Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 230531
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1131 PM CST Wed Feb 22 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 220 PM CST Wed Feb 22 2017

Record warm spell continued today with all climate sites breaking
daily records and some even all-time February highs. Highest temps
today occurred from eastern KS into our western CWA, where there
were no clouds and dewpoints in the lower to middle 40s. Nice
dewpoint gradient over the DVN CWA was evident on MSAS analysis
stretching from eastern TX all the way north into our western
counties. Deep mixing depths up to 900 mb also contributed to the
warmth. Storm system to impact the region Thursday afternoon
through Friday, was tracking into Nevada as of 20z this afternoon.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 220 PM CST Wed Feb 22 2017

Forecast focus in the near term is on precipitation timing
Thursday afternoon.

A weak cold front will push east overnight tonight and then stall
over central Missouri and southern Illinois. After looking at low
level moisture progs and surface wind fields, have added the
mention of patchy fog for areas east of MS RVR early Thursday. Do
not anticipate anything becoming dense or lasting that long like
this morning. Lows Thursday AM will be in the upper 30s to lower
40s.

Latest model solutions have the stalled front a tad further south
than in previous runs, before it begins to lift north as a warm
front late Thursday. Strong lift signal from latest model runs
supports an area of overrunning rain to develop north of the warm
front Thursday afternoon, from northern MO into the central
portions of the CWA by 00z Friday. QPF amounts will be rather
light and less than a tenth of an inch. Clouds to increase
throughout the day Thursday with easterly winds. However,
temperatures will still reach the lower 50s north of highway 30,
to the lower 60s in northeast Missouri and west central Illinois.
This is still above normal for late February.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 220 PM CST Wed Feb 22 2017

Thursday Night...

Showers and thunderstorms are forecast to develop mostly after
sunset in response to increasing warm air advection and convergence
along elevated 850-700mb warm front/jet nose. Presence of steep mid-
level lapse rates near 7 C/km, MUCAPE exceeding 500 J/kg, and
effective deep layer shear around 50 kts, warrant a low risk for
hail up quarter size. Expecting severe hail reports to be isolated
with pea to dime size more prevalent. The Storm Prediction Center
has outlooked the SW half of the CWA with a marginal risk for severe
thunderstorms.

Friday...

Strong spring-like storm system will impact portions of the Upper
Midwest.  There is uncertainty regarding the exact track of the sfc
low which will have implications on sensible weather across the DVN
CWA. Outside of the NAM, other models have trended southeastward.
The ECMWF/Canadian/GFS ensemble mean have a more rapidly occluding
low struggling to push north of the Quad Cities. Therefore, this is
a much colder scenario for highs across the NW third of the CWA.
Adjusted highs down slightly from the SuperBlend in this area, but
raised them in my SE. Looks like a very impressive NW to SE temp
gradient across E Iowa/NW Illinois from 40s (maybe colder) to
mid/upper 60s.

The dry slot should push most of the steady precip to the north of
the region by late morning, although it could linger across my far
NW through the day with a risk for some sleet or snow late Thursday
night through Friday.

Thunderstorm Potential...

There is a marginal risk for severe thunderstorms from the late
morning into the early afternoon mainly east of the Mississippi
River along and ahead of the cold front. Conceptually, this is a
high-shear low-CAPE setup. Since confidence is low on where these
storms form - they may develop just to the east of the CWA - do not
want to get too much into the details yet. Stay tuned to future
forecasts for updates.

Friday Night through Saturday Night...

Accumulating Snow Possible:

Strong 850mb cold air advection wraps in with deformation zone
precipitation bringing a good chance for light snow. Even though
temps have been anomalously mild the past 1-2 weeks, sfc temps are
forecast to fall into the 20s Friday night into Saturday morning -
cold enough to accumulate some of the snow that falls. A half inch
to around 2 inches are possible, highest north of highway 30. Main
concerns are stretches of icy/slippery roads and reduced visibilties
with wind gust up to 30-35 mph.

Sunday through Wednesday:

Chance for light rain and snow Sunday into Sunday Night. PoPs are
low between 20-40%, highest south of I-80. Then temps are forecast
to warm ahead of the next strong low emerging in the Plains. Could
have another round of showers and thunderstorms, and possibly a
changeover to snow on the backside of the low into Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1126 PM CST Wed Feb 22 2017

VFR conditions and clear skies will gradually become cloudy with light
rain developing by late afternoon and MVFR/IFR conditions probable
at most or all the terminals by 23/21Z ahead of a developing storm
system from the plains. Isolated thunder may occur by late afternoon
which is handled as vicinity wording at BRL/MLI. LIFR conditions appear
likely by late evening at most or all of the terminals.

&&

.HYDROLOGY...
Issued at 352 PM CST Wed Feb 22 2017

Area river sites on the Iowa and Cedar Rivers are forecast to rise
into minor flood stage by this weekend into early next week.
However, confidence on this occurring is low because the river level
forecasts are contingent on widespread 0.75 to 1.00 inches of rain
falling from Thursday night through Friday. For the aforementioned
reason, and since the risk for minor flooding is beyond 48 hrs from
now, decided to hold off on issuing river flood watches at this
time. Uttech

&&

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

&&

$$

SYNOPSIS...Gross
SHORT TERM...Gross
LONG TERM...Uttech
AVIATION...Nichols
HYDROLOGY...Uttech


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