Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 300844
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
344 AM CDT Sun Apr 30 2017

.SHORT TERM...(Today through Tuesday)
Issued at 344 AM CDT Sun Apr 30 2017

...Late Season Winter Weather Event Expected for Northeast
Nebraska...

Impressive mid-level cyclone was seen early this morning on water
vapor imagery over far southwest OK/eastern TX panhandle. This
system and associated 230 m H5 height falls will track northeast
today and into Iowa by Monday morning. Models continue to be in
excellent agreement in the synoptic scale features of the system,
but differences remain in the important details of low-level
thermal profile. For this forecast package we used a compromise of
the NAM/EC for thermal profiles as it appeared the GFS was to warm
near the surface given current temperatures and dew points. Best
forced ascent/PV advection early this morning was located over
western KS where some lightning is currently being reported with
the precipitation. Downstream from this area of lift was strong
low-level thermal advection leading to isentropic ascent and areas
of generally light rain. This current area of rain may tend to
lift off to the northeast late this morning with a short break
before the large-scale ascent associated with the cyclone shifts
northeast into the area. KOAX 88D indicates the freezing level
generally starts around 3500 ft, which agrees pretty well with the
latest high-resolution guidance. Thus as the precipitation
continues to spread northwest this morning we will likely see the
freezing level drop due to wetbulbing. This will likely result in
some sleet or light snow mixing with the rain around BVN/NLG and
potentially OFK, but no accumulations are expected this morning.

By mid to late afternoon today we will see a well-defined
deformation band set up from central NEb into northern IA with a
dry slot working into southeast NEb and southwest Iowa. Intense
vertical motion indicated in the models is likely responsible for
the afternoon temperature drop in our northwest CWA, but this
seems reasonable given the dynamics. As this occurs we will likely
see sleet and snow mix back in around 20-21Z time frame.
Accumulations will be difficult during the afternoon with the high
sun angle, but during the evening we should see more widespread
snow with potentially some impressive snowfall rates. Cross
sectional analysis indicates weak static stability wrapping around
the low into northeast NEb with some upright convection not out of
the question on the edge of the dry slot. This is when we should
see the bulk of the snow accumulations. There is low confidence in
the amount of snow that will accumulate due to a number of
reasons. Nevertheless given the vertical motion along with that
the max lift is generally occurring near or after sunset there is
the potential for some significant accumulations. We will issue a
winter weather advisory for 2 to 6 inches of snow. We will also
see north/northwest winds of 15 to 30 mph, but we generally feel
that snow may blow around while falling, but will be to wet for
lofting/drifting once on the ground. If the higher end snowfall
accumulations are realized there is some potential for tree damage
though as many of the trees have leafs. As mid-level saturation
increases again late tonight as the dry slot shifts east we will
likely see the rain/snow line advance southeast, potentially
reaching the I80 corridor by Monday morning but accumulations are
not expected that far south. Precipitation may end as a bit of
light rain on Monday morning, but all areas will likely be dry by
afternoon with brisk northwest winds behind the system.

Northwest flow is expected to develop behind this system with a
couple of weak weather systems affect the central Plains. The
first of these will pass through the area on Tuesday with some
slight chance of showers, but much of this activity is expected to
be south and west of the FA.

.LONG TERM...(Tuesday night through Saturday)
Issued at 344 AM CDT Sun Apr 30 2017

The next system in the northwest flow will move into the area on
Wednesday and bring a chance of showers to the area with continued
well below normal temperatures. Heights will then be on the
increase to end the work week and into next weekend. By next
weekend most global models agree in a blocking pattern setting up
with a ridge over the central US. This will likely lead to
temperatures returning to near normal values and dry weather.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1140 PM CDT Sat Apr 29 2017

Ceilings remained in the VFR category at KOFK during the evening,
but this should change overnight. Conditions should deteriorate at
KLNK and KOMA overnight, into the IFR category and then remain
about same through the day. North/northeast winds will be somewhat
gusty. For now, only mentioned a R/S mix at KOFK in the evening.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 7 PM this evening to 9 AM CDT
     Monday for NEZ011-016-030.
IA...None.

&&

$$

SHORT TERM...Boustead
LONG TERM...Boustead
AVIATION...Miller



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