Area forecast discussion
National Weather Service Hastings NE
1203 am CDT Friday may 24 2013
Update...
issued at 654 PM CDT Thursday may 23 2013
Made minor adjustments to hourly weather this evening.
&&
Short term...(this evening through friday)
issued at 355 PM CDT Thursday may 23 2013
Morning upper air analysis indicates middle to upper level ridging
over the central Continental U.S....with troughing over the west and east. A
closed middle to upper level low is also noted embedded within the
western Continental U.S. Trough. Increased middle to upper level flow surrounds
the western Continental U.S. Low...and also extends from central Canada
south/southeastward into portions of the Mississippi Valley and
northeastern Continental U.S.. middle to upper level flow over the Central
Plains however is fairly weak...maxing out at around 40kts near
300mb per 12z sounding data from klbf and koax. Water vapor
imagery clearly shows the middle level low over the western
Continental U.S....with increased values of middle level moisture extending from
the southern Continental U.S....north/northwestward into The Rockies and High
Plains. At the surface a ridge of high barometric pressure extends
from the upper Mississippi Valley...south/southwest into the
Missouri River valley. An area of low barometric pressure is also
noted over portions of Wyoming. Low level flow across our area
remains from the east/northeast for the most part...but is
beginning to turn more southeasterly across southwestern portions
of our County Warning Area as the surface ridge continues moving east...away from
our area.
An overall lack in kinematic forcing will continue promoting dry
conditions across our area through at least 06z tonight. Guidance
suggests multiple middle level perturbations will eject from the
western Continental U.S. Trough beginning tonight however...with some of
these perturbations rounding the top of the central Continental U.S. Ridge
thus helping to break down the ridge somewhat. Weak Omega ahead of
the middle level perturbations may be strong enough to promote middle
level clouds and perhaps some very light precipitation across
portions of our area tonight. That being said...increasing low
level return flow and resultant low level Theta-E advection will
likely play a larger role in cloud development and possible
precipitation production. Theta-E advection...both from return
flow near the surface as well as along the axis of a ~40kt low
level jet across our west...appears as though it will promote
enough isentropic upglide and saturation...primarily between the
305k and 320k surfaces...for stratus development across much of
our County Warning Area by sunrise Friday. Although not likely...forecast
proximity soundings from across our County Warning Area...per the
NAM...operational GFS and ec...suggest the lower troposphere may
become saturated enough for precipitation to be realized at the
surface across extreme southwestern portions of our County Warning Area during the
early morning hours Friday. Given all this...went ahead with ~20%
probability of precipitation across extreme southwestern portions of our County Warning Area 06z-12z
Friday.
Increasing low level Theta-E advection...along with
persistent...albeit weak...middle level Omega ahead of passing middle
level perturbations...will allow chances for precipitation to
overtake all of our County Warning Area during the day Friday. Quantitative precipitation forecast fields from the
NAM...operational GFS...ec and sref-mean all suggest measurable
precipitation will be possible across most all of our County Warning Area Friday.
That being said...precipitation rates do not appear as though they
will be all that high and precipitation at any given point in the
day may be spotty at best. So...opted to keep probability of precipitation in the 40-50%
range for the most part...but it is believed these probability of precipitation will be
increased tonight if future model runs continue indicating
measurable precipitation across much of the County Warning Area during the day
Friday.
Increasing low level moisture due to the aforementioned Theta-E
advection...working in concert with somewhat increasing middle level
lapse rates as middle level perturbations push overhead...should
promote at least some potential instability across portions of our
area on Friday. At this time guidance suggests locations across
our area...generally south of I-80 and west of Highway 281...could
see deep-layer MUCAPE values of around 1000j/kg...if not a touch
higher...Friday afternoon. Deep-layer bulk shear values on the
order of ~30kts are also expected across our area during this time
period. Given all this...severe weather is not currently
expected...but a few of the stronger updrafts could certainly be
capable of producing sub-severe hail and will mention this in the
severe weather potential statement.
