Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 161656
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1056 AM CST Thu Nov 16 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 740 AM CST Thu Nov 16 2017

Satellite imagery shows the leading edge of the stratus deck,
roughly from North English, IA to Galesburg, IL at 13z,
continuing to advance southward. KDVN 12z upper air sounding
showed only a shallow layer of moisture associated with this cloud
layer, just below below the sharp inversion based above 925 mb.
As the surface ridge axis over central IA continues to advance
eastward, lessening the low level north to northwest flow of this
moist layer, the southern progress should continue to slow.

Have updated the forecast for clouds reaching as far south as the
highway 34 corridor by late morning, then dissipating, as
suggested by the latest HRRR runs. This should be then followed by
increasing high thin cloud cover currently topping the upper
level ridge in the northern plains. If these low clouds hang on
longer than the next several hours, temperatures will continue to
struggle and likely not climb out of the 30s, well below current
forecast highs.

&&

.SYNOPSIS...
Issued at 325 AM CST Thu Nov 16 2017

A seasonably cold airmass was over the forecast area early this
morning with temperatures in the mid 20s to around 30. A northwest
wind ahead of an in-building ridge of high pressure over western
MN continued to advect cold, dry air. Satellite fog channel
images showed an extensive area of low clouds over the eastern
Dakotas, MN and WI creeping southward into eastern IA and
northwest IL. Aloft, the flow was northwest ahead of a broad ridge
over the plains. Further west, an upper level trough off the west
coast will be our next weather system, bringing rain Friday into
Friday night, then another day of brisk winds and falling
temperatures Saturday.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 325 AM CST Thu Nov 16 2017

Main challenges are cloud cover and temperatures as high pressure
traverses the region today followed by a return flow of moisture
and warm air advection aloft tonight.

Today, the current stratus field will continue to spill south to
southeast across the area early this morning. These low clouds,
associated with layer of moisture in the northwest flow trapped
under under a strong inversion 850 mb, have been poorly handled by
most models so far tonight. There is thus low confidence in how far
south the clouds will spread before thinning out under weak low
level subsidence and light winds with the high passing through the
area around midday. For now, have compromised with mostly cloudy
skies across the north with partly cloudy skies in the south, where
high clouds will be spreading in during the day. Weak mixing and
light winds will limit highs to the lower to mid 40s, with the far
north possibly not reaching 40 if the low clouds hang on through the
day.

Tonight, there may be some initial thinning in the clouds in the
evening, then overcast conditions are likely overnight as warm air
advection and moisture return develops above 850 mb.
Precipitation is likely to hold off until after sunrise, when high
res models and global models begin to bring in sufficient lift to
overcome the dry low levels. Light southeast winds and cloud
cover will likely limit lows to the lower to mid 30s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 325 AM CST Thu Nov 16 2017

The atmosphere will still be saturating Friday morning so
precipitation may not get started until late morning. Once
saturation occurs, light rain or a rain/drizzle mix will be seen
through sunset. The cloud cover and rain will suppress temperatures
and likely keep them in the 40s.

Friday night the main storm system moves through the area. The trend
with the models is to have the main low pass from Missouri into
central Illinois. Thus mainly rain will be seen across the area
Friday night with perhaps a few rumbles of thunder.

On Saturday cold air starts pouring into the area on strong
northwest winds as the storm system moves into the Ohio Valley.  A
familiar scenario develops for the area; will the rain end before
the cold air arrives.

Right now it appears that the rain will end first. However, one
cannot completely rule out a brief rain/snow mix just prior to the
rain ending.

The more important message Saturday will be the strong winds and
slowly falling temperatures. Sustained winds will be at least 20 to
30 mph with gusts to 35 mph, possibly higher. Temperatures are
expected to remain steady or slowly fall through the day.

Saturday night, quiet and dry conditions will be seen across the
area with decreasing winds. Temperatures should average below normal.

Sunday on...

Quiet and dry conditions will be seen Sunday through Wednesday. The
model consensus has storm tracks well north and south of the area.
There will be a dry frontal passage occurring Monday night/Tuesday.
Temperatures will generally average below normal.

Wednesday night, there are disagreements among the global models on
the track of a weak system moving through the western Great Lakes.
Moisture is limited and the better forcing remains across Minnesota
and Wisconsin. The model consensus has slight chance to chance pops
for potentially a rain/snow mix or perhaps some light snow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1056 AM CST Thu Nov 16 2017

At KCID/KDBQ/KMLI IFR conds will gradually improve to VFR later
this afternoon, with VFR conds continuing tonight. At KBRL VFR
conds will prevail through this taf cycle. Mainly southeast winds
around 10 knots or less.

&&

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

$$

UPDATE...Sheets
SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...08
AVIATION...Haase



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