Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 021719
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1219 PM CDT FRI OCT 2 2015
...Update to aviation forecast discussion...
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 306 AM CDT FRI OCT 2 2015
Water vapor imagery this morning shows the central plains
predominantly underneath dry northwest flow aloft while two upper
lows rotate over the east and west CONUS. A very weak vorticity lobe
is evident over Nebraska into central KS. However, the dry advection
from the northeast should evaporate any precip that falls from cloud
bases around 10 kft this morning.
As the weak isentropic lift weakens, cloud cover is expected to
clear westward with a mostly sunny Friday afternoon in store. A
noticeable cool bias from the MAV and MET guidance lead to siding a
few degrees higher than previous forecast, especially since temps up
to 925 mb do not cool much. Highs are generally in the middle to
upper 60s. Northeast winds today may occasionally gust between 15
and 20 mph in the afternoon.
For tonight, the upper trough axis is expected to be shunted
northward towards the western high plains, breaking down the upper
ridge. Isentropic upglide from this system will generate a cluster
of showers over western Kansas that will gradually track eastward
and weaken overnight. Latest short term guidance is trending slower
with the progression of these showers. In addition, ample subsidence
from the sfc to 10 kft will be difficult to overcome for showers
initially. So have gone with a dry forecast until Tuesday at 12Z.
Lows tonight will depend on how quickly mid level clouds progress
east by sunrise Saturday. A few models were trying to drop eastern
areas into the upper 30s, which is not out of the question
especially in low lying areas. Overall think the best radiational
cooling will result in low 40s for eastern KS, with mid 40s for
north central KS.
.LONG TERM...(Saturday THROUGH Thursday)
ISSUED AT 306 AM CDT FRI OCT 2 2015
Saturday and Saturday night, a longer wave length upper level trough
will remain stationary across the western US. A lead upper level
trough will lift northeast from the four corners region into the
central high plains. The lead trough will fill as if lifts
northeast. The best ascent Friday evening will occur across eastern
CO due more to isentropic lift and upslope flow. The models show a
complex of thunderstorms developing during the evening hours. These
showers and storms will slowly move east across western KS through
the night but will weaken as they encounter a drier airmass across
eastern KS. Most of the showers should remain west and southwest of
the CWA but a few showers and sprinkles may move into the western
counties during the day on Saturday but should dissipate during the
evening hours. Highs on Saturday will be dependent on sky cover.
Skies will remain mostly cloudy across the western counties of the
CWA, therefore highs will only reach around 60. The eastern counties
should see more insolation which will allow highs to reach the mid
to upper 60s.
Sunday through Wednesday, the H5 trough across the western US will
amplify into a closed upper low across southern CA on Monday and
slowly drift east into AZ By Tuesday. A down stream upper ridge will
amplify across the plains through the period. Temperatures will warm
into the upper 60s on Sunday, lower 70s on Monday and upper 70s to
around 80 by Tuesday and Wednesday. A deepening lee surface trough
across the central and southern high plains will allow southerly low-
level winds to advect deeper moisture northward across KS on
Wednesday. There may be a slight chance for showers and
thunderstorms on Wednesday.
Wednesday night through Friday, the upper low will drift into west
TX and become a cut off low as an upper ridge develops within the
northern branch of the jet stream across the northern plains into
southern Canada. The cut off low will slowly fill through the period
across west TX. Southeasterly 850mb flow will continue to advect
deeper moisture northwestward across KS. Also minor vort maxes or
weak upper troughs will rotate northward across the central plains
on the east side of the closed upper low over west TX. Expect
isolated to scattered showers and thunderstorms through the period
across the CWA. Highs will cool slightly back into the lower to mid
70s as cloud cover and rain chances increase.
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Saturday AFTERNOON)
ISSUED AT 1218 PM CDT FRI OCT 2 2015
VFR conditions are expected at all terminals for the duration of
the TAF period.