672
FXUS63 KDVN 260436
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1036 PM CST Wed Dec 25 2024

.KEY MESSAGES...

- Areas of fog and drizzle will develop this evening and
  tonight, becoming locally dense at times. A Dense Fog Advisory
  has been expanded to include areas up to the Highway 20
  corridor in Iowa.

- Temperatures are forecast to slowly warm through Saturday with
  much above normal temperatures across the area. Cooler
  temperatures are forecast by early next week.

- Daily chances for rain Thursday through Saturday.

&&

.UPDATE...
Issued at 920 PM CST Wed Dec 25 2024

We continue to monitor trends in the fog potential for this
evening through Thursday morning. Per the 26.00z observed
sounding, abundant moisture remains trapped in the lower levels
of the atmosphere due to a stout thermal inversion, with
saturation depth to around 800 mb. Widespread fog, some locally
dense, has been observed over the earlier Dense Fog Advisory
this evening, which is only expected to expand northward with
time. Already, KAWG (Washington, IA) is reporting 1/2 mile
visibility with steadily lowering visibility as far north as
Dubuque. The latest 26.00z HREF ensemble probability of
visibilities less than half a mile continue to be around 70 to
90+ percent for areas along and north of Interstate 80 late
tonight. Current visibilities over northwest Illinois remain a
bit more uncertain as visibilities have held steady there, so it
should take longer for them to drop. We will have to watch that
area for further expansion of the Dense Fog Advisory, but for
now, we have decided to expand the DFA northward towards the
Highway 20 corridor on the Iowa side of our forecast area. The
overnight shift will monitor for possible expansion. Guidance
also suggests that visibilities will gradually improve from
southeast to northwest after sunrise Thursday, so some
adjustments to the end time of the DFA may also be needed.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 215 PM CST Wed Dec 25 2024

This Evening - Thursday:

A Dense Fog Advisory is in effect south of I-80 where the fog
is first expected to develop this evening, before gradually
spreading to the N/NW overnight. Later shifts may need to expand
the advisory further to the north (across central and northern
sections of the outlook area). Hi-res models are showing some
improvement in visibilities across the southeast to east-
central counties late tonight as slightly more mild air advects
in from the ESE. If this occurs, the Dense Fog Advisory may be
cancelled early south of the Quad Cities. Further to the west
and northwest, dense fog may last through much of Thursday with
light and relatively moist low- level flow continuing through
the afternoon; headlines may be needed for this period and into
Thursday night as the fog expands once again.

Low-level theta-e advection within the ~0.5 - 1.5 kft AGL cloud
layer overnight will lead to periods of drizzle, spreading in
from south to north. This activity looks to continue off and on
through the day on Thursday. Total precip amounts through
Thursday evening will remain light due to the shallow moisture
and weak forcing, ranging from a trace to a few hundreths of an
inch.

For tonight, there is a chance for the patchy drizzle to
coincide with temperatures near freezing across the far NW
portion of the outlook area (mainly before midnight) leading to
a brief 1-3 hr window of freezing drizzle. Latest hi- res
models indicate areas along/north of Highway 20 (west of
Dubuque) with this potential for brief freezing drizzle before
changing to plain drizzle as temperatures warm to 33-34 F.
Current thinking is impacts will be limited with pavement temps
near to slightly above freezing. With that said, untreated
pavement could become slick for a brief time. The better chances
for more impactful freezing drizzle will stay a tier or two of
counties north of the outlook area. Steady southeast winds on
Thursday will continue to advect warm air into the region with
highs expected to range from the low 40s NW to upper 40s SE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 215 PM CST Wed Dec 25 2024

Zonal flow is forecast across the CONUS into early next week
resulting in several shortwaves moving across the area. This
brings almost daily chances of precipitation to the area through
Saturday. Looking at different model solutions also show short
periods of ridging and quiet weather. Thermal profiles continue
to support light rain across the area. Current forecast rainfall
amounts through next weekend range from 0.20 - 0.50" for most
locations.

Temperatures will warm each day Thursday through Saturday. The
current forecast has high temperatures on Friday and Saturday in
the lower 50s for central and southern sections.

Another shortwave approaches the region Monday night into
Tuesday with timing and placement differences between the GFS
and EC/CMC. This system may bring rain and snow to portions of
the Midwest but confidence on the details is low at this lead
time. The NBM has cooler temperatures moving back into the area
on Tuesday with highs in the 30s.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1036 PM CST Wed Dec 25 2024

Rather sloppy aviation conditions are expected late this
evening through the day Thursday as increasing low-level
moisture will support widespread LIFR/VLIFR ceilings and
visibilities due to fog, as well as some patchy drizzle. There
continues to be a bit more uncertainty on whether or not MLI
and BRL fall to 1/4SM visby tonight, given high-res model
probabilities of less than 1/2SM visby of 40 percent or less.
Some VLIFR conditions should linger through the TAF period for
CID and DBQ, but conditions should improve late in the day as
drier air filters in from the southeast, eventually scouring
out any fog and low stratus.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Dense Fog Advisory until 9 AM CST Thursday for IAZ040>042-
     051>054-063>068-076>078-087>089-098-099.
IL...Dense Fog Advisory until 9 AM CST Thursday for ILZ015-024>026-
     034-035.
MO...Dense Fog Advisory until 9 AM CST Thursday for MOZ009-010.

&&

$$

UPDATE...Schultz
SHORT TERM...Uttech
LONG TERM...Cousins/Uttech
AVIATION...Schultz