Area Forecast Discussion
Issued by NWS North Platte, NE

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607
FXUS63 KLBF 310450 AAB
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1150 PM CDT TUE AUG 30 2016

.SYNOPSIS...
Issued at 322 PM CDT Tue Aug 30 2016

Upper level synoptic flow over the CONUS is rather benign today. The
primary core of westerlies is located north of the border in Canada
in association with a strong shortwave trough tracking across the
southern edge of Hudson Bay. A pair of ridges were present over the
CONUS, one deamplifying over the Mid-Atlantic states and the other
become more established over the Central Rockies. Between these two
features was a stream of mid-level moisture, easily evident on water
vapor and 12z RAOBS, stretching from Mexico northeastward through
the Central Plains. In addition, a weak upper level low was slowly
pushing northeast, struggling with the competing flow between the
two areas of high pressure. As of 20z, the low pressure center was
over southwest Nebraska, helping to spark off widely scattered
showers and thunderstorms.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 322 PM CDT Tue Aug 30 2016

Scattered showers and thunderstorms will continue through the
remainder of the day, initiating on diffuse boundaries as a weak
upper level low moves overhead. An environment characterized by
anomalously high pwats, weak lapse rates through the low/mid levels,
and poor shear will be supportive of sub-severe storms capable of
producing heavy rainfall rates at times. Although the storms have
been very slow to move, not concerned about the potential for flash
flooding given the high flash flood guidance over the Sandhills
region.

Upper level low will become absorbed by a shortwave trough moving
southeast through the northern plains this evening. This will also
deflect the rich moisture tap to our south and lower precip chances.
Model guidance once again favors early morning fog from southwest
into north central Nebraka. Lingering cloud cover and the lack of
strong subsidence aloft will likely the potential for widespread
dense fog, but areas of 3sm or less will be possible in local river
valleys and other low lying areas.

Ridge axis becomes situated over the Great Plains by Wednesday
afternoon as an area of surface high pressure pushes north and east
of the cwa. This will reestablish southeasterly flow and retain our
low level moisture. A few storms will be possible in southwest
Nebraska tomorrow afternoon as low level moisture pools upslope into
an area of weak fgen in northeast CO, which is supported by light
qpf in both the NAM and GFS. If any storms develop the activity will
remain isolated and sub-severe as upper level support and deep layer
shear are both weak with a ridge axis overhead.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 322 PM CDT Tue Aug 30 2016

Wednesday night through Friday...the models continue to advertise
deepening low pressure across the Nrn High plains with sfc high
pressure over the Upper Midwest. This will draw moisture west and
north up onto the High plains. Both the GFS and NAM indicate
sufficient instability for storm development in the Panhandle Friday
afternoon or evening. The NAM suggested storms would fire on the
Laramie range Friday afternoon and move east through the Panhandle.
POPs for this feature are 20-30 percent. Winds aloft will be strong
with an approaching upper level low over the Pacific NW and the NAM
and GFS suggest around 1500 J/KG of MLCAPE for strong to marginally
severe storm development. The model consensus shows temperatures at
500mb falling about 1 degree Celsius and this would steepen lapse
rates.

H850mb winds increase to 30 to 50kt Thursday through Friday
supporting windy conditions Friday. Precipitable water increases to
near 1.50 inches in both models and the GFS...SREF...NAM and ECM
show good potential for morning stratus Thursday and Friday mornings
which should mix out by noon. The NAM...SREF and ARW/NMM visibility
products suggest a reasonable potential for patchy fog Thursday
morning but not Friday morning because winds Friday morning will be
stronger.

The temperature forecast uses blended guidance plus bias correction
for highs 80 to 85 both days with lows in the 50s to near 60. Bias
corrected data suggested dew points mostly in the 50s but rising
into the lower 60s Friday.

Friday night through Tuesday...isolated shower and thunderstorm
activity is possible overnight Friday into Saturday morning. The
plume of deep moisture...strong winds aloft and steepening lapse
rates...prime for storm development...shifts slowly east Saturday
and Sunday. Saturday night appears to be the best chance for storm
development and POPs are 50 percent. On Sunday the area most favored
shifts east into Eastern Nebraska.

The models keep low pressure on the Cntl high plains Monday and
Tuesday...south of the forecast area across KS. This would produce a
stationary front south of Nebraska and with cold air aloft the
models show a reasonable chance of showers and thunderstorms both
days. The ECM gives 0.5 to 2.0 inches of rainfall for this system
which represents a northward shift in the focus for rainfall.

Temperatures fall from the 80s Saturday to the 70s by Tuesday. This
includes bias corrected data which had a modest effect on the
forecast. Lows fall from the 60s Friday night to the upper 40s and
50s Tuesday morning.

The models are bringing drier air into the forecast area very slowly
and dew points would remain in the 60s in some areas until Tuesday
morning.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1150 PM CDT Tue Aug 30 2016

Isolated thunderstorms and rainshowers will continue over southern
Nebraska through the early morning hours. Some patchy fog with mvfr
ceilings and visibilities are possible over southwest Nebraska
towards sunrise. Fog is expected to be patchy in nature and should
lift through 15z. Thunderstorms will be possible through the day on
Wednesday south of Interstate 80 between KOGA and KLBF. KVTN will
see vfr conditions the next 24 hours.

&&

.LBF Watches/Warnings/Advisories...
None.
&&

$$

SYNOPSIS...Martin
SHORT TERM...Martin
LONG TERM...CDC
AVIATION...Power



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