Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 272049
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
349 PM CDT Wed May 27 2015

.SHORT TERM...(This Evening through Thursday)
Issued at 329 PM CDT WED MAY 27 2015

Forecast focus on rainfall potential tonight/Thursday. Water vapor
loop shows two waves moving into/across KS with the larger upper
low still located well west across ID. The 19z sfc map shows low
pressure across southwest KS 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 KS/NE and eastern CO. These storms are expected to congeal
into a couple of MCS 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 Thetae ridge/LLJ axis and evolution of
MUCAPE overnight suggests that persistent moisture transport
should set up across western KS into NE or just upwind of the
western parts of the CWA tonight. Although CAPE values are not
impressive this evening MUCAPE is fcst to increase to
1000-2000j/kg per the NAM. 850-300mb mean wind is ENE at around 25
kts while corfidi vectors suggest an ESE component owing to the
LLJ. Difficult part of the fcst 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 ESE
across central KS 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 LLJ and its this area that is of
concern for heavy rains across parts of central KS 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 tonights 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 CO and W KS.

.LONG TERM...(Thursday Night through Wednesday)
Issued at 329 PM CDT WED MAY 27 2015

Weak shortwave troughs in west-southwesterly flow aloft move through
KS 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
sig 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 KS 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 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 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 18Z TAFs through 18Z Thursday Afternoon)
Issued at 1217 PM CDT WED MAY 27 2015

Conditions are expected to remain VFR the majority of the period,
until ceilings begin to lower to MVFR late tonight/tomorrow
morning.  There is a large amount of uncertainty with timing and how
far a complex of storms will move east; therefore, have mentioned
VCTS at MHK after 06Z, although TOP/FOE may need to be adjusted with
this mention later.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH from 7 PM CDT this evening through Thursday
morning FOR KSZ008-009-020>022-034>037.

&&

$$

SHORT TERM...Omitt
LONG TERM...GDP
AVIATION...Heller





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