Area forecast discussion
National Weather Service Omaha/valley NE
1119 PM CDT Wednesday Jun 19 2013
Aviation...
06z tafs for koma...klnk...kofk.
VFR conditions expected through the period. Isolated storms
possible after 12z as warm front lifts north out of Kansas.
&&
Previous discussion... /issued 305 PM CDT Wednesday Jun 19 2013/
Short term...tonight through Thursday.
The primary forecast concerns in this period are potential for thunderstorms
and temperatures.
The large scale pattern at 12z featured a fairly strong 300 mb jet
segment of around 95 knots punching down toward central California.
A closed low at 500 mb was just offshore from Oregon. 12 hour
height falls of up to 120 meters were noted with the trough over the
far western US. Weak ridging was noted over the plains. This ridge
extended far to the northwest back into Alaska. A thermal ridge at
700 mb extended from The Four Corners region into Montana. At 850 mb
a band of dewpoints of 10 c or higher extended from West Texas up
into central North Dakota.
As can be typical this time of year...potential for convection is
not overly clear. Several of the short range models have been keying
on two areas for weak storms this evening...one in the southeast
part of our forecast area and one in the northwest. So...tried to
adjust probability of precipitation toward that thinking. Also...some activity could develop
over the High Plains and move east late tonight...similar to what
the 12z runs of the GFS/Canadian/NAM model suggest. This general
model blend scenario was kept into Thursday. Kept probability of precipitation 20-35 percent
in the morning then decreased chances from west to east during the
day as activity moves through the area. Depending on timing of precipitation
and cloud cover... highs could be affected. For now...went with 87-
90 in our western counties and 85-87 east. Highs in western Iowa
would likely be very late in the afternoon.
Miller
Long term...Thursday night through Wednesday.
Models show various solutions from late this week into the weekend
and confidence on any given model is not high. Will tend to go with
somewhat of a blend...giving the European model (ecmwf) and general large scale
pattern recognition the most weight.
Some severe storms appear possible Thursday evening/Thursday night
based on 12z NAM output. That model developed storms over the
Dakotas in the afternoon...which progess southward Thursday evening.
Instability and shear will be adequate for storm organization if
they develop...but confidence is not high. Pattern starts to turn a
bit warmer Friday...which may tend to force most of the convective
activity north of our area due to warmer middle level temperatures.
We should see a pattern change by the end of this period. A Rex
block over the Pacific northwest and western Canada Friday will
slowly weaken through the weekend. Our area remains in southwest middle
level flow...and timing shortwave energy moving out into the plains
to trigger convection will be difficult at least through the
weekend. Early next week...a 500 mb trough should develop out along
140 degrees west longitude...which then should help lead to downstream
development of a broad ridge from the southwestern US into the High
Plains. If that scenario does verify...it would normally lead to a
hotter and drier pattern for our area.
Miller
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
Fobert
