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Area forecast discussion
National Weather Service North Platte NE
1151 PM CST Mon Feb 20 2017

Synopsis...
issued at 343 PM CST Mon Feb 20 2017

500 mb analysis from this morning has a progressive pattern
noted across the Continental U.S.. a broad trough of low pressure extended from
North Dakota, south to central and southern Texas. East of this
feature, ridging extended from the Florida Panhandle north to
southern portions of Hudson Bay. Further east, a closed low was
located over the Canadian Maritimes. West of the central Continental U.S.
Trough, low amplitude ridging was located from The Four Corners
north into southern Wyoming. West of this feature, a trough of low
pressure extended south of the Alaska Panhandle into the eastern
Pacific, off the coast of northern California. Current WV imagery
has a nice plume of Pacific moisture from northern California into
the intermountain west. The leading edge of this moisture was just
approaching western Wyoming as of midday. Further east, abundant
Gulf and elevated moisture was streaming into the lower Missouri and
Mississippi Valley. At the surface, light rain showers developed
along a line from Valentine to Stapleton earlier this morning, as of
2 PM CST this line had dissipated. With partly cloudy to clear skies
present across western and north central Nebraska, temperatures
were in the upper 50s to lower 60s.

Short term...(this evening through tuesday)
issued at 343 PM CST Mon Feb 20 2017

Weak surface high pressure will track east across the area tonight.
Winds will quickly diminish this evening and become nearly calm as
the high moves across this evening. After midnight with the high
center east of the region, light southwest winds will begin to
develop. The airmass in place is rather dry, with dew points in the
lower to mid 20s tonight. With the clear skies and light winds, low
temperatures will fall to within a few degrees of the dew points in
the typical colder spots like the Platte River valley. Otherwise the
sandhills and north central Nebraska should remain in the lower to
mid 30s.

Westerly downslope winds will develop Tuesday, really giving a boost
to high temperatures. Record warmth is expected, with 70s expected
at all locations. The all time February record high for North Platte
is 79 degrees, and we'll be close with a forecasted high of 77
degrees. The other story Tuesday will be the elevated fire danger.
Gusty west winds, approaching 40 mph, will occur across northwest
and portions of north central Nebraska. In these areas lowest
humidity will be in the 20 to 22 percent range. Across southwest
Nebraska, humidity will be even lower, around 15 percent.
Fortunately winds won't be as strong, gusting to near 20 mph. This
would keep conditions from reaching critical levels. For now we'll
continue to mention in the hazardous weather outlook and have the
oncoming shift monitor for possible fire weather headline.



Long term...(tuesday night through monday)
issued at 343 PM CST Mon Feb 20 2017

Tuesday night through friday: in the mid range, precipitation
chances and the threat for a potential winter storm Thursday into
Friday is the main forecast challenge. Surface low pressure will
deepen over western South Dakota on Tuesday night. This feature
will then track east into central and eastern South Dakota late
Tuesday night into Wednesday. A Pacific cold front will be forced
through the forecast area during the day on Wednesday.
Temperatures will vary widely on Wednesday with mid to upper 50s
in the Pine Ridge, to possibly the lower 70s in the southern and
eastern portion of the forecast area. The latest mav guidance for
Wednesday now has a high of 72 for North Platte and 70 for Broken
Bow. Decided to compromise between the cooler met and warmer mav
numbers for highs Wednesday. That being said, forecast highs are
just under 70 in the southern and eastern forecast area Wednesday.
On Wednesday night, a secondary cold front will push into western
and north central Nebraska. How far this feature makes it south
is still up in the air depending on model choice. The GFS, nam12
and European model (ecmwf) solution push this front through the forecast area while
the Canadian stalls this out over central Nebraska. This is a
byproduct of the Canadian developing a surface cyclone over
northeastern Colorado while the other three solutions develop the
low over southeastern Colorado. That being said, the front is
expected to push through the forecast area by Thursday morning,
and temperatures should be cold enough in the central and northern
cwa for snow development Thursday, then the entire forecast area
for Thursday night into Friday.

With respect to snow and precipitation chances with this system. The
latest GFS and European model (ecmwf) develop a strong area of frontogenesis from the
Panhandle into the sandhills and northern Nebraska Thursday into
Friday, so lift shouldn't be an issue. Temperatures aloft and lift
in the dendritic layer is very favorable for snow development beyond
Thursday afternoon. The main question right now is how much will
accumulate. This is due to boundary layer thermal profile which are
right around the freezing mark, timing, being the middle of the
afternoon, and warm ground conditions. Ie, soil temps which are well
into the 40s per the latest unlimited mesonet Page. Will be issuing a
Special Weather Statement relating to this approaching weather
system given the uncertainties in snow accumulations and model
differences.

Friday night through monday: high pressure will build into the
Central Plains Friday night into Saturday. With fresh snowcover,
lows will fall off into the single digits by Saturday morning and
highs Saturday will struggle to get out of the 20s. A secondary
disturbance may spread some light snow to the forecast area Saturday
night into Sunday. This has been indicated with the European model (ecmwf) and GFS
solutions and was introduced into this forecast. Cold temperatures
will continue into Monday high generally in the 30s.

