Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service North Platte NE
339 am CDT Sat Jul 30 2016

Short term...(today and tonight)
issued at 339 am CDT Sat Jul 30 2016

Today and tonight...the weather situation today and tonight is
similar to Friday with three rounds of convection. The ongoing
convection across ncntl will dissipate this morning as the low level
jet weakens and lapse rates become less steep. This area of rain
formed as a result of the low level upper air disturbance
across South Dakota and steepening lapse rates.

Satellite suggests a second area of steep lapse rates across ern WY
and the neb Panhandle. It is believed this area will drift east
today and become the focus for severe weather this afternoon. The
Black Hills would be the source area of storm development. The hrrr
and NAM suggest the White River Valley in South Dakota as a source region. The
models show a plume of deep moisture moving up the cntl High Plains
late this afternoon the forecast shades the better rain chances...30
percent along Highway 61 and across the ern Panhandle.

A modest 30kt low level jet will form tonight and the model
consensus suggests another round of thunderstorms will form across
ncntl neb as a result of lingering evening convection...the steep
lapse rates and forcing from the low level jet.

The temperature forecast uses a four-way blend of guidance plus bias
correction for highs in the 80s and lows in the 60s. Sfc dew points
will rise into the mid to upper 60s for humid conditions.

Long term...(sunday through friday)
issued at 339 am CDT Sat Jul 30 2016

Mid range-Sunday through Monday night: right out of The Gate, there
are some significant model differences between the 00z nam12 and GFS
solutions tonight. First off, the nam12 develops a mesoscale convective system tomorrow
evening, pushing this feature to the southeast across the forecast
area Saturday night. The result is a frontal boundary which becomes
anchored along the Kansas/nebr border Sunday into Monday. The GFS is
similar but weaker with the mesoscale convective system and frontal boundary, lifting
washing this feature out Sunday night, allowing very warm air to
push into the forecast area for Monday. This shows up in the latest
statistical forecast guidance which has a 10 degree spread for highs
Monday with the GFS mav guidance much warmer than the NAM met
guidance. For highs on Monday, decided to weigh the forecast heavily
on the inherited forecast, weighted more toward the warmer mav
guidance. That being said, decided to limit precipitation chances
for Sunday night confining them to the southwestern forecast area as
both the NAM and GFS solutions do have a surface boundary anchored
across southern Nebraska. Will confine the chances to the evening
hours as the GFS lifts the front north overnight. Shifting into
Monday, as mentioned above, there are some significant model
differences with respect to temperatures on Monday as well as the
threat for thunderstorms late Monday into Monday night. With the NAM
having a front anchored to the south of the forecast area, it
remains the coolest solution for highs Monday. It also generates
precipitation Monday night as a low level jet crosses perpendicular
to the frontal boundary. The GFS solution is drier and confines
precipitation chances to Monday night in vicinity of of an approaching
surface trough/weak frontal boundary. Will hold onto pops for Monday
night as there is some mid level warm air advection which over
spreads the front Monday night. This warm air advection is
strongest in the east and that is where pops were retained.

Long range-Tuesday through friday: a trough of low pressure aloft
will push onshore Tuesday which will amplify ridging downstream
across the central and northern plains. Much warmer air will flow
into the forecast area on Tuesday which will result in highs
reaching the mid to upper 90s. The European model (ecmwf) solution does hold onto
some cooler air and additional low level moisture for Tuesday, so
decided limit highs to the middle 90s. The next threat for pcpn in
the extended will arise on Wednesday night as a cold front passes
through the forecast area. Temperatures behind the front will be
in the 80s for Thursday and Friday.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1151 PM CDT Fri Jul 29 2016

Initial forecast problem lies with potential for development of
low stratus and fog. Latest runs of rap/hrrr have backed off some
on potential for low clouds and there is no resprictions to vsby
indicated in lamp guidance. However serly winds in moist
environment tends to develop cloud cover near or just after
sunrise so have backed off some in light of newer guidance but
confidence is low either way.

The second issue is development of thunderstorms and rain overnight in association
with mid level disturbance and low level jet. Low level winds have not yet
developed as expected but short range models are similar in
developing a line also twd sunrise, but east of klbf and kvtn.
Have therefore not included mention in morning hours. NAM Keys in
on large scale convection twd the end of this taf period and have
included mention at kvtn.


Lbf watches/warnings/advisories...


Short term...cdc
long term...buttler

National Weather Service Glossary of Abbreviations