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Area forecast discussion 
National Weather Service Hastings NE
632 am CDT Thursday Apr 17 2014

Short term...(today and tonight)
issued at 438 am CDT Thursday Apr 17 2014

Map analysis indicates an upper tropospheric longwave trough axis
extending from north to south across the central Continental U.S....and an
upper tropospheric longwave ridge over the western Continental U.S.. an area of
enhanced vorticity also indicates the presence of an upper
tropospheric short wave over portions of the Central High plains.
Enhanced upper tropospheric jet energy extends from the northwestern
Continental U.S....southeast into The Four Corners region...and then
east/northeast into the middle-Mississippi Valley and Great Lakes
region. Upper tropospheric flow over our area remains fairly weak
however...only maxing out around 80kts near 29000ft above ground level per 00z
sounding data from klbf and koax. Water vapor imagery indicates
increased upper tropospheric moisture ahead of the aforementioned
short wave over the Central High plains...with some of this moisture
promoting high-level clouds over portions of the Central Plains. At
the surface an area of high barometric pressure is noted over
western Nebraska. The resultant lower tropospheric flow across our
area remains from the north/northwest. Finally...an area of
stratus...with a ceiling near 2000ft above ground level...is also being indicated
across the area by satellite imagery and observational data.

Subtle isentropic upglide and saturation...as depicted primarily by
the operational GFS along the 305-310k surfaces...will likely
continue to promote stratus over the area through sunrise. Guidance
suggests this stratus should dissipate around or shortly after
sunrise this morning as increasing diabatic heating and resultant
boundary layer height and mixing commence. Given all this...went
ahead with cloudy skies in the official forecast for much of the County Warning Area
through 12z...with clearing skies thereafter.

Guidance from the NAM...operational GFS and ec all suggest the upper
tropospheric short wave over the Central High plains will miss our
area just to the south. A resultant lack in Omega across our area
today and into tonight suggests dry conditions will be
observed...and such has been presented in the official forecast.

The infiltration of a cooler lower tropospheric air mass suggests a
cooler day will be observed today when compared to Wednesday...with
guidance suggesting afternoon temperature readings in the 50s will
be realized through most locations across the County Warning Area. Increasing
southerly lower tropospheric flow and resultant warm air advection
should then promote warmer conditions tonight when compared to early
this morning...with temperature readings by sunrise Friday in the
middle to upper 30s currently forecast across the area.

Long term...(friday through wednesday)
issued at 438 am CDT Thursday Apr 17 2014

Certainly no major changes were made to this 6-day period...as in
a very general sense we are still dealing with one somewhat
higher- confidence chance of showers/thunderstorms during the
Saturday daytime-Sunday night time frame...but tending to mainly
favor Saturday night...with then the next foreseeable rain chance
possible arriving around the middle of next week...which is still
officially represented in the forecast as a slight chance of
showers/storms on Wednesday. However...this second system still
has plenty of details to hammer out...as some models suggest that
subtle disturbances out ahead of the main one could break out
isolated/scattered convection as early as Tuesday/Tuesday
night...while there is also the distinct possibility that this
system could slow enough to delay better precipitation chances from
Wednesday into more-so Wednesday night/thurs...which is still beyond the
scope of this forecast period. In other words...although there are
currently no precipitation chances advertised during the Monday day-
Tuesday night time frame this is no guarantee to stay that
way...and likewise the slight probability of precipitation currently advertised for
Wednesday are not guaranteed to stay in place. With this typical
high degree of uncertainty in the day 4-7 range...we are better
off focusing on the shorter-range weekend system and its potential
for more beneficial moisture...but also its potential for at least
a few strong storms. Temp-wise...this time frame as a whole looks
to average at least slightly above seasonal normals...with high
temperatures on most days aimed somewhere between the upper 60s to
near-80 range.

As for potential non-thunderstorm related hazards...right off The
Bat on Friday sustained southerly wind speeds have been trending
upward closer to advisory-criteria...but at least for now kept
them averaging roughly 5 miles per hour below advisory levels...but this
bears watching. Fortunately for fire weather concerns...despite
the wind Friday increasing dewpoints should result in forecast
relative humidity values bottoming out no lower than the 30-35
percent...safely above the critical 20 percent threshold.

Diving into more detail and generally taking it one 24-48 hour
chunk at a time...

Friday/Friday night...the middle-upper level story involves a gradual
but very evident transition from northwesterly flow to
southwesterly flow...as a passing ridge axis during the day gives
way to an approaching southern stream shortwave trough Friday
night that reaches the 4-corners/southern rockies region by
sunrise Saturday morning. At the surface...steady daytime pressure
falls over the northern/Central High plains will crank up the both
the southerly winds and the warm air advection during the
day. As mentioned above...bumped up wind speeds another 3-5
miles per hour...generally looking at several hours of sustained speeds
around 25 miles per hour or slightly higher...and gusts around 35 miles per hour. Under
mostly sunny skies...highs Friday are forecast to jump 15-20
degrees above todays values...with most of the County Warning Area topping out
between 70-73. On Friday night...south winds remain breezy at
generally sustained 15-20 miles per hour with higher gusts although a surface
trough edges very close to the northwest edges of the County Warning Area by
sunrise...potentially bringing lighter breezes to that area. Kept
low temperatures very similar to previous...right around 50 degrees most
areas. Despite a strong southwesterly low level jet...elevated
moisture return remains rather meager and even though the 06z NAM
advertised a few hundred j/kg of cape overnight there is also
capping and lack of convergence...so expect any overnight
shower/storm risk to stay at least slightly north and/or west of
the County Warning Area.

