Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 152312

Area Forecast Discussion
National Weather Service Omaha/Valley NE
612 PM CDT Fri Sep 15 2017

.SHORT TERM...(Tonight through Monday)
Issued at 317 PM CDT Fri Sep 15 2017

A prominent vorticity maximum over the northern High Plains this
afternoon will weaken as it translates northeast across the
western Dakotas tonight. The trailing influence of this
disturbance is presently tracking through central into eastern NE,
and is responsible for weak elevated convection ongoing across the
area. Meanwhile, a related surface low over southeast SD as of
20z will continue northeast into MN tonight while an associated
cold front edges southeast into the forecast area.

Strong boundary-layer heating ahead of the cold front is
contributing to deepening cumulus development from north-central
into western NE. Current SPC mesoanalysis data indicate that the
cap is weakening along the boundary with warm-sector mlCAPE vales
of 1000-1500 J/kg. Latest convection-allowing model guidance is
suggestive that widely scattered storms will eventually develop
late this afternoon into evening with this activity potentially
affecting portions of northeast NE. Given the presence of steep
low to mid-level lapse rates and modest vertical shear, the
potential will exist for a strong storm or two capable of gusty
winds and perhaps some hail.

Persistent warm advection and isentropic upglide along a
nocturnal LLJ will support a continued chance of thunderstorms
overnight; especially over the northern half of the forecast

On Saturday and Saturday night, another strong shortwave trough
will eject from the northern Rockies into the northern Plains,
depressing the mid-level height field over the mid-MO Valley.
This will encourage the southward advance of the surface cold
front through the area with afternoon temperatures ranging from
the upper 80s over southeast NE to mid 60s north of the boundary
across northeast NE. The warm and humid conditions ahead of the
front will fuel thunderstorm development by mid to late afternoon
from portions of western IA into southeast NE. A few of these
storms could be severe and capable of large hail and damaging
winds. The showers and storms should taper off from north to south
on Saturday night as the front shifts south of the area.

Sunday and Sunday night, surface high pressure will quickly build
through the area ahead of a deepening lee trough over the High
Plains. Strengthening low-level warm advection on the backside of
the high will support increasing clouds through the day with highs
ranging from upper 70s south to around 70 north. Shower and
thunderstorm chances will increase Sunday night as the warm
advection is augmented by the approach of a low-amplitude
shortwave trough from the High Plains.

It appears that showers and thunderstorms will continue across
parts of the area through at least the first part of Monday with
the arrival of the aforementioned shortwave trough. High
temperatures will be affected by how quickly the clouds and
precipitation clear with readings in the mid 70s to lower 80s
currently forecast.

.LONG TERM...(Monday night through Friday)
Issued at 317 PM CDT Fri Sep 15 2017

An active weather pattern will persist through the long-term
period with a strong shortwave trough moving through the northern
and central Plains Tuesday night into Wednesday, and potentially
another system affecting the region by the end of the work week.
A surface front will oscillate back and forth across the area,
supporting a chance of showers and thunderstorms, especially from
Wednesday night into Friday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 612 PM CDT Fri Sep 15 2017

The aviation weather will be more active than it has been
recently. Low clouds are likely to fill in behind a cold front
that will be pushing through eastern Nebraska through Saturday.
TSRA possible this evening, mainly at KOFK but we could see
isolated activity at all three TAF sites later tonight. Did
mention some LLWS just at KLNK and KOMA for now, where low level
jet may be the strongest. Winds will shift to north or northwest
with the frontal passage.




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