Scientific Forecaster Discussion
Area forecast discussion
National Weather Service North Platte NE
347 am CDT Wednesday may 6 2015
Short term...(today and tonight)
issued at 347 am CDT Wednesday may 6 2015
Forecast focus will be precipitation coverage and chance for
severe this afternoon evening. Negatively tilted upper trough
over southeast Wyoming into northeast Colorado. Westerly extent of
deformation zone from Denver north through Cheyenne and then north
northeast into south central South Dakota. Some slightly stronger
showers on the eastern edge of the upper trough from south central
into north central Nebraska. Models have a fair handle on this
with NAM further east with precipitation over north central
Nebraska. With the southeast trajectory...up slope flow...showers
to continue over the higher terrain of the Nebraska Panhandle
through most of the day as the upper trough shears into the
Dakotas. NAM has a stronger wave rounding the bottom of the trough
with showers spreading to the northeast across western Nebraska.
GFS has most of ascent on leading edge of trough with best lift
from south central into northeast Nebraska this afternoon and
evening. Not a strong signature in either one to indicate dry
slot. But both models indicating clearing into northwest Kansas.
This will allow destabilization this afternoon with the heating of
the day and dry line bulge along the southwest counties. 1000-1500
joules of cape this afternoon from MC Cook north into Broken Bow.
Key will be clearing for destabilization. Good bulk shear of 30 to
40kts late this afternoon into early evening. Cool front moves
into the Nebraska Panhandle late this afternoon and then across
western Nebraska through the early morning. Highs today with good
mixing as winds increase through the morning and a warm start to
the day will climb into the upper 60s to low 70s and tonight the
temperatures will fall into the 40s over the eastern Nebraska
Panhandle to the 50s east.
Long term...(thursday through tuesday)
issued at 347 am CDT Wednesday may 6 2015
12z Thursday and beyond. The pattern remains active into early next
week...however there will be some lulls in the activity as passing
disturbances/shortwaves eject northeast from a southwestern Continental U.S.
Upper low. The main upper level low will be responsible for the
highest chances of probability of precipitation late this weekend...and depending on the
thermal profiles...we may see flakes of snow for our northwest
while the southeast gets severe storms.
The deterministic and ensembles all suggest split flow starting off
the extended periods...with a closed low west of the Great Basin.
This provides for a continued tap of SW flow aloft across the
Central Plains for which the closed low will eventually lift
northeast and take a negative tilt over northeastern Colorado.
There remains some slight timing issues between the main suite of
longer range models...but most indicate the closed low east of the
Front Range late Saturday night into early Sunday. From there the
models take the low northeast across The Heart of the sandhills
through Monday...with the cyclone ejecting northeast late in the
day. Ahead of this feature...multiple low-amplitude shortwave are
anticipated to pass through SW flow...providing for additional
shower activity Friday through Saturday.
Lee cyclogenesis associated with the main upper level feature will
play a Hugh role in the degree of destabilization of the troposphere
and how much cool air is drawn down to the surface. With the 06.00z
runs...the favored area of cyclogenesis is just south of the
tri-state region with an associated warm front along the northern
border of Kansas. Easterly upslope north of the low will more than
likely keep clouds socked-in and limited the amount of instability
for convective development...storms /if any/ would be elevated.
Timing of the low may work against widespread strong to severe
storms as well on Saturday as the models show the center advancing
toward north central Kansas by mid-afternoon...this would place much
/if not all/ of the forecast area north and west of the low. One
concern with that however will be the amount of cool air drawn into
the system. The GFS and European model (ecmwf) did a flip-flop tonight...with the ec
now indicating surface-700mb temperatures supportive of snow across our
northwest early on Sunday while winds gusts in excess of 30mph. The
GFS came in warmer...but possibly points to a mix late Sunday night
into Monday. Obviously it/S too early to definitely say snow or no
snow...severe or no severe...but what appears certain is that it
will be unsettled and Worth watching as this system will be
So for the forecast...did not deviate from the cr_int blend...which
has likely to definite probability of precipitation where needed. For ptype...it/S too
early to introduce snow wording for northwest Nebraska...too many
variables at play...and for the T-storm mention...favoring the
southern track of the surface low...but the dynamic nature of the system
will still provide for thunder...will go with -trw transitioning to
-rw...except for our far northwest...where showers will prevail.
The cr_int did produce an area of 0c or colder lows across our west
and especially northwest Monday and Tuesday morning...appropriate
frost headlines may be required.
Beyond Monday...transitory ridging will try to amplify over the
Central Plains...which would lead to less unsettled conditions and
warming in advance of the next trough of interest digging down the
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1131 PM CDT Tuesday may 5 2015
Winds across southwestern Nebraska are beginning to strengthen as low pressure
deepens over northeast Colo. Upslope moisture advection is
increasing causing ceilings to lower to IFR/LIFR. The forecast
suggests this process will spread north to Valentine overnight.
Winds may relax a bit Wednesday morning as low pressure drops
south into southeastern Colo. This in combination with the heating cycle
would allow ceilings to improve to VFR/MVFR 15z-19z.
Thereafter...storms should redevelop again and last until 03z-06z
east of Highway 83. West of 83...flight conditions should improve
from west to east by 21z-01z.