Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Goodland Kansas
241 PM MDT Sat Sep 20 2014
Short term...(this evening through sunday)
issued at 102 PM MDT Sat Sep 20 2014
Cold front will continue to move south tonight and into the
Oklahoma Panhandle after midnight. Surface instability will clear
the forecast area by 06z...but there will be some elevated
instability lingering through about 09z. NAM develops
thunderstorms just south of the forecast area after midnight...but
there is no sign of a low level jet and upper ridging aloft so will keep
probability of precipitation less than 15 percent.
Return flow/southeasterly surface winds will develop on Sunday.
Instability axis by the afternoon will be along the Front Range
and south into New Mexico and the Texas Panhandle. The upper ridge
does weaken slightly but there is no synoptic scale forcing for
precipitation. Will go dry with increasing high clouds from the
west in the afternoon. Temperatures will be near normal.
Long term...(sunday night through saturday)
issued at 241 PM MDT Sat Sep 20 2014
Main concerns for the extended forecast are the chances for
rain/storms from Monday through Tuesday and model disagreement with
the evolution of a couple systems from the middle to end of next
Best chances for precipitation through the extended forecast fall on
Sunday night through Wednesday. The brunt of the precipitation
should fall Monday through Tuesday as an upper level disturbance...
currently located along to just off the California coast...lifts
through the tri-state area. Moisture and thus instability should
continue increasing ahead of this system. As a result...precipitable
water values should approach 1.25 inches...above the 75th percentile
for this time of year. MUCAPE should reach 500-1000 j/kg and slowly
transition across the area from west to east. For Monday and Monday
night...weak wind shear...0-6 km bulk shear of 20-25 kts...is
anticipated. Based on these factors...rain production should be
quite efficient...a warm rain process...with tall skinny throughout
the column. Have increased probability of precipitation and refined precipitation amounts
according to latest guidance.
As for chances of severe weather...not seeing much in the way of a
favorable severe weather setup for Monday and Monday night.
However...on Tuesday...wind shear increases as a speed maximum begins to
move in from the west. 0-6 km bulk shear should reach 30-40 kts by
Tuesday afternoon and evening. With some clearing of the skies and
warming across the western half of the forecast area...an uptick in
instability is also anticipated with MUCAPE reaching 1000-1500 j/kg
and 850-500 mb lapse rates reaching 7-8 c/km. A few strong to severe
thunderstorms for Tuesday afternoon/evening can not be ruled out.
As for temperatures...this forecast is basically a persistence
forecast with little in the way of change due to a stagnant surface
weather pattern. Temperatures throughout the period should be near
to just above normal. One day of concern is high temperatures on
Tuesday. Thinking there is a good chance for stratus/fog and with
persistent upper level cloudiness...high temperatures may bust especially
across the eastern half of the forecast area. May need to lower
temperatures for these locations in future forecasts.
Models have come into slightly better agreement for the disturbances
near the middle to end of next week. A large upper level trough
slowly translates across the western United States. The trough may
begin to have an influence on our weather in terms of stronger south
winds and precipitation chances returning by Friday. The complicating
factor is an upper level low that develops and retrogrades back west
on Wednesday and Thursday. This could bring additional chances for
showers and storms. Models have shown this solution for a few runs
but have varied greatly in positioning and movement. Maintained low
to no probability of precipitation in the extended.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 501 am MDT Sat Sep 20 2014
A cold front is just about to move past kmck/kgld. Surface winds
behind the front will switch to the north around 10 knots. The
front will move well south of the taf sites after 18z...and expect
any thunderstorms that develop near the front to be south of
Interstate 70. VFR conditions will continue through the period.