Area forecast discussion
National Weather Service Omaha/valley NE
1232 am CDT sun may 19 2013
Aviation...
06z tafs for kfok...koma and klnk.
Although thunderstorm chances linger over the region through
Sunday afternoon/evening...19/06z forecast just carried mention
through 10z with initial round. After that residual moisture
could allow low clouds with IFR/lower range MVFR conditions
possible until daytime heating can improve conditions.
Howerver...mixing from continued showers/isolated thunderstorms would impact
that. Another round of convection expected Sunday afternoon and
evening.
Chermok
&&
Previous discussion... /issued 338 PM CDT Sat may 18 2013/
Discussion...
severe thunderstorm chances through Sunday evening are the primary
forecast concerns.
Western upper wave was drifting toward The Rockies this afternoon.
Strong southwest flow ahead of this system was overspreading High
Plains region...inducing cyclogenesis in southwest Nebraska and
western Kansas where skies had cleared. Strong instability has
developed ahead of this low with most unstable convective available potential energy running over
4000 j/kg from southwest Nebraska through central Kansas...just
ahead of dry line. Storm Prediction Center has just issued a Tornado Watch for these
areas covering western Nebraska through much of western into central
Kansas. For our area...broken middle level cloud cover has dampened
insolation this afternoon...holding temperatures in the lower 80s.
Overnight expect convection from western areas to roll east and
northeast across central into eastern Nebraska...and eventually
southwest Iowa...as low level jet pushing 40kt continues to pump
higher Theta-E air into our region. However...exact evolution of
western convection will have to be watched as several short range
models suggest a split in activity with one area lifting into
northeast Nebraska and another setting up over northern Kansas. But
others suggest a mesoscale convective system will roll right into eastern Nebraska late this
evening. At any rate...precipitation chances will be on the increase from
late evening on...with the threat of severe weather still there.
Models suggest elevated cape values will still be topping 2000 j/kg
as storms move in...so hail is certainly a threat. If storms do not
become elevated with time as expected...then winds could also be a
problem...especially during the late evening. Most likely areas for
severe would be near the Kansas border where a plurality of short
range ensemble members paint a swath of strong storms...or over
northeast Nebraska where several models point to mesoscale convective system track.
Activity should continue well past midnight before moving east of
our area Sunday morning. Looks like we could have a substantial lull
in activity during the morning before round two begins Sunday
afternoon. Upper trough will push farther into the plains...pushing
surface trough/low into eastern Nebraska and eastern Kansas.
Substantial instability will exist ahead of this boundary during the
afternoon...but shear profiles will be decreasing with time as we
head later in the afternoon owing to slackening gradient closer to
surface/upper troughs. Very steep low and middle level lapse rates on
the order of 8 c/km will exist over much of our area...and forecast
soundings show inhibition going away by middle to late afternoon. Mixed
layer cape values over 2500 j/kg are prognosticated over much of our
area...with 0-6km shear around 40kt. So supercells look likely with
large hail and damaging winds certainly...but tornado potential is
still in question. Low level shear is most pronounced in our far
southeast County Warning Area...but any warm frontal boundary that rotates north
around surface low will be a candidate to focus tornado threat as
well.
Severe threat will last through the evening before surface boundary
shifts east and focuses storms more in Iowa and Missouri. However
upper low cutting off just north of Nebraska and lingering middle
level instability will bring continued thunder chance into Monday.
That low will remain in our area through at least middle
week...bringing off and on showers and isolated thunderstorms along
with cooler temperatures. It looks like a warming trend is in store
for late in the week as upper low finally moves east and heights
begin to rise.
Dergan
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
