Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Omaha/valley NE
1156 PM CDT Friday Aug 29 2014

Short term...(tonight through monday)
issued at 300 PM CDT Friday Aug 29 2014

Other than lingering convection this evening main focus in short
term will be thunderstorm chances/strength on Sunday as active
pattern to persist through period.

Afternoon satellite imagery showed upper trough moving into
extreme eastern Nebraska with Pivot Point nearing Missouri River
as of 19z. Trough should be kicked eastward fairly quickly this evening
by upstream wave fast approaching northwest nebr. But besides current
convection ongoing to eastern nebr wave...may have to account for some
upstream convection...which had not yet developed as of
19z...working toward northwestern zones for a few hours this evening and some
last minute changes probable. With moisture plenty and wave
tapping some moisture off of Gulf system...slow movement could aid
in a few locations receiving heavy rain. However...given
moderately light deeper shear values present and clouds/earlier
convective overturning keeping ml cape values modest...severe
threat probably remaining isolated at best. That said...per Storm Prediction Center Maryland
1633 with low level cape and vorticity present with upper trough a
brief tornados not impossible ... if clear slot into southeastern nebr at
19z would allow it to further destabilize before being overrun by
clouds/light showers to the west. Plan on generally ending most
probability of precipitation by 06z. Little/no changes to lows tonight and with residual
moisture and light winds left in late night fog.

Short wave ridging ahead of next trough should bring a dry and
warmer day on Saturday and again little/no changes to temperatures. Left
in small late night probability of precipitation northwestern zones Sat night as low level
jet/warm advection increases ahead of next trough.

Although elevated convection could persist into Sun afternoon aided by
low level jet...per NAM/GFS...12z European model (ecmwf) generally kept area dry
until 00z Monday when strong upper jet punches into region on
south side of this next upper trough. Due to uncertainty in amount
of elevated convection preceding main late afternoon/evening
development left in morning probability of precipitation northwest 2/3rds and did not break up
the afternoon period to account for possible higher chances late in
the afternoon. Did boost maximum temperatures a few degrees south on Sunday as
that area did seem the less susceptible to impact of morning warm
advection clouds possible precipitation. Strong/severe storm chances appear
higher than past several days as 0-6km shear is stronger and maximum
temperatures nearing 90 should increase MLCAPE values. Although heavy
rain will likely occur with the activity as well...very hard to
pin down where axis of heaviest will occur as a case could be made
for it setting up just about anywhere in or even possibly just
outside the forecast area.

Although Labor Day will be kept dry for now...outside a lingering
morning mention far moving flow will allow approach of
next wave by afternoon in northwest nebr. Also front shoved south with
Sunday/S wave could stall out Monday afternoon before attempting to
lift north Monday night. Both of these items could allow some
additional inclusion in probability of precipitation in latter forecasts for Labor Day.

Long term...(monday night through friday)
issued at 300 PM CDT Friday Aug 29 2014

Because of aforementioned setup described above...small probability of precipitation were
included all zones Monday night and across the southeast on Tuesday.

Otherwise building upper heights with jet shifting farther north per
12z European model (ecmwf)/GFS lent itself to a dry forecast Wednesday along with warming
temperatures. Although prior forecast/00z models suggested a
continuation of the dry forecast Thursday...which was maintained...latest
GFS/European model (ecmwf) allowed a front to work into the northern zones at least on
Thursday as an upper wave dropped southeast through Canada. The new day
7 will include precipitation chances with this scenario and if trends
would persist...probability of precipitation may eventually be inserted to Thursday period as
well...especially north.


Aviation...(06z tafs for kofk...klnk and koma.)
Issued at 1153 PM CDT Friday Aug 29 2014

With showers dissipating over eastern Nebraska...only scattered
middle and high clouds are expected overnight. However areas of fog
and stratus are expected to form after 08z at all taf sites. Ceilings
between fl005 and fl012 with visibilities 1-2sm are likely 08z to 15z.
Then scattered clouds and light northwest winds are forecast for
the majority of the period after 15z.


Oax watches/warnings/advisories...


Short term...chermok
long term...chermok

National Weather Service Glossary of Abbreviations