Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 231149

Area Forecast Discussion
National Weather Service Quad Cities IA IL
649 AM CDT Sun Oct 23 2016


Issued at 340 AM CDT Sun Oct 23 2016

Clear and calm conditions were observed across E Iowa/NW Illinois
so far tonight. Temps similar to last night in the upper 30s to
middle 40s for the majority of observing stations. SPC mesoanalysis
had a sfc low over east-central North Dakota and a NW wind shift
entering into E South Dakota.


.SHORT TERM...(Today and Tonight)
ISSUED AT 340 AM CDT Sun Oct 23 2016

Today...Warm and breezy day ahead in the lower to middle 70s. A
fast moving mid-level vorticity max/clipper system forecast to
race through the Western Great Lakes, pulling warmer air
northeastward - made evident by a ~15 C 850mb thermal ridge. Sfc
winds will shift from WSW to NW during the afternoon as a cold
front moves through. The atmosphere is extremely dry behind the
front. Forecast PWATs are only near 0.25 inches! As could be
expected, forecast soundings display an exceptionally dry profile
and good boundary layer mixing.

Dewpoints and Winds: Usually in these meteorological setups,
models do not mix the sfc dewpoints low enough or develop gusty
enough winds. For dewpoints, went below SuperBlend values and
felt the CONSShort was trending things in the right direction -
dropping values into the lower 40s/upper 30s by mid afternoon.
For winds, have gusts of 20-30 mph out of the NW.

Fire Weather: It is worth a mention that, while not terribly
high, there is an elevated risk for crop field fire starts due to
the lower afternoon RH near 30-35%. And if fires were to ignite,
they would spread quickly in the gusty winds.

Tonight...Seasonally cool in the upper 30s/lower 40s on avg. Sfc
high pressure builds in immediately on the heels of the exiting
cold front. Uttech

.LONG TERM...(Monday through Saturday)
ISSUED AT 340 AM CDT Sun Oct 23 2016

Confidence remains high on storm system to impact the region around
midweek, with uncertainties still on track with impact to
precipitation amounts/location and also temperatures.

High pressure over the Great Lakes will be the dominant weather
feature to start the work week. Dry easterly fetch from the high
should hold at bay any precipitation threat well to our west into
at least the start of Tuesday. Highs Monday look to be about 10+
degrees cooler and closer to seasonal average with generally upper
50s and lower 60s. Lowered mins Monday night into the upper 30s
and lower 40s, or roughly 2-4 degs from blend and toward MAV/MET
guidance given light easterly winds, dry ground and at least
partial clearing. Still could be too warm (possibly some mid 30s)
if clouds remain thin or delayed, as easterly flow favorable to go
colder in drainage areas of Sauk Valley, Rock River Valley
including Moline, and also portions of west central Illinois
including Macomb.

As mentioned earlier, confidence is high on a storm system bringing
rain to the region midweek. A strong shortwave dropping south
through the Gulf of Alaska early this morning, will eventually lift
back north skirting the Pacific Northwest through Tuesday. Additional
shortwave energy rounding the base of the western trough will be
ejected across the Rockies and undercut ridging over the Central
Plains before progressing across the Mid-Mississippi Valley on
Wednesday. At which time some interaction with residual remnant
Pacific Northwest shortwave is likely, as this energy traverses
the Canadian Prairie. This interaction should lead to
amplification of the shortwave, with the strong upper level
forcing attendant to the curvature of flow leading to widespread
ascent and subsequent clouds and rain by Tuesday night through

The first slug of rain Tuesday late into Wednesday morning will be
focused within zone of strong FGen within northwest to
southeast baroclinic zone, and deep saturation with warm
850-700mb layer supports mainly rain of which could be moderate to
heavy at times. Given a ramping of precipitable water values to
around 1.3 inches or just over 2 standard deviations above normal
would expect to see potential for 2 to 3 inches of rain in this
band. The question remains just where will this set up, which is
tied to track and strength of surface low. GFS operational has
trended further south with the low and would suggest more of our
north 1/3-1/2 would be under the threat for this band of heavy
rain late Tue into Wed. Meanwhile, the GEM and ECM are
considerably further north and would place this band and threat
mostly near the MN/IA border into western WI. Concerns that the
northerly solutions are latching surface low with convection due
to feedback and latent heat, and that likely the track will end
up further south more from northwest to southeast in line with
orientation of baroclinic zone and also as advertised by GFS
ensemble mean. This again would put our northern 1/3-1/2
at increasing risk for seeing a band of heavy rain of potentially
1-3inches. Fortunately given as dry as it has been of late, and
with the bulk of the precipitation favoring stratiform would
not anticipate flash flooding, but certainly would think ponding
of water in low lying areas and fields, and some within bank
rises on creeks and streams possible.

Further south would anticipate that rain chances wouldn`t ramp up
until later Wednesday over far southeast Iowa, northeast Missouri
and west Central Illinois ahead of triple point. Some thunder
would be possible with a few hundred MUCAPE being shown in a few
models. Rain amounts would be generally 0.25 to 1 inch in these
areas. Still again a lot of uncertainty on track with impacts to
rain amounts and location, but confidence is high on rain late
Tue-Wed with some potential for a band of heavy rain amounts of
1-3 inches north of warm front with low confidence on just where
this will occur. Temperatures also very challenging as expect
readings to be held down into the 40s north of the warm front
while to the south where precip arrival delayed could see some 60s.

Wednesday night will see the rain showers tapering off from west to
east as the surface low shifts east of the region.

Upper ridge then builds back into late week for temperatures
rebounding to around seasonal normals. Starting to see some
agreement with GFS and ECM on another shortwave moving into the
region Friday night and Saturday for some rain chances, albeit
light amounts.


.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 640 AM CDT Sun Oct 23 2016

VFR conditions forecast through the period. However, gusty winds
will develop today ahead of and behind a cold front. As the front
moves through, WSW winds will veer to the NW and increase as a
result of daytime mixing into stronger 925-850mb winds. Gusts of
20-25 kts are likely during the afternoon before subsiding after 5
or 6 PM. Uttech




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