&&

Short term...(this evening through tuesday)
issued at 343 PM CST Mon Feb 20 2017

Weak surface high pressure will track east across the area tonight.
Winds will quickly diminish this evening and become nearly calm as
the high moves across this evening. After midnight with the high
center east of the region, light southwest winds will begin to
develop. The airmass in place is rather dry, with dew points in the
lower to mid 20s tonight. With the clear skies and light winds, low
temperatures will fall to within a few degrees of the dew points in
the typical colder spots like the Platte River valley. Otherwise the
sandhills and north central Nebraska should remain in the lower to
mid 30s.

Westerly downslope winds will develop Tuesday, really giving a boost
to high temperatures. Record warmth is expected, with 70s expected
at all locations. The all time February record high for North Platte
is 79 degrees, and we'll be close with a forecasted high of 77
degrees. The other story Tuesday will be the elevated fire danger.
Gusty west winds, approaching 40 mph, will occur across northwest
and portions of north central Nebraska. In these areas lowest
humidity will be in the 20 to 22 percent range. Across southwest
Nebraska, humidity will be even lower, around 15 percent.
Fortunately winds won't be as strong, gusting to near 20 mph. This
would keep conditions from reaching critical levels. For now we'll
continue to mention in the hazardous weather outlook and have the
oncoming shift monitor for possible fire weather headline.



Long term...(tuesday night through monday)
issued at 343 PM CST Mon Feb 20 2017

Tuesday night through friday: in the mid range, precipitation
chances and the threat for a potential winter storm Thursday into
Friday is the main forecast challenge. Surface low pressure will
deepen over western South Dakota on Tuesday night. This feature
will then track east into central and eastern South Dakota late
Tuesday night into Wednesday. A Pacific cold front will be forced
through the forecast area during the day on Wednesday.
Temperatures will vary widely on Wednesday with mid to upper 50s
in the Pine Ridge, to possibly the lower 70s in the southern and
eastern portion of the forecast area. The latest mav guidance for
Wednesday now has a high of 72 for North Platte and 70 for Broken
Bow. Decided to compromise between the cooler met and warmer mav
numbers for highs Wednesday. That being said, forecast highs are
just under 70 in the southern and eastern forecast area Wednesday.
On Wednesday night, a secondary cold front will push into western
and north central Nebraska. How far this feature makes it south
is still up in the air depending on model choice. The GFS, nam12
and European model (ecmwf) solution push this front through the forecast area while
the Canadian stalls this out over central Nebraska. This is a
byproduct of the Canadian developing a surface cyclone over
northeastern Colorado while the other three solutions develop the
low over southeastern Colorado. That being said, the front is
expected to push through the forecast area by Thursday morning,
and temperatures should be cold enough in the central and northern
cwa for snow development Thursday, then the entire forecast area
for Thursday night into Friday.

With respect to snow and precipitation chances with this system. The
latest GFS and European model (ecmwf) develop a strong area of frontogenesis from the
Panhandle into the sandhills and northern Nebraska Thursday into
Friday, so lift shouldn't be an issue. Temperatures aloft and lift
in the dendritic layer is very favorable for snow development beyond
Thursday afternoon. The main question right now is how much will
accumulate. This is due to boundary layer thermal profile which are
right around the freezing mark, timing, being the middle of the
afternoon, and warm ground conditions. Ie, soil temps which are well
into the 40s per the latest unlimited mesonet Page. Will be issuing a
Special Weather Statement relating to this approaching weather
system given the uncertainties in snow accumulations and model
differences.

Friday night through monday: high pressure will build into the
Central Plains Friday night into Saturday. With fresh snowcover,
lows will fall off into the single digits by Saturday morning and
highs Saturday will struggle to get out of the 20s. A secondary
disturbance may spread some light snow to the forecast area Saturday
night into Sunday. This has been indicated with the European model (ecmwf) and GFS
solutions and was introduced into this forecast. Cold temperatures
will continue into Monday high generally in the 30s.

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1150 PM CST Mon Feb 20 2017

VFR conditions currently prevail across western and north central
Nebraska and will continue through the taf period. Latest satellite
imagery shows scattered-broken high clouds moving into portions of western
neb, elsewhere clear skies are observed.

The main concern in the next 24 hours are winds. There is a
window for low level wind shear conditions beginning after midnight over the Nebraska
sandhills to the South Dakota border attributable to a belt of modest low-
level westerly winds develop. These low level wind shear conditions will impact
the kvtn terminal. Height of the top of the wind shear layer is
expected to be about 1500 ft above ground level with speeds of 40-45 kts based
on BUFKIT soundings. Low level wind shear conditions then diminish near mid
morning.

Tomorrow, westerly winds develop again with gusty conditions
anticipated by late morning. Strongest winds across northwest Nebraska
and the northern sandhills wherein gusts up to 30-35 kts are
expected. Winds will diminish in the late afternoon/early evening.

&&

Fire weather...
issued at 343 PM CST Mon Feb 20 2017

Elevated fire danger is expected Tuesday. Gusty west winds,
approaching 40 mph, will occur across northwest and portions of
north central Nebraska. In these areas lowest humidity will be in
the 20 to 22 percent range. Across southwest Nebraska, humidity
will be even lower, around 15 percent. Fortunately winds won't be
as strong, gusting to near 20 mph. This would keep conditions from
reaching critical levels. For now we'll continue to mention in
the hazardous weather outlook and have the oncoming shift monitor
for possible fire weather headline.

&&

Lbf watches/warnings/advisories...
none.
&&

$$

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