Area Forecast Discussion

FXUS63 KDVN 172123
Area Forecast Discussion
National Weather Service Quad Cities IA IL
323 PM CST Sat Feb 17 2018
Issued at 323 PM CST Sat Feb 17 2018
The upper level shortwave and associated quick burst of 1 to 2
inch snowfall was exiting into the western Great Lakes at mid
afternoon. At the surface, winds were turning northwest behind the
surface trough located roughly along the Mississippi River. A
surface high over the Dakotas will migrate southeast into the
forecast area under the progressive flow aloft, bringing a period
of quiet weather for the near term. 
.SHORT TERM...(This Evening through Sunday)
ISSUED AT 323 PM CST Sat Feb 17 2018
Main focus is on temperatures and potential for fog tonight, then
magnitude of warming Sunday as a strong warm advection return 
flow develops in the wake of the passing high. 
Low level moisture from the fresh snow cover and late afternoon
melting snow will enhance the likelihood for fog tonight as the 
surface ridge passes between 06z and 12z. Will go initially with 
"patchy fog" to "areas of fog" wording over roughly the northern 
2/3rds of the forecast area, which appears most favorable for fog 
formation. Mostly clear skies and fresh snow should allow enough 
radiational cooling to reach guidance temperatures from the upper 
teens north to mid 20s south.
Sunday: There may be some lingering fog over especially the east
and southeast until about mid morning, before surface winds
sufficiently increase and become southerly. For now, will have 
the fog dissipating by 8 am, but this may be too early. Otherwise,
the tightening pressure gradient will lead to south winds at 
least 15 to 25 mph by midday with associated mixing and warm air 
advection to conservatively push temperatures to highs in the 40s 
north to lower 50s in the far south .
.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 323 PM CST Sat Feb 17 2018
Active weather pattern for the Midwest early in the week. Locally, 
several rounds of precipitation are likely, some of which could be 
moderate to heavy.
A warm front will lift northward through much of the forecast area 
causing temperatures to rise into the 40s and 50s with 60s south of 
I-80. There is uncertainty on how far north the warm front will make 
it. The ECMWF is the warmest model. If the CMC/NAM/GFS continue with 
the colder NE flow in the northwest forecast area, will have to 
trend highs downward in that area.
Isentropic lift and significant 850mb WV transport will lead to 
periods of showers and embedded thunderstorms through Monday night. 
Forecast PWATs near 1.25 inches are highly anomalous at 3 standard 
deviations above the mean for the middle of February. This amount of 
moisture raises concerns for widespread rainfall amounts near and 
over 1 inch. Areal flooding is possible due to runoff over frozen 
ground. Additionally, break up ice jams could lead to some river 
Late Monday Night and Tuesday
As colder air filters in on NW winds behind a cold front, 
temperatures are forecast to fall below freezing across the west and 
northwest, which will lead to a period of freezing rain. The model 
blend ice amounts of 0.10 to 0.25 inches west of a line from western 
Dubuque County to Cedar Rapids to Sigourney seem reasonable at this 
juncture. However, this ice forecast is subject to change since it 
is days away. It's also worth a mention that the freezing rain (and 
possibly some sleet) may spread to the east toward the Mississippi 
River into Tuesday afternoon and evening before it ends. Will have 
to continue to monitor this period for potential winter headlines. 
Drying out as the cold front shifts to our east. The ECMWF is an 
outlier with widespread light snow moving in from the southwest for 
Wednesday evening and night. For now, will keep forecast dry. Highs 
will be slightly below normal.
Thursday on
Moderating temperatures to near or slightly above normal to end the 
week. From Friday into Saturday, active southwest flow aloft will 
likely bring more widespread precipitation into the area. Uttech
.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1150 AM CST Sat Feb 17 2018
A fast moving upper level shortwave will bring a 1 to 3 hour round
of moderate to heavy snow early this afternoon. This will result
in IFR conditions and possible LIFR, which is mentioned in the
terminals. An improvement to VFR is likely by evening, but the
confidence in the timing of this transitions from IFR to MVFR to 
VFR is below average. VFR conditions then follow overnight into
Sunday morning. 
LONG TERM...Uttech