Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200447
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1147 PM CDT Fri May 19 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 1016 PM CDT Fri May 19 2017

At 10 pm, a weakening complex of showers and thunderstorms was
lifting out of northeast MO into west central IL, brushing far
southeast IA. This is mainly stratiform rain with lightning
largely remaining confined south of the forecast area closer to
the gradient of MUCAPE confined to central MO into southern IL.
Over the rest of the area, increasing upper level lift was leading
to light rain or drizzle spreading into eastern IA from central
IA. Otherwise, brisk east winds and March-like temperatures in the
40s prevailed.

The next MCS, linked to a shortwave rotating northeast from KS
into SW IA is on track to move across the forecast area, likely in
a weakening fashion late tonight into the early daylight hours.
There is some suggestion that the heavier rainfall may split the
area, falling across the far northwest with the advancing sw IA
system, and across the south and southeast where a developing SW
MO system may brush the region overnight. Heavy rainfall is still
possible, considering the abundant mid and upper level moisture
but there is low confidence for widespread amounts exceeding 1
inch. Will continue to downplay the thunderstorm threat,
confining mention to mainly the south, closest to the steeper mid
level lapse rates and MUCAPE axis closer to the stationary front
well to the south.

&&

.SYNOPSIS...
Issued at 315 PM CDT Fri May 19 2017

A stationary frontal boundary extended east-west along Interstate 70
in MO. To the north of the front, temperatures were very cool due
to a northeast wind off of Lake MI with readings in the mid 40s
to mid 50s across the dvn cwa. To the south, temperatures were well
in the 70s to lower 80s with dewpoints in the mid to upper 60s.
Strong moisture transport/warm air advection was occurring in the
central/southern Plains with the nose of this low level jet in
western MO. Strong low level convergence was leading to a line of
thunderstorms in northeast KS into western MO and then into
northeast OK. These storms were moving to the northeast.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 315 PM CDT Fri May 19 2017

Forecast focus on more showers and thunderstorms.

Tonight: A warm moist airmass to our south will be lifted up and
over the very cool dome over the dvn cwa. This will be brought to
our area by a a strengthening low level jet of 30-40 knots. On the
nose of this jet there will be strong forcing/low level convergence
which is noted on time height sections. Forecast soundings indicate
PWAT`s increasing to 1.50 inches, which is currently in se KS into
sw MO as noted on SPC Meso Analysis page.

GFS/ECMWF/HRRR/ESRL HRRR/NAMNEST all indicate several rounds of
showers and embedded thunderstorms developing across the cwa this
evening and overnight. This should begin to spread into our far
sw counties by 00z (7 pm), and gradually working it`s way northeast.
With several rounds of showers and storms producing locally heavy
rainfall, have mentioned this in the grids especially after
midnight. With the very cool airmass and stable air in place the
stronger storms should remain south of the cwa. Minimum temperatures
will range from the mid 40s north to the lower 50s south.

Saturday: Widespread showers and thunderstorms in the morning
should gradually diminish to a scattered coverage by afternoon as
the stronger forcing lifts northward. However, low pressure will
be pushing northeast to about the Quad Cities later in the day
with warmer air flowing northward ahead of this low and cold
front. More showers and storms should develop during the afternoon
and depending on amount of instability some of the storms may
become strong to severe. This will be especially true east of the
MS River ahead of the front. SPC continues with a marginal risk in
our IL counties. One thing to note is the GFS is much farther east
with the surface low compared to the past couple of days so any
further shift to the east would confine any severe threat even
farther to the east. This would also impact temperatures. For now
we will forecast afternoon highs ranging from the lower 60s nw to
the lower to mid 70s se.

Rainfall amounts of 1 to 2 inches are likely across much of the
dvn cwa tonight through Saturday. This will impact some rivers so
refer to the hydrology section below. These rounds of MCS`s coming
from the southwest should stratify out as they push into the much
cooler airmass in the cwa. Therefore, this looks to be more of a
steady moderate to locally heavy rainfall situation rather than a
flash flood situation. This would be similar to last night`s/early
this morning`s event.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 315 PM CDT Fri May 19 2017

Saturday evening, as the low passes over the CWA, we will be mild
and moist at lower levels, but will see the dry slot working through
aloft. This will allow for a threat for thunderstorms, with a
sheared environment. What is not certain is the amount of CAPE at
that time.  This low confidence forecast cannot rule out severe
weather, but with the main triple point brushing the southeast 1/3,
a window of hail, marginal wind, and small risk of tornado will need
to be watched. By midnight, the occluding system will wrap cool air
in and the dry slot will be over the entire area, ending the threat
for significant rainfall.

Sunday appears cool and cloudy, though dry.  If any break up in the
stratocu occurs, we could warm to the upper 60s, but in the end a
forecast of upper 50s to lower 60s is a least error prone forecast
high.

Monday appears to have a dry morning, followed by increasing rain
chances by later afternoon, as the next upper trof swings down into
the Midwest. This energy will be dropping into the mean synoptic
trof, and the strengthening that is shown on the GFS/GEM/NAM does
not seem off base, but it prefers over the less amplified EC.  In
any case, a rainy Tuesday is possible, with highs cool again,
possibly as cool as today`s 50s. Beyond Tuesday night, northwest
flow to zonal flow will bring passing waves to the north and south,
which is a low confidence dry forecast for out area. Highs will
continue to be below normal. ERVIN

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1147 PM CDT Fri May 19 2017

IFR conditions will be the rule overnight through much of
Saturday. Initial MVFR ceilings are likely to lower to IFR at all
sites by 3 am with waves of light rain or drizzle moving through
early in the period and then again toward sunrise. There is a low
potential for thunderstorms, which has been limited to the BRL
site in the forecast. A low pressure system advancing from KS into
IA will to lift a warm front into the region during the day
Saturday, veering gusty east winds to the southeast by afternoon.
This front may also trigger thunderstorms, which are included
with PROB30 groups at MLI and BRL. There will likely be some
improvement toward evening, but forecast confidence in the timing
of this trend is low. For now, have a transition to MVFR at BRL,
MLI and CID by Saturday evening.


&&

.HYDROLOGY...
Issued at 1016 PM CDT Fri May 19 2017

Many area tributary rivers are on the rise due to recent rainfall.
The contribution from the tributaries, along with routed flow
from further upstream, is also producing rising levels and some
flooding along the Mississippi River.

A flood warning was issued for the English at Kalona, where levels
were rising rapidly from last night`s rainfall. Flooding is
forecast along the Iowa River at Marengo and Oakville by early
next week. With low confidence in the rainfall tonight through
Saturday, this is handled with a flood watch for now.

A flood watch also remains in effect for the Mississippi River at
Keithsburg and has been issued for Gladstone. Further downstream,
Burlington will likely return to flood stage by Monday and the
flood warning remains in effect.

&&

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

$$

UPDATE...Sheets
SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Ervin
AVIATION...Sheets
HYDROLOGY...Sheets



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