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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 191131
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
531 AM CST Tue Feb 19 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 316 AM CST Tue Feb 19 2019

Water vapor imagery this morning highlights the incoming upper 
trough rotating over the Four Corners Region while swath of mid 
level moisture streams across the central plains. Expansive amount 
of dry air is noted below 700 mb into the early afternoon, keeping 
much of the area dry with highs from the upper 20s to lower 30s. 
Short term models are highlighting an initial band of snowfall 
associated with a lead impulse from the main upper trough arriving 
into north central Kansas during the late afternoon while most of 
the CWA may only see flurries at most until the upper trough lifts 
into the western highs plains aft 23Z. The heaviest snow is progged 
to fall between 00Z and 12Z Wednesday where decent frontogenesis 
coincides with negative EPV values. Periods of moderate to heavy 
snow are expected during this time, reducing visibilities and quickly 
causing hazardous travel conditions.

Main changes to the forecast package starts with the increasing 
freezing drizzle and freezing rain potential along and southeast of 
the Kansas Turnpike as most guidance is signaling the dry slot 
lifting into east central Kansas aft 03Z. This dry slot will cut off 
ice formation resulting in snow mixing with freezing rain or 
becoming all freezing rain aft 05Z. Adjustments were made to areas 
south and east of the turnpike with lesser snowfall between 2 and 3 
inches in addition to a quick tenth of an inch of ice. The Topeka 
and Lawrence areas are centered in the transition zone where 
uncertainty increases for the depth of the drier air and how much 
freezing rain mixes in, impacting snowfall totals. After 
collaborating with neighbors, centered on higher probabilities for 
snow with lesser ice amounts to mix in, maintaining snowfall totals 
in the 3 to 5 inch range with a light glaze of ice. 

Further north for the counties near the Kansas and Nebraska 
border, have upgraded the Watch to a Winter Storm Warning, adding 
Cloud county into the group with expected snowfall amounts of at 
least 6 inches with locally higher amounts expected. Did not make 
major changes to snowfall totals with snow ratios being highest in
the colder airmass, ranging from 13 to 15:1. In addition, believe
precip type will remain all snow with the dry slot perhaps only 
having an impact over Brown county towards 12Z as the system exits
northeast. Accumulating precip comes to an end by 9 AM with a 
slight chance for light snow and/or freezing drizzle north of 
Interstate 70 through 18Z. Temps warm above freezing into the mid 
30s towards east central Kansas, while elsewhere upper 20s can be 
expected under mostly cloudy skies.

.LONG TERM...(Tuesday night through Monday)
Issued at 340 PM CST Mon Feb 18 2019

A period of relative calm and warming will likely take shape 
during the latter portions of this week before the next impactful 
system moves through the area by the first part of the upcoming 
weekend.

Thursday into Friday, heights rise over the region as surface high 
pressure takes firm hold -- at least for a couple days -- broad 
shortwave ridging works over the region.  H85 temps rise to around 
5C resulting in surface temperatures easily into the upper 30s to 
middle 40s from north to south from the Kansas/Nebraska border into 
east central areas.  Sunshine will be welcome but gives way once 
again to yet another storm system working into the region by late 
Friday into the early part of the upcoming weekend.  Strong WAA 
develops as a potent shortwave works through the deep longer wave 
trough anchored over the western CONUS due to a northern Pacific 
blocking pattern holding strong for the foreseeable future.  

As this system emerges from the central Rockies, it quickly exhibits 
very impressive dynamics over the area and deepens rapidly and 
evolving into a negatively tilted shortwave nearly right over the 
region as strong forcing for ascent develops through a deep layer of 
the troposphere.  An impressive 150kt jet streak intensifies over 
the region with the left front exit region nearly over the forecast 
area into the day Saturday.  Ensemble and deterministic models all 
seem to have fairly good agreement with the overall synoptic setup 
at this point and as a result H5 closed low features have good 
consistency regarding intensity and positioning.  As a result, 
surface cyclones also match well in intensity and temporal and 
spatial positioning.  This system looks like a classic early 
transition season Colorado Low.  Meaning that while there is 
potential for mixed precipitation and possibly high snow amounts on 
the northern and northwestern deformation zone regions, the WAA 
aspect should advect warm enough and deep enough air to be in the 
form of mostly liquid rain over much of the area for most of the 
residence time of the system before it exits the area.  Thus, it is 
possible from the looks of it right now that possible mixed precip 
and snow amounts could be for only a short period of time and mostly 
focused over north central into mainly northern areas of the region. 
 In light of recent storm systems this could be welcome news.  Also, 
there could be enough instability aloft to hear a few claps of 
thunder as the system moves through.  Too early to talk rain, snow 
or ice amounts.  But, the first half of the weekend does look wet 
and stormy.  

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 526 AM CST Tue Feb 19 2019

VFR at terminals to start period with focus for onset of snowfall
and duration overnight. Latest guidance is similar to previous
forecast with light flurries developing aft 20Z at KMHK and 21Z at
KTOP/KFOE with bulk of the snow arriving aft 23Z. Confidence is
high for snow to be moderate and heavy at times with LIFR to 
VLIFR categories likely. In the 06Z to 10Z time frame, forecast 
soundings indicate snow mixes with freezing rain at KTOP/KFOE. 
Easterly winds throughout the period are near 10 kts before 
weakening towards 12Z from the southeast.

&&


.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 PM this afternoon to 9 AM CST 
Wednesday for KSZ021>024-026-034>040-054>056-058-059.

Winter Storm Warning from 3 PM this afternoon to 9 AM CST 
Wednesday for KSZ008>012-020.

&&

$$

SHORT TERM...Prieto
LONG TERM...Drake
AVIATION...Prieto