Area forecast discussion
National Weather Service North Platte NE
708 PM CDT Wednesday Jun 19 2013
Synopsis...
issued at 310 PM CDT Wednesday Jun 19 2013
Upper level low is coming onshore in the Pacific northwest. A weak
ridge remains across the Southern Plains...while there is a broad
trough across the northeast Continental U.S./Southeast Canada. A surface low is
over the northern rockies...while a trough trails south along the
Front Range. Across much of the High Plains...winds this afternoon
have been gusty out of the south. So far no echoes have developed on
the local radar...although some middle/high clouds drift across the
area. Temperatures have warmed nicely into the 80s.
&&
Short term...(this evening through thursday)
issued at 310 PM CDT Wednesday Jun 19 2013
Trough will be one of the focus points for possible thunderstorm
develop late this afternoon into this evening. Flow is nearly zonal
and any develop along the higher terrain to the west should drift
east overnight. Also a strong ll jet will kick in late this evening
and will sustain or enhance convection across western
Nebraska...shifting over central Nebraska overnight. While decent
elevated instability...marginal shear environment should keep
activity coverage generally isolated...thus forecast is low probability of precipitation.
Expect activity to move east by the morning hours.
As the upper low pushes towards the northern rockies
tomorrow...ridge amplifies slightly which will help warm temperatures up
a couple of degrees...especially across the south. Highs into the
lower 90s across SW Nebraska...middle to upper 80s elsewhere. Also with the
ridge expanding...warmer temperatures aloft should provide a strong enough
cap to keep development at Bay through the afternoon hours. At the
surface...the low will push into Canada...with a secondary low
developing over S Dakota. From the secondary low...expect a
trough/dry line to continue south across the County Warning Area...into western
Kansas. Will have to monitor closely the cap as thunderstorm develop
is possible before 00z.
Long term...(thursday night through wednesday)
issued at 310 PM CDT Wednesday Jun 19 2013
For Thursday night...frontal boundary is expected to be stalled
across southern Nebraska. Ahead of this front...elevated mixed
layer will advect across the Central Plains region with the
southwesterly flow ahead of the approaching long wave trough
moving across the northern rockies. While this may contribute to
substantial capping during the daylight hours Thursday...as the plains
low level jet strengths after sunset and an upper pv anomaly
approaches...should be a middle level convergent region located north
of surface stationary front. The middle level instability combined with
the aforementioned forcing should allow sufficient lift to
generate nocturnal thunderstorms in the eastern portion of the
County Warning Area. Any development should move northeast after midnight and
should generally be out of the area toward daybreak...fairly
typical of nocturnal events in western Nebraska. Would expect that
with the degree of elevated instability there is moderate
confidence in the potential for severe hail overnight.
Friday upper heights build across the Midwest as the upper low moves
out onto the northern plains. This keeps the forecast area in
southwest flow aloft and forces a cold front southward across the
area as the aforementioned pv anomaly shifts northeastward
associated with the eastward propagating upper low. In addition...a
more definitive dew point gradient develops as the higher terrain
heats up and the atmosphere mixes more deeply further west. Ahead of
the cold front temperatures should rise quickly in the drier air...typical
for this pattern...and may reach triple digits in the southwest.
Also...this should set the stage Friday afternoon for a better
chance for surface based convective development near the front/dry
line interaction. In addition...deep layer shear will be better with
the increased flow aloft so storm organization should be better as
well. Any storms should progress across the area sustained by the
diurnally driven low level jet. As the front moves south it will stall as it
encounters the stronger low level jet.
For the weekend /Saturday through Sunday night/ there will be additional
iterations of a similar setup as the upper low progresses slowly
across the northern plains. Ahead of each approaching piece of the
trough winds should become south and push the boundary
northward...and then the subsequent push of cooler air drags the
front back south. In each case thunderstorm development will be a
possibility...augmented by whatever outflow boundaries remain across
the area from previous convection. However...southwest Nebraska may
not get as much as portions of the sandhills and northern Nebraska
in this type of setup so in general precipitation chances reflect this line
of thinking which models seems to get the idea of as well.
In the outer periods models generally agree on building the upper
ridge across the plains which seems to make sense given a more
active eastern Pacific in later periods as the mjo and associated
effects propagate eastward. This will mean a trend toward above average
temperatures and lessening chances for precipitation. Monday is the
transition day however as models suggest a weak short wave moving
into the northern High Plains. Confidence at this time is lacking so
precipitation chances for Monday and Monday night are not included
at this point.
&&
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 707 PM CDT Wednesday Jun 19 2013
Sct060 convective clouds will dissipate after the heating of the
day dissipates this evening. Skies will clear tonight. Strong
southerly flow will continue models giving strong indications of
stratus deck building in behind cool front through the early
morning. Winds will shift to the west northwest through the
morning.
&&
Lbf watches/warnings/advisories...
none.
&&
$$
Synopsis...masek
short term...masek
long term...jws
aviation...power
