Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 200457

Area Forecast Discussion
National Weather Service North Platte NE
1057 PM CST Sun Nov 19 2017

.SHORT TERM...(This evening through Monday)
Issued at 311 PM CST Sun Nov 19 2017

Northwest flow aloft will continue through the short term period
as a jet drops southeast into the central and southern plains. The
jet begins nosing across western and southwest Nebraska early
Monday with the strongest momentum reaching our southwest border
just before evening. Closer to the surface, winds are elevated as
h85 momentum reaches 40-45 kts by late afternoon. Soundings across
southwest and western portions of the CWA suggest enough
mixing/favorable lapse rates such that much of this will be
transfered to the surface. The latest guidance shows winds of at
least 25 mph across our west border with up to 25 mph across
southwest Nebraska by afternoon. The northwesterly component of
the surface wind is downsloping, but will be offset initially by
weak CAA. Regardless, temperatures on Monday will be noticeably
warmer. Guidance did trend upward a few degrees with the 12z run.
Widespread highs in the 60s appear likely, with mid or upper 60s
across southwest Nebraska. The above average temperatures will
promote low relative humidity as a dry continental airmass is in
place. Note that we may be over forecasting temperatures and wind
speeds and over forecasting the fall of RH, but wanted to capture
the potential for large range fire growth if the model generated
mixing is underdone (usually is in these situations.)

The amount of mixing Monday afternoon is still somewhat uncertain as
an upper level veil of cirrus is expected from the west by late
afternoon.  The later arrival of the cirrus would allow a greater
coverage of Nebraska fire zones 204 and 210 to reach RFW criteria
for an hour or two.

Weak southwest to westerly winds overnight with increasing high
level clouds will help overnight temperatures in the 20s and 30s.
The coolest readings will be in the river valleys where the wind
should largely decouple.  The forecast temperatures for tonight are
5-10 degrees warmer than last night.

.LONG TERM...(Monday night through Sunday)
Issued at 311 PM CST Sun Nov 19 2017

Long term continues to be characterized by fair weather. By and
large minimal sensible weather concerns. Main stories include a
sharp change in highs Tuesday compared to Monday followed by
warming trend that peaks Friday. Breezy winds are also expected
Friday along with a frontal passage anticipated later on. Largely
scant precipitation chances prevail through the period.

The large scale pattern is expected to become more amplified
across the CONUS the first 24 hrs (Monday night-Tuesday).
Upstream, a mid-level ridge will be building over the West Coast
into British Columbia. Elsewhere, there is expected to be
amplification of an upper-level trough as it translates
southeastward from southern Manitoba into the Upper Great Lakes
and Ontario. Meanwhile, a surface low associated with the trough
will be located in extreme western Ontario Monday evening with a
cold front extending across SD that will moving across the area
Monday night. Thereafter surface high pressure will fill in
Tuesday across the Northern and Central Plains extending from the
Canadian Prairies. Cold air will push into the region Monday night
and Tuesday with 850 hPa temperatures Tuesday ranging near -9 to
2 C, coolest in the east. While there will be increase in
cloudiness, dry conditions are expected Monday night. Highs
Tuesday are anticipated to be 15 to approaching 30 degrees cooler
than Monday, greatest difference in far north central NEB.
Nonetheless, highs are expected to be still near normal values
across southwestern NEB. Highs will then see a quick rebound
Wednesday with highs forecast in the mid 60s in far southwest NEB
to 50s in north central NEB.

Beyond Tuesday, the mid-level ridge upstream will persist and
dominate the large scale pattern through Thursday. Late Thursday-
Friday the ridge will brake down some as a shortwave trough tracks
eastward over the top from near Alberta and across the Northern
Plains. Locations will see well-above normal temperatures ahead
of a cold front Friday. Likewise the previous day, Thanksgiving,
will see well-above normal temperatures. Highs in the 60s are
expected Friday, reaching near 70 in extreme southwestern NEB
20-25 degrees above seasonable normal values. Another moderate
drop in highs is expected Saturday attributable to the
aforementioned cold frontal passage. Albeit highs this weekend
should remain slightly above-normal. Meanwhile, an upper-level
ridge then builds again upstream in the western CONUS Friday,
expanding and becoming more broad this weekend.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1057 PM CST Sun Nov 19 2017

VFR conditions will persist the next 24 hours across western
Nebraska. Scattered high cloudiness overnight into Monday morning
with broken high cloudiness by afternoon and through the evening.
West winds will gust to 20 kts Monday afternoon, then light agin
by early evening.


Issued at 311 PM CST Sun Nov 19 2017

After some consideration, we felt that a RFW was not needed for
Monday afternoon. The main arguments against a fire weather
headline are that RFW criteria spatial and temporal coverage are
not forecast and there`s the uncertainty from cirrus shading in
the afternoon. Shading would not only reduce mixing, thus
impacting wind speeds and temps/RH, but increase the fine dead
fuel moisture several percentage points. Given the low sun angle
this time of year, it would take very little fuel shading to
greatly reduce the rate of spread through our fine fuels. If full
sun remains, understand there may be localized RFW conditions for
a couple hours, most likely from 1300-1500 across southern
portions of NEZ 204/206 and potentially western portions of zone
210. We do not issue fire weather watches for uncertainty. So,
depending on trends and how tomorrow starts out, we may need a
short fused RFW. IF that were to occur, the most likely
location/s/ would be southern portions of NEZ 204 and all of 210.




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