Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 211112
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
612 AM CDT Wed Jun 21 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 234 AM CDT Wed Jun 21 2017

High clouds from left over convective anvils will continue to
spread across the area this morning. These clouds should give way
to mostly sunny skies later today. A subtle shortwave trough is
forecasted to track over the northern plains and upper Midwest.
This trough will send another front into portions of northwest KS
and central NE this afternoon. Deep mixing is again expected ahead
of the boundary, which will help weaken the cap for convective
initiation. Most of the models develop storms along this boundary
northwest of our area, and the coverage of storms initially
appears isolated to scattered. The steep mid level lapse rates and
dew points in the mid to upper 60s should yield mlcape around
3000-4000 j/kg. Given the relatively high bases and sufficient
instability large hail and damaging wind gusts will be the main
threats. The biggest forecast challenge is will the convection
maintain strength as it moves eastward off the boundary towards
the forecast area. As of now given the closer proximity to the
boundary north central and far northern KS have the highest
chances for severe storms. This will depend on the cold pool and
environmental shear balance, which will dictate the continuation
of vigorous convection. As the boundary layer begins to stabilize
the wind threat should gradually diminish. Although given the
model soundings show elevated cape remains present through the
evening there is the potential for a few strong to severe cells to
continue in our area. None of the models are showing a large
scale MCS, but individual storm clusters pose a threat through the
evening. If a sufficient cold pool could become established
additional development could be possible as a low level jet
increases and intersects the southern flanks. Therefore have kept
pops across most of the area through sunrise tomorrow. A few of
the high res ensembles show that the probabilities for strong wind
gusts seem to coincide with the slight risk.

.LONG TERM...(Thursday through Tuesday)
Issued at 234 AM CDT Wed Jun 21 2017

For Thursday and Friday, the models have trended a little quicker
with a cold front moving through the forecast area, now bringing
it through Thursday night. Because of this the better POPs are
forecast to be Thursday night. Models continue to show marginal
deep layer shear with the best instability pooling along the
frontal boundary. Additionally forecast soundings from the GFS and
NAM show the boundary layer remaining capped through the
afternoon. So the most likely scenario is for storms to develop
along the boundary and move south into northern KS in the evening
with some potential for producing large hail and damaging winds.
Temps should remain warm on Thursday with highs in the lower and
middle 90s. A cooling trend appears likely by Friday with highs
about ten degrees cooler.

The greatest uncertainty in the forecast continues to center
around whether surface high pressure builds in behind the initial
front or if a second surge comes through Saturday night and
Sunday. The ECMWF seems to be less consistent with this as the 00Z
run develops a surface low over the central high plains on
Saturday with upslope and moisture advection into central and
western KS. Models seem to be split with the NAM closer to the GFS
and the GEM somewhat like the ECMWF. The differences appear to be
with the handling of shortwave energy within the broad cyclonic
upper flow over the northern plains. The ECMWF and GEM want to
maintain some energy moving across ID and WY on Saturday while the
GFS and NAM shear this wave out over the northern Rockies. Given
the predictability of these shortwave details, will stick with a
blend of the various solutions and keep some chance for precip on
Saturday and into Sunday morning.

Return flow with warm air and moisture advecting north appears to
hold off until late Monday and mainly on Tuesday. So a relatively
cool forecast is expected to continue through the end of the
weekend with temps gradually warming back into the upper 80s and 90s
by Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 606 AM CDT Wed Jun 21 2017

VFR conditions expected through this afternoon and evening. Strong
storms may reach MHK in the late evening, and wind gusts would be
the main hazard. A few cells could produce restricted flight
conditions for a brief period mainly from heavy rain. Also low
level wind shear is expected lat evening and early morning as
well.

&&

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

$$

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



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