Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 192018

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

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 occuring 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

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 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1254 PM CDT Fri May 19 2017

IFR/ocnl low MVFR conds through the taf cycle. Several rounds of
showers and embedded thunderstorms will be spreading from southwest
to northeast across the taf sites beginning this evening through
Saturday morning. Northeast to east winds 10 to 20 knots.


Issued at 1259 PM CDT Fri May 19 2017

Rises are now forecast on area tributary river as well as the
Mississippi River. The flow on the Mississippi River is routed
from the north, with the higher flows arriving about 6 to 7 days
from now. The tributaries are responding to recent rain, and
forecast rains of 1 to 2 inches, thus we are going with watch
products rather than warnings on portions of the Iowa River. With
higher confidence on rises on the lower Mississippi than north, a
watch has been issued for Keithsburg, and warnings going out for
Gladstone and Burlington(cont).




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