Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 251739
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1139 AM CST Tue Feb 25 2020

...18Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 313 AM CST Tue Feb 25 2020

1001 hPa surface low was analyzed over the Missouri Bootheel early
this morning, with warm front extending into the Ohio River Valley
and a cold front into Arkansas. This low has lost considerable
strength over the past few hours, as its attendant 500 hPa shortwave
has started shearing out. We`ve stayed mainly dry as a result.
Temperatures as of 2 AM were in the lower to upper 30s.

Off to the west, a secondary shortwave/closed 500 hPa low was
located over western Nebraska and Kansas. This shortwave will be the
driving force of reinvigorated forcing across much of the mid-
Mississippi River Valley over the next 24 hours, and will be the main
focus of our weather for the short term period.

&&

.SHORT TERM...(Today through Wednesday)
ISSUED AT 313 AM CST Tue Feb 25 2020

Key Messages:

1) Continued south and eastward trend of QPF and snowfall.

2) Generally 1-3 inches expected in northwest Illinois and northeast
Missouri, with isolated higher amounts to 4 inches possible.

3) Increasing northerly winds may lead to blowing and drifting of
snow tonight and early Wednesday.

Discussion:

As has been the case over the past few days, newest guidance
continues to trend heavy QPF and subsequent snowfall further to the
south and east of our CWA. Regardless, still expecting accumulating
snowfall to impact portions of our area through the short term
period.

The aforementioned surface low will quickly race off towards the
Appalachians as the secondary shortwave takes its place across the
mid-Mississippi River Valley through Wednesday. As it does so, a
stream of CVA will sweep across the area, leading to a revamp of low-
level forcing. Leftover moisture in place across the area will ensure
the development of precipitation.

Expect this to begin through the morning, with a slow progression
into far eastern Iowa and northwest Illinois through the day. Dry
air will continue to fight the northward progression, which is
expected to keep everything along and south a line extending from
Rockford IL, to the Quad Cities, to Ottumwa IA.

Precipitation-wise, a rain and snow mix is likely for much of today
as surface temps rise this morning. Over time, especially into
tonight, the boundary layer will cool with a changeover to all snow
expected. Snow may become moderate at times this evening as
frontogenetical forcing increases, especially in Illinois.

Accumulation-wise, have once again lowered amounts with this
forecast package. Bulk of the snow will remain well east of the
Mississippi River, with the highest amounts of around 2 to 4 inches
favored in west central to north central Illinois. Much of the snow
will accumulate tonight into Wednesday morning with the cooling
surface temperatures and passing of the shortwave overhead.

The other concern will be the strengthening northerly winds
beginning this afternoon into Wednesday. This may lead to reduced
visibilities and difficult travel conditions, especially in areas
seeing the heaviest snow.

Regarding headlines, I have canceled the Winter Weather Advisory for
Van Buren IA and Scotland MO as expected snowfall amounts have
dropped over one inch. In coordination with surrounding offices, I
have delayed the start of the advisory for other counties until 21z
today as the main impacts from the snow are expected later this
evening into tonight (those will be the accumulating snow the gusty
north winds leading to blowing and driving).

Snow will taper off from west to east Wednesday morning, leading
cloudy skies in place for the remainder of the day. Afternoon highs
will be cooler as a result of cool northwest flow with building high
pressure over the Dakotas. This high will help keep the weather
quiet across the area heading into the early portion of the long
term period.

.LONG TERM...(Wednesday Night through Monday)
ISSUED AT 313 AM CST Tue Feb 25 2020

Northwest flow behind the departing low will usher colder air
into the region for the end of this week. Expect highs in the 20s
and 30s, and lows in the teens.

Cyclonic flow aloft could support isolated snow showers or a few
narrow bands of light snow from time to time through Friday. Models
are hinting on the first chance for light snow to be across the
south Thursday afternoon into Thursday night. Added slight chances
in a small area to account for this. Chances for precip beyond
Thursday are too low to mention in the forecast, but we may end up
seeing additional rounds of flurries or light snow showers on Friday.

A pattern change to above normal temperatures is forecast from
Sunday into early next week as 500mb heights rise and 850mb warm air
advection overspreads the mid to upper Mississippi Valley. The model
blend indicates a chance for rain by Monday/Monday night with
daytime highs in the 40s and possibly 50s in the south. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1136 AM CST Tue Feb 25 2020

VFR conditions with mid and high clouds along with gusty
northeast surface winds will continue this afternoon into the
early evening hours at all sites. Another round of light snow
associated with an upper level system will impact mainly the BRL
site with MVFR conditions due to lowering ceilings and
visibilities from roughly 03z to 12z overnight. MLI and DBQ have
lower confidence MVFR conditions forecast due to lowering
ceilings overnight. However this is below average confidence due
to the amount of low level dry air. All sites are expected to
improve to VFR by midday Wednesday.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory from 3 PM this afternoon to noon CST
     Wednesday for Des Moines-Lee.

IL...Winter Weather Advisory from 3 PM this afternoon to noon CST
     Wednesday for Bureau-Hancock-Henderson-Henry IL-McDonough-
     Mercer-Putnam-Warren.

MO...Winter Weather Advisory from 3 PM this afternoon to noon CST
     Wednesday for Clark.

&&

$$

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


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