Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Omaha/valley NE
632 am CDT Sat Apr 18 2015
Short term...(today through monday)
issued at 351 am CDT Sat Apr 18 2015
The chance for showers and thunderstorms through Sunday is the
primary forecast concern.
Upper low continued to spin across southern Colorado this morning...
and was making only slow progress to the east. Models are relatively
similar in moving low into the High Plains of Kansas this evening
before it opens up and swings through Kansas on Sunday as kicker low
drops southeast into southern Manitoba.
Ahead of the low this morning...plume of middle level moisture agitated
by sheared vorticity in warm advection Wing was leading to scattered
showers and thunderstorms from central Kansas into central and
western Nebraska. A few isolated showers were noted farther east
over our area. All activity was generally lifting north or
northwest...with no real push into eastern Nebraska as of yet.
Combination of radar and satellite trends...along with a blend of
short-range mesoscale models...suggests middle level moisture plume and
associated convection will rotate north and northeast this
morning...sweeping through eastern Nebraska and western Iowa. Best
coverage of storms will occur in northeast Nebraska with a more
scattered look to showers and isolated storms as we move southeast
of there. Most of this activity should be moving northeast of our
area in the early afternoon when focus of additional development
moves west with approaching middle level low and developing surface
That additional development will be conditional on amount of
clearing and subsequent instability seen in central sections of
Nebraska and Kansas. NAM is most aggressive in this regard and is
the odd model out in developing convection in central Nebraska near
surface circulation and along warm front extending into our western
County Warning Area. GFS/European model (ecmwf) and convection-allowing mesoscale models suggest
capping will hold in most of Nebraska...and instead developing
storms along dryline in Kansas. Expect this to be the the likely
scenario...but if storms do fire as NAM indicates there will be an
increased tornado risk in area of maximum low level shear/helicity
along warm front. Expect storms to fire by late afternoon in south
central Nebraska and central Kansas and lift north and northeast
with time during the evening. Again it looks like northeast Nebraska
will see the brunt of activity...with at least a small chance for
severe...with more hit and miss storms across the rest of the County Warning Area
during the evening.
After midnight...cold front will begin pushing toward northeast
Nebraska...and is expected to approach Interstate 80 by sunrise
before sweeping southeast of the County Warning Area during the morning.
Thunderstorms will be possible along and ahead of the front with
showers behind into the afternoon. Otherwise decreasing rain chances
are forecast Sunday afternoon with increasing northwest winds.
Much cooler air settles into the region Monday as European model (ecmwf) shows sub-
zero 850 temperatures and brisk northwest winds. Expect highs Monday
afternoon to remain in the 50s.
Long term...(monday night through friday)
issued at 351 am CDT Sat Apr 18 2015
Somewhat cool temperatures are expected during the week...with
increasing chances for precipitation by late week.
Northwest middle level flow will dominate the weather across the
Central Plains through middle week as upper low slowly trudges east
into the northern Great Lakes. While ripples in this flow could
bring a scattered shower...the main weather story will be our cooler
airmass remaining in place at least through Wednesday. Should see
lows in the 30s and highs perhaps topping 60 Tuesday and Wednesday.
A reinforcing cold front settling along the Kansas border is
forecast to lift back to the north Wednesday night and Thursday as
shortwave upper ridging moves into the plains. Could see scattered
showers or storms along this front as it lifts north. However better
chances for storms come Friday as upper low ejects through The
Rockies into the plains. There are sure to be timing issues with
this system...so pinning down timing/severity of convection risk
will have to be worked out with time.
Aviation...(12z tafs for kofk...klnk and koma.)
Issued at 630 am CDT Sat Apr 18 2015
Variable conditions are expected through much of the period as
upper low over Colorado tracks east with cold front moving in
after 06z. Periods of thunderstorms likely with timing of events
the main challeange.