Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 211808
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1208 PM CST Sun Jan 21 2018

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 302 AM CST Sun Jan 21 2018

Fog so far tonight has been limited to where the last vestiges of
snow cover likely exits across far northwest and northern
portions of Buchanan county. Elsewhere, a stratus deck, lack of
strong convergence in weak wind fields and shallow moisture has
prevented fog from becoming anything more than an aviation impact.
At the surface, a nearly stationary warm front extended east from
a southeast CO low into west central MO. Temperatures were in the
30s and 40s north and northeast of the boundary, while both
temperatures and dewpoints were in the 50s to the south. The CO
low was forming ahead of an upper low moving into the Rockies,
which will eject northeast, strengthen and pass through the
forecast area as an occluded system Monday. This will lead to a
variety of spring-like weather challenges in the near term,
followed by at least a brief return of more typical wintry weather
Tuesday.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 302 AM CST Sun Jan 21 2018

Main focus is on temperatures and onset of drizzle, rain and
possible thunderstorms tonight as the warm front advances north
into the area followed by increasing upper level forcing and
elevated instability late tonight. 00Z/21 models are in good
agreement with the surface low advancing toward the far northwest
MO/southeast NE area by 12z Monday, driving the warm front to
roughly the eastern IA and northwest IL highway 30 corridor.

Today, the progression of lowering clouds, fog and onset of drizzle,
already delayed tonight, continues to be problematic in the near
term and forecast confidence is low. Current trends suggest fog will
continue to thicken across the north by dawn. As the warm front
begins to advance northward, fog should also develop in the south
and overspread much of the area by midday. Forecast soundings
indicate low level saturation deepening under a pronounced dry mid
layer, indicating possible drizzle. The forecast has been kept along
these lines today with areas of drizzle and fog, but the potential
for dense fog appears low. Temperatures will see only a slow
recovery with the unfavorable light east to southeast winds and have
highs from the upper 30s north to lower 50s in the far south,
where the warm front should advance by early evening.

The warm front will continue northward tonight, and become
stationary across eastern IA into NW IL by morning. Strong warm air
advection develops aloft overnight spreading Gulf moisture and PW
values possibly above 200 percent. Widespread rain should result,
with enhanced elevated convergence on potential 40kt plus
southwest winds at 850 mb and sufficiently steep elevated lapse
rates to result in isolated to scattered thunderstorms. Widespread
QPF amounts of a quarter to half inch are projected across
especially the northeast half of the forecast area, or eastern IA
into northwest IL, late tonight. Temperatures will follow an
atypical diurnal trend, with readings holding steady or rising
into the lower 50s overnight in the warm sector across the south,
while the north may hold in the upper 30s to lower 40s.

.LONG TERM...(Monday through Saturday)
ISSUED AT 302 AM CST Sun Jan 21 2018

On Monday the main storm system moves through the area.

The initial round of forcing will exit the area Monday morning. The
overall areal coverage of rain is expected to decrease during the
morning as drier air aloft moves through the area.

Ahead of the dry air some embedded thunderstorms are possible over
the northeast half of the area. Patchy to areas of fog will be
possible across the northern half of the area during the morning as
the front moves north.

Monday afternoon another round of strong forcing will move from
Missouri into Illinois. This forcing should allow a narrow line of
thunderstorms to develop west of the Mississippi in eastern Missouri
that quickly moves northeast across Illinois. These thunderstorms
may produce some small hail given low freezing levels aloft. Gusty
winds may also occur if storms can become surface based.

Monday night rain will mix with and change over to all snow as
colder air moves into the area. During the transition period one
cannot fully rule out a brief period of sleet/freezing rain.

Overall snowfall amounts Monday night generally look to be under an
inch for much of the area. However, amounts around or just over an
inch may be seen east of the Mississippi and north of I-80.

Tuesday/Tuesday night breezy, dry and colder conditions will be seen
across the area as the next high builds in behind the departing
storm system.

Wednesday on...

Quiet and dry conditions with warmer temperatures will be seen
Wednesday through Friday as high pressure moves toward the east
coast. Temperatures should average above normal. Attention then
turns to next weekend.

Next weekend the global models have another storm system moving
through the Midwest. The timing differences are actually not that
great. However, there are more significant differences regarding
track and whether or not it is a single system or two separate
systems. The track will play significantly into the precipitation
type.

Right now the model consensus has chance to likely pops Friday night
and Saturday followed by dry conditions Saturday night/Sunday.
Precipitation type, which may change depending upon the storm track,
is currently rain with a rain/snow mix late Friday night and
Saturday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1208 PM CST Sun Jan 21 2018

Busy TAF period with IFR and LIFR flight rules dominating the
period. The next few hours may see some sites bouncing back to
MVFR, this should be short lived. Most sites will see a DZ then
rain through the period. Very minimal improvements to TAF sites
expected late in period.

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...08
AVIATION...Gibbs



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