Area forecast discussion
National Weather Service Omaha/valley NE
251 PM CDT Tuesday Jun 18 2013
Discussion...
morning showers/thunder have given way to a fair weather day across
the area. Subjective 12z upper air analysis indicates upper-level
ridging continuing to build over The Rockies/High Plains...with
shortwave across WI/Iowa that helped generate morning activity...as
well as another embedded shortwave in western Nebraska/eastern Colorado...and
with a deepening trough creating 500mb height falls up to 60m along
the Pacific coast. Upper-level jet streak extended from eastern Iowa
into New England...with jet segments coming ashore in or and in
Southern California. Higher 700-500mb lapse rates were located from Colorado/Wyoming
westward into The Rockies. High pressure at 850mb was centered in
Kansas...with temperatures warming into the 20s c as far east as klbf...and
with 8c+ moisture returning up to southern Nebraska/southern Iowa. Surface
high at 18z was centered in southeast Nebraska/soutwhest Iowa...with return
flow across central/western Nebraska. Area of rain showers/thunderstorms and rain was still
festering just south of the Kansas/Nebraska border.
Main forecast concern is convective potential on Wednesday/Wednesday
night/Thursday morning...followed by warming temperatures through
the weekend and into next week along with whack-a-mole thunderstorm
chances. Models still differ substantially on timing and extent of
thunderstorms on Wednesday through Thursday. NAM/4km WRF keep the
area dry tonight and much of Wednesday...with just scattered
convection after 00z Thursday that grows upscale in central Iowa. GFS
has some scattered convection on Wednesday afternoon...with broader
swath to the west in the evening and to the east and south
overnight. European model (ecmwf) also develops convection along the river in the
afternoon...which dies quickly in the evening...followed by
convection along the river again on Thursday morning. Sref ensemble
members are all over the map...ranging from the drier side to wetter
Wednesday afternoon/evening to wetter Wednesday night/Thursday
morning. Overall...confidence is low...but leaned closer to NAM/GFS
compromise. Kept Tuesday night and Wednesday morning dry as height
rises move out of the area...with shortwave approaching by Wednesday
afternoon. Went with a slight chance in the afternoon as wave
approaches and chances in the evening for possible upscale
growth...tapering to slight chance north/chance south after
midnight. Included a slight chance mention on Thursday morning east
of the river. Again...confidence would be on the low side...but
think Thursday will remain dry across the area much of Thursday and
Thursday evening once that activity moves out. Could see the
potential for an mesoscale convective system moving southeast out of South Dakota to skirt the
northeast County Warning Area Thursday evening/night...and have kept slight chance
probability of precipitation up there.
For Friday through Monday...have played closer to the European model (ecmwf)
scenario...which keeps the County Warning Area capped during the day with the
potential for nighttime convection. Think the biggest threat would
be on Sunday evening/Sunday night...as a weak front slips across the
County Warning Area and provides some convergence...while a shortwave seems likely
to eject across the County Warning Area. By Monday...risk is too low for storms
with any kind of diagnosable coverage to put in probability of precipitation at this time.
Have increased temperatures a degree or two through the extended to get
away from the tendency for guidance to steer toward climatology...as
mex guidance remains in the 90s in most places...and GFS/European model (ecmwf)
indicate 850mb temperatures consistently in the 20s and warming
to the middle 20s c late in the period.
Mayes
&&
Aviation...
18z tafs for koma...klnk...kofk.
Precipitation continued to decrease in coverage as of just after noon near
the taf sites. Expect that clouds will decrease through the afternoon.
VFR conditions should prevail until late tonight when some 4-6
mile visibility restrictions will be possible.
Miller
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
