Area forecast discussion
National Weather Service Hastings NE
1219 am CDT Tuesday Jun 18 2013
Update...
issued at 1219 am CDT Tuesday Jun 18 2013
WV imagery shows a well-defined vorticity maximum embedded in northwest flow over
the Dakotas/MN. A few showers/thunderstorms are still on-going with this
feature. Multiple models develop showers/thunderstorms north of I-80 before dawn
..presumably associated with this vorticity maximum and associated jet
streak. So some adjustments have been made to overnight pops/wx.
Meanwhile...a small mesoscale convective system continues over the Panhandle and while
there has been some tempo clearing over S-central Nebraska...blow-off
cloud debris will overspread the area through the rest of the night.
Temperatures/dwpts/winds are on track. So no substantial changes needed.
&&
Short term...(this evening through tuesday)
issued at 440 PM CDT Monday Jun 17 2013
The main concern during the next 24 hours continues to center
around the very tricky...and constantly-evolving thunderstorm
chances...or lack thereof in this northwest flow pattern. Although
at least a low-end risk for severe storms continues this
evening/tonight mainly west of Highway 281...it does not look to
be nearly as widespread/significant as the Sunday evening event.
20z objective surface analysis indicates a fairly non-descript
pattern across the area...with the main synoptic-scale cold front
noted well to the south across OK/northwest Texas. It has been
completely rain/thunder-free the entire day so far cwa-wide. With
the main surface front to the south...and a modest 1018 millibar
ridge axis centered just north of the County Warning Area...breezes this afternoon
are generally some variation of northerly/easterly at no more than
10 miles per hour. Aloft...water vapor imagery and short term model data
depicts the continuation of west-northwest flow aloft over the
Central Plains...flowing over the top of a fairly low-amplitude
ridge extending north-south through the central/southern rockies.
There are generally three shortwave troughs/ripples of note across
the region...one departing eastward along the Kansas/MO/OK border
area...one sliding southeast across ND...and the other a fairly
subtle disturbance drifting southeast across northwest Nebraska...which
has helped trigger some thus-far non-severe thunderstorms still
50-100 miles west- northwest of the County Warning Area at this hour. Visible
satellite imagery reveals nothing more than a scattered fair
weather cumulus field over most of the County Warning Area...with a few thicker
middle-cloud areas drifting into northern/western counties out ahead
of the western Nebraska convection. High temperatures are generally on
track to top out somewhere in the 80s most all areas.
Late this afternoon into tonight...pinning down the hourly details
of probability of precipitation/thunderstorms continues to be a challenge. Regarding the
big picture aloft between now and sunrise...the very subtle middle
level disturbances rotating around the top of the ridge across the
Wyoming/co/northwest Nebraska area will continue to drift southeast...while
the somewhat more organized disturbance now over ND will reach the
north central Iowa by sunrise. For the forecast...have considered a
variety of deterministic and high-res model solutions
tonight...which invariably paint at least slightly different
pictures...but leaning mainly toward the hrrr/4 km-WRF solutions
which seem to have a decent handle on the ongoing convection to
the west. Through 7pm...have kept the majority of the County Warning Area pop-
free...with only slight chances creeping into about the northwest
1/3 of the County Warning Area as convection develops overhead and/or drifts in
from the northwest. Between 00z-04z/7pm-11pm...spread at least
slight 20 percent probability of precipitation into even the far southeast
counties...while raising into the 40-50 percent high-chance range
across much of the west. By 00z...latest rap indicates an
environment at least marginally supportive of severe
weather...with roughly 1500 j/kg of 0-1km cape mainly in the
northwest 1/2 of the County Warning Area...and 30-40 knots of 0-6km deep layer
shear. As the evening wears on...instability is prognosticated to drop
off slowly...but likely remain highest in Kansas zones. After
midnight...current probability of precipitation may not be nearly high enough if in fact a
semi-organized batch of convection develops overhead or moves
in...but given inherent uncertainty have capped probability of precipitation at no more
than 40-50 percent for now. Generally have followed Storm Prediction Center sref
severe thunder probabilities by continuing a mention of strong to
marginally severe storms in the hazardous weather outlook mainly
west of Highway 281...with an expectation of a broken line of
convection drifting in. Worst-case scenario would seem to be a
60-70 miles per hour wind event if storms can organize into a cold pool...but
in theory this seems fairly unlikely given that convection should
lose intensity as it heads east out of western Nebraska/northwest
Kansas...so will only highlight a marginally severe threat at this
time. Later in the night...there are suggestions by models such as
the NAM that a modest ribbon of low-middle level Theta-E advection in
the 850-700mb layer could spark a new round of elevated convection
mainly within the northeast quadrant of the County Warning Area in closest
proximity to the southeast-drifting Dakotas shortwave...and thus
have put probability of precipitation back into these northeast zones through the night in
case this occurs. Made little change to low temperatures...with nearly
all areas settling within a few degrees of 60. Also...cannot
completely rule out some light fog tonight...but not expecting
widespread visibility restrictions of 1-2 miles or less that would
require formal inclusion in the forecast.
