Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 231742 AAC
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1242 PM CDT Tue May 23 2017

...18Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 322 AM CDT Tue May 23 2017

Early morning water vapor imagery shows a closed mid level
low over northwest MN dropping southward with some
attendant showers. This mid level low was one of a series of
impulses embedded within a large trough axis extending through
Quebec province. One such weaker perturbation was rippling
up across the southern CWA attim resulting in a rain shield
swiping portions of far northeast MO, southeast IA into west
central IL. Another impulse was noted crossing the MO River
Valley and coupled with the sagging mid level low look to bring
continued chances for showers and possibly a few storms next 24+
hrs.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 322 AM CDT Tue May 23 2017

Models in very good agreement on diving MN mid level low due south
through IA and into MO by 12z Wed. Upper diffluence on front flank
of the low, PVA attendant to perturbations rotating around the
circulation (including aforementioned MO River Valley shortwave
timed for PM arrival), and any pockets of heating and subsequent
destabilization aided by cold air aloft of -20c at 500 mb all look
to work in tandem to encourage precipitation development today.
The best focus and hence greatest areal coverage appears to favor
east of the Mississippi River where upper forcing aligned with
low level convergence ahead of a weak surface low and cold front.
Similar to yesterday with the cold air aloft can`t rule out some
isolated small hail with any of the more robust convection.
Severe threat is non-zero especially if NAM verifies with 0-6km
bulk shear increasing to 40 kts over portions of the CWA along and
east of the Mississippi this afternoon, but instability would be
the limiting factor with SBCAPE only shown around 100-200 j/kg
within the higher shear axis, thus overall risk far too low for
any inclusion at this time. But, any changes in instability will
need to be monitored. Something else to monitor may be funnel
cloud potential this afternoon over N IL ahead of weak low and
front where non-supercell tor parameter is showing up on several
models within area of enhanced stretching potential. The funnel
threat is also non-zero and too low for mention, with better
overlap of surface vorticity and stretching potential focused east
of CWA into NE IL. PWATs around 1 inch will also support brief
periods of locally heavy rain to where some locations could see
around 0.25 inch or more, especially east. Highs today will be
modulated by clouds and precipitation. Warmest readings may be
through the heart of CWA which could largely find itself
positioned between better coverage east and west. Expecting highs
in the lower to mid 60s. Potential though to see temps drop back
into the 50s at times with rainfall of any duration, again this
appears most favored east.

Tonight, precipitation chances will persist mainly in the form of
showers. Again the best coverage looks to favor eastern CWA within
overlap of low level convergence zone and upper level diffluence.
Lows tonight fairly uniform in the upper 40s, with potential to be
a few degrees warmer in areas where clouds persist.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 322 AM CDT Tue May 23 2017

Wednesday

Upper-level low forecast to pull away from E Iowa/NW Illinois as it
rotates through the Mid Mississippi Valley. Expect scattered mainly
light showers, cloudy skies, and well below normal temps. Current
blended highs are in the lower 60s. But for areas where showers are
a little more prevalent, upper 50s are more likely. There is a low
chance for an isolated thunderstorm south of I-80. However, due to
marginal instability, areal coverage of thunderstorms will be very
low, if at all.

Thursday

Dry and warmer into the lower 70s. An 850mb ridge is progged to move
east of the area Thursday night - kicking off elevated positive
theta-e advection. Looks like only a slight chance for isolated
showers across the far W/NW forecast area. Most locations will
probably remain dry into early Friday morning.

Friday and Saturday

SW flow aloft should bring a series of shortwaves through the
Midwest, during which time there are chances for showers and
thunderstorms. However, confidence this far out with respect to the
location of a warm front, the most likely timing for precip, and the
threat for severe weather is low. For temps and moisture, blended
guidance has highs well into the 70s and dewpoints rising to near 60
F by Friday afternoon.

Sunday and Monday

Near normal temps in the 70s with low chances for showers and
storms. If dry trends of the ECMWF/CMC continue, may be able to
remove PoPs during specific 6-12 hour periods. The GFS is wetter
because it has a further westward extension of an upper-level low
that is positioned over the Northern Great Lakes region. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1243 PM CDT Tue May 23 2017

MVFR to VFR conditions today across the area have the potential to
turn into IFR and LIFR overnight as low pressure slowly moves
across the area. Flying conditions should generally improve in the
next 2 to 6 hours across the area with CIGs starting to reach VFR
heights. Later tonight CIGs could drop to IFR and LIFR. Low
confidence at this time has precluded them from being adding at
this time.

&&

.HYDROLOGY...
Issued at 424 AM CDT Tue May 23 2017

Flood warnings continue on the Mississippi River at Gladstone and
Burlington. The river level at these two sites is steady, but
minor flooding is expected to continue through this week as runoff
from recent rainfall routes downstream.

Flood watches remain in effect for Dubuque, Camanche, Rock Island,
New Boston, and Keithsburg on the Mississippi River, and for
Marengo on the Iowa River. Due to uncertainty with the amount of
routed water and with forecast rainfall, confidence is not high
enough to upgrade to flood warnings. Based on the latest
observations, confidence is very low on Marengo reaching flood
stage.

&&

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

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...Uttech
AVIATION...Gibbs
HYDROLOGY...Uttech


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