Area forecast discussion
National Weather Service North Platte NE
335 am CDT Thursday Jun 20 2013
Synopsis...
issued at 335 am CDT Thursday Jun 20 2013
500 mb analysis tonight has a large area of low pressure extending
from off the coast of Washington state...eastward to southern Idaho. A
trough of low pressure extended south into Southern California. Further
east...a ridge of high pressure extended from the lower Missouri
Valley nnwd into southern Saskatchewan. A second trough was noted
across New England. At the surface...a surface trough of low
pressure was noted along the nebr/Wyoming border southward into eastern
Colorado. A decent pressure gradient across Nebraska was present
this morning...which has led to mild readings in the upper 60s and
lower 70s as of 3 am CDT. Across the eastern Panhandle...isolated
thunderstorms have developed over the eastern Panhandle over the
past couple of hours and continues to lift to the northeast into
South Dakota.
&&
Short term...(today and tonight)
issued at 335 am CDT Thursday Jun 20 2013
Main forecast challenge continues
to be thunderstorm chances across the High Plains as southwesterly
flow aloft continues. The models...most notably the NAM solution...have
struggled with placement of thunderstorms and rain showers overnight tonight. The high res
RUC has been playing catch up over the past couple of hours...and
has finally caught on to the ongoing convection over the eastern
Panhandle counties at this time. This activity is expected to weaken and
dissipate over the next 2 to 4 hours as the low level jet weakens
and shifts east toward sunrise. In the meantime...will monitor and
may need to include probability of precipitation across the north central for this morning
through 15z if activity increases in intensity and coverage. Right
now...based on the forecast of the 850 mb low level jet...belief is that
convection will end toward sunrise. For today...southeasterly and easterly
winds will develop across the area as a frontal boundary washes
out over the Panhandle. Easterly flow will push 65 to 70 dew
points west...to a line from North Platte to Valentine by 00z. Sb
convective available potential energy depicted in the latest NAM solution are running 4000 to 5000
j/kg across southwestern and central Nebraska by 00z...which is
more than enough convective potential for thunderstorms. The main
unknown in all of this though...is whether or not the cap will
hold this afternoon. If the cap can break...plenty of deep layer
shear exists to support supercell thunderstorms. Since the cap is
weakest in the southwest and central...with cins approaching zero
by 00z Friday...will place some 20 to 30 probability of precipitation in these areas for
this evening. Into the overnight...a h700 front will lift north
across the forecast area...stalling across the northern forecast
area toward 12z Friday. As this feature lifts north...a nice 850 mb
low level jet will develop...with enhanced lift and increased precipitation
chances across the north overnight tonight. With this in
mind...shifted chance probability of precipitation from the southwest and central
County Warning Area...northward into north central Nebraska overnight.
Long term...(friday through wednesday)
issued at 335 am CDT Thursday Jun 20 2013
Large upper level low pressure system will slowly migrate east into
the northern rockies Friday evening. This keeps the upper flow aloft
southwest across our area...with a quasi-stationary surface front
extending northeast to southwest through the local area. The Gem
regional and NAM models are in good agreement...and have the front
late Friday afternoon along a line from Oneill...to North
Platte...to Imperial. Extremely unstable conditions will reside
in vicinity of the front...with bulk shear favorable for severe storms across
northern Nebraska and South Dakota. Inversion/cap will probably keep
surface based convection at Bay during the day along the front. Farther
west near the Black Hills and portions of northwest Nebraska to the
north of the front...moist Post frontal easterly upslope flow should
result in thunderstorm development by late afternoon. Shear will support
supercells with this initial development. During the evening a very
healthy southerly low level jet will nose northward from Kansas into the
stationary front lying through the area...with elevated storms
likely to develop just to the north of the front across the
sandhills and north central Nebraska. Some of these will likely be
supercells capable of large hail. The earlier mentioned convection
that develops across the Black Hills/northwest Nebraska region
should congeal into an eastward moving mesoscale convective system...and ride just north of
the front across northern Nebraska and southern South Dakota. All in
all it appears it could be a stormy night...with development of
storms during the evening across northern Nebraska as the low level jet
increases...followed by the eastward moving mesoscale convective system rolling off the High
Plains.
Saturday looks similar to Friday...with the stationary front
remaining across the area. NAM is quite similar to Friday
afternoon with the frontal location...roughly along an
Oneill...to North Platte...to Imperial line. This is in question
however...as the expected mesoscale convective system/convection from Friday night will
likely play a role in where front ends up. The front could end up
farther south during the morning Saturday...perhaps down into
northern Kansas. Even if this were to occur...the front would likely
lift back to the north as a warm front Saturday afternoon. Just
not certain where the final resting place will be by late Saturday
afternoon when surface based convection could try to fire along the
front. The more likely scenario would be for elevated storms to
develop to the north of the front Saturday evening/overnight
across northern Nebraska and South Dakota. Similar to Friday
night...some of the storms could be severe.
It appears by Sunday that the large upper level low which has
been anchored in the Pacific northwest...will move east/northeast
into southern Canada. This should help finally drive the
stationary front south into Kansas. This will be short lived
however...as the European model (ecmwf) advertises the front returning north through
the area Sunday night into Monday as a warm front. Some scattered
thunderstorms are possible as the front returns north Sunday night and
Monday morning. This may be the last of the better precipitation
chances for awhile...as both the GFS and European model (ecmwf) build an expansive
ridge of high pressure. There are some differences with the
placement of the ridge...with the the European model (ecmwf) across the western
Continental U.S. With the center...and the GFS across the Southern Plains.
Slight chances for storms are possible in both model solutions...in
a ring of fire type scenario. Will wait to add any chances at this
point however...and see if models come into better agreement with
the center of the ridge.
Temperature wise...it looks pretty warm with the ridge building to
our south and west. The hottest temperatures the next several days
will be across west and southwest Nebraska...where daily highs in
the 90s are anticipated. Conditions a little cooler farther north
and east...but highs will still flirt with 90 degrees from time to
time.
&&
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1232 am CDT Thursday Jun 20 2013
Thunderstorms will continue across the western Nebraska Panhandle
through the early morning. Fairly strong southeast flow is expected
to continue also ahead of a cold frontal passage which will move
through western Nebraska through the day on Thursday. Confidence not
high that thunderstorms will move east out of the Panhandle and have
left kvtn and klbf dry. Models suggesting stratus developing over
western Nebraska through the early morning and lingering into middle to
late Thursday morning. Strong moisture advection and in upslope
regime have included in 20th 06z tafs.
&&
Lbf watches/warnings/advisories...
none.
&&
$$
Synopsis...clb
short term...clb
long term...Taylor
aviation...power
