Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Dodge City Kansas
631 am CDT Sat Sep 20 2014

..updated aviation section...

Short term...(today and tonight)
issued at 246 am CDT Sat Sep 20 2014

Mainly zonal flow was noted at middle and upper levels across the
northern tier of states, with western Kansas located near the
southern edge of the westerlies. The remnants of a tropical
system were located across southwestern Texas and a closed upper
level low was situated off the coast of Southern California.
Shortwave troughs embedded in the flow across the northern plains
will amplify into a deep trough over the upper Midwest by tonight.
A lead shortwave trough was passing through the northern plains
early this morning, resulting in a weak cold front progressing
into Nebraska. A few thunderstorms were located along this front
in central and eastern Nebraska as of 3 am. As this lead system
passes today, the associated weak cold front will move into
southwestern Kansas this afternoon. Thunderstorms are expected to
develop with daytime heating somewhere across southwestern Kansas
and then gradually develop southward/southeastward with the middle
level flow toward the Oklahoma state line by evening. Surface
based cape values will be as high as 2000 j/kg; but low to middle
level winds will be fairly weak. Hence, rotating updrafts are not
expected. However, 50-60 knots winds at 250mb may provide enough
storm top ventilation to promote hail as large as quarters. Given
the weak convergence and marginal forcing for ascent, storms will
probably not be all that widespread. Highs today will be mainly in
the middle to high 80s to lower 90s ahead of the front. A more vigorous
shortwave trough will amplify over the upper Midwest tonight,
pushing another cold front into western Kansas. A few thunderstorms
may linger tonight in elevated fashion. Temperatures tonight will be
just slightly cooler than the previous night, with lows in the lower
to middle 60s.

Long term...(sunday through friday)
issued at 406 am CDT Sat Sep 20 2014

An extended east Asian jet from China to near the dateline breaks
into highly amplified blocky flow around 160w with anticyclonic wave
breaks around 30n/170w and off the Southern California coast.
Considerable uncertainty exists in the extended period as a blocky,
amplified flow evolves over North America, and confidence in
synoptic scale details is very low beyond day 5. Tropical
thunderstorm activity shows little coherent organization that
projects onto a Madden-Julian oscillation. It does appear that a
Kelvin wave has propagated rapidly through the western hemisphere
and is approaching Africa, and thunderstorm activity should
increase in the western Indian Ocean by late September. However,
there is little agreement among numerical models on evolution of
any coherent signal through early October. Global relative angular
momentum is trending up and is approaching climatological values
with a large increase around 40n. Mountain torque peaked a few
days ago but still remains strongly positive. The atmosphere still
is best represented by phase 4 of the weickmann-Berry phase space
diagram, which favors anticyclonic flow in the western United

Large differences in deterministic model solutions develop late next
week as sharp ridging evolves 130-140w and another trough digs
into the western United States. The European model (ecmwf) has vacillated between a
ridge in the southwestern United States with a progressive trough
lifting northeast over the ridge and a deep trough in the central
rockies by 28-29 September. The GFS ensemble members all have a
deep trough somewhere between 110w and 120w by 27 September, but
the Gem ensembles differ widely between maintaining a ridge and a
mean trough over the western part of the country. The differences
in model solutions and lack of strong large scale signals in
observational data make guessing at how the flow will evolve
extremely difficult. The best guess is that ridging will persist
from Mexico into the southwest United States and that the trough
next weekend will lift out to the northeast instead of wallowing
into the central part of the country, but there is very limited
confidence in this solution. Regardless of how the trough evolves,
it will be a transitory feature, and the base state flow with a
ridge in the western United States and a trough in the eastern
part of the country is likely to return by early October.

Confidence is higher in evolution of the flow through the first part
of next week. The vigorous upper level trough in Saskatchewan will
dig into the upper Midwest Sunday, and a second surge of cool air
will invade Kansas Sunday morning. Drier air will move into most of
western Kansas behind an initial cold front that will pass this
afternoon and evening, but there may be some showers in the elevated
frontogenetic region behind the second cold surge in far southwest
Kansas yet Sunday morning. Cold air advection Sunday will keep
temperatures several degrees below values observed Saturday. Stratus
likely will form in far southwest Kansas Saturday night and persist
at least into Sunday afternoon in the southwest corner of the state.

Troughing will develop in the Lee of The Rockies as the upper level
low off the Southern California coast propagates into the central
rockies Monday morning. A narrow corridor of low level moisture will
spread north through eastern Colorado and extreme western Kansas
Monday. Considerable middle level directional shear will evolve Monday
as the upper level trough approaches and middle level winds increase.
If the stratus dissipates and allows heating of the boundary layer,
sufficient instability will develop to support formation of at
least a few severe thunderstorms in eastern Colorado that
subsequently will propagate into western Kansas late Monday
afternoon or evening. An area of thunderstorms likely will move
across western Kansas into central sections of the state by
Tuesday morning as the upper level trough moves into the Central
Plains and closes off near the Black Hills.

The upper level trough will be slow to move east with rising heights
in the eastern United States and a ridge amplifying from the
southwestern states into the northern plains. Another minor trough
rotating around the upper level cyclone will move into Kansas
Tuesday and support additional thunderstorm development. The upper
level cyclone will open up and evolve into an elongated trough
across the central part of the country Wednesday. An upper level
anticyclone will develop in the northern plains Thursday, and part
of the upper level trough will retrograde back to Kansas Thursday.
As such, the chance for thunderstorms will extend into at least
Friday and possibly Saturday before the upper level trough finally
lifts out as the next trough digs into the western United States.

There is no really cool air to tap, and the low levels of the
atmosphere will remain fairly warm through the week. Temperatures
will be near seasonal averages with day to day variations dependent
more on cloud cover than any air mass changes.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 628 am CDT Sat Sep 20 2014

VFR conditions can be expected today. A weak cold front entering
northwestern Kansas early this morning will reach the Oklahoma
border around sunset. A few thunderstorms with bases near 050 and
local visibilities around 3 miles are likely to develop along the
front near ddc after 21z. A reinforcing surge of cold air will move
into Kansas tonight, and thunderstorms will increase in coverage
from ddc to the Oklahoma border after 03z. Ceilings 020 to 030 will
form in ddc and gck after 06z as the secondary surge of cold air
encounters Richer low level moisture.


Preliminary point temps/pops...
ddc 90 64 82 55 / 30 30 10 10
gck 89 62 81 55 / 30 30 10 10
eha 88 61 76 59 / 20 20 20 20
lbl 89 64 82 57 / 20 30 20 10
hys 90 60 77 49 / 30 30 0 0
p28 91 67 84 54 / 20 30 10 0


Ddc watches/warnings/advisories...


Short term...Finch
long term...ruthi

National Weather Service Glossary of Abbreviations