458 
FXUS63 KTOP 170927
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
427 AM CDT Fri May 17 2019

.SHORT TERM...(Today and tonight)
Issued at 425 AM CDT Fri May 17 2019

08Z water vapor imagery shows an upper low over northern NV with an 
upper trough axis extending southeast through AZ. With a second 
upper low near Hudson Bay, shortwave ridging had set up from the 
southern plains into Saskatchewan. Surface obs showed a high 
pressure system over the lower MS river delta. An area of low 
pressure was noted over the central high plains of CO with an 
inverted trough/cold front extending east across southern NEB and 
southern IA. The surface pattern has favored southerly return flow 
and higher dewpoints had been advecting inland over south TX. 

For today models are in good agreement that the dynamics associated 
with the upper low across NV should remain west of the forecast 
area. As a result the surface low and dryline extending south of the 
low are progged to remain out across the high plains and western KS. 
Meanwhile the surface front is expected to retreat north as a warm 
front due to the deepening surface low and continued warm and moist 
air advection north. Forecast soundings show a reasonable capping 
inversion remaining over the boundary layer through peak heating. So 
think precip chances are less than 20 percent today. The RAP is the 
one solution that develops some QPF across north central KS by this 
evening. It also happens to be the most aggressive in developing 
convection along the dryline this afternoon. With not much movement 
of the surface low or the dryline, boundary layer winds are 
generally forecast to parallel the dryline with any convergence 
localized to western KS. So there is some question as to whether 
storms will be that numerous along the dryline. Since the majority 
of the convective allowing models show storm development closer to 
the surface low, think the RAP may be overdone. If storms are able 
to make it into north central KS, there would be more than enough 
CAPE for severe hail and winds. Forecast soundings prog a weakness 
in the mid level wind profile late this afternoon suggesting 
discrete storms this far east of the dry line may be hard to come 
by. There is good agreement in a strong pressure gradient once again 
today. So south winds are expected to gust around 35 MPH. As for 
highs, the models all show a general cooling at 850MB implying temps 
may not be as hot as they were on Thursday. With forecast soundings 
mixing the boundary layer to around 825MB, think mid and upper 80s 
are plausible and have generally gone a little warmer the MOS 
guidance expecting good insolation. 

Winds should remain breezy for much of tonight. There are some 
indications from the forecast soundings for some elevated 
instability to remain in place as height falls spread east and 
inhibition weakens. So there is some potential for thunderstorm 
development overnight tonight. Although it's not clear if there will 
be any focus for lift as the nose of the low level jet and better 
theta-e advection is forecast to be east and north of the forecast 
area. So I only show a chance for showers and thunderstorms mainly 
after midnight. Forecast sounding progs of elevated CAPE values 
between 1500 and 2000 J/kg would support a risk for severe storms 
with large hail and damaging winds. Southerly winds and continued 
moisture advection into eastern KS should keep lows tonight in the 
upper 60s to around 70. A surface boundary may move into north 
central KS from the west late enough in the night to allow winds to 
calm down and help temps fall into the lower 60s.

.LONG TERM...(Saturday through Thursday)
Issued at 425 AM CDT Fri May 17 2019

Saturday...

By Saturday morning, the second of a series of shortwave troughs 
will be positioned across the High Plains region with a surface 
trough axis extending from the TX Panhandle through north-central 
KS. Warm advection showers and storms may be ongoing by sunrise 
across portions of the forecast area. There is varying depictions 
with respect to the strength of EML amongst guidance, although the 
combination of modest midlevel height falls and WAA should allow for 
scattered storms through mid-morning. A few could be severe with 
upwards of 2000 J/kg of MUPCAPE and 35-40 kts of effective shear. 
Stronger height falls are progged to overspread the CWA by peak 
heating Saturday afternoon as the midlevel shortwave trough pivots 
across the Plains. This should allow for additional surface based 
convection during the afternoon and evening. Steep lapse rates will 
contribute to 2000-3000 J/kg of MLCAPE. While overall deep shear is 
progged to near 50 kts by afternoon, the high-amplitude nature of 
the midlevel trough will result in backed midlevel winds -- not 
favorable for discrete convection. As a result, anticipate numerous 
storm clusters capable of large hail and damaging winds. 
Deterministic and ensemble guidance suggest widespread 1-2" rainfall 
amounts through Saturday evening. Flood/flash-flood threats should 
remain low through Saturday, given the recent stretch of dry 
weather. 


Saturday night through Sunday night...

Any lingering shower/storm activity will end from southwest to 
northeast Saturday night/Sunday morning as the shortwave trough 
ejects northeast of the forecast area. A brief period of dry 
conditions are expected Sunday night through Sunday night as 
subsidence behind the initial shortwave trough overspreads the CWA. 
Weak CAA behind the surface front will limit temperatures to the 60s 
and lower 70s Sunday with Monday morning lows in the 40s and 50s. 


Monday and Tuesday...

The third of a series of midlevel trough axis will eject into the 
Plains Monday into Monday night. A warm front is progged to lift 
northward through the day, nearing the KS/OK border by late 
afternoon. As forcing for ascent overspreads the warm sector by 
midday Monday, widespread thunderstorm activity is expected across 
southwest KS/western OK/TX Panhandle. Similar to Saturday's 
scenario, the high amplitude nature of the trough will result in 
numerous storm interactions and upscale growth into an MCS by early 
afternoon. The warm front is progged to continue lifting northward 
through the evening, with the MCS tracking along the boundary across 
the forecast area. Storms will likely be elevated upon arrival to 
the forecast area, and the strongest updrafts could produce large 
hail. In addition, any established cold-pools could pose a damaging 
wind threat. Flash-flooding is likely to be the primary concern 
however. A very moist profile consisting of Pwat values exceeding 
1.25" -- near the 90th percentile at TOP -- will result in very 
heavy rainfall. Deterministic and ensemble guidance are quite 
alarming with QPF outputs ranging from 2 to 5+ inches Monday - 
Tuesday morning. Generally the heaviest axis of precipitation is 
currently progged to track across the southeastern half of the 
CWA. This scenario would likely result in widespread flash- 
flooding and river rises. The exact track of the MCS and 
associated rainfall swath can and will likely shift over the 
coming days, please continue to check back through the weekend as 
this has the potential to be a significant flood event. This round
of shower/storm activity should push east of the forecast area by
Tuesday afternoon with the northeastward progression of the 
midlevel trough. 

Wednesday through Thursday...

Additional shower and thunderstorm activity is possible Wednesday 
night through Thursday. Model solutions diverge with the track of 
the next midlevel trough, therefore confidence beyond Wednesday is 
low. That being said, any additional rainfall will only worsen 
flooding concerns through the remainder of the week. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1149 PM CDT Thu May 16 2019

LLWS continues overnight, with gusty south to southwesterly winds
increasing by mid-morning and persisting until sunset. LLWS once
again develops by sunset. VFR conditions are otherwise expected
through the period.


&&

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

$$

SHORT TERM...Wolters
LONG TERM...Baerg
AVIATION...Skow