Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 181158
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
658 AM CDT Mon Sep 18 2017

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 AM CDT Mon Sep 18 2017

Short wave upper trof currently acrs the east central Rockies
embedded in west-southwesterlies, will look to progress acrs the
local area tonight into early Tue morning. This feature to bring the
next chance of rain in the near term. Then the synoptic scale
pattern acrs the CONUS to become more amplified and blocked again by
mid to late week, with interactions between Atlantic tropical
systems and western CONUS longer wave inland progression. In the
process, maybe a low to medium chance for precip by midweek but no
real drought buster evident at this time through the end of the week.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Mon Sep 18 2017

Will continue to build upon the slowed upstream upper wave
progression acrs the area and further delay the onset of incoming
precip/showers into the western CWA until mid afternoon. Thus with
just varying amounts of high clouds filtering the insolation until
then, may trend a bit warmer with high temps today in the low to mid
70s. If more sunshine bleeds through and lasts longer, there may
even be some upper 70s or 80 degree readings, like some of the
guidance highs suggest. But cool start to the day in the lower 50s
and not the most warming of wind directions from the east to
southeast makes for hesitation of going too warm for now.

Mid afternoon to evening expect sctrd elevated showers and some
embedded thunder(if guidance MUCAPEs of 200-500+ J/KG are on
target)to move east acrs the fcst area with highest coverage from 5
PM though 11 PM CDT, before decreasing support and continued eastward
progression bring about a diminished precip scenario after Midnight.
with recent history of incoming areas of precip encountering dry air
layers and decaying below projected potential, will just cover the
event with moderate to high CHC POPs for now. Low confidence on
projected QPF amounts and where they will occur, but for now will
lean toward the less bullish of guidance or even undercut those
values in some places. This translates into advertising rainfall
amounts that most locations receive(that manage to get hit by
passing showers or a thunderstorm) from a few hundredths, up to 2
tenths of an inch by 12z Tue morning.

Currently accepted llvl convergent areas with a bit more moisture
feed on nose of southerly LLJ, support a chance for at least
moderate rainfall amounts of 0.25 to 4 tenths in an inch with a few
swaths along and south of I80. But again, with recent rainfall
events/history, low confidence in these kind of details but tried to
hammer out a potentail scenario anyway to advertise with this
monring`s fcst package. The various 00z and latest run models range
from most areas just getting a trace to a tenth of an inch for the
entire event, to the bullish and PWAT juiced NAM with a more defined
convergent llvl circulation which produces more thunderstorm
clusters and localized swaths of areas getting over an inch of
rainfall. Low shear values indicate not much of any chance for
strong to severe storm occurrences late this afternoon and tonight.

Will go with lows in the upper 50s to low 60s for most of the area
late tonight. Will not put it in the grids for now, but with light
east to southeast convergent sfc flow/winds, there may be a chance
for at least patchy fog late tonight tonight into early Tue
morning.   ..12..


.LONG TERM...(Tuesday through next Sunday)
ISSUED AT 330 AM CDT Mon Sep 18 2017

Tuesday/Tuesday night...
Warm front is generally suggested south of I-80 on Tuesday. However,
absence of appreciable forcing due to building heights aloft will
limit any precipitation chances. High temp forecast is rather
challenging due to proximity of boundary and likelihood of some
clouds. Overall though with limited precipitation potential, dry
antecedent conditions and increasingly southerly flow I am favoring
warmer GFS/MAV guidance with around 80 to mid 80s for highs Tue from
north to south. Progged 850 mb temps of 16C to 18C would actually
support more widespread mid/upper 80s if more solar insolation and
deeper mixing occurs.

Wednesday/Thursday...
Will have chances for showers/storms during this period, as a cold
front is shown to settle into the region and eventually stall or
become stationary before lifting north as a warm front on Thu.
Upper level height falls/ large scale ascent is shown to be pulling
away from the region and lends to lower confidence with coverage,
thus have capped PoPs in the chance category for now. NAM/GFS
0-6km bulk shear magnitudes 18z Wed-00z Thu are weak/low at around
20 kts, but they offer strong instability 2500-3500 j/kg owing
largely to surface dew point pooling in the lower 70s ahead of the
front, which seems high given antecedent dry conditions and likelihood
of deeper mixing. However, if occurs wouldn`t rule out a strong
pulse type storm or two.  Highs likely to be in the 80s most areas
with lows mainly in the 60s.

Friday through Sunday...
Highly amplified upper pattern expected during the period with deep
upper trough over the western CONUS and a ridge over the eastern CONUS.
Strong ridge looks to become blocky as high pressure aloft strengthens
while series of tropical systems in Atlantic basin form REX block.
This will likely lead to a period of very warm/hot weather with no rain.
Expect highs well into the 80s with some areas around 90 or in the
lower 90s.

Given such a deep upper trough out west also can`t see how we won`t
eventually have a decent chance at some rain. It`s just seemingly a
timing issue of when blocky pattern breaks down and allows the trough to
make inroads into the Midwest. Will be watching the early to mid portion
of next week (9/25-9/27) for these better rain chances.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
ISSUED AT 642 AM CDT Mon Sep 18 2017

Besides some patchy MVFR fog mainly away from the terminals this
morning, A VFR day until showers and a few thunderstorms approach
from the west late this afternoon. With lower confidence on
strength and coverage maintaining as they approach, have just
placed a VCNTY window wording late afternoon into evening at CID
/DBQ/MLI. But tried to time a From group for a few hours with
thundershowers at BRL this evening, where low level flow and
moisture convergence support a better chance for that area to
experience some convective activity. Surface winds east to
southeast at 5-12 KTS today into this evening. After the sctrd
showers move east, light east to southeast winds and higher DPTS
may allow for at least some patchy MVFR fog to develop in the
VCNTY of most of the TAF sites after Midnight into early Tue
morning. There may even be a chance for some patchy dense fog.
  ..12..

&&

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

$$

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



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