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Area forecast discussion...updated 
National Weather Service North Platte NE
603 PM CDT Thursday Jul 31 2014

Short term...(this evening through friday)
issued at 315 PM CDT Thursday Jul 31 2014

A weak area of surface low pressure was centered near Oneill this
afternoon. A weak front extends south/southwest from this low into
south central Nebraska. It appears that the best convergence near
the front is across south central Nebraska...and this is where a
couple of isolated thunderstorms have developed in the last hour.
Cannot completely rule out the possibility of an isolated storm in
eastern Holt and Wheeler counties...but chances are looking slim.

Overnight tonight expecting skies to clear completely for the most
part...and with a fairly dry airmass in place...expecting lows in
most locations to once again drop into the 50s.

Northwest flow aloft will dominate the weather Friday. Nearly all
models indicate that a weak wave will rotate southeast within the
flow during peak heating Thursday afternoon...and have added a
slight chance for thunder to account for this across north central
Nebraska. NAM model does indicate around 1250 j/kg of MLCAPE and
0 to 6 km shear of 30 kts...so a strong storm cannot be ruled out.
Otherwise a warm day expected...with highs in the middle to upper 80s
at most locals.

Long term...(friday night through thursday)
issued at 315 PM CDT Thursday Jul 31 2014

Although models are in decent agreement on the hemispheric scale
with long wave number and position...models differ on the southern fringe
of the main band of westerlies across Canada and the northern portion of
the U.S. Therefore there are timing diffs with individual short
waves in the split flow that results from the previously mentioned
westerlies and the weaker flow over the western U.S. Unfortunately this
results in uncertainty in weakly forced regimes such as this and
hence mainly slight chances for thunderstorm activity during the
weekend.

Specifically for the medium range...Friday night into
Saturday...western states upper ridge will build eastward into the northern
High Plains as the eastern states upper trough slowly moves southeastward. A weak
upper pv anomaly moves quickly southeastward on the fringe of the upper high
across the High Plains...weakening as it moves south. Short range
models differ on placement of this feature and therefore forcing
associated with it...albeit weak...is also handled differently. Some
weak middle level forcing does result in tandem with some elevated
instability Friday night into the first part of the day Saturday.
Small thunderstorm chances are in the forecast for this
scenario...though confidence on significant measureable
precipitation is limited. High temperatures will increase to at or slightly
above average values for this time of year...with lows doing much
the same.

The overall eastern states mean trough position remains in place along
and east of the Mississippi River as a strengthening Atlantic high
develops westward. The result of the halting of eastward progression of
significant large scale features will be to decrease the
amplitude of upper features across the u... the westerlies
remain strong across southern Canada. Quick moving upper pv anomalies
will flatten the western states ridge which will develop northwest flow
across the High Plains by middle week. GFS suggests the most
significant pv anomaly will top the flattening ridge in confluent
flow Tuesday evening into Wednesday as upper heights decrease across the
northern states. This will push a decent cold front across the plains
and will be accomapnied by good middle level fgen supporting deep
layer lift across the area. Steep low level laspe rates ahead of
this feature Tuesday afternoon and evening...along with an
increasing low level jet by evening results in better chances for widespread
precipitation across western and north central Nebraska for this
period. Timing of the frontal passage...allowing upper dynamics to
work best with favorable thermodynamic setup...will be best in the
northwestern portion of the area according to the GFS...but timing diffs
between the models /as mentioned previously/ will make all the
difference. Still...forecast has best overall precipitation chances in the
Tuesday to Wednesday time frame. Beyond this...precipitation chances lessen as
front continues to move south of the area. Typically the models
develop too much precipitation across western Nebraska in day 2 Post
frontal regimes and have therefore limited chances for the
Thursday forecast. Temperatures will remain quite warm on Monday
across the area...but begin to fall beyond this back into the low
to middle 80s by Wednesday and Thursday.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 603 PM CDT Thursday Jul 31 2014

VFR is expected all areas tonight and Friday. Another round of
isolated thunderstorms may develop Friday. The disturbance of
interest is currently across eastern Montana and would likely move into
ncntl Nebraska at or above 18z Friday.

&&

Lbf watches/warnings/advisories...
none.
&&

$$

Short term...Taylor
long term...jws
aviation...cdc

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