Area forecast discussion
National Weather Service Omaha/valley NE
1217 PM CDT Thursday may 23 2013
Aviation...18z tafs for kofk...koma and klnk.
Clearing is finally taking place across the taf sites with klnk
the last to clear out but this should be within the first hour of
the taf. Otherwise...VFR conditions are expected throughout the
taf cycle as surface winds become more southeasterly and increase
Friday morning. MVFR ceilings possible once again by late in the taf
period but did not include that quite yet.
Kern
&&
Previous discussion... /issued 328 am CDT Thursday may 23 2013/
Discussion...
cloudy skies continue across most of the area...with some clearing
sliding into the northern County Warning Area. Subjective 00z upper air analysis
indicates weakening upper low centered in northeast/southwest
WI...with upper low also over Washington...and strengthening ridge in
between over the High Plains. 500mb height rises across the
Central Plains indicate ridge is building in as eastern low exits.
850mb low was centered in northern lower Michigan...with trough axis
trailing across southern WI/central Iowa/southwest Kansas. 850mb
moisture was mainly confined to the MS River Valley and
eastward...but 8-16c dewpoints had returned to the Texas Gulf Coast
and Rio Grande Valley...with flow off the Gulf favorable for
moisture return. Surface ridge axis at 07z extended from ND
through central South Dakota/central Nebraska/eastern Kansas...with surface low
developing in northeast nm.
Main forecast concerns revolve around thunderstorm potential for the
Holiday weekend into next week. Upper-level pattern will transition
from Omega block to western trough/Central Ridge through the rest of
this week...with the trough/ridge making eastward progress through
the weekend and into early next week that will place the central US
under southwesterly upper-level flow. Pattern will thus be
favorable for convection from Friday night through days 7-10...as
pattern is in no hurry to break down. Main inhibitors to convection
will be proximity to upper ridge early in the period...then
potential for capping later in the period. Convection would be
favored as shortwaves slide through the upper-level flow...but of
course...timing these individual impulses is challenging to say the
least more than a couple of days in advance. Have nudged temperatures
upward through much of the forecast as middle-level temperatures
warm...with 850mb temperatures warming into the upper teens to low
20s by the end of the period.
Have backed off morning probability of precipitation on Friday...as isentropic lift and good
warm/moist air advection really get going in the afternoon in
eastern Nebraska...and likely closer to evening in western Iowa.
Soundings are not especially unstable...and think any precipitation on
Friday would be more of a character of showers with a few rumbles
than general thunderstorms. Am not convinced of widespread coverage
based on NAM/sref forecasts...and thus have kept probability of precipitation in chance range
during the day...with a small area of likelies in the northeast County Warning Area
in the evening before low-level jet veers to the east and takes
support for precipitation eastward with it.
Believe Saturday morning will actually be pretty much dry in the
County Warning Area...as low-level jet re-orients itself into western Nebraska...with a
middle-level shortwave ridge moving through. By afternoon...a warm
front will become established across north central to southeast
Nebraska...which should provide a focus for some storms on Saturday
afternoon and evening. Can't rule out potential for a couple of
severe storms...though better potential will be west of the County Warning Area.
Storms are likely to form into a complex that moves across the area
on Saturday night. A similar pattern looks to be in place for
Sunday...with much of the morning likely to be dry behind the
exiting overnight complex...followed by convective development west
of the area that moves across on Sunday night.
From Monday Onward...forecast continues to have a parade of slight
chance to chance probability of precipitation in every period. Forecast will by no means be
a washout. Some of those days...tstorm chances will focus in the
afternoon and evening...while others focus in the overnight periods
when convection fires further west. There will likely be dry
periods in the mix as well. The ecwmf trends much warmer than GFS
by middle to late week and would imply capping with 12-14c 700mb
temperatures...while the GFS brings the surface low much closer by then and
keeps temperatures several degrees lower. All in all...much uncertainty
remains...and have kept probability of precipitation from getting too aggressive until
periods are closer and better agreement is established.
Mayes
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
