Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 240042
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
642 PM CST Mon Jan 23 2017

.SHORT TERM...(tonight through Thursday)
Issued at 330 PM CST Mon Jan 23 2017

...Significant Winter Storm Set to Impact the Area Tuesday into
Wednesday...

The 12Z subjective upper air analysis indicated a a seasonably
strong 150 kt H25 jet from southern CA into the central Plains.
This was associated with a potent mid and upper level shortwave
trough, which had 100-150 m H5 height falls this morning over the
southwestern US. Downstream there were steep H7 to H5 lapse
analyzed over the high Plains with delta-t values of 20+ C.
Models still have a fair amount of uncertainty with regards to the
synoptic/mesoscale evolution as this system emerges onto the
Plains on Tuesday. The GFS continues to be slow to develop a closed
mid-level circulation, slower to deepen the system, and farther
north. Although the track of the system appears in the realm of
possibility given the ensemble guidance, given the weak static
stability it appears that the GFS model is to slow to deepen the
circulation. Thus we continue to prefer a consensus of the
UK/EC/CMC/NAM.

This evening should start off quiet, but low-level WAA will
increase after midnight and eventually lead to showers developing
along the H85-H7 warm front. This area of precipitation will
increase in coverage as it lifts to the north toward the SD
border on Tuesday morning. We should also see a marked increase in
precipitation intensity as stability decreases on Tuesday morning.
Exactly where this strong frontogenetic band becomes nearly
stationary is likely where the heaviest of the snow will fall, and
currently this appears to be over the highway 20 corridor and
north into SD. During the afternoon we should see additional
development farther south as the strong CDPVA in the H7 to H4
layer increases. This will likely be rain south of I80, but maybe
a mix of rain and possibly some sleet showers north of I80. As we
get into Tuesday evening we will see the rain and snow line start
to collapse south toward I80 as cooler air works into the region,
while the deformation snow band continues in the northern CWA. We
will also see winds increase later on Tuesday afternoon, and
especially into the evening as the surface low tracks into
southern IA. Winds of 15 to 25 MPH with gusts to near 30 MPH
likely.

Again, given the small differences in the track of the system and
how weakly stable the atmosphere is there remains considerable
uncertainty to the forecast. The CMC would develop another
frontogenetic band within the highly unstable air near the I80
corridor on Tuesday evening with saturation that appears to start
lower and work vertically. Although given the static stability
this is possible, we are discounting this for now with the lack of
baroclinicity in the area of this band in the CMC. Also decreasing
forecaster confidence is some of the higher resolution guidance
would lift the initial frontogenetic band farther north into SD/MN
(similar to the GFS), which is also possible as models tend to
concentrate the lift in these bands to low in the atmosphere. That
said we are less than 18 hours from the start of the event, and
thus will make some adjustments to the headlines. We will upgrade
the watch to a warning where we have our highest confidence of 6+
in of snow as well as some blowing and drifting. We will issue a
buffer advisory south of the warning for 2-5 in and some blowing
and drifting. But some adjustments to these are possible or even
likely with time.

.LONG TERM...(Thursday night through Monday)
Issued at 330 PM CST Mon Jan 23 2017

This system in the short term will lead to a pattern shift across
the CONUS with the flow pattern become northwest for the central
and northern Plains. This will likely lead to a drier pattern, but
also quiet variable with temperatures. Current extended will have
a dry forecast with near seasonable temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 637 PM CST Mon Jan 23 2017

Pockets of IFR cigs across the area at the start of the period.
IFR conditions are expected to decrease to LIFR by 06Z then LIFR
conditions should remain through the rest of the forecast period
as winter storm system moves into the region.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 3 AM Tuesday to 9 AM CST Wednesday
     for NEZ030>034-042>044-050.

     Winter Storm Warning from 3 AM Tuesday to 9 AM CST Wednesday for
     NEZ011-012-015>018.

IA...Winter Weather Advisory from 3 AM Tuesday to 9 AM CST Wednesday
     for IAZ043.

&&

$$

SHORT TERM...Boustead
LONG TERM...Boustead
AVIATION...Fobert



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