Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 251742
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1242 PM CDT Tue Jul 25 2017

.SYNOPSIS...
Issued at 335 AM CDT Tue Jul 25 2017

H5 analysis from earlier this evening, had high pressure located
over eastern New Mexico with a low amplitude ridge extending north
into southern Wyoming. This ridge has become suppressed over the
past 24 hours thanks to an upper level low over central
Saskatchewan. A trough of low pressure extended south of this
feature into northern Montana tonight. A secondary, weak low was
located off the coast of northern California, while a low and
trough of low pressure extended from southern Quebec, south into
the Mid Atlantic states. Across the central plains tonight, a weak
shortwave had lifted across eastern South Dakota and northeastern
Nebraska. Thunderstorms in association with the shortwave, had
since weakened over northeastern Nebraska overnight. At the
surface, a cold front was located from northeastern Montana into
western North Dakota. Weak low pressure was located over
northwestern South Dakota with a surface trough extending south
into eastern Wyoming and northeastern Colorado. East of the
trough, a decent pressure gradient was noted across western and
north central Nebraska and this led to southerly winds overnight
and very warm temperatures. At 3 AM CDT, temperatures ranged from
66 at Gordon to 81 at North Platte and Thedford.

&&

.UPDATE...
Issued at 1117 AM CDT Tue Jul 25 2017

Added the remainder of north central Nebraska to the heat advisory
given latest observed trends and hi-res guidance. KVTN, KANW, and
KONL are currently reporting heat index readings of 94 deg, 94
deg, and 93 deg, respectively. Highest heat index values are
anticipated in Keya Paha to Boyd counties with values around 105
deg.

&&

.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Tue Jul 25 2017

Today and Tonight: Over the next 24 hours, temperatures and fire
danger today, followed by rain chances tonight are the main
forecast concerns. For today, a strong low over Saskatchewan, will
track into western Ontario. This feature will force a cold front
south into southwestern and south central South Dakota by 21z this
afternoon. Immediately south of the front, decent southerly winds
and a nice tongue of hot air will be pushed into the sandhills
and southwestern Nebraska. As is the case with these approaching
cold fronts, we tend to torch out and highs are warmer than the
MET guidance, as well as the MAV guidance. With dry air also being
pushed into western Nebraska ahead of the front thanks to
southwesterly and south southwesterly winds, we will probably see
temps in excess of 100 degrees this afternoon. As for highs today,
given the setup, utilized the warmer MAV as a starting point for
highs, then boosted them 1 to 3 degrees, based on location. For
Valentine, highs were boosted the most as the cold front is just
off to the north of them. Further south, impacts to temperatures
from the appg. front will be decreased somewhat, and only made a
slight upward adjustment to the MAV temps in swrn areas.

With respect to enhanced fire weather conditions this afternoon. As
we mix today, especially along and west of an Ainsworth to North
Platte line, minimum relative humidity will fall off to around 20
percent by the mid to late afternoon hours. Winds with abundant
mixing will peak in the 15 to 25 MPH range this afternoon and that
is utilizing h85 winds from the NAM12. There may be even higher
gusts during peak heating, as we should mix well above H85 given the
expected clear skies. Yesterday, we had several fire starts from dry
lightning, and with an approaching front, we could see more this
afternoon, especially in the northern sandhills. That being said, am
leaning heavily toward hoisting a red flag warning for zones 208 and
possibly portions of 204 and 206. Realize that the RH is marginal
here, however the southerly winds and the initial dry lightning
threat will trump the lack of critical RH.

Convection is expected to fire INVOF the front in the 21z to 00z
time frame late this afternoon. The latest NAM12 soln does indicate
a weakening cap along the front which would favor northern Nebraska
initially for thunderstorms. These should be fairly elevated
initially, which would make dry lightning a concern. Chances for
more widespread convection and thunderstorms will increase into the
evening hours, as strong mid level warm air advection will push into
western Nebraska. This increased WAA is ahead of an approaching
shortwave trough which lifts out of northeastern Colorado and
eastern Wyoming this evening. Have inserted the highest pops across
northern Nebraska, INVOF the appg cold front, and in the east, where
deeper low level moisture exists.

.LONG TERM...(Wednesday through Monday)
Issued at 335 AM CDT Tue Jul 25 2017

On Wednesday, synoptic vertical forcing from a weak passing shortwave
should be sufficient enough to keep the mention of thunder going
in the forecast through the afternoon. Some residual monsoonal
moisture will be in place ahead of a weak frontal boundary
bisecting the Sandhills with westerly flow providing the lower
level moisture behind the front. PWATS are not overly impressive
and storm motion will be sufficient that the chances of a good
heavy rain are low. Still, lighter wetting rains are possible,
which would briefly ease the rangeland fire threat. The greatest
probability of additional storms Wednesday will be across north
central Nebraska, but clouds and cooler temperatures will be
observed by all, again lowering. the range fire threat. The latest
guidance is suggesting highs in the lower to mid 80s forecast
area wide.

Cool high pressure settles northeast of the forecast area Thursday
allowing easterly upslope flow across the Sandhills by mid-
afternoon. Temperatures will remain below seasonal norms with highs
in the lower to mid 80s once again.  The high builds east into
Friday with a return to southerly flow across our westerly zones by
mid-afternoon.  Temperatures will begin to moderate with highs
pushing into the upper 80s.  Enough cool air will recycle in our
north central zones to keep readings in the lower to mid 80s.  Aloft
a ridge of high pressure will retrograde west and build, which
places the Sandhills in northwest flow.  The models show a weak wave
passing through Friday afternoon through Saturday morning while
enough moisture remains for storms.  At this point northwest
Nebraska and possibly our far southwest look to get in on the
action, but cannot rule out thunderstorms elsewhere.

The ridge will build across the Great Basin this weekend and largely
remove the monsoonal and Pac moisture from the central Plains.
Lesser clouds and weak rising heights would suggest that
temperatures will return back into the 90s during the peak heating
of the day both Saturday and Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1229 PM CDT Tue Jul 25 2017

Aviation concerns continue to revolve around thunderstorms this
afternoon through tonight. Latest satellite imagery shows
predominantly high clouds across portions of western NEB. Current
thinking is isolated-scattered -TSRA/TSRA will develop initially
in northern NEB to northwest NEB and the eastern NEB Panhandle
late this afternoon-early evening. Thereafter, isolated-scattered
thunderstorms possible across the remainder of the area tonight,
into southwest NEB to central NEB. Greater confidence in
thunderstorms affecting KVTN terminal than KLBF terminal thus the
mention of TSRA and strong winds in the former. LLWS conditions
will affect portions of southwest to south central NEB late this
evening through the small hours also. Upper levels winds at the
top of the layer forecast around 40-45 kts with upper height
about 1500 ft AGL. Lastly, winds will shift tonight as cold front
advances southeast becoming north-northeast and this direction
will persist through tomorrow.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT /7 PM MDT/ this evening for
NEZ005>010-025>029-036>038-057>059-069>071.

Red Flag Warning until 8 PM CDT /7 PM MDT/ this evening for
NEZ204-206-208.

&&

$$

UPDATE...ET
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Jacobs
AVIATION...ET


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