Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 162319
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
519 PM CST Fri Feb 16 2018

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 PM CST Fri Feb 16 2018

Latest sfc analysis was indicating 1030+ MB ridge center acrs the
lower MO RVR Valley, sliding eastward toward pressure rise max
northwest of the OH RVR Valley. This system to make for a clear
chilly evening, before temperatures take an upward trend again over
the weekend. Embedded wave seen now dropping acrs northern Idaho on
current water vapor loop, will bring a light precip event acrs the
area on Saturday, followed by unseasonably temperature trends and
eventual moisture feed up the central CONUS fueling a larger
precip event acrs the region by early next week.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 315 PM CST Fri Feb 16 2018

Tonight...The above mentioned upstream ridge center will slide east
right acrs the DVN CWA this evening, bringing about decreasing sfc
wind fields under lingering clear skies. Temps should drop quickly
after sunset, especially in areas of lingering although glaciated
snow cover and lower DPT pools. There could be quite a bit of
variance in temps acrs the area through midnight because of these
conditions...ranging from low teens or even upper single digits acrs
snow covered river valleys of the northeast, to 20s hanging on in
the snow-less south/southwest. Then high clouds streaming in from the
southwest along south half of upper jet axis overhead, as well as
increasing southeast to southerly sfc flow behind departing ridge
axis, will make for a non-diurnal steady to slow rise temp trend
after midnight, especially west of the MS RVR.

Saturday...Digging upper trof down acrs the region with organizing
sfc reflection frontal system, will sweep thru the CWA from late
morning and the afternoon. Most of the latest run models produce at
least light precip swaths/bands moving in ahead of the front after
mid morning in the northwestern CWA, spreading eastward acrs the MS
RVR through early afternoon. Other areas of precip will look to
stream up from the southwest out of MO into the southern and
southeastern CWA by late morning and into the afternoon as well.

The pre-frontal WAA regime will be in full swing and afternoon highs
will range from the mid 30s in the north, to the lower 40s or even
mid 40s in the southern snow-less areas. But the warming initially
realized only in the low levels and the precip should be mainly a
wet light snow along and north of I80. South of I80, initially snow
as well, but warming deepening enough for a transition to rain-snow
mix or even all rain into the afternoon. Several models even migrate
the rain-snow mix line a tier of counties or two north of I80 as the
afternoon progresses, before the precip exits off to he east by late
afternoon. Some concern, with fcst soundings showing evapo-cooling
buffer layers aloft, that the precip will stay mainly an all wet
snow along or even juts south of I80, but will continue with the mix
wording for now and transition to all rain in the south. As for
snowfall amounts, still just expect a range from a wet dusting, up
to a half inch generally along and north of I80. It may be hard to
truly measure how much falls with expected melting along the
warming sfc layer.    ..12..

.LONG TERM...(Saturday Night through next Friday)
ISSUED AT 315 PM CST Fri Feb 16 2018

Main forecast concern in the long term is the system from Sunday
into Wednesday of next week.  Strong WAA will result in rain and
thunderstorms.  As the system moves out Tuesday and Wednesday, the
chance for snow or a wintry mix will return to the area.  The threat
for ice jam flooding, flooding of creeks and streams, and severe
weather exist with the system on Monday.

Sunday, strong H85 WAA coincident with southwest flow will bring
spring like temperatures to the area.  This will aide in further
melt of snow across the area.  Temperatures are forecast to reach
the 40s across the south and the 50s across the south.  I think if
anything this forecast is too low as models with stong WAA this time
of year often under do temperatures.  Think that the I80 corridor
could actually see 50 degree temps by the time the daily climate
comes out.

Monday morning through Tuesday morning...attention turns to a
progressive warm front and surface low prog to track across the CWA.
 H5 forcing is rather weak as the setup is more of a longwave trough
across the SW CONUS.  Strong H85 WAA with LLJ speeds of 50 kts is
forecast.  This will bring warmer air and extremely high PWs for
February to the area.   This PW will lead to possible heavy rainfall
from convection on Monday.  Multiple rounds of rain are expected.
The current setup looks like a typical HSLC severe weather setup.
MLCAPE of less than 500 J/kg but large low level shear could lend
itself to severe weather.  This will be especially true if the warm
front stalls across the area.  I think this is possible with the
snowpack to our north and the cooler Lake Michigan.  This will be
the determining factor for strong to severe thunderstorms.  Overall
amounts of half an inch of rain to 1.5 inches of rain are possible
across the area.

After Monday...cooler air moves into the area.  There are timing
differences between guidance models.  This will greatly affect any
lingering pops for Tuesday into Wednesday.  As a result of this,
have continued overall R/S mix where temps are near freezing.
Pattern becomes less active until the end of the week when another
chance for precip returns to the area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 512 PM CST Fri Feb 16 2018

VFR conditions will persist tonight with increasing mid/high clouds and
light winds turning southerly. On Saturday, a fast moving upper level
disturbance and attendant surface cold front will bring a chance of snow
and MVFR conditions by late morning through the afternoon. Southerly
winds will increase to around 10 kts during the day on Saturday.

&&

.HYDROLOGY...
Issued at 315 PM CST Fri Feb 16 2018

Concerns with flooding exist with the current forecast for Monday.
PWs of 1 to 1.2 inches are in the extreme for February.  This with
the strong vertical motion due to the H85 WAA along with convection
will lead to moderate to heavy rain across the area.  With ice still
on area rivers and creeks flooding looks possible.  NCRFC has a high
potential for ice jamming on the Rock River at Joslin.  Those with
interests along area rivers should pay attention to future
forecasts.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Gibbs
AVIATION...McClure
HYDROLOGY...Gibbs



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