Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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423
FXUS63 KDVN 241146
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
546 AM CST Tue Jan 24 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 416 AM CST Tue Jan 24 2017

Widespread stratus remains in place over the region early this
morning under ridging at the surface and aloft. Temperatures were
hovering in the lower to mid 30s with light winds. All eyes are on
the strong upper jet and embedded shortwaves lifting out of the SW
U.S. and the associated lee side surface low spinning up over SE CO.
This is on a track to lift northeast across KS today then across IA
tonight and Wednesday, possibly sending a swath of heavy snow across
Nebraska and NW IA, while rain and thunderstorms are likely along
and east of the surface low track. The local area will see a little
bit of everything, with the far north and west most likely to see
light snow accumulations.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 416 AM CST Tue Jan 24 2017

The forecast remains largely on track for widespread rain
developing late today, then mixing with snow in the north overnight.
Forecast models have narrowed to a near consensus with the surface
low passing through east central IA overnight. Out ahead, have
delayed the onset of precipitation today, closer to the arrival of
sufficient forcing to overcome an initially dry deep layer aloft.
This will lead to primarily light rain showers at the onset and
mainly in the afternoon over especially the north. Temperatures will
be slow to rise through the 30s with the developing easterly winds
with the exception of the far south, where the advancing surface
warm front and low chances for rain should lead to at least lower
40s.

The strongest forcing arrives in the strong cyclonic vorticity
advection and jet exit region ahead of the advancing upper level low
in the evening. This, combined with steep mid level lapse rates and
850 mb strong thetae advection on the nose of 40 kt plus winds at
850 mb will support at least scattered elevated thunderstorms. With
the 850 mb low lifting through central IA overnight, most of the
wintry precipitation will remain northwest of the forecast area.
However, sufficient forcing and dynamic cooling will support a mix
over especially the IA highway 20 corridor, which will be close to
the gradient of much heavier snow accumulations likely not far to
the north and northwest. Cannot rule out several inches of snow in
our northern tier of IA counties, especially if slightly more
southerly solutions like the ECMWF and Canadian pan out. However,
confidence in this is too low at this time to add our northern
counties to the advisories already in place just to the north and
west. Further south, the dry slot will end the rain or drizzle for a
period overnight in northeast MO, SE IA and west central IL. The
lack of cold air, with surface as temperatures hold primarily in the
mid and upper 30s through the night, and initially low snow to
liquid ratios will also be unfavorable for accumulation of what will
likely be wet snow in the overnight period.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 416 AM CST Tue Jan 24 2017

Wednesday and Wednesday Night:

Models now in fairly good agreement with a ~995 mb low in eastern IA
by 6 AM Wednesday. ECMWF is furthest south with sfc low near
Burlington, NAM/GFS are north over the Cedar Rapids area. The ECMWF,
and to some degree the Canadian, have consistently had more of a
southern track and slightly cooler thermal profiles over the past
several days than the NAM/GFS.

Aloft, there is the left exit region of a 300mb jet, and a positively
tilted trough that has a closed circulation. This upper- level low
will slowly weaken through the day, transitioning into an open
wave as it merges with a large downstream trough over eastern
Canada.

Snow Potential:

Precipitation during the morning (6 AM to Noon) will be trending
north leaving much of the CWA with very light amounts. One area of
concern is along/north of the highway 20 corridor, especially on the
Iowa side. Here, there is a much higher probability for either
periods of rain/snow showers or even steady rain/snow. Boundary
layer temps are marginal for efficient snow accumulations; however,
~1-2 inches is possible by the evening.

As the 850mb theta-e ridge/moist axis pivots and sinks south with
time, wrap around moisture will rotate through the entire CWA,
bringing a good chance for periods of light snow and a chance for
brief moderate snow showers. By Thursday morning, a dusting to an
inch or two is expected - highest far north.

In addition to the snow, northwest winds will be gusting 30 to 35
mph.

Thursday:

Cooler in the upper 20s and lower 30s with flurries or scattered
light snow showers. Little, if any, additional snow accumulation.

Friday - Monday:

Pattern change to near average temps in the 20s and 30s. Weak
disturbances in northwest flow aloft will bring periods of flurries
and snow showers. POPs are low this far out and there will be plenty
of dry periods as well. Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
ISSUED AT 545 AM CST Tue Jan 24 2017

Stratus with MVFR ceilings will remain in place today with light
and variable winds becoming easterly as a developing surface low
approaches from the plains. Some guidance suggests ceilings may
lift to VFR levels during the afternoon, but confidence in this
occurring was too low to include except at BRL. Some bands of
showers and isolated thunderstorms are expected to develop by mid
afternoon and continue into evening. The potential for thunder is
too low to mention at this time. Overnight, low level winds
strengthen and veer more southeasterly with precipitation becoming
more widespread at CID and DBQ, where a mix of snow and rain is
expected, and sleet cannot be ruled out. As the low pressure
center moves into eastern IA, ceilings are likely to lower to IFR
with rain or drizzle becoming the main precipitation type along
with fog.

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Uttech
AVIATION...Sheets



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