Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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241
FXUS63 KDVN 191753
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1153 AM CST Fri Jan 19 2018

...18z AVIATION UPDATE...

.SYNOPSIS...
Issued at 255 AM CST Fri Jan 19 2018

Temperatures were relatively mild for January in the mid 20s to
around 30 over most of the area early this morning courtesy of
southwest winds and thin cirrus. An increasing zonal flow aloft
and warm air advection will keep the warm air in place today
through Saturday. A developing storm system off the west coast
will affect the region from Saturday night through Monday night
with precipitation and then slightly colder temperatures early
next week.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 255 AM CST Fri Jan 19 2018

Temperatures are the primary challenge throughout as warm advection
continues southwesterly low level flow. Today looks to be similar
to yesterday, except there will likely be more widespread and
thicker high level cloud cover as widespread cirrus topping the
flattening ridge over the plains continues to stream eastward.
Southwest winds may be a tad stronger, depending on the extent of
mixing into the stronger winds in the sharp inversion roughly
above 925 mb. Based on observed and forecast mixing depths,
continued receding of the remaining snow cover and observed
temperatures upstream, kept highs in a range from around 40 to 45.
This is close to a blend of warmer guidance highs, and well above
the WRF, which has mainly 30s, likely due to the model hanging on
to too much snow cover. If anything, highs may end up being too
cool, especially south of I-80 where highs in the upper 40s would
be possible if cloud cover is less than anticipated.

Tonight, the combination of high clouds and light southwest winds
should again hold temperatures in a range from around 25 north,
where there may still be a few patches of snow, to the lower 30s
in the far south. This is close to what is indicated by a blend of
models when the too cool WRF is excluded.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 255 AM CST Fri Jan 19 2018

Quiet, dry, and warmer than normal conditions will be seen on
Saturday along with increasing clouds. Attention then turns to the
next storm system.

Saturday night into Sunday will be interesting. First, the models
are probably too moist. Second, the lower parts of the model
atmosphere are too cold. The second problem lies with the models
initializing a snow field too deep and too far south which causes
the models to produce a widespread freezing rain event for the area.
Lastly, the models still have differences regarding the overall
track of the storm system.

The snow field will be essentially gone by sunset Saturday. Taking
this into account and the moist bias of the models, temperatures
Saturday night should be a few degrees warmer which would lower the
potential for any ice to that of freezing drizzle for areas
generally north of highway 30.

So, the model consensus has slight chance pops south of I-80
Saturday evening with chance pops across the entire area late
Saturday night into Sunday morning. Fog will also be a risk given
warm, moist air moving over the cold ground.

As forcing and moisture increase Sunday afternoon, the drizzle will
turn over to rain with areas of fog continuing.

Sunday night the storm system moves through the area. Even with the
differences in storm track, the area generally looks to be on the
warm side of the storm with an all rain event. The model consensus
has likely to categorical pops for the entire area.

Monday on...

On Monday rain will continue during the morning. However, the models
are showing a respectable punch of dry air moving into the area so
the rain may stop or taper back to just drizzle. Regardless, once
the cold front passes, the cold side of the storm system will
arrive. Rain will mix with and turn over to all snow late Monday
afternoon into Monday night. During the transition period a wintry
mix of sleet and freezing rain looks possible which would impact the
evening commute.

The model consensus has chance to likely pops on Monday that taper
down to chance pops Monday night.

Tuesday through Thursday the model consensus has dry conditions for
the area with temperatures generally at or slightly above normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1142 AM CST Fri Jan 19 2018

Don`t buy the quick onset of lower stratus and fog that the NAM is
developing late tonight into Sat morning, and thus will advertise
another VFR TAF cycle with persistent southwesterly sfc winds and
passing high clouds. More of note may be a marginal low level wind
shear scenario setting up as early as this evening, if sfc winds
under sharp inversion can drop below 8 KTs. FCST soundings
advertise 40+ KTs at 1800 to around 2000 FT AGL from 240 to 250
degrees this evening and into the overnight. This flow aloft is
expected to decrease by mid Sat morning, if not earlier.   ..12..

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...08
AVIATION...12



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