Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 220900
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
400 AM CDT MON AUG 22 2016

.SYNOPSIS...
Issued at 330 AM CDT Mon Aug 22 2016

Clear, calm and comfortably cool the rule this morning with
surface high pressure ridge in control. Temperatures were
in the lower to middle 50s, which is about 5-10 degrees below
normal (58-65). A strong low level inversion coupled with 850 mb
temperatures of 10C would suggest we could see a few drainage
sites dip into the upper 40s prior to daybreak. Surface and
850 mb analysis shows ridging firmly in control over much of the
nations midsection. Northerly winds have scoured out deeper
moisture, but it lurks not far off from the Mid-South to the Gulf
Coast and into south Texas. In the upper levels of the atmosphere
the flow was northwesterly with the area in between an anomalously
deep trough over Hudson Bay, and split stream shortwave energy
advancing through the Intermountain West. Some of this energy will
combine with a rapid increase in moisture for a round of wet
weather midweek. Until then, more splendid late summer weather is
on tap.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Mon Aug 22 2016

Today, will see generally sunny skies with gusty southerly winds
developing between departing high pressure and deepening low
pressure over the Dakotas. This combination will push highs to near
normal (78-85), with mixing depth and progged low level thickness
and verification of highs from yesterday supportive of highs in
the upper 70s and lower 80s. These winds with deeper mixing will
likely maintain or draw down dew points into the 50s and possibly
even a few upper 40s making for another very comfortable day.
Around the region, there may be a few high based showers well to
our northwest today from portions of northwest Iowa into Minnesota
and portions of Wisconsin on the nose of elevated moisture
transport. Most, if not all of the cloud cover attendant to this
activity would likely also stay to our northwest.

Tonight, skies should be mainly clear. The lingering pressure
gradient should be sufficient enough to maintain enough of a
south to southeast wind at around 5 mph to 10 mph for a milder
night. Lows are expected to bottom out in the upper 50s to lower 60s.
However, some lows in the mid 50s will be possible in favored
river valleys and other drainage locations should winds fully
decouple.

.LONG TERM...(Tuesday through next Sunday)
ISSUED AT 330 AM CDT Mon Aug 22 2016

Tuesday...Assessing the latest 00z run models, seems most of the day
Tue to be mainly dry in warming llvl south-southeasterly return
flow, just a low chc for some precursor warm air advection isolated
showers making it into the south or southwest Tue afternoon. Highs
in the low to mid 80s with sfc DPTs climbing into the mid to upper
60s by late afternoon. Short wave/vort max aloft embedded in broad
southwesterlies out that way, will look to push east-northeast acrs
Neb into the MO RVR Valley by late in the day. This forcing to
combine with a deep convective index max acrs eastern Neb into
western IA to initiate thunderstorms in the MO RVR Valley VCNTY Tue
afternoon and evening. Most of the models still advertising a brisk
southwesterly 40-45+ KT nocturnal LLJ streaming acrs IA Tue night
feeding a resultant MCS from the upstream convective activity. This
high THTA-E feed with PWATs climbing over 2 inches by Wed morning to
fuel heavy rain potentail as forcing progs suggest the main MCS
making it into the CWA from the west not til after 4 AM CDT Wed
morning. But there are signs of a sctrd wing of precursor elevated
warm air advection wing storms acrs portions of the local fcst area
well before then.

Isolated to wdly sctrd storms into the western and northwestern CWA
before midnight, then more development further east into IL through
3 AM while the main complex moves acrs western into central IA. Some
model variance on how far north or south acrs IA the main MCS and
heavy rain axis will propagate eastward along, but the H85 MB
thermal ribbon rule suggests along and south of I80. The precursor
WAA wing elevated storms may produce some hail, otherwise locally
heavy rain the main threat late Tue night into early wed morning.
Strength of the LLJ, extent of THTA-E feed and forcing progs suggest
some areas along the convergent LLJ axis may get over 2 inches of
rain by Wed morning. Rain/storm-outflow cooled lows in the mid to
upper 60s for Wed AM lows.

Wednesday...Will continue to walk the MCS acrs and out of the CWA
Wed morning. Bulk shear profiles increase over 30 KTS by Wed
morning, and there will be the chance of storms flaring up and
possibly being able to produce gusty wind bursts as they move along
and east of the DVN CWA by late morning. Lingering heavy rain swaths
may also produce some issues Wed morning before noon. Then both the
00z run GFS and ECMWF shunt the main frontal boundary and storm
outflow enhanced edge along and south of the IA/MO border into
central IL by Wed evening. Much of the CWA to the north could very
well be convective debris plagued and have trouble warming up to
guidance highs and thus limited instability rebound by evening. The
next incoming wave and llvl impingement should focus along the WSW-
to-ENE oriented boundary from KS...acrs northern MO into central IL
for Wed evening storm redevelopment. So current thinking and this
placement would keep the most significant storms and heavy rain along
and south of the local area Wed night, with secondary band of
overrunning showers and storms moving acrs the southern third of the
CWA. Of course, depending on how much rainfall these areas get Tue
night Wed AM, more rain Wed night may produce some localized
flooding or flash flooding.

Thursday and Friday...with the medium range models especially the
favored 00z ECMWF suggesting broad SFC and upper ridging this period
while the llvl front sags south, after a few lingering showers in
the south clear Thu morning, this period could be mainly dry until
later Fri night when some elevated return flow warm air advection
showers may move acrs the western CWA. Below normal temps this
period as well with highs in the 70s and lows in the 50s.

Next Saturday and Sunday...The battle will be on with the next
upstream wave rolling northeast out of the central Rockies and
encountering the broad ridge complex in place acrs the upper MS RVR
Valley and western GRT LKS. While a few higher based elevated
showers and cloud cover may move acrs the area Sat, timing of the
main wave by the Euro suggests more organized showers and storms will
chug acrs the mid and especially upper MS RVR valley Sunday into
Sunday night. Precursor elevated WAA wing storms ahead of the main
wave possible in or near the DVN CWA earlier Sat night. Temps will
try to moderate back to normal over the weekend but cloud cover may
limit this process during the daytime.   ..12..

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
ISSUED AT 1144 PM CDT Sun Aug 21 2016

Surface ridge is overhead tonight, resulting in light to calm
wind until morning. Surface winds will pick up from the south
after daybreak and will be gusty around midday. Otherwise, the
only potential aviation concern is risk for fog this morning with
the light wind. Currently it looks like there is enough subsidence
in the dry air mass to limit fog development to localized areas of
shallow ground fog, and thus have not mentioned fog in TAFs as the
chance is too low.

&&

.DVN Watches/Warnings/Advisories...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...12
AVIATION...DMD



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