Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 212331
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
631 PM CDT Wed Jun 21 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 343 PM CDT Wed Jun 21 2017

At 3 PM...scattered showers and thunderstorms continued to move
southeastward across the eastern Iowa and northwest Illinois. Due
to precipitation, temperatures were much cooler than forecast and
ranged from the lower 80s south of a Mount Pleasant to Galesburg
line to the lower 70s along the Highway 20 corridor. Dew points
were generally in the lower 60s across our north of our area to
the upper 60s in our south. Using theta-e for my analysis, a warm
front stretched from Des Moines southeastward to Macomb Illinois.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 343 PM CDT Wed Jun 21 2017

Tonight...As elevated warm front tries to lift north and short wave
aloft ripples by to the east, expect the current elevated sctrd
shower and thunderstorms to wane and move off to the east after 8
PM. Then the local area may have a lull as the warm front lights up
again with sctrd nocturnal convection to the north acrs MN and WI.
Then will have to watch a llvl convergent zone along a NE-to-SW
oriented boundary along the western IA/MN border region into eastern
Neb for later night development. If this were to occur, it could
tail down southeastward into the northwestern third of the CWA late
tonight after 3 AM. Some of this could be strong, but late night
arrival make for less of a severe chance with temporary lack of
better forcing as it moves away from it`s source region of lift.
With this area currently indicated to be capped, some and lowered
confidence that this area of upstream storms may form at all and
then make it down into the area. Will just go with low to moderate
CHC POPs in these northwestern and northern areas for now.  milder
night with lows in the upper 60s to around 70, if the llvl warm front
can make it`s retreat north like most of the model solutions suggest.

Thursday...Again, just a low to moderate chc for lingering storms
out of Wed night north of I80 through mid Thu morning. Then the heat
and higher humidity will be on for the rest of the day in the warm
sector, with a building EML capping the area off for the afternoon.
High temps in the upper 80s to lower 90s, with sfc DPTS in the mid
to upper 60s making for late afternoon CAPES of 2000-3000+ J/KG and
Heat Index readings of 95 to near 100 degrees acrs the southern
2/3`s of the fcst area. Bulk of the latest run models sag the
upstream sfc front acrs western IA and Omaha, up acrs northeastern
IA/southeastern MN and western WI where it looms by 00z Fri. Just a
low chance that storms fire early off this feature by late afternoon
and make it into the northwestern CWA before 00z.   ..12..

.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 343 PM CDT Wed Jun 21 2017

Thursday night...The above mentioned boundary will look to become a
convective focal point Thu evening from acrs western and
southwestern IA, up through northeastern IA, southeastern MN and
western WI, as another short wave ripples acrs in steering upper
Midwest westerlies and the northern fringe of EML erodes. If it
fires more in this upstream location, the potentail is for then a
linear MCS with bowing segments propagating down southeastward
acrs the DVN CWA feeding on high THTA-E/CAPe airmass...with an
inherent damaging wind threat and intense rainfall under mature line
segments. Projected 0-3km shear vectors aren`t quite optimum for
mesovortice development, but can`t totally rule that phenomena/spin
up tornadoes out. Activity should weaken late Thu night/early Fri
morning as it plunges toward the southern CWA after 4 AM CDT.
Another scenario that can`t totally rule out as well, as if the
front sags a bit further south and the local area becomes the
initiation point Thu evening, then initial supercells and associated
severe threats will be possible, but more model solutions point to
the upstream development off to the northwest, then a maturing MCS
probably linear or quasi-linear comes surging through the area
overnight Thu night.

Friday...This day still shaping up to be a drying/less humid, breezy
post-frontal day with highs in the upper 70s to lower 80s acrs most
of the DVN CWA. The latest run medium range models continue to
suggest the passing front to the east and south to act as moisture
interceptor of the gulf tropical system remnants, and focus
resultant very heavy rains up the TN and OH RVR Valleys.

Saturday and Sunday...Latest suite of medium range models and
ensembles continue to suggest general Upper Midwest and GRT LKS
troffiness over the weekend, with associated northwest flow below
normal temp regime still on track. Incoming thermal profiles/lowered
thicknesses suggest highs in the mid to upper 70s on Sat, struggling
to make the low to mid 70s on Sunday even with deeper mixing. Some
locations along the Hwy 20 corridor may be held in the upper 60s
especially if enough ambient cellular CU develops. Overnight lows
well down in the 50s with even some upper 40s possible especially
Sunday night. As for precip chances, some signs of a short wave trof
embedded in northwesterlies aloft, combining with diurnal instability
to produce sctrd showers and a few storms Sat afternoon and evening,
possibly similar to these past few afternoons(Mon and Tue)but with
less thermodynamic "bite" and thus hopefully less hail/wind gust
potential.

Monday through next Wednesday...In general, medium range guidance
and mean pattern ensembles acrs the mid CONUS, suggest the GRT LKS
troffiness to eventually give way back to more progressive
westerlies with return flow warming into mid next week. This could
also make for a re-establishment of the storm/MCS track in or near
the local fcst area, or at least from the northern plains acrs the
upper Midwest and into the GRT LKS. The 12z GFS is quicker with this
scenario with convergent return flow storms track setting up acrs the
northern plains into MN By Tue night, with the llvl baroclinic
ribbon strom focus then getting shunted south in or near our area of
concern Wed into next Thu. The ECMWF adjusts this potentail storm
track close but not til later Wed into Thu.  in any case, will
moderate temps and POPS upward into the mid week period.   ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 630 PM CDT Wed Jun 21 2017

A large area of showers and a few thunderstorms over eastern Iowa
will impact terminals early this evening. With high cloud bases,
the main threat will be visibilities briefly dropping to MVFR
levels. These showers are expected to exit the area by 03z,
followed by VFR conditions. Low level wind shear conditions are
expected to develop toward 06z at CID, DBQ and MLI as winds
around 2000 ft increase to 40 kts, above surface winds that will
be less than 10 kts from the south. LLWS will dissipate by 13z,
followed by breezy south surface winds and VFR conditions
Thursday. There is a low potential for thunderstorms, which are
not included in the forecasts at this time.

&&

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

$$

SYNOPSIS...Cousins
SHORT TERM...12
LONG TERM...12
AVIATION...Sheets



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