Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 231153

Area Forecast Discussion
National Weather Service Topeka KS
553 AM CST Fri Feb 23 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 419 AM CST Fri Feb 23 2018

As of 09Z Friday morning, longwave mid-level trough continues to be
positioned across the Great Basin region. At the surface, a ridge
axis extended from south TX into eastern MT. Goes-16 nighttime
microphysics display reveals an expansive stratus field across the
CWA. As the surface ridge traverses the CWA, drier low level air
will advect into the area, decreasing low level cloud cover from
northwest to southeast through the day. The back of the stratus
resided from near CNK to OMA at 09Z. Fog has been ongoing for much
of the night with visibilities across the CWA greater than 1 mile.
Temperatures across the region range from the upper 20s in north
central KS to the low to mid 30s across east central KS. Given the
lack of dense fog, do not expect any concern for freezing fog
through the morning hours. Visibilities are also expected to
continue improving through the morning hours. Although little
moderation to the current air mass has taken place over the last 24
hours, the increased solar insolation should allow temperatures to
range from the upper 30s in north central KS to the lower 40s across
east central KS.

The main weather concern through the short-term period is the
potential for freezing drizzle/rain late tonight through Saturday
morning. The aforementioned trough will eject across the central
Plains late tonight into Saturday. Lee cyclogenesis is progged to
take place across northeast NM through the day today. In response
WAA will begin to overspread the region after 06Z Saturday and more
so after 12Z Saturday. Initially, scattered rain showers are
possible after 00Z this evening for areas southeast of I-35 in
response to a weak lead shortwave lifting across the Ozarks. Later
in the overnight, all solutions increase isentropic upglide within
the 280 to 295K layer after 06Z across the entire CWA. All forecast
sounding solutions suggest no cloud-layer ice will be present.
Therefore we are relegated to rain, drizzle and their frozen
counterparts. Given the lack of deep moisture, would suspect the
primary precip type(s) will reside with drizzle or freezing drizzle.
The biggest question mark is the placement of the freezing line. 00Z
runs this evening from GFS/NAM/ARW/NMM solutions all had a slight
northwestward shift in the freezing line location in comparison to
yesterday`s 12Z runs. At this point in time the freezing line is
progged to bisect the area from southwest to northeast. Will not
issue any headlines with this forecast package as some uncertainty
remains with total QPF amounts and the exact location of the
freezing line. As a result will allow the day shift to further
investigate with hi-res guidance this afternoon.

.LONG TERM...(Saturday through Thursday)
Issued at 419 AM CST Fri Feb 23 2018

Strong isentropic upglide continues over the lower few thousand feet
into at least midday Saturday as the upper wave passes, with mid
levels continuing to struggle to saturate until perhaps in the
afternoon to keep cloud ice very limited. By this time, southerly
winds will be bringing wet bulb temps to most if not the entire area
well above freezing, keeping most precip in this event in drizzle or
light rain. Still have questions on timing of how fast the warming
will occur (and where temps will start at 12Z) and models do vary
notably in strength and timing of the surface low reflection as it
crosses the central Plains during the day. Still, believe most
locations will see at least minor accumulations of liquid precip,
with still enough depth of moisture in the far southeast for some
thunder as well, but not confident enough in the coincidence of
critical temperature and precip accumulations for any headlines yet.

The next upper wave passes Sunday but Pacific high pressure in place
keeps impacts limited to some mid cloud. Southwest flow aloft then
takes hold into midweek when the next wave exiting the southwest
states enters the region. With a few days of modification (high
temps back into the 50s and 60s), precip chances are much better
with this wave, with elevated thunderstorm potential returning.
Character of the upper pattern becomes more uncertain in the late
week though near to above normal temperatures are most likely.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 544 AM CST Fri Feb 23 2018

MVFR stratus continues across much of the area this morning. The
back-edge of the cloud shield extends from near KCNK to KOMA.
With its current track and speed it should yield VFR conditions at
MHK near 13Z and the Topeka terminals near 15Z. MVFR stratus is
expected to build back in after 01-02Z this evening. Cloud heights
will further decrease through the evening with VLIFR to LIFR
condition expected by 04-06Z timeframe as light freezing drizzle
overspreads the terminals. Currently mention MVFR vsby, although
further refinement and lower vsby are certainly possible in
subsequent forecasts.




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