Area Forecast Discussion
Issued by NWS North Platte, NE

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212
FXUS63 KLBF 210443
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1143 PM CDT Wed Sep 20 2017

.SYNOPSIS...
Issued at 341 PM CDT Wed Sep 20 2017

Expansive upper low over southwest Canada with a trough extending
into the the PacNW and northern Rockies will be the feature of note
for the upcoming few days across the western United States. Several
PV anomalies rotating around the upper low with one exiting the
Dakotas, and another significant anomaly moving out of northeast
Oregon. Closer to home clear skies prevail and temps near average
for this time of year.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 341 PM CDT Wed Sep 20 2017

Quiet weather across western and north central NE tonight as upper
level height rises move across the Dakotas and 120m+ height falls
move onto the west coast. This will deepen the upper trough out to
the west and put the area in southwesterly winds aloft. A low
level jet will develop overnight in response to strong jet across
the north central states and modified by the typical surface
pressure rises across the plateau region further west due to the
faster cooling rate at night than in the better moisture on the
Plains. While this could signal a fog or stratus setup, low level
moisture doesn`t look sufficient at this point and model guidance
also has no signal at this time. So a clear and cool night looks
in store.

For Thursday southwesterly flow aloft continues over the area. With
upper trough continuing to dig along the west coast this puts the
High Plains in a favorable pattern for hot, dry weather and model
guidance continues to back that up. Surface pressure falls increase
in the lee of the Rockies in the favored northeast corner of CO as
an upper PV anomaly moves through the trough into NV by the end
of the day. With fairly dry low levels in place across the area it
should then allow the dryline to mix eastward under strong
insolation through the day. For specific discussion of fire
weather issues see the fire weather section below. The result for
the temperatures forecast is to nudge the forecast toward the
higher end of the guidance most areas. GFS/NAM 850 temps are
forecast above the 30 yr daily max according to the SPC sounding
climatology so certainly an anomalous setup for this time of year.
The forecast is not for record values at this time but will have
to be watched and forecast soundings in the southwest certainly
support low 90s. Temps further north and east will be a little
cooler since moisture will be slightly better there.

.LONG TERM...(Thursday night through Wednesday)
Issued at 341 PM CDT Wed Sep 20 2017

The main forecast challenge this forecast period will be
thunderstorm development on Friday and precipitation amounts through
the weekend.

A trough will be situated across the western CONUS and slowly move
eastward through early next week, while high pressure is situated
across the eastern part of the US.

Friday through Monday, a cold front will slowly move into the
northwest Sandhills Friday morning, sagging slowly southward across
northwest Nebraska before stalling and becoming quasi stationary
across far north central Nebraska down towards southwest Nebraska.
This front will be situated in this location from Friday night
through Monday which will be the driving force for thunderstorms to
develop along the stationary front with training of thunderstorms to
be the biggest focus for moderate to heavy rainfall development.

Tuesday and beyond, the front will finally move southeast out of the
area, bringing a cooler air mass over southwest and north central
Nebraska.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1125 PM CDT Wed Sep 20 2017

Latest satellite imagery shows a swath of high clouds over west
central NEB, otherwise skies are clear. Surface plot shows
generally light breezes occurring, strongest in the far west and
far north (up to 14 kts). VFR conditions will prevail through the
TAF period along with mostly clear skies. A modest low-level jet
overnight will prompt LLWS conditions across portions of western
NEB, strongest in far northern and northwest NEB. Upper height of
the wind shear layer is forecast about 1500 ft AGL with winds at
the top of the layer up to 45 kts. LLWS conditions diminishing by
mid morning. Increasing southerly winds tomorrow afternoon with
gusts up to 25 kts, strongest outside the eastern Panhandle.

&&

.FIRE WEATHER...
Issued at 341 PM CDT Wed Sep 20 2017

As mentioned above, especially southwest NE will be in an
anomalously warm pattern for Thursday which typically lends itself
to fire weather elements reaching critical values. Tomorrow will be
no exception and as such a red flag warning was issued for
critically low RH values as well as winds reaching red flag
criteria for zone 210. With full sunshine expected through the
day the low levels will be able to mix out easily which will cause
low level dew point temps to drop as well through the afternoon.
This will give the appearance of having the dryline moving east
but think the eastward propagation of the dryline will be limited
to where winds have more of a westerly component and hence the
issuance of the red flag only for fire zone 210 at this time.
Confidence on RH values dropping to below 15 percent is good,
however confidence on winds reaching criteria of above 25 MPH is
not as high. As the surface low develops in northeastern CO tmrw
afternoon, winds should actually lessen the closer you get to the
low and weaker surface pressure gradient. Believe for now though
that there will be a period in fire zone 210 where the
juxtaposition of the higher winds and low RH will be there by late
afternoon. Zones further east will need to be watched for a
further eastward mixing of dry low levels.

Friday will also be a day to watch due to stronger winds across the
area. However moisture increasing, although slow at first, looks to
keep RH values above critical values. Still these same areas will
need to be watched for drier low levels developing through the day,
and a drastic wind shift coming later Friday night.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 7 PM MDT Thursday for NEZ210.

&&

$$

SYNOPSIS...Stoppkotte
SHORT TERM...Stoppkotte
LONG TERM...Gomez
AVIATION...ET
FIRE WEATHER...Stoppkotte



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