Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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677
FXUS63 KDVN 250529
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1129 PM CST Fri Feb 24 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 332 PM CST Fri Feb 24 2017

20z surface observations showed a 996mb surface low pressure located
across northern Illinois and Indiana. Cold northerly winds produced
temperatures ranging from the lower 30s over Independence to lower
40s over Macomb and Princeton. A 500 mb vort max associated with
the trailing upper level low over western IA and an associated
deformation zone helped to spawn widespread wintry precipiation
across much of central Iowa. This vort max was slowly moving to
the east and will serve as the main weather producer in the short
term.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 332 PM CST Fri Feb 24 2017

Clear slot across the area will pull to the east as the
deformation zone associated with the surface low moves to the east
today and tonight. Main forecast concern will be snowfall amounts
and the diminishing trend of the precipitation.

Actual track and strength of the sfc low was further south and lower
than previously expected. As a result the onset of snow has been
delayed across much of the area until 00z Saturday. Freezing
drizzle has occurred across most of the advisory area. As colder
temperatures and more moisture overtakes the clear slot this
freezing rain will transition into snow.

Guidance has come down in overall QPF amounts from this system.
The HRRR is the less aggressive of all the guidance and suggests
about an inch in overall snowfall for the northern zones. The rest
of the model suite has the northern zones getting 2 to 4 inches.
Our forecast of 1 to 3 inches across northern zones in the winter
weather advisory.

Tomorrow should be free of precip, could see some patchy drifting
snow from the winds, otherwise, main impacts would be slick roads
due to moisture on the roads and the drop of temps into the 20s
and teens.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 332 PM CST Fri Feb 24 2017

Flow pattern aloft turns zonal to southwest through the first half
of next week ushering in warmer air, with temperatures moderating
back above normal with highs mainly in the 40s/50s. A series of
waves will move through the flow accompanied by precipitation
chances. Very low precip chance for Sunday with onset of WAA and
initial low amplitude wave, but moisture is rather meager. Any
precip should it occur would be sprinkles or light rain, but mostly
virga which could lead to cooler highs than currently forecast
for Sunday. Better signal and subsequent precip chances appear to
be for Tuesday as a stronger wave moves across the Upper Midwest
and Great Lakes. Given this more northerly track consensus from the
models I have kept the precip type mainly rain, with just a mention
of snow Monday night in lead WAA precip potential.

In the wake of the Tuesday system the flow pattern turns northwesterly
for mid to late week. A series of Clipper systems are shown by the
models, one around Thursday and another around Saturday. Both these
systems are shown to pass mainly to our northeast at this time, thus
precip chances appear small as the area will largely reside in dry
warm sector with moisture starved cold frontal passages. Will see
up/down temps during this time favoring above normal in warm sector
ahead of systems then cooling back near to a little below normal in
the wake.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1123 PM CST Fri Feb 24 2017

An area of light snow will be ending from west to east the next few
hours with clearing skies and VFR conditions by 25/09Z and through
the rest of the period. Northwest winds of 15 to 25 MPH will decrease
to westerly at 5 to 10 MPH by late afternoon on Saturday.

&&

.HYDROLOGY...
Issued at 332 PM CST Fri Feb 24 2017

Rainfall in the past 24 hours along with routed flow north of the area
will lead to rises on area streams and rivers. In general though heavy
rainfall was not as widespread, thus the main trend today is for most
crests in next 7 days being lowered by 1/2 to over a foot from those
forecasts issued yesterday and many areas seeing only within bank
rises. This is the case on the Iowa River at Marengo, which is now
staying below FS and therefore cancelled the Flood Watch. One exception
is on the Cedar River, where the recent rainfall combined with above
normal flows has actually led to higher confidence on minor flooding
near Conesville. As a result, I have upgraded the Flood Watch to a
Flood Warning as it is shown to rise above FS within the next 24 hours
cresting by early next week. On the Mississippi River, the recent rainfall
along with routed flows will lead to rises over the next 7 days, with
several sites shown to reach or exceed flood stage toward the end of
the 7 day period. However, confidence is low given the noticeable lowering
trends past 24 hrs and uncertainties in snowmelt and amount of routed
water north of the area. As a result, no Flood Watches for the Mississippi
at this time, but can`t rule out eventual watches and possibly a few
warnings in the next 7-14 days depending on snowmelt and routed water.

&&

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

&&

$$

SYNOPSIS...Speck
SHORT TERM...Gibbs
LONG TERM...McClure
AVIATION...Nichols
HYDROLOGY...McClure



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