Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 260527
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1127 PM CST Fri Nov 25 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 305 PM CST Fri Nov 25 2016

The latest sfc analysis was indicating ridge axis from the southern
plains, up into the southwestern GRT LKS. Extensive stratocu deck
was seen on the latest VIS satellite loop just to the northeast of
this feature from acrs the Upper MS RVR valley, acrs the GRT LKS and
much of the OH RVR Valley. Aloft, a strong vort max was seen on
water vapor imagery as well as the swirl in the above mentioned
cloud deck on the VIS imagery. Clearing of the cloud deck pushing
acrs western int central IA in post wave subsidence regime.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 305 PM CST Fri Nov 25 2016

Tonight...The main challenge will be the extent of clearing and the
subsequent effect it will have on overnight temps and fog potential.
Current movement of back edge of the stratocu deck would have it
along and east of the MS RVR by 03z this evening acrs the northern
2/3`s of the CWA, and the south third already cleared by then. But
then some concern that some of the deck acrs southeastern MN to flow
down acrs at least the northeastern third of the CWA in the wave`s
wake. This along with nocturnal processes and potentail of more
cloud formation under H85 MB or lower inversion, may bring a halt to
the current eastward cloud migration seen on the sensory imagery
after dark. But other parameters seen on the latest run Hires models
and NAM/GFS suggest the upstream subsidence, as well as eventually
backing llvl flow in the cloud layer to the west and then southwest
late into a drier air source region to help along the clearing
process from west-to-east. As a happy medium, will slow the clearing
at the MS RVR during the mid evening and thru Midnight, and wrap
some clouds back acrs the northwestern third of the fcst area
overnight. The southern third will clear out first this evening and
may stay mainly clear into Sat morning.

Will still go with widespread lows in the upper 20s to lower 30s
with some clearing in mind(if even toward dawn for just a few hours
in some spots. But if clouds maintain through Sat morning, such as
over the northeastern third of the CWA, those areas may have trouble
dipping out of the mid 30s. As for fog, several models set up a
light south to southwest return flow convergent ribbon on the west
side of passing sfc ridge lobe after midnight acrs the central and
western CWA. If this occurs under clear skies, there may very well
be areas of fog developing along it and some of it dense. But with
all the uncertainties and lower confidence in this phenomena, will
just introduce patchy fog for now.

Saturday...After what lingering cloud cover and fog clear off Sat
morning, robust llvl warm air advection regime for this time of year
takes over as the day progresses just to lee of amplifying upper
ridge acrs the plains. Increasing south to southwesterly sfc winds
to 10-15 MPH by afternoon, along with sunshine will set the stage
for a well above normal and seasonably mild day. It`s just how deep
we van mix into building arm wedge aloft centered on H85 MB. most
models suggest just marginal mixing depths(H935 to H925 MB at best)
for highs in the upper 40s along Hwy 20, to the mid 50s in the far
southwestern CWA and that`s the way the fcst will go. But just a
little deeper mix up closer to H9 MB like the ECMWF is doing would
translate to widespread low to mid 50s, with a few areas pushing the
upper 50s in the southwest by mid afternoon.  ..12..

.LONG TERM...(Saturday Night through next Friday)
ISSUED AT 305 PM CST Fri Nov 25 2016

Above normal temperatures into Tuesday with a moderate rain event Sunday
and then cooler mid-week back to near normal temperatures.

Long Term Forecast Confidence Assessment...Above average or good. Little
sensible weather issues until late Sunday. Then a moderate rain event
with possibly a few rumbles of thunder. Limited run to run and inter-
run discrepancies suggest above average confidence on amounts and timing
late this weekend. General temperatures appear should be mostly within
3 degrees of guidance with mins mid to late next week possibly 3+ degrees
too mild for later evaluation.

Saturday night...increasing mid/high clouds after midnight with light
south winds should keep lows mostly in the lower to middle 30s.

Sunday and Sunday night...a swath or two of rain with possibly some
isolated embedded thunder by Sunday PM and Sunday night. Precipital
water values of .75 to 1 inch suggests widespread moderate rain amounts
of .25 to .75 inches. Mild with highs mostly in the lower 50s with lows
mostly in the low/middle 40s. South winds increasing to 10 to 20 MPH
by afternoon and into Sunday night.

Monday...A stalled front just to the northwest will keep area mild with
limited forcing for low chance POPS but lots of clouds. Continued south
winds of 10 to 15+ MPH should allow for highs well into the 50s. Patchy
fog may be an issue for later shifts to consider, have kept isolated
embedded thunder in mainly for forecast continuity. Monday night...cool
frontal passage with a weak wave may allow for more light to moderate
rain amounts with possible isolated thunder. Lows should fall into
the 40s southeast to 30s northwest as cool air filters in overnight
with clearing skies toward morning.

Tuesday through Friday...clearing skies Tuesday and then fair with a
return to near normal temperatures with lows 25 to 35 and highs mostly
in the lower 40s. Local techniques support with light winds lows may
be 3+ degrees colder with mid and possibly lower 20s mainly in north
and northwest sections.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1116 PM CST Fri Nov 25 2016

Patchy IFR and MVFR fog is developing in the area of light wind
and clear skies on the back side of the surface ridge. Area TAF
sites are expected to see MVFR visibilities due to the fog
overnight.  Fog should dissipate shortly after sunrise with VFR
conditions the remainder of the TAF period.

&&

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

$$

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



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