Friday:  Next storm system will be taking shape
in the southern/central Plains with an increasing moisture transport
from the south. With the cooler temperatures over the area this will
spread warm air advection rain across the cwa. The GFS is a bit
faster in bringing this rain into our sw cwa late Thursday night.

Friday night through Sunday: Storm system will be impacting the cwa
with a stronger moisture transport off the western Gulf. The ECMWF
indicates a cool and prolonged rain event with a slow moving system
with the potential for heavy rainfall. On the other hand, the GFS
pulls a surface low out of the southern Plains and into eastern MN
on Saturday. This would allow for a warmer and more unstable airmass
with showers and thunderstorms likely. This system also has the
potential for producing severe weather, depending on amount of

Early next week:  Next on the hit parade is another storm system
arriving in the Tuesday/Wednesday time frame. However, low
confidence this far out in the intensity and track of this system.
Currently, the GFS takes the surface low across MN and WI while
the ECMWF has the low tracking across MO.



.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1151 PM CDT Tue May 16 2017

Widespread thunderstorms over central and western Iowa will
likely decrease in intensity as they move into eastern Iowa
tonight, but are appearing likely to reach the CID, DBQ and MLI
terminals before sunrise with at least brief MVFR conditions.
Scattered to isolated cells may linger until mid morning before
dissipating. During the overnight, conditions may come close to
low level wind shear thresholds due to strong southwest winds
just above the surface. However, at this time it appears this
vertical transition to stronger winds will not be sharp enough to
justify a LLWS in the forecasts. Wednesday, most of the day looks
to be VFR with gusty south winds at the surface. Scattered strong
to severe thunderstorms are possible from mid afternoon through
the evening.




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