Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 140419
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1119 PM CDT Fri Apr 13 2018

...06z AVIATION UPDATE...

.UPDATE...
Issued at 602 PM CDT Fri Apr 13 2018

Have gone out with a wind advisory for Saturday for our northwest
Illinois counties. Looking at the current 20 to 30 mph winds over
that area and a tightening pressure gradient, there is sufficient
forecast confidence that winds should reach at least 25 to 30 mph
sustained with gusts over 45 mph likely. This matches wind advisories
for the same time frame over adjacent counties in Wisconsin and
north central Illinois.

&&

.SYNOPSIS...
Issued at 246 PM CDT Fri Apr 13 2018

18Z surface data has a strong low in southeast Nebraska near KLNK. A
stationary front ran east from the low east to KOTM, then east
northeast passing between KVYS and KC75, and then into northwest
Indiana. Dew points north of the front were in the 30s and 40s.
South of the front dew points were in the 50s and 60s.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 246 PM CDT Fri Apr 13 2018

The front stalled late this morning and is slowly sinking south
based on observations and radar. The front may stall again late this
afternoon or evening but will eventually push south of the area by
sunrise Saturday.

Radar trends show convection developed earlier in northern Missouri
but stratified out as it moved northeast. Based on satellite trends,
drizzle or light rain with an isolated thunderstorm should continue
through 5 or 6 PM.

The first problem is the overall severe risk for late this afternoon
and evening.

The scenario that appears to be developing is as follows; severe
convection will continue to develop in southwest Iowa and move east.
With sunset, this convection will induce more storms along the
frontal boundary that should rapidly develop eastward along the
front.

Under this scenario, areal coverage of convection and stratiform
rain will quickly increase across the area during the evening.

Thus a large area of rain will develop across the area this evening
with embedded thunderstorms. The primary severe risk still looks to
be hail. However, south of the front one cannot fully rule out
damaging winds from surface based convection.

Winds late tonight will be on the increase as the main surface low
continues to strengthen. Wind gusts of 35 to 40 mph are very
possible late tonight.

Saturday will be windy with rain. Sustained winds of 20 to 35 mph
are expected with gusts up to 45 mph possible. At this time there
are no plans to issue a wind advisory but that could change over the
next 12-18 hours.

An unstable layer of air aloft is expected to allow isolated
thunderstorms to develop Saturday that may produce some small hail.

Temperatures Saturday will be well below normal with readings
ranging from the upper 30s in the highway 20 corridor to near 60 in
the far south.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 246 PM CDT Fri Apr 13 2018

Cold, damp with mix of rain and potentially some wet snow by Sunday
the main forecast challenge.

Long Term Forecast Confidence Assessment...fair or average with once
again the wrap around cold air with precipitation in the deformation
zone the issue. Trends continue to suggest cold air aloft to support
any decent precipitation by Sunday to be more snow than rain with some
minor accumulation on grassy and exposed surfaces for a few hours.

Saturday night...rain likely at times and possibly some drizzle at times
with damp and blustery NE winds with some light fog. The precipitation
along and north of highway 30 may mix with or change to sleet and especially
a wet snow by morning with possibly an inch on exposed surfaces in
the far north and west. Lows around 30F in the far NW to mid to upper
30s in the central and south.

Sunday and Sunday night...continued cold and damp with chances of mainly
light snow and some rain and snow mix with nearly steady temperatures
with blustery Northerly winds. Highs nearly steady in the 30s with
some locations possibly picking up an inch or two of wet snow on grassy
and exposed surfaces for at least a few hours before melting.

Monday through Friday...remarkably cold pattern continues with below
normal temperatures and dry to mainly dry. Highs in the 40s and 50s
with lows mostly in the 20s and 30s. Overall, at least 10 degrees below
normal for mid April over the next 5 plus days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1112 PM CDT Fri Apr 13 2018

Flight conditions expected to tend mostly toward IFR and lower MVFR over the
next 24 hours, as a storm system over the Plains pushes slowly eastward.
Expect periods of showers/rain and light fog through today, with a few
thunderstorms possible mainly early this morning. As colder air deepens tonight
the rain may mix with or begin to change to snow late in the period at CID and
DBQ. Winds will generally by northeast at 15-25 kts with gusts over 30-40+ kts
at times.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...Wind Advisory from 7 AM to 7 PM CDT Saturday for Carroll-Jo
     Daviess-Stephenson-Whiteside.

MO...NONE.
&&

$$

UPDATE...Sheets
SYNOPSIS...08
SHORT TERM...08
LONG TERM...16
AVIATION...McClure



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