Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 170533
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1133 PM CST Sun Feb 16 2020

...06Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 PM CST Sun Feb 16 2020

The latest sfc analysis was indicating a quasi-stationary boundary
oriented from west to east from just north of Sioux City, over along
and south of the Hwy 20 corridor locally. South of that feature,
despite weak mixing regime and cold start to the day, temps have
climbed into the upper 30s to mid 40s acrs much of the CWA. Elevated
Fgen narrow band of snow is staying off to the north acrs NE IA into
SW WI, with just some virga clipping the Hwy 20 corridor. Aloft,
broad west-northwesterlies have tomorrow`s weather maker wave seen
on water vapor imagery embedded in them over the eastern ID/MT
border region.

&&

.SHORT TERM...(This Evening through Tonight)
ISSUED AT 315 PM CST Sun Feb 16 2020

Tonight...A mix of cloud patches and clear zones this evening. Some
concern that there may be fog re-development in the far east this
evening after dark, but will bank on increasing southeast sfc winds
of 4-7 MPH and ongoing afternoon insolation/drying limiting the
threat in those areas. Then as the above mentioned upstream short
wave approaches, low to mid level south-southwest flow increases
overnight especially after midnight with indications of a 25 KT H85
MB jet. A warm wedge inversion increases aloft overnight and becomes
pronounced on favored fcst soundings from H9 to H85 MB. Moisture
transport/conveyor increases as well, but top-down saturation is
hampered until late for precip to make it to the sfc especially
points east of the MS RVR. But soundings are adequate for precip
to blossom/break out from southwest to northeast along and west of
the MS RVR especially after 2-3 AM, NAM precipital water pushes a
half inch west of the MS RVR by 12z Mon, but may be too generous.

Expect non-diurnal temp trends tonight with coolest sfc readings
occurring mid to late evening, with a steady to slow rise into early
Monday morning(WAA and cloud cover increase). Depending on when the
vertical layer saturation becomes adequate enough for precip arrival
at the sfc, if it occurs with sfc temps still at or just below
freezing, there may be a 1-3 hour window of light freeing rain.
This may occur form along the I80 corridor west of the MS RVR or a
tier of counties south of there after 2 AM, with colder soundings
showing more snow possibly mixed with sleet further north at
Cedar Rapids and toward Dubuque in the pre-dawn hours. further
south acrs southeastern IA and northeast MO, expect the boundary
layer to recover enough to support mainly rain by late tonight.
QPF amounts should be light with layer saturation processes in
mind at least through 12z Monday. But a bit of concern that there
may be a light glaze of ice possible from just south of I80 to the
Hwy 30 corridor(again mainly along and west of the MS RVR) from 3
AM to 6 AM that may be a hamper for early morning commute in
those areas. But the window may be short lived with increasing sfc
wet bulb zero`s from the south, and feel any risk may be covered
by a special weather statement as opposed to a full blown advisory
at this juncture. 12 hour lows in the low to mid 20s in the far
north, to near 30 in the south occurring mid to late evening.
..12..

.LONG TERM...(Monday through Sunday)
ISSUED AT 315 PM CST Sun Feb 16 2020

Monday

Main Message:

Rain and some snow (north) is likely on Monday. Any mix in
central sections will quickly changeover to all rain as surface
temperatures warm through the mid to upper 30s. Minor snow
accumulations are possible north of highway 30, but with limited
impacts due to the warming temperatures. Areas along/north of
highway 20 stand the best chance for a window of slippery travel
conditions before melting begins during the late morning, or by
midday. Confidence is low on the exact precipitation type in the
far north, and it`s worth a mention that a brief period (1-2
hours) of heavier snow is possible before the changeover to rain.

Setup:

A surface trough early Monday will begin to consolidate into a
closed low late in the day. The favored track of the low is across
eastern Iowa into central Lake Michigan. Upper divergence in the
left exit region of a nearly zonal jet will become widespread
across the area and will be accompanied by strong isentropic lift
downstream of a 500mb vorticity max.

Timing:

Expect a quick increase in precip coverage after 6 AM,
coincident with a ramp up in 700mb omega. Thermal profiles
support a mix or all snow for a time in the north with a quick
changeover to all rain south of highway 30. Confidence on the
exact p-type is low because max wet-bulb aloft and surface temps
are forecast near freezing for a period Monday morning. Still
anticipate the entire CWA, even in the far north, to get above
freezing for highs. Our latest forecast has mid 30s reaching
north of the highway 20 corridor. This should lessen impacts on
pavement if snow accumulates earlier in the morning.

The expected track of the low should pull a dry slot, depicted in
700mb RH model plots, into the SW forecast area during the morning,
then spreading east/northeast from there. For this reason, the
lowest QPF (a tenth or less) is forecast in the southwest and the
highest is in the far north (0.20-0.40"). Something to consider
is the potential for moderate to briefly heavy precip Monday
morning with steep mid-level lapse rates near 7 C/km. The NAM has
low MUCAPE values during this time, which could be overdone but is
a sign that there could be a few convective elements in the mixed
precip or snow across the north. A deformation band of snow could
clip the far northwest/north with a little snow into Monday
evening before this system completely pulls away.

Snow Potential:

Due to the low confidence on precip type Monday morning in the
north, used fairly low snow-to-liquid ratios between 5-8:1.
Combining these numbers with CONSAll model blend QPF, slightly
weighted more toward the ECMWF, produced about 1-2 inches of
accumulation north of highway 20. If the convective elements do
not materialize, snow amounts may be minimal in this area.
Conversely, an hour or two of moderate to heavy snow could push
amounts up near 3 inches. Thus, there is some room for changes to
the forecast with the current amounts being the most likely
outcome at this stage.

Models made a notable southward shift in the track of this system
and with the band of highest QPF. Thermal profiles, however, are
only a touch colder than previous forecasts. The GEFS mean
snowfall accumulation has about 1-2 inches in the far north. The
HREF is mostly under 1 inch but has jumped southward from the old
00Z run.

Tuesday On

Below normal temps return for the middle of the week. The model
blend has Wednesday/Wednesday night as the coldest period with highs
in the teens and 20s and lows in the single digits above and below
zero. A lack of extensive snow cover over most of the CWA should
lessen the punch of this modified arctic air mass compared to the
one last week. Moderating temps are forecast late in the week
with mid- level height rises and mild 850mb downsloping flow
overspreading the Central U.S. Uttech

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
ISSUED AT 1133 PM CST Sun Feb 16 2020

Precipitation with an approaching weather system will likely
arrive later than earlier forecasts, resulting in prevailing VFR
conditions through the rest of tonight. Current thinking is that a
brief period of freezing rain will be possible roughly 12z to 15z
Monday at CID, MLI and DBQ, before changing to rain or drizzle
through the rest of the day. BRL is expected to have all rain
from this system. With the onset of precipitation, ceilings and
visibilities are likely to quickly deteriorate to IFR or possible
LIFR and remain restricted through the entire day. A cold front
that follows may bring at least a brief round of rain showers
Monday evening, followed by gusty northwest winds and improving
conditions to MVFR. These details are broad brushed in the ending
6 hour period of the forecasts due to product length.

&&

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

$$

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


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