Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 272328 AAA

628 PM CDT Fri Mar 27 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 329 PM CDT FRI MAR 27 2015

Recent water vapor imagery showing upper ridge over the western
states beginning to slide east as a shortwave approaches the
Pacific Northwest. Another smaller scale wave was diving south
along the quick upper flow into the Upper Mississippi Valley.
Modest surface ridge was over eastern Kansas with light winds,
while cloud cover was steadily increasing, both form high cloud
topping the ridge and mid-level isentropic upglide in central
Nebraska. Very light precipitation has resulted in this area
despite ceilings of several thousand feet. Local temps were in the
lower to middle 40s early this afternoon, with values topping the
60 degree mark in western portions of the state.

Models are quite similar with isentropic lift deepening with time a
a moderate low level jet develops tonight. Low level moisture remains
a challenge, but could easily see very light precip continue south
and east with time this evening. The upper wave to the north brings
more considerable forcing and as it continues south, bring slightly
better precip chances to far eastern, mainly northeastern locations.
The exit of this wave and drier air working in from the upper ridge
should end any precip by dawn. With models sounding showing
near-surface temps a few to several degrees above 0C and cloud temps
able to reach ice crystal formation levels, have broad-brushed both
rain and snow as precip types.

East to southeast winds increase overnight into Saturday as surface
high pressure dives south behind behind the northern wave into the
middle Mississippi Valley while surface pressures quickly fall in
the High Plains as the Pacific Northwest wave crosses the Northern
Rockies. This will result in a rather strong low level thermal
gradient over the area with rather clear skies, with highs ranging
from the mid 50s northeast to near 70 in the far west.

.LONG TERM...(Saturday Night through Friday)
Issued at 329 PM CDT FRI MAR 27 2015

Models continue to show a boundary moving through the forecast
area mainly during the morning hours Sunday. The solutions have
converged on a common timing of the frontal passage which has it
exiting east central KS around noon Sunday. Because of this have
removed the chances for precip during the afternoon. Preceding
the front, there is a fair amount of warm air advection with a
decent elevated mixed layer capping the boundary. Additionally the
strongest forcing from a shortwave passing by looks to affect
areas across IA more so than into northeast KS. So models have the
better saturation and vertical motion clipping northeast KS
beginning early Sunday morning. So the better chances for precip
should be across far northeast KS. Since the better forcing looks
to pass northeast, have kept chances around 30 percent. Have high
on Sunday in the mid and upper 60s expecting some cold air
advection with the northerly winds by the afternoon.

Monday and Tuesday continue to look dry with temps warming into
the 70s. The synoptic pattern looks to split with southern stream
energy moving across TX and energy in the northern stream moving
from the northern Rockies into the adjoining plains.

Another front is progged to move through the central plains
Wednesday night. This is about 8 to 12 hours slower then previous
solutions had. Because the GFS/ECMWF/GEM are similar in this
slower progression, have altered the POP forecast to reflect
better chances for showers and thunderstorms Wednesday night.
Based on the GFS solution, there may be enough instability and
deep layer shear for any thunderstorms to pose a severe weather
risk. We`ll have to continue monitoring trends as it gets closer.
Raised the forecast for high temps on Wednesday into the mid 70s
due to the slower timing of the front as well.

Uncertainty increases for Thursday and Friday as the GFS and ECMWF
differ on when a modified Canadian ridge of high pressure moves
through the plains. The GFS drys things out with cooler temps
moving in on Thursday while the ECMWF brings another surface wave
across the central plains and possibly another round of precip
Thursday night and Friday morning. The WPC was not that excited
about the consistency of the recent ECMWF runs which only adds to
the uncertainty in the forecast. At this point have leaned a
little towards the ECMWF due to its better verification and kept
mild temps and a low chance for precip into Friday, but confidence
in this forecast is low as there are only the two solutions to


.AVIATION...(For the 00Z TAFs through 00Z Saturday Evening)
Issued at 521 PM CDT FRI MAR 27 2015

VFR conditions are expected to persist through the forecast at the
sites. Fast moving system will bring clouds AOA 3kft tonight with
stronger low level lift expected to occur early this evening with
some light rain or snow flurries but coverage and intensity is
very low so will not mention in the actual TAF this evening. Light
and variable winds will become southeast after sunset and persist Sat.




LONG TERM...Wolters
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