Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 201748

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1248 PM CDT Sun May 20 2018


Issued at 330 AM CDT Sun May 20 2018

The latest sfc analysis was indicating a weak wave acrs the south
central CWA ATTM, rippling along a frontal boundary. This feature a
reflection of a vort max aloft, currently driving isolated to sctrd
convection acrs the area. Another larger short wave aloft was
embedded acrs the southwestern plains in wavy southwesterlies/
steering flow aloft. This wavy pattern to continue to produce
occasional chances for precip in or near the local area into early
Tue, before large closed upper low gets established acrs the western
Intermountain region, amplifying blocking upper ridging acrs the MO
and MS RVR Valleys for a break in the action by midweek.


.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sun May 20 2018

Today...Will continue with isolated to sctrd coverage to the showers
and thunderstorms this morning, before the above mentioned southwest
plains shortwave starts to eject out toward the lower MO RVR valley.
The lift should bring an uptick/another wing of sctrd showers and
thunderstorms moving up from the southwest and acrs the CWA
(especially south of I-80) from late morning and into the
afternoon. By then with western GRT LKS llvl ridge squeezing down
further south and main sfc front shunted south, bulk of LLVL flow
acrs the local area to be east northeasterly, thus overspreading
convection to be elevated. Some steep mid layer lapse rates and
drying in layers aloft may foster some hail production with the
stronger cells today, but uniform southwest flow aloft and
marginal bulk shear values may limit severe potential. Elevated
THTA-E feed to still produce locally heavy rain under passing
storm cells/ clusters. Some signs this activity to weaken as it
tries to migrate north of the I80 corridor. Fcst deep convective
index max regions acrs the southern 2/3`s of MO and eastward up
the OH RVR valley supports a better chance for more significant
convection acrs those areas later this afternoon and evening. As
for highs today, with expected cloud cover and post-frontal
northeasterly boundary layer fetch will go quite a bit cooler than
previous days. Many areas along and north of I80 may have trouble
getting out of the 60s.

Tonight...The main short wave will look to progress right acrs the
mid to upper MS RVR Valley, with one or more MCS`s or convective
clusters progressing acrs the higher instability region of MO, south
half of IL, Southern IN and the OH RVR Valley. This again will have
an impact further to the north acrs the local area, and just expect
sctrd secondary elevated convection to continue, or even regular
showers with just some thunder. Again, this activity may have trouble
holding together as it tries to migrate northeastward of the I-80
corridor or Hwy 30. Ongoing northeast sfc winds of 10-15 MPH should
limit fog production tonight, as well as cool advect temps in the
50s for lows. Some upper 40s even possible in the far northeast.

.LONG TERM...(Monday through next Saturday)
ISSUED AT 330 AM CDT Sun May 20 2018

Monday and Tuesday...passing wave to continue to induce sctrd showers
an a bit of thunder on Monday, especially east of the MS RVR, before
that activity will look to wane into Tue morning. Temps in the 60s
and 70s on Monday with cloud cover, should warm into the upper 70s
and low 80s on Tuesday as things dry/clear out.

For the rest of the extended, like mentioned in the synopsis, large
western CONUS upper trof/closed low will make for a blocked pattern
again acrs much of the CONUS, with upper ridging arching up the MS
RVR Valley potentially making for a precip lull period for the mid
to late week. Will have to watch for ridge-riding convective systems
or decaying debris fro these systems possibly spilling in from the
west or northwest during this period, but the next main chance for
showers/storms may not come until later Friday into Saturday as
upper trof energy breaks down the upper ridge acrs the upper


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1243 PM CDT Sun May 20 2018

A strong warm front remains poised over far southern Iowa into
central Illinois. Along and north of this front, widespread MVFR
to IFR cigs and visibility will continue to be a threat this
afternoon through Monday morning as moisture overrides the cooler
air. Easterly surface winds will continue at 10 to 20 KTs through
late tonight, before decreasing Monday morning after 12Z. Showers
and thunderstorms are possible through the period, with the
greatest coverage early this afternoon in locations south of
Interstate 80 in Iowa and Illinois, then later tonight, as an
upper low emerges from the plains, a widespread area of rain and
embedded thunder will spread over the entire area from southwest
to northeast. That rain, and lower CIGs and visibility will move
out between 12Z and 18Z Monday. Since lower cigs often linger well
past the rain on these type of warm frontal events, I have left
lower MVFR cigs in through 18Z Monday.




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