Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 120541
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1141 PM CST Sat Nov 11 2017

...06z AVIATION UPDATE...

.UPDATE...
Issued at 920 PM CST Sat Nov 11 2017

Low amplitude wave shifting east from NE. Isentropic ascent and
strengthening mid level frontogenesis leading to band of rain
south of I-80 near Hwy 34. Radar returns a bit high likely due to
bright banding, thus the bark is worse than the bite and this is
just a band of light rain with ceilings still around or above 6kft
agl. Additional light rain was occurring over northeast IA as
well ahead of another low amplitude wave progressing east from SD.
Forcing attendant to these waves should continue to promote an
expansion of precipitation rest of this evening into the overnight.
Mesoanalysis shows near surface wet bulb temps above freezing
except for a small portion of far NW IL, thus rest of tonight
should be generally rain for precip type although a sleet mix in
initial development with evaporational cooling is possible but
best potential would be confined to Galena to Freeport to Mount
Carroll areas roughly.

Attention is also focusing back west with a more vigorous shortwave
shifting e/se from MT. This wave is progged to move quickly and
pass across the region by mid morning Sunday through midday. This
energy looks to aid in strengthening mid frontogenesis and
deformation band north of mid level low tracking over southeast IA
and west central IL Sunday AM. 00z NAM is offering some robust
lift to the tune of 15 to 20 microbars/sec (-12c to -18c layer) in
the dendritic growth zone by 12z Sunday through 18z, and consequently
is wetter from previous runs depicting over 0.25 to just over 0.5 inch
in the band as it shifts across areas mainly near/north of I-80.
The magnitude of the lift dynamically cools the column and leads to a
change over to potentially a moderate/heavy wet snow for a time in
these areas Sunday AM. Wet ground and temps above freezing would likely
limit accums, but some visibility issues and rate could overwhelm
some surfaces especially grassy areas. Not ready to bite off on this
yet as just one piece of guidance, but a very interesting signal
nonetheless that will need to be monitored closely and assessed in
other models. CAMs still support mostly rain including HRRR, although the
01z run is showing a change over to snow over portions of north central
into northeast IL by around 14z-17z.

Bottom line, mainly rain tonight with some sleet possible at onset, while
a wintry mix of rain/snow/sleet possible in far NW IL. Sunday AM could
bring a change over to snow for a time mainly north of I-80, but confidence
low at this time, but next shift will be taking much closer look and
will have full suite of model guidance to assess whether any changes
are needed.

&&

.SYNOPSIS...
Issued at 313 PM CST Sat Nov 11 2017

The sky was mostly cloudy across the area during the early
afternoon hours. A wind from the southeast averaged 10 to 15 mph.
Early afternoon temperatures were mostly in the 35 to 45 degree
range. In central Iowa, pockets of drizzle and light rain were
beginning to fill in.

&&

.SHORT TERM...(This Evening through Sunday)
ISSUED AT 313 PM CST Sat Nov 11 2017

The main forecast challenges in the short term period are
precipitation types/timing/amounts tonight into Sunday morning.

In the near term, top-down saturation is continuing with lower
clouds and pockets of drizzle starting to show up in central Iowa.
This process will continue into the evening hours with light rain
and some drizzle spreading from west to east.

The HRRR/RAP are among the warmer solutions for precip type
overnight into Sunday, while the 12z Nam was more extreme, colder
at the surface and warmer aloft. This solution resulted in more
widespread freezing rain before a late change over to snow. Have
favored a model bland for the thermal profile. The net result is
rain over most of the forecast area through the event. The
exception would be areas along and north of Highway 30. A mix of
rain, snow and possibly some patches of freezing rain on elevated
surfaces, is expected from Dubuque to Freeport late tonight. As
Fgen forcing increases near and after daybreak, cooling should
result in a quick change to rain/snow or all snow. The far
northeast portion of the forecast area, from Galena and Freeport
to Mt. Carroll, could see some light accumulations around a half
inch on grassy surfaces. Any snow will quickly melt off and end
through late Sunday morning.

Sunday will be a raw day, with a north breeze and afternoon temps
only rebounding into the upper 30s to mid 40s.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 313 PM CST Sat Nov 11 2017

Sunday Night through Wednesday

Dry to start the week with temps warming into the 40s and 50s. A
500mb ridge will then begin to flatten Tuesday afternoon and evening
ahead of an approaching low amplitude shortwave trough.

A period of rain is likely from Tuesday night into Wednesday when
deep layer warm air advection and 700-500mb omega are maximized.
Forecast PWATs are around 1 inch, but this is a quick moving system
so expecting lighter rainfall totals. The ECMWF/CMC have less than
0.25" for most areas, while the GFS is wetter with up to 0.50"
across the southern few tier of counties.

The GFS has steep enough mid-level lapse rates to yield ~200 J/kg of
MUCAPE Tuesday night, so maintained slight thunder chances in the
forecast roughly across the southern two-thirds of the CWA.

Thursday through Friday

Active NW flow pattern brings another chance for rain sometime
during the Thursday afternoon through Friday period. Models vary on
timing with the GFS/CMC about 12-24 hours quicker than the ECMWF.
The ECMWF even lingers precip through part of Friday night. The
details associated with this system will likely continue to change
over the next several days. Model blend temps are near normal during
this time.

Saturday

Conditions dry out and forecast temps are slightly below normal. The
ECMWF/CMC are much stronger with 850mb cold air advection for the
upcoming weekend than the GFS, which would have implications on
temps beginning Saturday night. Uttech

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1134 PM CST Sat Nov 11 2017

Expect a deterioration into MVFR and IFR conditions overnight and
lingering Sunday. Periods of light rain will be found overnight
with some sleet possible in the early onset of the precip. Sunday
AM expect there to be a band of light to moderate rain at the
terminals, with the potential for the rain to mix with or change
to snow at DBQ, CID and MLI before ending by midday. Deepening
northerly winds will usher drier air in and bring clearing skies
and return of VFR conditions from NW to SE by mid Sunday afternoon
through early Sunday evening.

&&

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

$$

UPDATE...McClure
SYNOPSIS...RP Kinney
SHORT TERM...RP Kinney
LONG TERM...Uttech
AVIATION...McClure



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