Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 300856
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
356 AM CDT Sun Apr 30 2017

.SYNOPSIS...
Issued at 330 AM CDT Sun Apr 30 2017

Water vapor imagery loop showing strong cut-off mid level low
rolling into the southwestern plains, while large scale convective
episode ongoing from the southwestern plains and up the OH RVR
Valley. More of a stratiform field to the north of that activity
trying to spread north and northeast acrs the local area but
encountering tight north to northeasterly llvl pressure gradient and
flow making it a battle to push northward. The main upper low center
projected by most 00z model runs/decent agreement to eject out
northeastward over the CWA by Mon morning, and not move into the
northern GRt LKS until Tue and continue to be a WX maker for the
time being including a possible stronger thunder storm episode this
afternoon and evening for the local area.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sun Apr 30 2017

Today...Stratiform precip shield will move acrs mainly the
southeastern half of the CWA this morning, with spotty lighter rain
or drizzle to the northwest and north of it. extrapolation of more
widespread moderate with pockets of heavier stratiform rain and
embedded thunder will look to keep just south and southeast of the
DVN CWA through mid morning, but areas from Kahoka MO to northeast
of Macomb may get and unneeded additional 0.25 to 0.40 tenths of an
inch of rain aggravating any ongoing nuisance urban and small
stream flooding in those areas from previous heavy rain episodes on
Sat. But will bank on stratiform nature over a period of time
limiting flash flood threat this morning through midday. Like the
00z 4KM NAMnest idea of a lull period acrs much of the local fcst
area from 15z through noon or 1 PM after the stratiform shield exits
off to the east...maybe just some lingering sprinkles in spots during
that window.

Then as the upper low moves into eastern KS and it`s leeside deep
lift and shear fields move acrs eastern IA and IL, with upstream dry
slot streaking acrs eastern KS and western MO, the stage will be set
for rounds of afternoon into evening thunderstorm activity moving up
acrs the region. Both llvl and deep layer shear fields continue to
be advertised by most models and fcst vertical profiles to be very
strong to extreme in or near the local area this afternoon and
evening. But the real wild card continues to be the extent of
instability available for this strong shear to utilize. Some signs of
advancing warm front to lee of llvl cyclone, and associated triple
point interacting with at least 200-500 J/KG MUCAPES moving up acrs
western IL and to the I80 corridor along and east of the Quad City
area from mid afternoon into early evening. If this shear and
thermodynamic profile where to verify, could see the scenario of
sctrd low topped supper cells with damaging wind and tornado threats
in these areas from 3 pm through 7-8 pm. More prime area possible
just to the southeast of the CWA and could see an upgrade from
Slight to enhanced severe risk acrs central into southern IL later
this morning. Otherwise, again like the 00z 4KM NAMNest idea, as
well as a few other Hires solutions of suggesting bands or spokes of
broken lines of showers and thunderstorms moving up acrs the area
this afternoon just to lee in in-building dry slot. Couldn`t rule
out at least an isolated severe storm further to the west, but
better chances appear to be along and east of the MS RVR.

With saturated grounds and more of a convective burst heavy rain
scenario, could see localized flash flood potentail in the south and
east this afternoon with the bands of storms, but coverage and storm
progression uncertainties preclude the need for a widespread flash
flood headline at this juncture unless things change later this
morning. High temps may occur not until late afternoon or early this
evening with warm sector and adjacent areas arrival at that time.
Large temp gradient from northwest-to-southeast and tricky temp fcst-
"bust" potential scenario in between. Some higher sfc DPTS possible
in the warm sector pushing the upper 50s or 60 degrees in our far
southeast, but again confidence low with this as well as the above
mentioned instability uncertainties. But the potentail is there.

Tonight...With currently accepted model choices and storm
progression, see the more organized bands or evolving squalls of
storm lines moving north and northeast out of the DVN CWA by 9-11
PM or so this evening, possibly faster. Then a dry slot lull
during mid evening into the overnight, before sctrd light showers,
sprinkles or even drizzle arrive from the west well after
midnight as the upper low approaches. Lows back down in the 40s
toward dawn Monday morning.   ..12..


.LONG TERM...(Monday through next Saturday)
ISSUED AT 330 AM CDT Sun Apr 30 2017

The occluded upper and surface low will continue to strongly
influence our weather through Monday evening, as moisture wraps
around the low, after Monday evening, dry air will begin to win the
war on the latest wet pattern. While showers on Monday will be
scattered in nature, the morning and early afternoon hours are
expected to see enough move through most location to still indicate
a likely POP. Like the past few days, it will be windy, cloudy, and
cold. Highs will stuggle to climb out of the 40s once again.  No
doubt this low will have a significant dent in this month`s climate
data.

What follows this pattern will not be above normal temperatures, but
a slow climb back to near seasonal normals by the end of the week.
The cool, but dry air over the region will result in wide diurnal
ranges, with highs in the lower to mid 60s and lows in the mid 30 to
near 40. This could allow for some frost potential in the north, and
that will be more closely addressed as we move into a quieter
pattern where details like this can be explored with higher
confidence.

In the extended, there is a few periods of lingering low pops, due
to earlier runs showing another storm brushing southwest of the
area, but that is a lower threat than currently indicated. The one
wet model is the ECMWF 00z run, but that seems to be overly wet
given the strength and track of the system.

ERVIN

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1147 PM CDT Sat Apr 29 2017

Expect mainly periods of light rain and drizzle overnight, with
the exception of KBRL, which will likely see a period of heavier
rain prior to daybreak. IFR ceilings and MVFR visibilities will be
the dominate conditions. Later this afternoon, showers and
embedded thunderstorms will push from south to north across the
area and have timed a several hour window at each site. Some of
the storms could be strong with gusty winds and briefly IFR
visibilities, details for later TAF issuances and updates.

&&

.HYDROLOGY...
Issued at 330 AM CDT Sun Apr 30 2017

Heavy rains yesterday fell mainly southeast of a line from Iowa City
to Mt Carrol Illinois. That axis is farther south than QPF fields
that were used in river forecasts yesterday. In the southeast 1/2 of
our area, rainfall of 1 to possibly 3 inches did occur, and fell
most heavily in the Rock, Green, La Moine, Mississippi, and Illinois
River basins. Flooding is already forecast at moderate levels for
many of these areas, and statements concerning each are already
sent.

Today`s rainfall is mainly forecast to be less than 1 inch. These
amounts were already included in river forecasts run last evening.
Locally higher amounts are possible today, as thunderstorms are
expected this afternoon and early evening. Movement of storms is
unlikly to parallel basins, thus the impact of storms should not be
a widespread influence.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Ervin
AVIATION...RP Kinney
HYDROLOGY...Ervin



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