264
FXUS63 KDVN 211737 AAB
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1237 PM CDT Thu Sep 21 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 911 AM CDT Thu Sep 21 2017

With current radar and satellite trends, expect a weakening of the
precipitation through the rest of the AM. RAP suggests that
overall nocturnal jet should weaken and lead to the demise of the
precip. Cloud shield will likely hang on through most of heating
as a result have lowered highs today where heaviest rain fell.
HRRR and RAP both catch onto this idea. As a first stab, have
blended both 12Z runs of these models.

&&

.SYNOPSIS...
Issued at 330 AM CDT Thu Sep 21 2017

Stalled frontal boundary with unseasonable precipital water
(PWAT)feed of 1.5 to 1.9 inches into it by convergent southwesterly
LLJ, making for a "drought buster" in one night for the heart of the
DVN CWA. Mid summer-like storms re-forming and moving acrs the same
areas/training clusters, have made for swaths of very heavy rainfall
of 2 to over 5 inches from Fairfield and Washington in southeastern
IA, northeastward through the Quad City area. After this mess fades
this morning, re-energized southerly flow up through the region to
blow out the clouds and set the stage for continued unseasonable
heat through the end of the week and into the weekend. Blocked
synoptic pattern acrs the CONUS should still break down sometime
early next week and lead to the next main precip chances as well as
much cooler temp regime.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Thu Sep 21 2017

Today...Will carry some lingering POPs through mid morning along and
south of I80 for ongoing nocturnal elevated THTA-E fed convection,
higher POPs than what most models suggest after 12z. But there are
signs that the low level jet(LLJ) southwesterly feed starting to
veer, and should continue to do so into the morning period, allowing
the current activity to decrease diurnally. Until then, localized
flooding possible where the thunderstorm activity producing heavy
rain, "trains". Cloud shield off the nearly stationary to slowly
southward migrating MCS should limit much widespread fog formation
in moist convergent llvl flow, but will keep at least patchy fog in
the north through mid morning in case some thinning occurs. Then
most 00z and latest run models strengthen southerly push-
southwesterlies aloft amplify, allowing the stalled boundary to
retreat back north as the day progresses. This should scour out
lingering convective debris by afternoon, allowing warm air
advection and mixing to make for another unseasonably hot/humid day.
But some concern that if convection lingers longer in the morning
than currently anticipated, delaying boundary retreat combine with
suddenly saturated sfc layer, that highs in the low 90s may be hard
to achieve in many locations.  But if they make at least the low
90s, DPTs in the upper 60s to lower 70s helped by the recent
rainfall, will produce heat indices in the upper 90s to near 100
again this afternoon.

There may be a low chance for an isolated shower or storm popping up
along the retreating front midday and into the afternoon, but
ongoing shear profiles continue to be marginal at best and will just
go with some slight chances in the far northwestern CWA through mid
afternoon for now.

Tonight...mainly clear with south winds maintaining at 5-10 MPH
keeping keep lows well up in the 60s. Will also bank on these
winds/mixing to limit fog tonight in the recent hard hit heavy rain
areas.

.LONG TERM...(Friday through next Wednesday)
ISSUED AT 330 AM CDT Thu Sep 21 2017

Brief overview on the longer term, blocked pattern with warm dome
high pressure stalled overhead will continue to make for
unseasonable heat locally into the weekend. With enough mixing and
sunshine, Friday could be a few degrees off record warmth with highs
in the lower 90s acrs much of the area. But sfc DPTs are projected
to mix down more in the mid 60s, helping make for somewhat lower
humidity levels. Timing when the blocked pattern breaks down and de-
construction agent L/W trof and upper jet transition zone adjusts
eastward acrs the region, still somewhat variable in the latest run
medium range models. Atlantic tropical system/s will also have to be
taken into account, but for now the transition time with next main
precip chances continues to be late Monday into Tuesday. Then much
cooler airmass to follow for the mid to late next week period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1237 PM CDT Thu Sep 21 2017

Cloud cover is starting to break up across the area as southerly
flow takes over. As clouds clear, areas where heavy rain fell last
night may lead to the development of MVFR and possibly IFR fog at
MLI and BRL. Otherwise, expect VFR conditions through the period.

&&

.CLIMATE...
ISSUED AT 330 AM CDT Thu Sep 21 2017

Record Highs for today September 21...

Moline.........92 in 2007
Cedar Rapids...93 in 1920
Dubuque........94 in 1891
Burlington.....94 in 1908

Record Highs for Friday September 22...

Moline.........95 in 1937
Cedar Rapids...94 in 1930
Dubuque........92 in 1937
Burlington.....94 in 1937 and other years

&&

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

$$

UPDATE...Gibbs
SYNOPSIS...12
SHORT TERM...12
LONG TERM...12
AVIATION...Gibbs
CLIMATE...12