Area Forecast Discussion
Issued by NWS North Platte, NE

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921
FXUS63 KLBF 281727 AAA
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1227 PM CDT Wed Jun 28 2017

.SHORT TERM...(Today and tonight)
Issued at 412 AM CDT Wed Jun 28 2017

The main forecast concerns revolve around storm potential again this
evening and overnight. There is potential for strong to severe
thunderstorms, mainly after 6 PM CDT. SPC Day 1 Outlook has the
majority of the local forecast area in a MRGL risk area with a SLGT
risk area south of a line roughly from Big Springs to North Platte.
Latest IR satellite imagery shows skies clearing across much of
western NEB with ongoing convection leaving eastern NEB. Latest
water vapor imagery shows the main impulse/shortwave trough over
western NEB tracking eastward, otherwise an upper level trough
extends southwest into northern CA with the closed low located over
central Alberta and western Saskatchewan.

The upper level trough will continue to revolve eastward and move
into the Northern Rockies today with the closed low moving more into
Saskatchewan while zonal flow prevails in the mid-levels aloft
overhead. A weak cold front has advanced through much of the local
forecast area associated with a surface low in the eastern Dakotas
that has a central pressure near 998 mb. The front will clear the
remainder of local forecast area during the early morning and is
expected to lie south and east of the forecast area in the afternoon
from west central KS to eastern NEB. Surface dew points will range
from the upper 40s in far western NEB to mid 50s towards central NEB
this afternoon. Thermodynamic profiles should be conducive for
instability ranging from weak (MLCAPE less than 1000 J/kg) to
moderate instability (MLCAPE exceeding 1000 J/kg) in portions of
southwest NEB to north central NEB. Less instability elsewhere in
the local forecast area. NAM in comparison with the GFS and RAP is
the most bullish in the quantity and distribution of moisture, and
current thinking is the latter are too low. Otherwise, lapse rates
are supportive with 700-500 and 850-500 exceeding 8 C/km in much of
the High Plains and southwest NEB. Current thinking is main threats
will be hail and damaging wind with a lower threat for tornadoes in
comparison to yesterday. Current thinking is convection will
initiate across the High Plains and move into and across western NEB
this evening into the small hours.

.LONG TERM...(Thursday through Tuesday)
Issued at 412 AM CDT Wed Jun 28 2017

As a shortwave trough progresses east across the Dakotas and
Nebraska Thursday, it will drive a cold front southeast across the
region. The front should be mostly southeast of our area by peak
heating, and this would be where the higher potential for stronger
storms would be. The front has slowed a bit from the previous
forecast and will have to watch and see if front slows anymore. SPC
has shifted the Thursday, Day 2, severe threat a bit farther west
into the eastern portions of our area. This is likely to account for
a possible slower frontal passage and will continue to monitor.
There is some MUCAPE (elevated) post frontal which lingers into
Thursday evening, so a strong storm or two is possible even behind
the front due to good wind shear aloft and lift associated with the
shortwave disturbance.

Flow turns northwest aloft Friday through Saturday, with drier mild
air filtering into the area behind Thursday`s cold front. Gusty
northwest winds are expected Friday with good mixing as H850mb winds
of  20 to 25 kts mix to the surface. A pleasant first half of the
weekend with highs in the upper 70s to mid 80s Saturday with light
winds. The next shortwave will dive southeast across the area
Saturday night and Sunday. This will strengthen a leeward trough
Saturday night with a south to southeast wind developing. This will
rapidly draw warm moist air back north into the area Sunday,
resulting in possible strong storms and an MCS late Sunday afternoon
and Sunday night.

Upper level ridging begins to expand north and east across the area
first of next week. As of now looks mainly dry and on the warmer
side with highs in the mid 80s to lower 90s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1227 PM CDT Wed Jun 28 2017

The on-going jet streak across Nrn Colo and daytime heating appear
to be the genesis for front range thunderstorm development this
afternoon which should move east this evening and affect Swrn Neb
overnight. Isolated thunderstorms are possible Thursday along and
south of I-80.

There is also a disturbance moving across the Tetons which should
spark storms off the Big Horns this afternoon. This appears to
grow weakly upscale this evening across Wrn SD which could affect
Nrn Neb overnight.

Lastly, some level of storm development is expected on the Laramie
Range which could also move east and affect the Sandhills overnight.

Thunderstorms chances Thursday are in place, mainly north of
Interstate 80, with the best chance across Ncntl Neb east of
KVTN.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...ET
LONG TERM...Taylor
AVIATION...CDC



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