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Area forecast discussion 
National Weather Service Topeka Kansas
1143 PM CDT Wed may 27 2015

..aviation update...

Short term...(this evening through thursday)
issued at 329 PM CDT Wednesday may 27 2015

Forecast focus on rainfall potential tonight/Thursday. Water vapor
loop shows two waves moving into/across Kansas with the larger upper
low still located well west across Idaho. The 19z sfc map shows low
pressure across southwest Kansas with a warm front located from Great
Bend to just north of Wichita east toward Chanute. The waves are
helping convection to develop within the instability axis across
western Kansas/NE and eastern Colorado. These storms are expected to congeal
into a couple of mesoscale convective system complexes later tonight bringing the risk for
additional heavy rains to some parts of the area.

Main question is where the heaviest rains may fall overnight
tonight. Analysis of 850mb Theta-E ridge/low level jet axis and evolution of
MUCAPE overnight suggests that persistent moisture transport
should set up across western Kansas into NE or just upwind of the
western parts of the County Warning Area tonight. Although cape values are not
impressive this evening MUCAPE is forecast to increase to
1000-2000j/kg per the NAM. 850-300mb mean wind is east-northeast at around 25
kts while corfidi vectors suggest an east-southeast component owing to the
low level jet. Difficult part of the forecast is trying to discern exact
location of greatest rainfall risk and at this time it would
appear that one complex may develop this evening and move east-southeast
across central Kansas roughly along/south of I-70 along the sfc-850mb
front. A secondary complex may develop later toward 06z further
north on the nose of the 40kt low level jet and its this area that is of
concern for heavy rains across parts of central Kansas overnight. Have
decided to highlight the potential for heavy rains with a Flood
Watch that is limited in space and time given uncertainties not
only with tonight's evolution but also the potential impact on
subsequent storm development and evolution later tomorrow through
Friday. Simply put there is a risk for excessive rains beginning
tonight and that could last through Friday evening but confidence
in where is low for now. Would expect morning convection on
Thursday to wane with time as another round of storms could
develop across eastern Colorado and west Kansas.

Long term...(thursday night through wednesday)
issued at 329 PM CDT Wednesday may 27 2015

Weak shortwave troughs in west-southwesterly flow aloft move through
Kansas for Thursday night into Friday. Short range models differ on
timing of these impulses so timing of best precip chances is hard to
pin down. However, given antecedent soil moisture and any additional
precip that develops tonight and Thursday, areas of heavy rain will
be a concern. Finally on Friday afternoon and Friday night,
stronger upper trough and associated cold front move through, ending
significant precip chances for much of the area, with the only potential of
light showers to linger into Saturday morning in the east central.

Saturday through Wednesday...after system moves through Friday
night, eastern Kansas is in weak northwest flow aloft just to east of
upper ridge axis. As upper ridge moves slowly east, benign weather
continues until at least Tuesday night, while low-level temps
gradually warm. Medium range models are in decent agreement with
this scenario and the area should have a good chance to dry out for
awhile. 12z European model (ecmwf) tries to bring a shortwave trough across Nebraska
late Tuesday night, flattening the ridge, and would lead to some
precip chances for late Tuesday night into Wednesday. GFS and
gfsensemble on the other hand would keep things dry until Wednesday
night at least. Given previous run of European model (ecmwf) was in better agreement
with GFS runs, have left the middle of next week dry at this time.
Max temps should warm from the low 70s over the weekend into the
lower 80s toward the middle of the week.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1143 PM CDT Wednesday may 27 2015

Confidence in timing precip at the terminals remains low as models
show varying solutions. In general have gone with the idea that
after the initial convection slowly moves in, storms could fall
apart mid to late morning with the weakening of the low level jet
and initial vort Max passing northeast. Then there may be another
chance for scattered ts during the peak heating of the day.
Continued with VFR cigs, but feel like MVFR visibility will occur with
the precip. If intensity remains high, IFR visibility could occur, but
instability is weaker across northeast Kansas so I expect an overall
weakening trend as storms move northeast.


Top watches/warnings/advisories...
Flash Flood Watch until 7 am CDT Thursday for ksz008-009-020>022-



Short term...omitt
long term...gdp

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