Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 152043

Area Forecast Discussion
National Weather Service Quad Cities IA IL
343 PM CDT Thu Mar 15 2018

Issued at 343 PM CDT Thu Mar 15 2018

18Z surface data has high pressure over the upper Midwest with a
stationary front from the Ohio Valley into the central Plains. Dew
points were in the teens and 20s from the Great Lakes into the upper
Midwest and northern Plains. Dew points in the 30s and higher ran
from the lower Ohio Valley into the central Plains on south.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 343 PM CDT Thu Mar 15 2018

Late this afternoon through tonight
Assessment...high confidence

Quiet and dry conditions will be seen from late this afternoon
through tonight. Deep dry easterly flow should prevent the
development of any precipitation in the area until after
sunrise Friday.

Assessment...medium on precip occurrence/type but low on timing

The question on precipitation initiation Friday boils down to when
does the moisture overcome the dry air.

Based on RAP trends, there is a very real possibility that
precipitation initiation will not occur until late morning in the
far southwest and south areas. If this occurs, the probability
increases that precipitation will be mainly in the form of rain.

However, atmospheric profiles from the models are indicating a very
strong potential for cooling of the atmosphere when precipitation
finally initiates. This cooling may allow rain to refreeze into
sleet before it reaches the ground. If this occurs, a rain/sleet mix
would be possible on the leading edge of the precipitation before
changing over to all rain as latent heat release warms the lower

Right now precipitation should be south of an Oskaloosa, IA to
Quincy, IL by 10 AM Friday and south of a Vinton, IA to Macomb, IL
line by 1 PM. Precipitation may be as far north as an Independence,
IA to Peoria, IL line by 4 PM. There appears to be reasonable
agreement that areas north of a Manchester, IA to Kewanee, IL line
will likely remain dry until sunset Friday.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 343 PM CDT Thu Mar 15 2018

Main focus is on the system lifting out of the southwest spreading
a wintry mix of precipitation through the area Friday night into
Saturday morning. Overall forecast confidence is average to below
average due to uncertainties with the amount of moisture, timing
and thermal profiles that are critical for the precipitation
types. Sunday and beyond, the next system has trended toward a
more southerly track from previous forecasts, resulting in a much
lower impact on the forecast area with mainly rain expected. The
rest of the week looks mostly dry with near to below normal

Friday night into Saturday: Warm advection and upper level forcing
will result in widespread precipitation Friday evening. A filling
upper level low is progged by model consensus to track from
southeast Nebraska through SE IA or northeast MO overnight, while
at the surface, low pressure tracks nearly due east, just south
of this feature, spreading an inverted trough across the forecast
area. The process of top down cooling due to web bulb effects in
the initially dry low level airmass, then cold air advection as
surface winds turn northeasterly will cool the low levels
sufficiently to change the rain to freezing rain or sleet, mainly
north of interstate 80 overnight. Considering 4 inch temperatures
running in the 35 to 37 degree range this afternoon, and pavement
temperatures likely initially much warmer, the potential for
freezing rain accumulation on paved surfaces looks low. May have
ice accumulations of less than .1 on elevated surfaces overnight,
especially along the highway 30 corridor, but forecast confidence
too low this far out to go with an advisory at this time. Further
north, deeper into the cold air, where there will be less of a
warm layer aloft, the precipitation may change to snow by early
evening and remain snow until ending Saturday morning. This may
lead to up to 1 inch of accumulation of wet snow, especially
northeast of a line from Dubuque to Freeport. Far northeast MO,
southeast IA and west central IL will likely see just rain with
amounts roughly in a .10 to .25 range. All precipitation is
expected to end from west to east by mid morning Saturday,
followed by clearing skies late in the day with temperatures
returning to the 40s.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1211 PM CDT Thu Mar 15 2018

VFR conditions will be seen through 15z/16 as high pressure moves
into the eastern Great Lakes and a storm system moves out of the
Plains. After 15z/16 VFR conditions will slowly deteriorate to
MVFR as the storm system moves slowly across Missouri into
southern Illinois. Dry low level easterly flow may delay the onset
of precipitation and MVFR conditions until after 18z/16.




LONG TERM...Sheets
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