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Area forecast discussion
National Weather Service Hastings NE
656 PM CDT Sat Apr 19 2014
Short term...(this evening through sunday)
issued at 352 PM CDT Sat Apr 19 2014
..multiple episodes of thunderstorms will bring needed rainfall tonight
into tomorrow will minimal threat of severe...
Aloft: westerlies were split over the Continental U.S.. the fairly zonal
branch along the US-Canada border will remain stronger and more
progressive. The southern branch will be more amplified but weaker. The
primary features to impact the forecast area will be a northern stream
shortwave trough that will move into Ontario tonight. This trough will
be followed by another that will track east along the US-Canada
border tonight and tomorrow. This trough will be located over
Manitoba by sunset tomorrow. The southern stream low currently over northern
mex will advance into the Southern Plains tomorrow.
Surface: low pressure was over the Canadian prairies...associated
with the first shortwave trough. Its cool front extended
S...bisecting Nebraska to a Lee-side low over western Kansas. At 19z the front
was located roughly from Ord-Kearney-Beaver City. This front will
make a little forward progress tonight-tomorrow...and will
probably become modified by thunderstorm cold pools.
The rest of this afternoon: partly-mostly cloudy. The first
storms should go up over western Kansas in vicinity of the Lee low and
then approach the Beaver City-Phillipsburg area early this
Dewpoints were in the upper 40s and 700-500 mb lapse rates were
very steep. However...the elevated mixed layer /eml/ and poor
moisture has resulted in a skinny cape profile. Deep layer shear
will be 25- 30 kts near the front...but only 15-20 kts ahead of
15z/sref maximum mean MLCAPE is forecast to just barely reach 1000
j/kg over north-central Kansas just prior to sunset. Thereafter...MUCAPE
will decrease. Expect a strong storm or two initially with hail
possibly up to nickels and wind gusts up to 50 miles per hour.
Tonight: thunderstorms will move in from the SW. They will be outflow
dominant due to the lack of strong shear and unidirectional flow
parallel to the front. So while individual storm movement
initially will be about 23020kt...movement could be modified due
to cold pool boundaries. Interestingly...while this is far from
an ideal heavy rain situation...once the low-level jet redevelops
..corfidi vectors decrease to 10 kts or less. By 06z low level jet
convergence will diminish with minimal flow into the front. So
expect a decrease in thunderstorm coverage by midnight.
For what it/S Worth...the 12z WRF-nmm develops all of the thunderstorms
along and to the cool side of the front.
Fog: rain under the frontal inversion will significantly moisten
the low-levels. What the remnant cold pools do to the wind field
remains uncertain...but did include the threat of patchy fog
within the frontal trough 3am-10am sun. Tough to tell how dense
visibilities could be.
Sun: very low confidence in cloud cover and temperatures. The day could
start off with a lot of stratus on the cool side of the front.
This casts significant doubt on high temperatures.
The approach of the upper trough will reignite thunderstorms in a somewhat
more favorable environment. Tonight/S rain will push dewpoints
into the 50s. 15z/sref suggests MLCAPE of 750-1000 j/kg in the
preconvective environment. However...environmental wind fields
will weaken significantly. 0-6 km shear at or below 10 kts will
result in outflow dominant pulse-type storms. This will limit the
threat to hail up to the size of nickels at worst. The cape
profile will be skinny once again.
Where thunderstorms develop...highly localized hefty rainfall looks
probable. Precipitable water will be 1-1.25" ... east of Highway
281. This is 2 Standard deviations above normal for middle April.
Long term...(sunday night through saturday)
issued at 352 PM CDT Sat Apr 19 2014
We start out the long term Sunday evening with a split flow
regime...with an upper level jet well to the north near the
Canadian border and to the south across Texas and east into the
northern Gulf of Mexico. A shortwave trough will continue to move
east across the Central Plains with the trough axis crossing the
County Warning Area Sunday evening. Dewpoints will be in the 50s...which will help
boost instability some...but it still looks fairly modest MUCAPES
not likely exceeding 1000 j/kg. Wind shear will be weak as
well...generally in the 5 to 15 knots range in the lowest 6 km. This
will give US a shot at some strong to marginally severe
thunderstorms early. Hail will be mainly what to watch out for and
any storms should be more pulse-type in nature. Although we stand
a better shot at rain in our southeast where moisture is more
Bountiful...we perhaps stand a bit more of a shot at some severe
hail in our north where shear may be near 20 kts in the lowest 6
km near a surface trough/frontolytic stationary boundary...but
this will be a fairly small window as instability decreases during
the evening and the trough axis moves east. Some locations could
get a good dose of rain as storm motion will be slow. This will be
rather hit or miss...but a better chance of a soaking in our
Wind will be significantly stronger behind the trough by late
Sunday night into Monday morning with a tightly packed surface
pressure gradient helping to boost north wind. This should
decrease during the afternoon as the gradient relaxes and a
surface high approaches. Wind could still be strong enough in the
afternoon...however...to mention near critical fire danger in the
severe weather potential statement. With the potential for rain from Sunday and Sunday
evening...our fuel status by then is questionable...but a mention
in the severe weather potential statement probably would not Hurt.
Tuesday should be dry with shortwave ridging passing by...with
increasing wind speeds from west to east with an increasing
pressure gradient due to a developing trough in the Lee side of
the Rocky Mountains.
By Wednesday...a surface low is forecast to pull out of the Rocky
Mountains into the northern Great Plains associated with a
negatively tilted shortwave. A narrow warm sector will develop to
the south of the front where instability will increase. Although
there are consistency issues among numerical models and
differences in solution...there is potential for storms to develop
along the Lee trough/dry line and move east as the cold front
sweeps into the Central Plains. Dewpoints along the axis of
instability could hit near 60 degrees. Bulk shear will also be in
the 35 to 40 knots range. This along with the negatively tilted
trough will give US a decent shot at some severe storms Wednesday
afternoon and into the night.
We dry out behind the trough axis heading into rest of the work
week and into the weekend.
Aviation...(for the 00z kgri taf through 00z Sunday evening)
issued at 645 PM CDT Sat Apr 19 2014
Multiple chances for thunderstorms exist at the terminal over the
next 24 hours as a weak boundary will meander in the vicinity of
the terminal and weak disturbances track northeast across the
local area. The best chance for any unsettled weather this
evening will be during the 03-09z time frame...when MVFR ceilings and
visibilities will be possible in scattered to locally numerous
thunderstorms. Overnight...with the low level jet focused to the southeast
of the terminal...expect convection to diminish...and for
prevailing VFR conditions to return through early Sunday
afternoon...when additional storms advect in from the southwest.
Confidence in timing for Sunday afternoon too low to mention
anything other than a thunderstorms in the vicinity at this time...with winds eventually
increasing to near 10 kts out of the south tomorrow afternoon.