Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 222024
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
324 PM CDT Wed Apr 22 2015

.SHORT TERM...(This Evening through Thursday)
Issued at 234 PM CDT WED APR 22 2015

Water vapor imagery showed the closed mid-level low continuing to
spin north of the Great Lakes region, keeping the forecast area in
northwesterly flow aloft.  At the surface, high pressure was
centered over the area with light northeasterly winds keeping
temperatures cooler than normal with afternoon highs only reaching
into the mid/upper 50s. The mid-level low should start to pivot a
bit further east tonight into Thursday as a weak mid-level ridge
develops over the Central and Southern Plains. The region will
remain under the influence of surface high pressure tonight through
Thursday as it slowly shifts eastward, causing winds to shift to the
southeast by Thursday morning. There is some uncertainty with how
cool low temperatures will drop tonight as there are model
discrepancies with regards to cloud cover overnight. The NAM is most
aggressive with bringing in an overcast low cloud deck while other
models suggest only few to scattered cloud cover developing early
Thursday morning. Have trended more toward the cloud cover being few
to scattered and, thus, have continued to trend on the lower side of
temperatures with lows in the mid/upper 30s north to near 40 degrees
south, but will need to closely monitor conditions through the
overnight hours. With these temperatures in mind, in combination
with the light winds, cannot rule out the potential for some patchy
frost to develop in extreme northeast Kansas where temperatures are
expected to drop into the mid 30s.

With winds shifting to the southeast on Thursday, expect afternoon
temperatures to be a few degrees warmer than today with highs
reaching into the low/mid 60s. Model soundings are in agreement with
having increasing low-level cloud cover through the day with several
short-range models even suggesting the potential for a few isolated
showers to develop. However, there is very little in the way of
available lift to support the development of any precipitation so
have continued with a dry forecast for Thursday yet cannot
completely rule out a stray sprinkle or two.

.LONG TERM...(Thursday Night through Wednesday)
Issued at 234 PM CDT WED APR 22 2015

Forecast focus remains on Friday severe storm risk. Feel that the
12z ECMWF is a realistic compromise between a weaker sfc depiction
of the NAM and more northerly sfc low solution of the GFS. In
summary...all models depict a potential significant severe weather
event across the area Friday evening.

Expect scattered elevated convection to develop later Thursday
night through midday Friday as an initial upper wave moves into
the Plains and enhances WAA/moisture advection within axis of 40-50kt
LLJ however given lack of a 850mb boundary/focus will keep precip
chcs in the 30-40 percent range.

By 12z Friday expect the main upper wave to be around the Four
Corners region inducing sfc pressure falls across southwest
Kansas. Looking at current obs across north/central TX the idea of
upper 50s to lower 60s dewpoints reaching into central KS by 21z
Friday appears reasonable and expect this to be the case near
south of the warm front which should move toward a Salina to
Emporia line in the 21z to 00z time frame. The dry line should
also be located somewhere along a Salina to Wichita line based on
latest ECMWF. All models are depicting a 100-125kt 300mb jet streak
overspreading the area by 00z Sat which will provide a window for
6KM shear of 60-70kts to exist in concert with MLCAPE of
1000-1500J/KG and limited capping which should be eliminated by
dynamic lift of the upper wave. Most concerning will be the 00z to
06z time frame when 0-1km shear will increase markedly and could
support some risk for stronger tornadoes if sufficient sfc based
instability exists. Main uncertainties remain timing and location of
the sfc low and associated warm front and initial development.
NAM/GFS/ECMWF all vary to some degree in location of details. For
now will keep emphasizing the potentially dangerous set up later
Friday evening and focus on the details in the next 36 hours.

Beyond Friday night some lingering showers early Saturday before
dry and cool weather moves into the region for the rest of the
weekend. The next upper low is still forecast to dig into the
southern Rockies by Monday. The GFS is the only model that
supports a wet or more northern solution while the GEM/ECMWF are
dry across the area. For now will keep low precip chcs early next
week but wouldn`t be surprised if trends support dry weather next
week with the highly amplified pattern with near or below avg
temps.

&&

.AVIATION...(For the 18Z TAFs through 18Z Thursday Afternoon)
Issued at 1230 PM CDT WED APR 22 2015

VFR conditions will still be the result of high pressure influence
over the region through tomorrow noon. Winds shift to the
East/southeast by the end of the period. Some showers may develop
West of KMHK but should remain there this period. The biggest impact
will be scattered to possibly broken mid to high clouds.


&&

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

$$

SHORT TERM...Hennecke
LONG TERM...Omitt
AVIATION...Drake





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