Area forecast discussion
National Weather Service Hastings NE
1245 PM CDT Sat may 25 2013
Update...
issued at 1131 am CDT Sat may 25 2013
This will serve as the noon estf update.
Temperatures over our Kansas counties are rapidly approaching 80f. So high
temperatures have been raised all areas for this afternoon.
The Flood Warning for Sherman/Howard counties was allowed to
expire at 1030am. Calls to regional dispatch indicate waters were
receding. However...coordinated with the rfc and we will be
closely monitoring area rivers particularly north of I-80 after the
very heavy rains last night. Highest total so far is 4.28" 2 west of Loup
City.
Thank you very much to all coop/spotter/NE-rain/cocorahs observers.
The boundary left by last ngt's mesoscale convective system will play an important role in
thunderstorm development this aftn-eve. Mean S low-level flow will be
maintained just east of the Lee trough which will result in convergence
and ascent along this boundary. We/ve noted a plume of very warm
middle-level temperatures on the ddc sounding which will advect over the forecast
area today. This will delay thunderstorm develop until late...and could
keep it from occurring at all S of the boundary.
Radar and visible satellite shows an mesoscale convective vortex just SW of the forecast area near
hys. This will be a wildcard as it could trigger thunderstorms in the warm
sector...but does it occur during the daylgt hrs? It/S heading NE
and will move across our southeast counties. If it holds off until tonight
then it could be east of the forecast area.
With very little cloud cover north of the boundary...diabatic heating
will destabilize the atms. Temperatures in the 80s...dewpoints in the 60s and
middle-level lapse rates of 8 degree c/km will result in MLCAPE of
2000-3000 j/kg. Middle-level shear will be around 30 kts...supportive
of supercells due to backed low-level southeast winds.
0-1 km ehi will be in excess of 1 where winds are backed. This
combined with lowest local heights suggests tornado potential will be
along and north of a line from lxn-hjh.
Satellite-derived precipitable water shows a plume of subtropical moisture extending north
from the Caribbean into the Central Plains. Lbf/oax/top 12z soundings
are all 150-170% of normal. Any clustering of thunderstorms will threaten
flash flooding...especially here heavy rain occurred last night.
Ordinary storm mvmt will be 05025 kts. Supercell mvmt: east 10-15 kts
which could also be trouble for excessive rainfall.
Severe weather potential statement and ehwo have been updated with our latest thinking.
Update issued at 920 am CDT Sat may 25 2013
Mesoscale convective system has basically exited. Radar is showing some showers still
percolating from hlc-phg and drifting NE toward the state line.
These showers /with an occasional rumble of thunder/ were developing
as the remains of the low level jet are still largely perpendicular to the
convectively-reinforced warm front that extends west-east across northern Kansas.
Expect these showers to eventually end. So short-term adjustments
through noon have adjusted probability of precipitation and skycover accordingly.
12z lbf/oax/top soundings support high temperatures in the low-middle 80s east
of Highway 281 and middle-upper 80s to the west.
We will continue to evaluate thunderstorm and severe weather potential for this afternoon-
evening. Certainly the boundary laid down from this mesoscale convective system will be
watched closely.
Please follow our lsr/rtp/lco products for the impressive rainfall
totals overngt. Many reports of 2-3" in a swath from Sherman-Hall-
Hamilton-Clay-Thayer counties. This may set the stage for some
flooding with multiple threats of thunderstorms the next several days.
&&
Short term...(today and tonight)
issued at 423 am CDT Sat may 25 2013
Focus remains on thunderstorm potential.
Thunderstorms continue early this morning with mesoscale convective system rolling east across
central/eastern Nebraska. Main impact currently from convection is heavy
rainfall...with many locations north of Interstate 80 picking up
at least an inch of rain. We have had one report of 3.13 inches so
far at Loup City with rain still falling.
This initial round of convection will continue to move east/end this
morning then attention turns to additional chances for convection
this afternoon. Surface boundary has settled near the Nebraska/Kansas Stateline and
front is prognosticated to lift northward this afternoon into SC Nebraska...with surface
low oriented in eastern Colorado and dry line along the High Plains
region. Frontal boundary and any residual outflow boundaries will be
focus for convection again this afternoon/evening and boundary placement
will need to be monitored closely. Cap looks to hold initially
however models are indicating development along the dry line and
along/north of warm frontal boundary...and have followed closer to
rap model for potential development this afternoon. Storms for
today/tonight have the potential to be more volatile with severe
parameters indicating potential for supercells. Instability is
prognosticated around 4000 j/kg with shear of 40kts or so and storms will
be capable of producing very large hail...damaging winds and even
tornadoes in vicinity of boundaries. Heavy rainfall/flooding also
remains a concern due to the heavy overnight/early this morning
and precipitable water values are on the order of an inch to inch
and a half and are a 100 to 150 percent of normal. All of this
being said...models are not consistent in frontal position which
is key to development this afternoon. Again feel rap and latest sref
run has a better handle on the farther south warm frontal position
across our area today...and will need to monitor closely.
Otherwise...look for some warmer temperatures this afternoon and steady/gusty
winds with the highest wind speeds expected across NC Kansas/south
of warm front...where windy conditions are possible with gusts of
30+ miles per hour.
Long term...(sunday through friday)
issued at 423 am CDT Sat may 25 2013
Sunday through Friday. Main forecast concerns will be
chances for thunderstorms most every day and temperatures through
the period.
A very active weather pattern will affect the forecast area through
the period. An upper level low develops in the western Continental U.S. And
gradually moves through the northern rockies and into the northern
plains by Friday. This upper low will send waves into the forecast
area through the period. The models are similar in the main
features...but the European model (ecmwf) has a little stronger amplitude middle week.
Each of the waves will have a chance for some thunderstorms when
they move through. It certainly will not be a rain out...it will not
rain all of the time...but there will be chances for some showers
and thunderstorms at various times during the period.
The best chances for thunderstorms will be Sunday afternoon and
Sunday night...during which time the cape approaches 5000 j/kg.
Another good chance will be Monday afternoon and Monday night with
convective available potential energy over 5000 j/kg again. Beyond Monday the models have a few
timing differences with the upper level waves that move through the
area and therefore timing thunderstorms is more of a challenge.
Temperatures will be the warmest Sunday through Tuesday then slowly
cool off toward the end of the week. Temperatures should still
remain above normal for this time of year.
&&
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1244 PM CDT Sat may 25 2013
Uncertainty is above average due to thunderstorm potential.
This aftn: VFR with a slight chance of an IFR thunderstorm after 21z. South-southeast winds
will gust to around 22 kts.
Tngt: VFR much of the night but there is a slight chance of a thunderstorm. Just
cannot pinpoint it at this time. Gustiness of south-southeast winds will diminish
around sunset...but there could be some occasional gusts to near
20 kts.
Sun through 18z: VFR. South-southeast winds gust up to 25 kts.
Ceiling confidence: medium
visibility confidence: medium
wind confidence: high except near thunderstorms
weather confidence: low due to thunderstorm potential
&&
Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&
$$
Update...halblaub
short term...Fay
long term...jcb
aviation...halblaub
