Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 161740
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1240 PM CDT Sun Jul 16 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 305 AM CDT Sun Jul 16 2017

Line of thunderstorms in WI has moved into portions of northern IL
and as expected has gradually weakened and diminished in coverage.
An isolated storm in Stephenson county was strong but remained
just below severe levels.

In the meantime, a weak cold front extended from southern WI to
northern IA. Ahead of the front, warm moist air was located
across the dvn cwa with 2 am temperatures in the upper 60s to mid
70s with dewpoints in the mid 60s to lower 70s.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 305 AM CDT Sun Jul 16 2017

Forecast focus on thunderstorm chances today.

Today: Weak cold front will continue to slide slowly southward
across the cwa. The few showers or storms early this morning
should end for a time, and then redevelop south of Interstate 80
this afternoon, with daytime heating. SPC has a marginal risk of
severe storms in our southern cwa with gusty winds and hail
possible. While the bulk of the storms should remain below severe
levels, can`t rule out an isolated severe storm or two. Bulk shear
is quite weak but steep mid level lapse rates of around 7c/km and
MUCAPES to around 4500 J/KG is noted on forecast soundings. This
would favor mainly pulse storms. Any storms that form should move
south of the dvn cwa by late this afternoon, as the front shifts
south of the area.

In the wake of the front, cooler northeast winds and low level
moisture will likely aid some low cloud development with additional
Lake Michigan enhanced clouds perhaps advecting into portions of
northeast IA and northwest IL. This will keep the coolest
temperatures in our ne cwa. Highs should range from the upper 70s
in our ne cwa, to around 90 in our far sw cwa.

Tonight: High pressure will build into the Great Lakes region
sending cooler and much less humid air into the cwa, on northeast
winds. Skies should be clear to partly cloudy. Lows will range
from 55 at Freeport, IL to 67 at Memphis, MO.

.LONG TERM...(Monday through Saturday)
ISSUED AT 305 AM CDT Sun Jul 16 2017

Hot and humid weather returns this week, along with periodic chances
for thunderstorms. This will be the result of a developing, more
zonal upper level flow that will allow the upper level high and
thermal ridge over the Rockies and Great Basin to nudge eastward,
reaching the Central Plains and MS Valley mid to late week. This
setup, with the active westerlies along and north of the forecast
area, associated embedded shortwaves, and boundaries wavering over
the region will support several rounds of thunderstorms in
or near the forecast area beginning mid week.

The week starts out with a relatively cool and dry airmass courtesy
of high pressure over the Great Lakes. Monday`s highs range from the
upper 70s over northwest Illinois to the mid 80s over southeast Iowa
into northeast Missouri. The warm air advection and moisture return
commences at 850 mb Monday night, sending highs into the upper 80s
to lower 90s for Tuesday, while dewpoints return to the upper 60s to
lower 70s. Models continue to suggest a possible surface boundary
and focus for convection over the far northwest, where low pops are
maintained for the afternoon.

Wed and Thu are shaping up to be the warmest days of the week, as a
southwest 850 mb flow advects temperatures in the lower 20s celsius
into much of the forecast area. Have continued to trend near to
above the guidance blend with highs in the lower to mid 90s over the
central and south. These highs could potentially be on the low side,
especially for Wednesday. Thursday may see the boundary possibly
wavering southward over the area with associated convection, cloud
cover and moisture pooling leading to even lower confidence with
respect to forecast highs. The combination of temperatures into the
90s and dewpoints in the 70s may drive heat index values near to
above 100 in the afternoon hours both Wed and Thu.

The latest runs of both the GFS and ECMWF suggest the synoptic
boundary may push south through much of the forecast area Thu night
and gradually return northward Friday to require at least chance
pops for thunderstorms. This also points toward lower forecast highs
than the previous two days. Little change is advertised for Saturday
with continued very warm temperatures, high humidity and chances for
thunderstorms. However, there is typical poor model consensus this
far out with the timing and track of a potentially more organized
surface low and its associated boundaries, thus confidence is low
for both temperatures, and pops that are introduced in a slight
to low chance range.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1234 PM CDT Sun Jul 16 2017

A cold front is pushing through the area today bringing in MVFR
CIGs and a chance of thunderstorms along and south of the
boundary. At 17Z the cold front was roughly along I-80 and was
progressing southward at a good pace. Most notable with this front
is a sharp wind shift from west to east-northeast. South of the
boundary is where thunderstorm chances will persist until early
evening, with the thunder threat noted only in the BRL forecast.
Overnight there is a brief potential for fog though likely not as
impactful as this morning.

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Sheets
AVIATION...Wolf



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