Area forecast discussion
National Weather Service Omaha/valley NE
1132 am CDT sun may 19 2013
Update...
a couple of vorticity maxima were noted on satellite and radar late
this morning...one lifting north into northwest Iowa...and another
moving northeast into north central Nebraska. Eastern vorticity was
taking showers and isolated thunderstorms with it...so expect a few
more hours of pesky showers in west central Iowa. To the
west...showers and thunderstorms were beginning to fire along a
spoke of vorticity around western center...bubbling up in our far
western County Warning Area. Not expecting anything major with these storms as
instability has remained in check due to lingering morning rains.
However instability is expected to increase markedly across a good
part of eastern Nebraska and western Iowa this afternoon as
southerly flow draws moistening low level air north and middle level
temperatures cool with approach of upper trough/low. Middle level lapse
rates greater than 8 c/km are expected. Rap cape forecasts suggest
surface based values will approach 2500 j/kg over the southern half
of our County Warning Area where sunshine is most likely and south of warm frontal
boundary slowly lifting toward or just north of Interstate 80 by middle
afternoon. Shear profiles will be weakening with time with approach
of upper/surface lows...but 40 to 50kt of 0-6km bulk shear is still
expected across southeast Nebraska through 00z..coincident with
relative maximum in cape field. And 0-1km storm-relative helicity
approaches 120. So at least moderate instability will bring a hail
threat to much of the southeast half of the County Warning Area...while shear
profiles are more favorable to a variety of severe modes farther to
the southeast. While tornado threat looks to be lower than what the
models showed yesterday...it is certainly not zero in far southeast
Nebraska.
Am expecting continued development of scattered thunderstorms
through the afternoon as broad ascent overspreads the area ahead of
upper low. A couple of clusters or lines could form from time to
time in our west or southwest County Warning Area and move northeast. But the best
severe threat will come later in the day...say after 4 PM...in
southeast Nebraska and southwest Iowa where warming/moistening will
occur outside of contaminated air to the west where intermittent
storms/clouds will tend to dampen threat of surface-based storms.
Dergan
&&
Previous discussion... /issued 641 am CDT sun may 19 2013/
Discussion...
have updated forecast for temperature trends as temperatures dip into the
lower 60s...as well as for precipitation trends. County Warning Area is currently
dry...with showers just southeast and just northwest...and both of
those areas weakening as showers approach. Think County Warning Area will largely
be dry through the morning...though did hedge with slight chance
probability of precipitation in the late morning in case some showers/isolated thunder
sneak into the area. Should see quick temperature recovery this
morning with relatively low cloud cover...and winds will return
out of the southeast as outflow from overnight convection mixes
out. Still potential for thunderstorms - including severe - this
afternoon and evening...particularly in the southeastern County Warning Area where
shear profiles are better.
Mayes
Aviation...
12z tafs for koma...klnk...and kofk.
Complex forecast again for the next 24 hours regarding timing and
location of thunderstorms and rain. Morning should be clear of
activity...with showers and thunderstorms increasing in the
afternoon. For now...have kept a fairly generic mention over a
broad time swath...but this is one of those cases where storms may
indeed linger in vicinity of airports for several hours. Timing of
storms may need to be adjusted though...as situation becomes more
clear. Storms would have potential to reduce visible and maybe
ceilings to MVFR briefly...with gusty winds also possible.
Activity should clear through during the evening...with lingering
showers through the night that are less likely to cause category
restrictions.
Mayes
Previous discussion... /issued 408 am CDT sun may 19 2013/
Discussion...(today through next sunday)
issued at 408 am CDT sun may 19 2013
The main forecast concern during this period is severe weather
potential this afternoon and tonight.
To start out the day expect generally drier weather once last
nights convection leaves the area in the next couple hours. This
dry weather should be short lived once the main upper low shifts
east into Nebraska this evening allowing a surface front to shift
across the area. Severe weather parameters indicate best potential
for severe weather is across far southeastern Nebraska where a
moderate risk for severe weather exists. Here...deep layer shear
values push 50 knots along with plenty of surface based
instability. The main severe weather threat in this area is large
hail...damaging winds and possibly a few tornadoes. Elsewhere the
severe weather threat is lower...but still remains. Away from the
moderate risk area hail and wind are the primary severe weather
threats.
For Monday and Tuesday the upper low lingers across the area. With
deeper moisture prognosticated over the northern half of the County Warning Area...have
favored higher precipitation chances there. Also temperatures will
be cooler with highs in the 70s on Monday and generally in the 60s
on Tuesday. Thereafter the cooler weather lingers until the upper
low finally departs on Thursday and high pressure is established
by the end of the week.
Djp
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
