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136
FXUS63 KDVN 260450
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1050 PM CST Wed Nov 25 2020

...06Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 310 PM CST Wed Nov 25 2020

The latest sfc analysis was indicating the main sfc low was rolling
acrs central IL, while aloft the upper level low was tilted slightly
to the west with the center of circulation northeast of STL looking
at the water vapor imagery. The brunt of the warm conveyor was
streaming well to the east of the region up the eastern OH RVR
Valley, while a pinched off TROWAL fed weakening DEF zone was moving
east acrs the north half of the CWA/north of I80. The thunder
chances have shifted off to the southeast under the main low/
convective looking clusters acrs central IL this afternoon. 24 hour
QPE suggests a swath of 1 inch to near 1.75" has fallen from
Sigourney IA, to Tipton IA and to just west of MT Carroll. The low
pressure system will pull away and eventually take the precip and
clouds with it for a decent late week and into the weekend period.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 310 PM CST Wed Nov 25 2020

Tonight...The main challenges tonight will be timing the exiting
cloud deck and if there will be renewed fog development. the
slightly off-stacked low complex is on track to reach north central
IN by 6-7 PM this evening. The weakening def zone will largely be
moving out of the area or decayed into marginal light rain patches
acrs NW IL at the start of the period. Still some satellite vort
lobe influences on the western flank of the departing cyclone to
possible induce enough lift to ring out some patchy drizzle in
spots(especially the east half through mid evening). Then upstream
ridging currently acrs the central plains will look to press eastward
acrs the area by midnight and into Thu morning. Thus the lift should
be shut off by then, but the incoming subsidence inversion may trap
the extensive stratocu deck that`s in place acrs the region and
prevent it from clearing from the west like most model solutions want
to do. Night time during late fall also conducive to keeping clouds
trapped in longer than the models want them to.

Like the previous shift stated, with sfc winds backing to the west
and possibly southwest while decreasing late tonight, and any
clearing skies would foster dense fog development into Thu morning
especially over the heavier rain swaths. But with the uncertainty of
clearing, will keep patchy to areas of fog possible especially o the
west after midnight and before dawn in areas more likely to clear
from the west, if they can. The HiRes models now target central to
northeast IA in converging, backing southwest sfc wind fields toward
dawn with dense fog, and just clip the northwestern CWA with
visibility reduction. But with uncertainty, will mention fog in
much more of the area than that. Back to this evening, there may be
transient localized swaths of fog development in areas where north
wind back and converge, but again hopefully the cloud cover will
prevent a more widespread fog problem before midnight. Will bank on
post wave boundary layer cool advection from northwest IA to get the
low temps down into the low to mid 30s west of the MS RVR, and upper
30s to near 40 in the east. If clouds hold tight these values will
be too cool in the west.

Thursday...Will walk out or mix out any lingering stratus or fog as
the morning progresses for mostly sunny skies. That until a passing
frontal system down acrs MN and WI possibly brings a cloud increase
acrs the north by late afternoon. Increasing southwesterly boundary
layer mixing flow to drive highs in the mid 40s in the far
northeast, to the lower 50s southwest. More cloud lingering will
make these optimistically mild, while deeper mixing more than H925
MB indicate by the fcst soundings would add a few degrees to the
fcst highs. All in all a decent Turkey Day probably in store for
tomorrow.   ..12..

.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 310 PM CST Wed Nov 25 2020

Key Messages:

1. Sensible quiet weather through the period.
2. Active pattern will lead to mainly temperature changes through
the period.

Discussion:

From a sensible weather perspective the period will be quiet with a
a couple of cold fronts and shifts in temperatures along with some
windy conditions.  Aloft, a much different story with strong
dynamics through the period and a highly energetic flow.  As is
usual in these cases, the overall forecast skill/confidence is low
as small changes to locations and timing of waves can greatly affect
the sensible weather.  While the current forecast has the area
mainly dry, this could change and later forecasts should help
improve on the skill and forecast confidence.

At the beginning of the period, largescale flow will be SW aloft
leading to mild temperatures on Friday.  Upstream, a strong
shortwave is expected to move into the area and bring cooler temps
to the area for Friday night.  This cold front looks to be a dry
passage across the area.  Saturday, zonal flow will lead to mild
temperatures again.  Sunday another wave is expected to move SE into
the area and interact with a closed low across Arklatex.  Models
keep this low east area and then set up what appears to be an omega
block for next week with cooler air again.  Next week could see more
active weather but this dependent on where those closed lows are and
I just don`t have high confidence in where they will be.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1049 PM CST Wed Nov 25 2020

LIFR and IFR will dominate the start of the period. However,
expect a slow gradual improvement to predominantly MVFR with
pockets IFR by morning and then eventually VFR by Thursday
afternoon in clearing, as low pressure continues to pull away
from the region and developing west/southwest winds usher in drier
air.

&&

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

$$

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