Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 290529
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1229 AM CDT Sun Mar 29 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 335 PM CDT SAT MAR 28 2015

A rather strong upper level wave was crossing Montana early this
afternoon with areas of convection just ahead of it, pushing the
longwave ridge east into the Plains. East to southeast surface winds
dominating local conditions with pressures falling to the northwest
and temps ranging from the upper 40s northeast to middle 60s
southwest.

The Northern Rockies wave will provide changing conditions over the
next 24 hours. South to southeast winds will likely pick up somewhat
overnight as 850mb winds increase to 40-55kt, bringing improved low
level moisture into the area with some stratus likely in central and
eastern areas by late tonight. These conditions should keep temps
tonight rather warm, likely not too far from Friday`s highs. The
wave remains mainly to the north, with west to northwest mid level
flow off the old ridge keeping deep moisture rather hard to come by.
Appears mid/upper forcing with the wave for isolated to scattered
showers with very modest, high-based CAPE in place in mainly north
and east late tonight into early Sunday. Pacific cold front follows
late tonight into midday Sunday with moisture still unable to be
deep enough for surface-based convection. Northwest winds increase
quickly into the 15-25 mph range behind the front with modified air
surging in. Models vary considerably on how dry the low levels will
get, with dewpoints continuing to fall as winds subside in the late
afternoon. At this point, RH values look to be close enough to
concerning levels to support a Fire Weather Watch for western areas
in the afternoon. Highs remain on target to reach the mid 60s to
near 70 despite the post front airmass.

.LONG TERM...(Sunday Night through Saturday)
Issued at 335 PM CDT SAT MAR 28 2015

Sunday night through Tuesday continues to look pleasant with dry
weather expected to prevail as temps gradually warm. Models show a
weak boundary moving through the area late Monday night and
Tuesday morning. Limited moisture and no real organized synoptic
scale forcing suggest this boundary should move through dry and
wash out across east central KS Tuesday afternoon. The main effect
the boundary may have is to limit boundary layer mixing on
Tuesday. Because of this have kept afternoon highs in the mid and
upper 70s.

There is good agreement on a cold front moving into north central
KS Wednesday afternoon and through the forecast area during the
evening and overnight Wednesday. The GFS continues to show a fair
bit of instability with MUCAPE values on the order of 2000 J/KG.
And while deep layer sheer could be stronger, it may be enough for
some kind of linear MCS with the front. Questions still remain as
to how the instability will evolve towards the evening, since GFS
forecast soundings show much of the CAPE to originate from
boundary layer parcels. As temps begin to cool, the model quickly
diminishes the instability. Nevertheless there appears to be the
potential for some strong storms Wednesday afternoon and Wednesday
evening. Because there is good agreement in timing of the front,
have increased POPs to the likely category for Wednesday night.
However there remains differences on the strength of the surface
ridge behind the front so there could be adjustments needed to
later forecasts. Highs Wednesday continue on track for the mid 70s
to near 80, and based on 850MB progs of temp, am pretty
comfortable with this forecast.

The differences in the strength of the surface ridge Thursday make
forecasting temps for Thursday a little less confident. The ECMWF
with its weaker ridge, wants to keep temps a little warmer.
However with the GEM and GFS both showing a little more low level
cold air advection, have trended temps cooler especially across
northern KS. There is better agreement in the GFS/ECMWF/GEM for a
second surface wave to move through the central plains Thursday
night and Friday morning. This will bring chances for more precip.
At this point temps appear to remain warm enough for precip type
to remain liquid. There is some question as to how much
instability there will be as models tend to track the surface low
across southern KS. The warmer and more humid ECMWF would have
enough instability for chances of thunder to persist. With this in
mind have maintained a mention of thunder generally south of I-70
for Thursday and Thursday night. Precip chances should be
diminishing through the day Friday as the system lifts towards the
Great Lakes with cool dry air filling in. Friday and Friday night
appear to be the coolest periods with highs generally in the 50s
and lows in the mid 30s. With some insolation and an end to the
cold air advection, temps should rebound into the 60s for
Saturday.

&&

.AVIATION...(For the 06Z TAFs through 06Z Sunday Night)
Issued at 1225 AM CDT SUN MAR 29 2015

Minimal changes from previous TAF issuance. Southeast winds veer
out of the southwest by 09Z with scattered showers and potential
SCT to BKN cigs around 3000 ft through around 14Z. Just above the
deck, around 1500 feet, expect southwest winds at 40 to 50 kts,
but should stay just below LLWS criteria. Winds turn out of the
northwest by mid morning Sunday with gusts to 20+ kts.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH this afternoon FOR KSZ008-020-021-034-035.

&&

$$

SHORT TERM...65
LONG TERM...Wolters
AVIATION...Barjenbruch/67






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