Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 180843
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
343 AM CDT Sat Apr 18 2015
.SHORT TERM...(Today and Tonight)
Issued at 342 AM CDT SAT APR 18 2015
Showers and thunderstorms developing this hour across northeast
Oklahoma into south central and north central Kansas, with cell
movement toward the north northwest and the cluster moving more
northerly. This area is forecast to move across the forecast area
through the morning hours today.
Struggle with the forecast continues to be timing and coverage of
precipitation chances. After initial energy lifts across Eastern
Kansas through early afternoon, next uncertainty will be for chances
later in the afternoon. HRRR develops a cluster of showers in south
central KS, but would anticipate a break between the systems with
subsidence behind the main wave inhibiting convective development.
Have higher chances in the morning, with lower chances middle
afternoon, followed by an increase from west to east through the
evening into the overnight hours as the main wave finally starts to
get an easterly push, from both a northern US shortwave and an upper
jet traversing the southern states. With a lull in precipitation
and possibly some better sunshine out west, this would boost
instability and chances for severe thunderstorms as late day storms
develop along the dryline to our west and along the northward
advancing warm front. Primary threat would be hail, but closer
proximity to these surface features in north central Kansas could
bring an isolated tornado risk there. General precipitation chances
continue in the overnight hours ahead of the upper low as it
continues to slowly move east. Highs for Saturday in the middle 70s
west to near 70 east, with lows in the 50s.
.LONG TERM...(Sunday through Friday)
Issued at 342 AM CDT SAT APR 18 2015
By Sunday morning the mid/upper low will be centered over SC KS and
NC OK as it progresses eastward. During this time the low will
become more of an open wave as another shortwave digs into the
northern plains and upper Midwest. These waves will bring a cold
front through the region during the day Sunday. In the morning the
better chance for showers and some thunder should be in southern KS
where the front and mid level low are more coupled in the vertical.
By 18Z the models are hinting at an increase of instability on the
order of about 1000 j/kg ahead of the front that should stretch
across eastern KS. Lapse rates are not overly impressive, and deep
layer shear could reach 30 kts. Although the better shear will be
further southeast over southern MO where the flow aloft is slightly
stronger. Therefore kept a mention of thunderstorms for east central
KS during the afternoon. A majority of the precip should clear the
area around 03Z in the evening.
A sharp pressure gradient behind the front will support northwest
surface winds around 15 to 25 mph with gusts as up to 35 mph
especially in NC KS. Cold air advection on the backside of the wave
drops temps into the lower 40s and upper 30s by Monday morning.
Winds do not completely decouple Sunday night so there is little
concern for frost. On Monday winds remain gusty with high temps
generally around 60 and partly sunny skies. Monday night will not be
the classic set up for frost with a expansive high building
southward, but the winds do decrease and temps are forecast to reach
the mid to upper 30s. Therefore could not rule out the possibility
for frost perhaps in preferred sheltered locations.
NW flow aloft develops over the region as the northern stream wave
deepens over the Great Lakes. The models are beginning to advertise
embedded shortwaves within the NW flow, which track over the plains
around mid week. This will bring small chances for either showers or
thunderstorms. Late in the week a southern wave crashes the southern
CA coast and tracks northeastward towards the center of the country.
There are some differences on how far north the instability reaches
ahead of the system, and there are additional waves in the NW flow
that could interfere with the southern stream system. Confidence in
any solution is low at this point.
.AVIATION...(For the 06Z TAFs through 06Z Saturday Night)
Issued at 1134 PM CDT FRI APR 17 2015
Tricky forecast period as short term guidance has had difficulty
in determining timing and location of precip thru 12Z. However
latest models continue to show sct showers with a few embedded
TSRA impacting sites after 07Z at KMHK and 08Z at KTOP/KFOE. May
see brief MVFR conditions shortly after sunrise with the heavier
precip before it exits eastward early afternoon. Low confidence
thereafter as main system does not arrive into the area until
Sunday morning so will leave mention of VCTS.