Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 221000
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
400 AM CST Thu Feb 22 2018

.SHORT TERM...(Today and tonight)
Issued at 357 AM CST Thu Feb 22 2018

The 09Z water vapor imagery shows there has been little change in
the synoptic pattern from 24 hours ago. The long wave upper trough
remains over the western half of the country with a another
shortwave rotating through the base of the trough. A second
shortwave was digging south through the Pacific Northwest. At the
surface, high pressure was centered over the Upper Midwest with a
ridge axis extending through the southern plains. However the
surface high has been weakening as indicated by the gradual pressure
falls over the last several hours.

Surface temps are going to play a critical role in the forecast
today and whether precip falls in the form of freezing rain or just
rain. In general models re in agreement that the low level warm air
advection patter will persist through the day and into this evening.
Isentropic surfaces also indicate upglide within the deep saturated
stable layer near the surface for much of the day. Then there is the
wave that is beginning to rotate out of AZ that could provide
forcing more measurable precip. There is also reasonable agreement
that humidity levels within the dendritic growth zone are only going
to dry out through the morning and remain dry through this evening.
So in a way this should simplify the precip type part of the
forecast. With a lack of ice in the cloud today freezing rain is
likely to be the predominate precip type. Hence the focus on surface
temps. The continued warm air and moisture advection is expected to
keep low overcast over the area through the day with more of an
easterly wind than a south wind. As a result there is not a low of
warm air moving in from the south and the latest HRRR/RAP/ARW
struggle to bring the freezing line to around EMP and TOP by the
late afternoon. As a result, think much of the forecast area will
have to contend with freezing rain and freezing drizzle through the
day. The current area of scattered showers is expected to lift north
of the area by late morning. With continued isentropic upglide,
think that freezing drizzle is likely to persist through the later
morning and early afternoon. Than the wave over AZ should lift out
across the area late this afternoon and early evening with another
round of freezing rain. Highs today will not see much of a bounce
from current temps with readings expected to range from the upper
20s across north central KS to the mid 30s in far east central KS.
Clouds tonight may try to scatter out from west to east as light
winds shift to the northwest and some drier air tries to work into
the area. For now think at least mostly cloudy skies are likely
through the morning so have lows tonight in the mid 20s to lower
30s.

.LONG TERM...(Friday through Wednesday)
Issued at 357 AM CST Thu Feb 22 2018

The main takeaway from the extended period is one more round of
wintry precipitation is expected Friday night/Saturday morning
before more tranquil weather returns for the second half of the
weekend.

After precipitation exits the region later this evening a brief 18
to 24 hour lull in precipitation is expected Friday before the
next chance of rain and wintry weather returns to northeast KS
Friday night. Model solutions continue to converge on a neutral to
slightly negatively tilted shortwave trough traversing the area
Saturday afternoon. Lee cyclogenesis is progged to take place
across northeast NM late Friday night. In response a modest LLJ
on the order of 20-30kts should slowly increase BL moisture
through the pre-dawn hours. Increasing isentropic ascent between
280-295K may yield rain showers or drizzle during the pre-dawn
hours Saturday morning as well. ECMWF and NAM thermal profiles
continue to suggest the potential for freezing drizzle across the
entire CWA, while the GFS limits any freezing precipitation to
north of I-70. Given the weak WAA prior to 12Z, will hedge thermal
profiles towards the NAM/ECMWF solution. Therefore have freezing
drizzle mentioned across much of the CWA through 12Z. The only
area without a mention of freezing drizzle is east central KS
where temperatures will rise above freezing the quickest. At this
point, ice accumulations continue to look minor -- less than
0.10" -- with the heaviest amounts across north central KS. Aside
from the wintry concerns, a few thunderstorms are possible given
mid- level lapse rates near 6 C/km. The GFS -- the furthest north
solution with the surface low track, suggests upwards of a couple
hundred J/kg of MUcape may exist Saturday afternoon -- especially
southeast of the KS Turnpike (I-35,335,70). As a result, continue
with a mention of thunder in forecast Saturday afternoon.

A secondary shortwave trough looks to dig into the western CONUS
over the weekend and eject into the central Plains late Sunday
night into Monday. However, little moisture return will limit
precipitation coverage. At the moment have a dry forecast for
Monday. Surface ridge will push east of the CWA by Tuesday,
allowing high temperatures to approach 60 degrees Tuesday
afternoon! Long range solutions continue to suggest another
shortwave trough will dig into the southwestern CONUS and eject
into the central Plains by midweek next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1124 PM CST Wed Feb 21 2018

Freezing drizzle and rain is moving through the taf sites. There
may be some sleet and or snow mixed in at times. There may be a
period of just freezing drizzle in the late morning. Another round
of precipitation is expected in the late afternoon although the
sites might be above freezing at the surface. Ceilings will only
gradually lower through the day eventually going to LIFR.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight CST tonight for
KSZ010>012-023-024.

Winter Weather Advisory until 6 PM CST this evening for KSZ008-
009-020>022-026-034>040-054-055.

Winter Weather Advisory until noon CST today for KSZ056-058-059.

&&

$$

SHORT TERM...Wolters
LONG TERM...Baerg
AVIATION...Sanders



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