Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 251143
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
643 AM CDT Thu May 25 2017

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 AM CDT Thu May 25 2017

Water vapor imagery reveals a pair of mid level circulations over the
Ohio and Tennessee valleys. At the surface low pressure has
consolidated along the IN/OH border. Cyclonic flow around the low
was sloshing stratus back across much of the eastern half of the cwa
keeping temperatures into the lower to middle 50s. Skies were mainly
clear into the western cwa and most of the rest of IA due to
subsidence attendant to surface high pressure ridge extending from MN
arrowhead through central IA to the LA Gulf coast. The clearing skies
in the western cwa has allowed temperatures to drop into the lower to
middle 40s, with some patchy fog also being observed with variable
visibilities due to a shallow, steep low level inversion.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 315 AM CDT Thu May 25 2017

Overall, warmer and mainly dry conditions expected in the short term
as the surface high pressure ridge shifts across the cwa.

Increasing subsidence today with ridge building in should bring about
decreasing clouds east, while mostly sunny west. Highs today with
the sunshine will top out in the upper 60s and lower 70s and with light
winds will make for a real pleasant day.

Tonight, while the surface ridge shifts east the mid level ridge will
build in then deamplify as weak low amplitude wave(s) plow through
the ridge. This weakening lift combined with mid level theta-e
advection will bring the prospects for some sprinkles and a few high
based light showers, possibly as early as early evening in some areas
west of the Mississippi River. Really no worse than a dampening of the
pavement in any areas that see the spotty precipitation, with most areas
staying dry tonight. Increasing clouds and developing southeast winds
will yield a milder night for many with lows in the lower to middle 50s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 315 AM CDT Thu May 25 2017

Friday

The NAM/GFS/Canadian track a mid-level vorticity max, or ripple in
the mid-level WSW flow, through Iowa and Illinois during the day.
The main threat is lightning strikes. However, with MUCAPE around
1000 J/kg and presence of some SBCAPE in a marginally sheared
environment (35 kts of 0-6 km bulk shear). Isolated small hail or
gusty winds are possible.

PoPs are in the 30-40% range, representing the scattered nature of
any showers and storms. Forecast highs range from the lower 70s far
north to near 80 F far south.

Saturday

A deeper trough is progged to move into the Plains and Midwest.
Greatest forecast challenge is determining the location of the sfc
warm front and potential for severe thunderstorms.

Recent runs of the NAM/GFS nudge the front up into the far southern
CWA where there is a slight risk for severe thunderstorms per the
latest Storm Prediction Center Day 3 outlook. Damaging straight line
winds and large hail are the main threats. Large hail is also
possible north of the warm front. If storms form in our area, deep
layer shear of 40-50 kts is supportive of rotating updrafts or some
supercellular structures.

It is important to note that the ECMWF/CMC are further south with
the front. If this scenario verifies, most or all of the severe
storms would occur south of the DVN forecast area. Thus, still low
confidence on exact placement of the warm front. Stay tuned to the
forecast through this week.

Sunday through Wednesday

GFS/ECMWF/CMC continue advertising transition to a NW mid-level flow
regime and a cooler pattern. PoPs are generally 20-30% through this
four day stretch, highest during peak diurnal heating. Rain that
occurs will most likely fall in the form of brief showers. The
threat for heavy rain is very low. Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 627 AM CDT Thu May 25 2017

Stratus with ifr and lower mvfr cigs is rotating w/sw around low
pressure over the Ohio Valley. The stratus and subsequent lower
conditions has reached DBQ and MLI. The stratus deck is thin and
with surface heating and incoming subsidence should see decreasing
clouds with bases lifting to vfr by midday to early afternoon.
The stratus and lower conditions could reach CID and BRL or
develop briefly with heating mid to late morning, but confidence
is low thus have left scattered mvfr bases but omitted any cigs
for now opting for vfr. Patchy fog can`t entirely ruled out late
tonight, but the potential appears to low given an increase in
southerly winds and mid level cloudiness.

&&

.HYDROLOGY...
Issued at 1220 PM CDT Wed May 24 2017

Confidence has increased this morning along the Mississippi from
Camanche to Keithsburg reaching flood stage, and thus have
upgraded to flood warnings from the watches already in effect. It
should be noted that forecast crests will likely change at these
locations, so these will need to be monitored with later forecasts
and statements. For specific height forecasts, please see that
latest flood warning statements. Flood warnings continue for both
Dubuque locations, Gladstone and Burlington.

Have decided to go with flood watches for Bellevue, Fulton and
Gregory Landing this time as confidence of these locations reaching
flood stage remains low. That being said, these 3 locations will be
monitored, with a final decision of flood warning issuance
with Bellevue and Fulton occurring within the next few days.

&&

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

$$

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


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