Area forecast discussion
National Weather Service Omaha/valley NE
1128 PM CDT sun may 19 2013
Aviation...
06z tafs for kofk...koma and klnk.
An upper low from north central nebr into western South Dakota will continue to circulate
over the region through Monday. Showers and isolated thunderstorms
and ceilings at times around 1-2k feet above ground level will rotate around the
system tonight...probably mainly just impacting kofk. At this time
it appeared surface winds rotating around system will continue to
feed lower level dry air toward lnk and Oma. However...if winds
remain light enough much of the night...some fog could form later
tonight at those sites. Heating on Monday could cause additional
shower and isolated thunderstorm development. Coverage of thunderstorms Monday afternoon
was uncertain and only a prob30 in showers were mentioned in 06z
forecast.
Chermok
&&
Previous discussion... /issued 342 PM CDT sun may 19 2013/
Discussion...
short term forecast concerns will be ongoing severe weather then
lingering thunderstorms later tonight and shower and
thunderstorms with the cyclonic flow around the slow moving 500 mb low
over the Dakotas through Wednesday.
As of middle afternoon...have a couple of tornado watches in effect
for parts of southeast Nebraska into western Iowa.
The morning oax sounding...we still had around 1 inch of
precipitable with steep middle level lapse rates of 7.6c/km. At
h300...there is an extended 90-110kt jet from the West Coast to the
Texas Panhandle. This jet is forecast to progress across Oklahoma
today and curve northeast to Iowa and Minnesota tonight...with upper
level divergence from northeast Kansas...then Missouri to eastern Iowa
and Wisconsin overnight. The 500 mb low was centered over Wyoming and South Dakota
with areas of vorticity rotating northeastward around the low through
the 500 mb flow. The area of low pressure over Wyoming is forecast to
Dumbell...and rotate into Nebraska and then northeast again into
eastern South Dakota...and then North Dakota during the day Monday.
This will cause height falls over the plains today...the upper
Midwest tonight and the upper Mississippi Valley Monday. At 700 mb/800 mb
these were nearly stacked areas of low pressure centered over the
South Dakota/ND border with low pressure extending southward toward the Nebraska/Kansas
border. The capping 700 mb temperatures were well to the south in OK
and southern MO and the belt of stronger 850 mb 45 to 50 knots winds
stretched from Texas toward Missouri. The swath of deeper moisture
extended from Texas across OK into Kansas with pockets in Nebraska.
By the start of the evening period...instability is expected to
range from 1000-2500j/kg with 0-6km bulk shear of 30 to 55kts
over the southeast third of the forecast area. Per the Storm Prediction Center
mesoanalysis...the most unstable surface based instability was
located over south central Kansas at 2030z. Complex short wave
energy will pivot northeast and rotating around the 500 mb lows. We
have one line of thunderstorms moving through now...however instability
will continue to be drawn northward into the early evening hours.
The general southwest to northeast flow will veer more with time
then drying of the deep moisture with an eastward shift of the
organized severe weather. That being said...moisture will continue
to rotate around the upper with some shower and thunderstorms
activity rotating back into parts of the area overnight. The middle
tropospheric low will remain over the Dakotas Monday and Tuesday
and will will keep the area under the risk for showers and
isolated thunderstorms. Highest probability of precipitation will be over northeast
Nebraska during this time frame. Monday through Wednesday will see
cooler temperatures will highs in the 60s and 70s.
During the extended as another cyclone spins over the Pacific
northwest...deeper moisture will return to the plains. This too is
a slow moving system and will bring showers and thunderstorms to
the region Friday into Sunday.
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