Subtle low level warm air advection should promote slightly warmer
weather tomorrow when compared to today...but not by much. An
overnight low temperature near 50 is forecast for most locations
tonight with an afternoon high temperature in the upper 60s to
near 70 for Friday.
Long term...(friday night through thursday)
issued at 355 PM CDT Thursday may 23 2013
Primary forecast concern through the long term remains with
multiple thunderstorm chances...as the active upper level pattern
continues across the region.
Hasnt been any significant changes in the models with the upper
level pattern at the start of the forecast period...as the plains
remain with ridging in place...set up between a low pressure
system over the East Coast and another over the Pacific northwest. The first
of a number of low amplitude disturbances to affect the region
makes its way across the area Friday night...and aided by warm
air/moisture advection via a srly low level jet...bring thunderstorm chances
to the County Warning Area. Models in good agreement showing instability also
beginning to work its way north...primarily affecting the
southwestern half of the County Warning Area...and along with sufficient shear
values...certainly cant rule out some strong/severe thunderstorms.
Into Saturday...expecting the morning hours to be affected by the
overnight activity...with some uncertainty how quickly things may
move out. Should be a lull in the activity into the
afternoon...before additional thunderstorm chances return as the
next upper level disturbance moves in from the southwest. Ahead of
this next disturbance...surface low pressure in place over the
Front Range/High Plains looks to strengthen a bit. Looking to see
a tightening pressure gradient across the area as a result...with
high pressure still in place over the Midwest...with increasing
southerly winds expected. One concern is where a surface warm
front will set up...with the potential for it to end up draped
across the northern half of the County Warning Area by late afternoon. Models
continue to show several thousand j/kg of cape developing as
dewpoints/moisture continues to pool along the front...but also
show capping in place. Question is whether convection can get
going in the area of weaker capping /mainly across portions of SC
neb/...and if it does how much there would be. Again...while deep
layer shear isnt great...its sufficient for strong/severe
weather...plus there is plenty of instability in place along with
the potential surface frontal boundary. Plenty to keep an eye on for
Saturday.
Any ongoing activity looks to continue to affect the area during
the overnight hours...and potentially into the morning hours on
Sunday...but there is some question on what would be going on
beyond that. Some of the 12z models came in showing not a whole
heck of a lot going on during the daytime hours...but still cant
rule out some late afternoon thunderstorms...so will continue to
keep some lower probability of precipitation going. But...whatever break there is doesnt
look to last long...with the next round of thunderstorms moving
with the latest disturbance...and a stronger corridor of the low level jet
nosing into the County Warning Area. Without a front moving through to push the
better moisture in place out of the region...instability certainly
remains in place...so the threat for some thunderstorms to become
severe continues.
Looking at Monday through Wednesday...the overall story doesnt
change significantly...the County Warning Area remains under southwesterly flow in
the upper levels...with continued periodic thunderstorm chances as
these disturbances move through. Uncertainty in the forecast grows
with time...Wednesday for example...the GFS shows a middle/upper level
trough swinging right into the Central Plains...while the latest
European model (ecmwf) shows a cutoff low over the Arizona/Mexico border. Many details
to work through in the coming days.
As far as temperatures go...not expecting any notable
swings...with highs remaining above average overall...ranging
anywhere from the upper 70s to middle/upper 80s. Mild overnight lows
in the upper 50s/60s also expected.
&&
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1156 PM CDT Thursday may 23 2013
The taf period will begin with VFR conditions and end with MVFR to
IFR conditions. An area of stratus along the High Plains will
spread northeast across the Central Plains and reach kgri around
08z and ceilings will drop to the MVFR category. In increasing low level
flow...warmer moist air will be drawn northward and shower and
thunderstorm development is expected after daybreak with convective
potential carrying into the day. Southerly winds will be on the
increase today with gusts near 30kts possible. Heading into Friday
evening...ceilings may lower to IFR category.
&&
Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&
$$
Update...heinlein
short term...Bryant
long term...ado
aviation...Fay