Saturday/Saturday night...things turn more active precipitation-wise as
the shortwave trough over the southwestern Continental U.S. Lifts northeast
into the Central Plains...likely in at least a few smaller pieces
as opposed to one cohesive strong wave. At the surface...the main
feature will be a weak cold front that gradually sags southward
across the County Warning Area...turning winds northeasterly in its wake. As for
the daytime hours...there are still a ton of questions regarding
precipitation chances...and thus for good reason probability of precipitation have been held no
higher than the 30-40 range despite what some model quantitative precipitation forecast fields
look like. For the morning hours...confined only slight probability of precipitation to
roughly the northwest half of the County Warning Area...and even this could be
pretty iffy. Then during the afternoon...at least somewhat better
chances for showers/storms could occur especially after 21z/4pm
and quite possibly in a rather narrow corridor along the surface
frontal zone. There is still uncertainty exactly where this
frontal zone lies...and thus the somewhat broad-brushed probability of precipitation.
Should daytime storms fire...models such as the 06z NAM suggest at
least a marginal severe threat could exist...given 0-1km MLCAPE on
the order of 1000-1500 j/kg but deep layer shear only on the order
of 20-30kt...likely yielding slow-moving storms with mainly a
hail/wind threat. Even if afternoon storms fail to
materialize...Saturday evening/night should feature better chances
for more widespread convection as upper forcing increases and
interacts on the frontal zone near 850mb. Given that this is still
a few days away...opted to leave probability of precipitation very similar to previous
forecast with nothing above 60 percent quite yet. Could easily
see a threat for strong storms with locally decent rainfall
continue into the night...but instability should be on the decline
especially after 03z/10pm especially if convection is in fact
fairly widespread. Was a bit surprised to not even see a 5 percent
severe probability introduced by Storm Prediction Center on the day 3 outlook...and
unless things change quite a bit in future model runs would expect
at least a 5 percent severe risk added 24 hours from now on the
day 2 outlook. Temp-wise...assuming that high clouds are not
overly abundant...should see potential for a decent rise in the
wake of a milder night...and bumped up highs 2-3 degrees in many
areas...ranging from near-70 far northwest to upper 70s/near-80
south and southeast.

Sunday daytime through Monday night...the main middle-upper level
theme during this 48-hour period per consensus of the ooz
European model (ecmwf)/GFS is that the aforementioned slow-moving shortwave trough
will gradually exit east of the region through Sunday
night...followed by a period of shortwave ridging ahead of the
next disturbance. The net result is that widespread 30-50 probability of precipitation
were maintained for Sunday daytime...which for those with plans
means that at least part of the day could be wet with showers and
isolated non-severe storms...but probably not a true washout
either. Given the slow system departure especially per the
European model (ecmwf)...introduced a slight chance of lingering showers across
mainly the southeast 1/2 of the County Warning Area for Sunday night...but kept
Monday-Monday night dry at least for now. Temp-wise...made little
change with Sunday mainly upper 60s and Monday mainly low 70s.

Finally for Tuesday daytime-Wednesday daytime...as mentioned
earlier opted to stick with only a slight chance of showers/storms
on Wednesday...but will have to keep an eye on the preceding few
periods in case some lead energy ejecting out of the next western
Continental U.S. Trough can spark some convection. Although the details are
still quite sketchy...confidence is pretty high that a large-
scale western Continental U.S. Trough will set up in some way/shape/form by
mid-week...putting the Central Plains in warm and potentially
windy southerly flow out ahead of it. Although way too early to
say whether the local area sees a legitimate severe thunderstorm
threat with this system...the calendar suggests parts of the
central Continental U.S. Will have to keep an eye on this one.
Temp-wise...left Tuesday with highs mainly middle-upper 70s...but
nudged up Wednesday a few degrees into mainly the 79-83 range. On
one last note...there are no sub-freezing temperatures forecast during
this 6-day period...and although its still too early to say for
sure whether we are done with freeze concerns for the
season...climatology dictates that the probability of another
freeze will be getting increasingly low with time.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 626 am CDT Thursday Apr 17 2014

MVFR conditions to continue to start the taf period...with VFR
conditions expected by 15z.

Stratus...with a ceiling near 2000ft above ground level...persists across much
of the region as of 1130z and guidance suggests this stratus will
persist for another few hours. Increasing diabatic heating and
resultant boundary layer height and mixing Post-sunrise should
then promote diminishment in this stratus. Given all this...went
ahead with a ceiling near 2000ft above ground level through 15z...with periodic
clouds near 12000ft above ground level expected thereafter. The surface wind will
remain fairly light and at times variable to start the taf
period...but is then expected to become sustained from the
southeast at around 08kts to finish the taf period. Visibility
restriction is not expected at gri through the next 24 hours.

&&

Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&

$$

Short term...Bryant
long term...pfannkuch
aviation...Bryant