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FXUS63 KARX 301853

Area Forecast Discussion
National Weather Service La Crosse WI
153 PM CDT Sun Apr 30 2017

.SHORT TERM...(This evening through Tuesday night) 
Issued at 153 PM CDT Sun Apr 30 2017

Early this afternoon, water vapor satellite imagery and surface
analysis showed a large, almost vertically stacked system over
southern Kansas. Local and regional radars showing two main bands
of precipitation, one from northwest Wisconsin into eastern
Nebraska and the other from central Illinois across southern Iowa
and northern Missouri into Nebraska and Kansas. In between these
two bands, not much was happening other than some occasional very
light showers or sprinkles.

The 30.12Z models are in agreement in maintaining the upper level
low as a closed system as it lifts northeast across the Great
Lakes and into southern Ontario late Monday night into Tuesday
morning. This will take the surface low from northeast Kansas
across eastern Iowa to northeast Wisconsin through Monday
afternoon. Several short wave troughs will rotate around the upper
level low and are expected to bring moderate to at times strong pv
advection in the 500-300 mb layer across the area overnight into
Monday morning. The best low level moisture transport will occur
this evening when this will be aimed right into the forecast area.
This will then move off to the east overnight but start to bend
back to the northwest around the upper level low and feed into the
deformation band. The frontogenesis with this system will be deep,
extending from the surface up to 300 mb, and be moderate to at
times strong in strength. This will start to move in late this
afternoon and then remain over the region tonight. The upper level
portion of this will move off to the northeast Monday while the
low level, 1000-700 mb layer, will be weak but linger over the
area through Monday. On the 290K isentropic surface, the up glide
will arrive in conjunction with the frontogenesis and should be 
on the order of 2 to 5 ubar/s this evening. This will diminish 
overnight into the 1 to 2 ubar/s range overnight and then continue
into Monday morning as the trowal wraps around the upper level 
system tonight and then moves across the region. With all this 
forcing, expecting the band of showers across Iowa and Missouri 
to lift into the area this evening and then move across the area 
through the night. Even though the forcing will be much weaker 
Monday, still expecting an prolonged period of light rain as the 
frontogenesis and trowal/isentropic up glide moves across the 
area, but there may not be a lot of QPF with amounts generally 
under a tenth of an inch. There may still be a little bit of 
lingering precipitation into Monday night when enough cold air 
works in that some snow could mix in with the light rain. Not 
expecting any accumulation as amounts will be very light. All the 
precipitation will then end Tuesday as the system moves off into 

.LONG TERM...(Wednesday through Sunday) 
Issued at 153 PM CDT Sun Apr 30 2017

Northwest flow will be established behind the current system. This
will allow a short wave trough topping the western upper level
ridge to move over the Missouri River Valley Wednesday. This will
then form another upper level low over the middle Mississippi 
River Valley Wednesday night that then lifts northeast through the
Ohio River Valley Thursday and Thursday night. Some showers from 
this system could impact the area from Wednesday afternoon into 
Thursday before the forcing shifts well away from the area. The 
rest of the week then looks dry as the upper level ridge shifts 
east over the Midwest.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1218 PM CDT Sun Apr 30 2017

Low pressure over the Southern Plains will rotate northeast into
the region tonight. Moisture surging around this system will
spread showers and isolated thunderstorms into the area by later
this afternoon into this evening. Was not confident enough to
include thunderstorms in the TAFS as storms will be isolated in 
coverage. The bulk of the rain looks to push north of the 
KRST/KLSE sites after midnight. Otherwise, look for MVFR 
conditions early this afternoon to deteriorate into IFR/LIFR 
conditions as cloud ceilings/visibility come down with the 
approach of the storm system. Gusty northeast winds are expected 
to become light and variable after midnight as the surface low 
moves in overhead. This low will remain overhead for Monday for 
scattered showers amd continued IFR conditions.



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