Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 011119
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
619 AM CDT Fri May 1 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 332 AM CDT FRI MAY 1 2015

Water vapor loop shows nearly zonal stronger flow aloft across the
northern Rockies and northern Plains states with a well-defined
shortwave trough from the eastern Dakotas into northwest MN.  A band
of showers is associated with lift ahead of upper trough moving
through western MN trailing back into northeast Nebraska at this
time.  Forcing associated with this system should stay well to north
of forecast area today.  However, regional radar loops show showers
and isolated thunderstorms occurring with trailing cold front/trough
from central Nebraska into northwest KS.  There is some disagreement
among models but NAM, RAP and HRRR show remnants of this high-based
precip making it into north central KS by early afternoon and then
moving across far northeastern KS during the rest of the afternoon.
While confidence is not high in measurable precip with this
activity, have continued slight chance POPs for far northern
counties this afternoon.   Something similar could happen again
tonight with developing showers and thunderstorms over western
Nebraska, which is forecast by some models to persist and move into
far northern parts of our area tonight.  Once again, without a
stronger upper level system or recognizable front coming through,
this will be a low chance event, with slightly better chances to our
north.

Considerable mid and high level cloudiness today could make high
temp forecast tricky.  Still think enough sunshine will get through
to allow highs to reach the mid to upper 70s.

.LONG TERM...(Saturday through Thursday)
Issued at 332 AM CDT FRI MAY 1 2015

By Saturday, fairly zonal mid-level flow will be in place with
surface high pressure prevailing across the southeastern U.S. and
surface low pressure extending along the High Plains. Models
continue to show a few weak embedded shortwaves developing within
the zonal flow on Saturday as a vort max skims just north of the
CWA. However, with no surface feature to help further support these
waves and with model soundings showing a decent amount of dry air in
the low levels, have only slight chance PoPs in across far northern
and far northeast Kansas Saturday morning with dry conditions by the
afternoon as the associated vort max lifts to the northeast. With
the above-mentioned surface pattern in place, southerly surface
winds should boost high temperatures into the upper 70s/low 80s.

Have gone with a dry forecast Saturday afternoon through Sunday
before the next system moves into the region, which will be the
beginning of a wet stretch of weather that looks to extend through
the latter part of next week. Models show the surface low advancing
eastward toward the CWA on Sunday, resulting in an increased
pressure gradient, breezy southerly winds, and thus good warm air
advection that should support the warmest temperatures of the week
with highs reaching into the low/mid 80s. Precipitation chances will
increase Sunday night through Monday as a cold front slowly sags
southeastward across the CWA. However, models show the front
stalling out over the southern portions of the forecast area and
pivoting over the area before lifting northward as a warm front to
just north of the KS/NE border on Tuesday. As a result, have chance
to likely PoPs for thunderstorms from Sunday night through Monday
night. Even though the cap looks to significantly weaken through the
day on Monday and the amount of available instability is modest,
wind shear looks to be fairly weak across the region, thus limiting
the potential for strong storms. With the warm front lifting into
Nebraska, ECMWF/GEM actually keep Tuesday predominantly dry while
the GFS tries to hold on to some scattered precipitation chances, so
have lowered PoPs. However, thunderstorm chances increase once again
by Tuesday night as a mid-level trough becomes negatively tilted and
begins to lift northward into the central U.S.  This approaching
trough will not only provide additional forcing to support
thunderstorm development, but also push another area of surface low
pressure into the area by mid week.  However, there are still model
discrepancies in the evolution of the mid-level trough as it lifts
northward and in the timing of the passage of the cold front, which
should track eastward across the area sometime during the latter
part of the week. As a result, there is uncertainty still with when
this system will exit the region. At this time, have chance to
likely PoPs in from Tuesday night through Thursday night. The best
potential for some more-organized storms looks to be during the mid
to late week period in which the combination of the surface low
pressure system and mid-level trough should provide decent forcing
along with decent instability and some slightly improved wind shear.
At this time, temperatures next week look to be fairly steady with
highs in the 70s and lows in the 50s to low 60s.

&&

.AVIATION...(For the 12Z TAFs through 12Z Saturday Morning)
Issued at 613 AM CDT FRI MAY 1 2015

Expect considerably high level cloudiness today. But clouds should
be at 10,000 ft and above. A very weak upper system could affect
area tonight and isolated showers are a possibility. However,
coverage is expected to be too isolated to mention in TAFs.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...GDP
LONG TERM...Hennecke
AVIATION...GDP





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