Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 010526
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1126 PM CST Wed Nov 30 2016
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Thursday)
Issued at 253 PM CST Wed Nov 30 2016
Water vapor imagery showing a stacked upper low over the Upper
Mississippi Valley making slow eastward progress with some low and
mid cloud rotating around behind the surface cyclone. Mid and lower
cloud has been rather persistent especially over northern areas with
temps fairly steady in the upper 30s.
Winds become somewhat more westerly tonight, with speeds at 925mb
remaining around 20kts. The more persistent cloud should slowly work
off to the east as the stacked system does the same. Despite the
clearing skies, the stronger winds over the boundary layer should
keep lows in the 20s. Modest zonal flow develops aloft Thursday with
surface pressure gradient weakening. Low level thermal fields don`t
change much, but more early-midday sunshine should help push highs
slightly warmer than today, with apparent temps notably warmer as
well in lighter winds. Some high cloud ahead of a weak wave may move
into southern areas in the afternoon.
.LONG TERM...(Thursday night through Wednesday)
Issued at 253 PM CST Wed Nov 30 2016
The long term forecast is very complicated today with a large
scale or long wave upper trough establishing itself over the
CONUS. Eventually, the first real arctic airmass should move into
the central plains by the middle of next week. Along with the cold
air,the weather pattern looks active with increasing chances of
winter precipitation late in the forecast period.
From Friday through the weekend...The short wave moving into the
western US attm moves south into Mexico and cuts off from the
westerlies by Friday afternoon. Ahead of this feature, short range
ridging takes place over the southern plains and moisture is
transported north into the plains in southwest flow aloft. All
the models breakout precipitation across the southern plains by
Friday evening and then into Kansas by Saturday morning. The GFS
is the most aggressive with the moisture return and QPF over NE
Kansas Saturday. Meanwhile, a northern stream short wave trough
is forecast to move through the plains Saturday night which should
clean out the moisture and precipitation by Sunday morning.
At the surface, the large area of high pressure over the plains
and Missouri valley on Friday moves east allowing southerly flow
to develop. Given the overall weakness in the return flow, the GFS
looks overdone with this moisture return and pops were limited to
small chance Saturday and Saturday night. Based on
thermodynamics, the precipitation should be mainly light rain on
Saturday with some snow/rain mix possible Saturday night. QPF
looks very low however and impacts should be minimal.
The upper low over northern Mexico is forecast to eject out early
next week by the GFS/ECMWF. The passage of this upper low should
occur Monday afternoon through Tuesday morning. This should mainly
be a rain event, but we could see some snow on the early Tuesday
under the upper trough.
The spread between the 12Z GFS and 12z ECMWF with respect to the
arctic air arrival in eastern Kansas in the Tue/Wed timeframe is
significant. The ECMWF has the cold air arriving Tue while the GFS
has it coming in behind a sharp frontal passage Wednesday. The
official forecast brings the brunt of the cold air in by
Wednesday. There is the potential for a winter event sometime
around the middle of next week but there is significant
uncertainty given the current models.
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1125 PM CST Wed Nov 30 2016
VFR conditions are likely through the TAF period with west winds
generally less than 10 kts.