Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 252046
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
246 PM CST Tue Feb 25 2020

.SYNOPSIS...
Issued at 245 PM CST Tue Feb 25 2020

The upper level shortwave that helped produce the accumulating light
snow across northeast Missouri, far southeast Iowa and west central
Illinois this morning was seen on satellite water vapor imagery
weakening and exiting northeast toward Lake Michigan early this
afternoon. While area radars showed some remaining banded
reflectivity over northern IL into southeast Iowa, little
precipitation was reaching the ground due to dry air in the low
levels. A much larger, stronger upper level low, the second
feature involved with this complex storm system, was taking shape
over western KS. Temperatures over the local area were in the mid
30s to around 40 with gusty northeast winds from 15 to 25 mph with
a few sites gusting over 30 mph. The brisk winds were occurring
in the tight pressure gradient between low pressure, now over West
Virgina, and high pressure moving out of the Northern Rockies.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 245 PM CST Tue Feb 25 2020

The forecast challenge remains centered on the potential for
another round of light snow. Our latest forecast continues the
trend over past few cycles lowering expected snowfall amounts and
shifting the main snow axis further southeast. Based on this and
the later onset of snow this evening, the Winter Weather Advisory
has thus been cancelled for our Iowa and Missouri counties and now
confined to Bureau, Putnam, Hancock and McDonough counties in
west central Illinois beginning at 6 pm. Even there, forecast
snowfall totals for tonight of 1 to 2 inches may be optimistic.
However, with air and surface temperatures dropping well below
freezing, slick roads will be possible and the gusty northwest
winds of 15 to 25 mph will cause some low end drifting snow
leading to slick roads and hazardous travel conditions. Current
timing has any snow quickly ending around sunrise, thus the
expiration time was moved up from noon to 9 am.

Snow will begin this evening as upper level lift ahead of the
central plains low and weak upper level jet level diffluence
overspread the region. This forcing is strongest across the
southern half of the forecast area and will produce snow as it
reaches the deeper moisture axis in place across just to the east
and southeast. All models have this low weakening and filling into
a longwave trough, resulting in rapidly diminishing forcing
overnight. There is a near model consensus showing an axis of
developing light snow roughly southeast of a line from Sterling,
IL to Burlington, IA this evening, then shifting eastward out of
the area by roughly 7 am.

The roughly tenth of an inch or less QPF and increasing snow to
liquid ratios inching toward the mid teens will support snowfall in
the range of 1 to 2 inches. This will likely result in a sharp
cutoff in accumulations, with a dusting a best further west along
the MS River and and far northwest IL. There is some suggestion in
hi res models of possible elevated banding that could produce
flurries over east central Iowa overnight, but this potential looks
too low to mention due to the dry layer aloft seen on KDVN soundings
today, which is even more pronounced on forecast soundings for areas
to the northwest.

Wednesday looks brisk and a bit colder with cloud cover gradually
decreasing as high pressure approaches from the west in the
afternoon. Highs may only reach the upper 20s along the highway 20
corridor to the mid 30s central and south.


.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 245 PM CST Tue Feb 25 2020

Below normal temperatures and mostly dry conditions will be seen to
end the month of February. Warmer conditions return to the area
Sunday and continue through much of next week.

Wednesday night-Friday night...cyclonic flow will be seen to begin
the extended forecast, as the southern stream wave merges with the
northern stream low over southeast Ontario. Cold air will continue
to filter into the Midwest with strong CAA aloft and 850 mb temps
dropping into the -12 to -13C range. This will keep highs in the
upper 20s/low 30s and lows in the teens through Saturday. If we had
more of a snow pack other than across our north, then temps may have
been even colder.

A weak surface low is progged to move into southwest IA by 18z
Thursday. Moisture is lacking, but this system still may bring
flurries or very light snow to portions of the area and have
maintained slight chances for this possibility across the far south.
Cloud cover will also increase with this system, especially
across the south and have raised Friday min temps a degree from
the NBM. The latest NAM and ECMWF bring in another weak clipper on
Friday night that may bring more flurries and clouds to the area.

Saturday-Sunday night...quiet conditions will be seen, as mid level
ridging tracks over the area, transitioning the pattern to
southwest flow. WAA aloft and late February sun will help boost
afternoon temperatures into the 40s and even lower 50s. Raised
highs on Saturday and Sunday from the model blend, as initial
load of highs was on the lower side of guidance. I also have
noticed that the blend has been too cold as of late with our past
warmup on Sunday.

Rest of extended...A closed low develops over the southwest CONUS
Sunday night. How and when this low ejects out of this area will be
key as to what impacts we may see early next week. The 12z GFS/CMC
show a stronger jet associated with this low compared to the 12z
ECMWF. This results in the low lifting out faster and as a
positively tilted trough near the CWA on Wednesday. Conversely, the
12z ECWMF has a weaker jet and a more meridional flow ahead of
the wave, resulting in a negatively tiled trough over the area on
Wednesday. Right now, the best chances for precipitation are
centered on Monday night with rain initially, changing to snow as
the night progresses.

&&

.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...NONE.
IL...Winter Weather Advisory from 6 PM this evening to 9 AM CST
     Wednesday for Bureau-Hancock-McDonough-Putnam.

MO...NONE.
&&

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Gross
AVIATION...Sheets


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