Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 210312

Area Forecast Discussion
National Weather Service Quad Cities IA IL
912 PM CST Sat Jan 20 2018

Issued at 857 PM CST Sat Jan 20 2018

Updated to lower mins a few more degrees to around 30 or upper 20s
along the Hwy 20 corridor where stratus has yet to arrive. Do
expect these areas to turn cloudy and temps should rebound into
the mid 30s overnight. Elsewhere, with generally cloudy skies
tonight temps will remain near steady in the mid 30s to lower 40s.
Some fog is likely tonight, mainly focusing on areas along the
Hwy 20 corridor the rest of this evening ahead of the cloud cover,
with patchy fog overnight. Not sure about drizzle potential tonight,
as models verifying too moist and cloud bases continue to rise into
the range of 2500-3500 ft agl. For now have kept mention of drizzle,
but delayed mention until after midnight. Any drizzle will be
predicated on developing lower cloud bases, and this would be appear
to be most favored across our southern CWA late tonight and
especially further south/west on nose of strong low level warm
advection. This warm advection takes aim on the region on Sunday and
should provide expansion of fog/drizzle during the day leading to
damp/dreary conditions.


Issued at 300 PM CST Sat Jan 20 2018

An area of low clouds advanced north to Interstate 80 during the
afternoon hours. Temperatures were mostly in the 40s area-wide,
and actually warmer over some areas north of I-80 where the sky
was clear.


.SHORT TERM...(This Evening through Sunday)
ISSUED AT 300 PM CST Sat Jan 20 2018

The main forecast issues in the short term period involve
prospects for dense fog and freezing drizzle overnight.

Low level moisture and synoptic lift will be on the increase from
south to north tonight. Expect widespread drizzle and some fog to
develop. Surface temperatures near freezing are mostly likely
along Highway 20 in Iowa, and cannot rule out a light glaze of ice
in this area early Sunday morning. Will likely have to wait until
closer to event time to get a good handle on impacts, if any.
Various high resolution model guidance develops fog overnight as
well. Highway 20 has the most lingering snow cover, albeit light,
and would be a favored area for dense fog. Confidence in
coverage/timing is low and will pass along for later shifts to

Rain will increase in coverage through the day Sunday, with
persistent patchy fog. Expect highs near 40 north to around 50
degrees south.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 300 PM CST Sat Jan 20 2018

Long term forecast focuses on the system ongoing at the start of the
period.  After this system moves out of the area a more normal to
slightly warmer weather pattern is expected.  Next weekend, another
system seems likely.  Current therm profiles suggest mainly rain at
this time.

Strong H5 trof expected to be just west and south of Iowa.  H5
divergence will aid in large scale vertical motion across the area.
Strong H85 WAA will also lead to rising motion on a largescale. The
overall jet structure does not support additional lift via a jet
streak until Monday morning.   With the warm draw today, it appears
that the blended models are too low with temperature and moisture
return tomorrow. The NAM still believe there is snow where there is
no snow and is bring air temps down to low.  For temps, went with a
superblend/ECMWF 50/50 blend.  This brings the 50s into the area.

As far as convection goes, there is a chance for elevated convection
associated with the terminus of the H85 LLJ.  This is why isolated
thunder has been kept in the forecast.  What does appear possible
now is clear slot convection Monday morning across the eastern CWA.
At this time, upper level divergence and a jet streak will lead to
chances for rain.  During this period, all of the guidance suggests
that 0-3km CAPE will be around 100 - 125 J/kg.  Looking at the low
level wind field, strong 0-1km shear also exists.  The sfc winds are
backed and the 0-1km shear vector is out of the SW.  This appears to
be a good set-up for HSLC tornadoes.  If the CAMs develop cells on
the clear slot, or even a broken line, there will be a threat for
HSLC tornadoes, especially as the 0-3km shear increases from 12z to
18z on Monday.  This will need to be monitored by later shifts.

As the colder air wraps in, a transition to snow seems likely.
Currently the forcing in the dendritic layer is short-lived so it
appears that at the transition time the heaviest snow will occur
before the drier air scours out remaining moisture.  Overall
accumulations are very light save the NE CWA with a pivoting nature
of the system will result in longer chances for snow.  Still
accumulation in this area is less than 2 inches at this time.


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
ISSUED AT 541 PM CST Sat Jan 20 2018

The TAF cycle will begin with VFR conditions at DBQ and CID, and
MVFR conditions in low clouds at BRL and MLI. Eventually
expect low clouds and MVFR to IFR ceilings to evolve into CID and
DBQ this evening, while remaining generally MVFR in low clouds at
BRL and MLI this evening. Back edge of the stratus continues
advancing northward through northern MO and central IL, and there
is the potential for some improvement to VFR on ceilings at BRL
late this evening into the early overnight. Should this occur will
likely see at least MVFR fog develop, thus generally MVFR
conditions to dominate at BRL. Still anticipate conditions to
deteriorate to IFR and LIFR with pockets of VLIFR in low clouds
and fog at all sites, but have delayed mention until late tonight
and Sunday AM timed more with arrival of deeper moisture and
frontal boundary stalled across the region. Also expect areas of
drizzle and light rain late tonight and Sunday with isentropic
ascent and moisture advection.




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