National Weather Service Raw Text Product

982 
FXUS63 KTOP 081803
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1203 PM CST Fri Mar 8 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today through Saturday) 
Issued at 348 AM CST Fri Mar 8 2019

As of 09Z Friday morning zonal midlevel flow was present across 
the Central Plains with an embedded shortwave trough traversing 
KS. Scattered showers and sprinkles were noted earlier this 
morning, although all precipitation has pushed east of the 
forecast area. Nighttime microphysics satellite reveals an 
expanding area of low cloud cover and fog. Generally visibilities 
have remained greater than 1 mile, although brief periods of <1 
mile are possible through the morning, especially south of I-70. 
Cloud cover is likely to remain stubborn through the day with 
mostly cloudy skies anticipated, which will make for a tricky 
temperature forecast this afternoon. GFS/RAP/HRRR forecast 
soundings depict boundary mixing heights nearing 925-900 mb which 
could translate to temperatures near 50 for areas along/south of 
I-70. Given the persistent stratus, have opted for highs in the 
mid 40s along/south of I-70, with 30s/40s northward where several 
inches of snow depth remains. 

Our attention then turns toward midlevel trough which is currently 
along the CA coast. WAA is progged to rapidly increase after 00Z 
this evening across the entire forecast area. Given the pre-existing 
low-level moisture in the form of stratus, drizzle is expected area-
wide through 06Z. As the main midlevel trough axis encroaches the 
area overnight, the stout EML should erode allowing for a transition 
to rainfall to occur area-wide. Model solutions continue to progress 
the surface low from Salina to St. Joseph overnight into Saturday 
morning, allowing dew points to surge into the upper 40s to low 50s 
southeast of its track. As the EML erodes, 100 to 400 J/kg of MUCAPE 
is likely to be realized across the southeastern half of the CWA, 
with the highest values across Anderson County. Considerable 
uncertainty remains with the near-surface temperature profile and 
the strength of the inversion. GFS and CAM forecast soundings depict 
a weak surface inversion by 12Z, while the NAM and ECMWF maintain a 
stronger surface inversion. With the strongly shear environment 
expected Saturday morning, if the GFS/CAM solutions come to fruition 
a few damaging wind gusts would be possible. As the midlevel trough 
ejects northeast of the forecast area late Saturday morning/early 
afternoon, precipitation will end from southwest to northeast. Total 
rainfall amounts are likely to range from near 0.1" in North-Central 
KS to near 0.75" in far Eastern KS. 

A strong surface pressure gradient (8-10 mb across the CWA) combined 
with 850 mb winds  near 50 kt will yield windy conditions late 
Saturday morning through sunset. Current expectation is for sustained 
winds between 25-35 MPH with gusts 40-50 MPH. A wind advisory may 
need to be considered in subsequent forecast issuances. A brief 
period of "spring-like" temperatures is anticipated early Saturday 
afternoon with highs in the 50s across Eastern KS, 40s elsewhere. 
CAA will increase by late afternoon, decreasing temperatures into 
the 30s and 40s area wide by sunset.

.LONG TERM...(Saturday night through Thursday)
Issued at 348 AM CST Fri Mar 8 2019

Models are in agreement that as a surface ridge builds south
Saturday night, shortwave ridging develops aloft over the central
plains through Sunday night. Additionally there is expected to be
dry air moving into the area with the surface ridge. So with 
little in the way of moisture or forcing for precip, the weather 
is expected to remain dry Saturday night and into Monday morning. 
Temps are expected to be 5 to 10 degrees below normal with lows in
the 20s and highs in the 40s. 

By Monday afternoon, the surface ridge is expected to begin
weakening while a low level return flow develops over the surface
ridge. There is good consensus for a strengthening warm air advection
pattern Monday night and through the day Tuesday as moisture gets
lifted along the isentropic surfaces. So precip chances should be
on the increase late Monday afternoon and through the night. With
the warm air advection pattern, models develop a decent warm nose
over the forecast area by Tuesday morning, and as a result it
looks like snow is less likely than perhaps some freezing rain
where temps do fall below freezing. Although it is not clear 
temps will fall significantly below freezing Monday night or 
Tuesday morning as overcast skies limit radiational cooling while 
the low level warm air advection pattern persists. So have trended
Tuesday morning lows a degree or two warmer with areas near the 
NEB state line and where there could still be some snow pack 
around freezing. With this in mind, have a wintry mix of freezing 
rain and sleet for areas along and north of a line from Concordia 
to Holton. 

The stronger dynamics are progged to lift across the forecast area
Tuesday night and Wednesday morning. There are still some timing
differences among the models with the upper low and how quickly
the dry slot works its way into northeast KS. But the overall
trend in POPs should be to lower through the day Wednesday. Models
show a bit of a negative tilt to the wave as it lifts north
Wednesday morning. While GFS forecast soundings show limited
instability until the dry slot moves in Wednesday afternoon, have
kept a slight chance for thunder late Tuesday night and into
Wednesday given the pattern and somewhat steeper mid level lapse
rates ahead of the wave around 6.5 C/km. Models develop a strong
pressure gradient on Wednesday as the surface low lifts north of
the forecast area. This is expected to promote good mixing of the
boundary layer while 925MB temps potentially increase to around
+14C across eastern KS. Thinking there could be some partly sunny
skies by the afternoon as well, so have increased highs to around
60 which may still be on the conservative side if the warm air 
advection is as strong as the models indicate. For north central
KS, the warm air advection looks to be weaker and only have highs
in the lower and mid 50s. 

For Thursday, dry air is forecast to move in as the surface 
pressure rises. Aloft models suggest a broad cyclonic pattern 
develops with no obvious shortwave. With this in mind think precip
chances are to low to mention. Renewed low level cold air
advection should hold temperatures generally in the 40s. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1139 AM CST Fri Mar 8 2019

For the 18Z TAFS, visibilities and CIGS will improve slightly this
afternoon. An upper level trough and associated surface low will
approach the area this evening. Rain and thunderstorms will 
develop and overspread the forecast area tonight. Damaging wind
will be possible with stronger storms. Visibilities and CIGS will
drop into the low-end IFR category with precip around. Periods of
LIFR will also be possible at times. Rain and storms should exit 
the area by midday Saturday. Surface winds will increase as the 
precip exits and will be very gusty through the day. 

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for KSZ008-020.

&&

$$

SHORT TERM...Baerg
LONG TERM...Wolters
AVIATION...Teefey