Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 092017
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
317 PM CDT Sun Mar 9 2014
.SHORT TERM...(This Evening through Monday)
Issued at 317 PM CDT SUN MAR 9 2014
19Z water vapor imagery shows the mean westerlies are well north of
the forecast area along the Canadian border. A closed lows was seen
spinning over the Gulf of California. So there is relatively weak
flow aloft with a dry airmass in place as seen on the 12Z TOP RAOB.
At the surface, a trough axis was noted along the NM and CO front
range with a second surface trough over eastern NEB. This has
created a decent pressure gradient with ridging over the southern
plains and gusty southwesterly winds have advected warmer air into
central and eastern KS.
The forecast for tonight and Monday remains dry as models keep the
mean flow aloft to the north and surface ridging along the gulf
coast. This should prevent any strong forcing from affecting the
area and with no real deep moisture advection. Mild temps continue
to look favorable and have not needed to change the prev forecast
much. Some wind keeping the boundary layer mixed overnight should
help to keep min temps in the middle and upper 30s. With models
bring 925MB temps of 15 to 20C into north central and northeast KS,
highs in the lower to middle 70s looks plausible.
.LONG TERM...(Monday Night through Sunday)
Issued at 317 PM CDT SUN MAR 9 2014
The Tuesday and Tuesday night periods are shaping up as the most
troublesome periods of the remainder of the forecast. Fairly good
model agreement in the main features of the wave now approaching the
northwest ConUS making east-southeast progress into the Central
Plains Tuesday, though have some lower confidence overall with the
way the northwest flow energy is sheared out with time, with some
lingering cutting off back into the Four Corners, and how the cold
air with the northern branch is handled. Cold front comes through
rather stacked for rapid pressure rises behind it and still looking
like temp fall for much of the area as the day passes. Just where
highs end up remains a considerable challenge with very wide SREF
ranges on its 09Z and 15Z runs, but mainly just increased the
gradient at this point. Winds look to be the main issue with 925 mb
winds in the 35-45 kt range and advisory levels seem quite possible
in the midday to early evening hours. Low level moisture ahead of
the front is not high but minor CAPE may develop in far southeast
locations just ahead of the front. At this point the mid-level cap
looks strong enough to keep deep moist convection in check.
Mid/upper forcing with the wave and the surge of cold air may be
enough for light precip development behind the front Tuesday
afternoon through Tuesday evening, though moisture aloft is largely
lacking, with lift diminishing as the ice growth zone moistens.
Though air from northwest Canada comes in, temps there are not
terribly cold, and with snow formation aloft in question and warm
days ahead of it, not expecting much if any accumulations.
After temps back into the 40s Wednesday, modification returns for
Thursday under westerly downslope winds. A weak front should pass
Friday but very modified air with it and the upper wave well north
keeps the forecast dry and little change in sensible weather. Modest
precipitation chances come around Sunday with rather good model
agreement in another northwest flow upper wave, this one
intensifying as it comes through. Temps struggle to support much
chance for snow, but at this point will go with a mix.
.AVIATION...(For the 18Z TAFs through 18Z Monday Afternoon)
Issued at 1208 PM CDT SUN MAR 9 2014
A dry airmass will allow VFR conditions to persist into Monday.
There is some concern for low level wind shear due to an increasing
low level jet. However forecast soundings do not indicate a sharp
discontinuity in wind speeds between the boundary layer and the
low level jet. Therefore will not include wind shear at this time.