Turning to the Tuesday daytime period...uncertainly just keeps
growing...with some models continuing to paint daytime morning
convection possibly as a continuation of the overnight
activity...and especially within the northeast 1/2 of the County Warning Area in
closest proximity to the shortwave trough glancing by to the east.
However...based on various factors including
uncertainty/consistency with previous forecast and less quantitative precipitation forecast in
previous model runs...have opted to go ahead and leave the
majority of the daytime hours rain/thunderstorm-free for
now...while acknowledging that the next few shifts may have to
insert some Post-sunrise probability of precipitation with limited notice. For
example...the previous 12z NAM was essentially dry during the
day...but the new 18z run now has plenty of daytime
convection...which could easily be overdone per the 12z 4km WRF-
nmm...which fits the more common conceptual picture of lack
of forcing in the wake of the Iowa shortwave trough that continues
passing southeast. This conceptual picture of this pattern would
also suggest the best afternoon storm chances would be in our
western counties...and thus at least for now...the only
official thunderstorm chances in the County Warning Area tomorrow are from 3-7pm
in western counties...with no strong signal for severe storms
should they occur. As has been the case lately...be prepared for
some potentially notable changes to the timing/magnitude of these
storm chances...as looking even beyond the first 12 hours is
proving Dicey...and morning convection could be a wild card.
Temperature-wise tomorrow...assuming daytime convection does not Blossom
and cloud things up...expect another seasonably warm day and
nudged up highs slightly...getting most places between 81-86
degrees. Breezes will start out light but pick up to 10-15 miles per hour
from the southeast as the afternoon wears on with higher gusts.
Long term...(tuesday night through monday)
issued at 440 PM CDT Monday Jun 17 2013
Primary forecast concerns through the long term period revolve
around precipitation chances.
The start of the long term period Tuesday evening/night shows the
region remaining under the influence of weak/broad ridging in the
upper levels...between areas of low pressure near the far northestern Continental U.S.
And the Pacific northwest coast. Expecting that there will be activity ongoing
over the High Plains by 00z...with the main concern being how far
east/how much of the County Warning Area ends up being affected. This activity
looks to take its time sliding east...with low probability of precipitation in place through
the early/middle evening hours. Models remain in decent agreement
showing the western portions of the County Warning Area seeing the better chances of
seeing thunderstorm...but its possible not a whole heck of a lot
will make it...so there isnt a big ramp up in probability of precipitation during the
overnight period.
As we look toward Wednesday and into Thursday...precipitation
chances remain in the forecast...but nothing is certainly clear
cut. Models are in good agreement showing that above mentioned Pacific
northwest upper level low pressure system sliding inland Wednesday
morning...but by Thursday morning has only moved into the Washington/ID/Mt
border area. The main question lies with the timing/location of
pieces of energy ejected out ahead of the main low. Its impact on
the County Warning Area will depend on the strength of the ridge...which at this
point look to remain fairly flat/broad...not strong enough to shift
those better chances to the north. Plenty of uncertainty already on
Wednesday...some models show the west with the better chances/others
the east...and decided at this point to keep probability of precipitation on the lower
side. Wednesday night...didnt make significant changes to the probability of precipitation
/which remain in the chance category/...with there still being some
support of another round of activity from the west sliding
through...but with others starting to trend away from that wasnt
going to increase those chances.
By 12z Thursday...models starting to depict some slight
amplification of the ridge over the plains as that Pacific northwest low
remains in place. Main question is with precipitation chances...and
what/if anything is lingering in the east in the morning and will
anything fire in the west during the afternoon. Accompanying this
bump up in the ridge is warming temperatures in the Lower/Middle
levels...and capping starts to become more of a concern. Some
models have started trending toward that cap building in and keeping
the day dry...but a few are hanging on to the potential for some
lingering activity...so while probability of precipitation were lowered...they were not
completely removed at this point.
The forecast for Friday and Saturday is dry. Though the upper level
pattern is becoming more southwesterly as the Main Ridge axis
becomes more orientated in a SW/NE direction just east of the
County Warning Area...the warmer middle level temperatures/capping and location of surface
boundaries looks to keep the better chances just off to the County Warning Area.
For Sunday and Monday...precipitation chances look to make a return to the
County Warning Area. The low over the Pacific northwest finally starts to shift to the east/NE
into central Canada...breaking down/shifting the ridge once in place
over the Central Plains...and again allowing for the opportunity for
disturbances in the main flow to bring chances for thunderstorms.
As far as temperatures go...expecting to see a gradual warming
trend...mainly into the Friday/Sat time frame with that
amplification of the ridge...before moderating back down a touch
into sun/Mon. Currently have highs rising to the 90s for both Friday
and Sat /addition upward adjustments may be needed/...with middle 80s
to middle 90s for sun/Mon.
&&
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1219 am CDT Tuesday Jun 18 2013
Rest of tngt: VFR with mostly broken cirrus. However...we do need to
watch potential for a tempo MVFR or IFR visibility in developing showers/
thunderstorms. Winds will be light and mostly from the NE.
Tue: VFR but there is potential for tempo MVFR or IFR visibility in scattered
showers/thunderstorms until 15z. Southeast winds will average around 10 kts.
Tuesday through 06z: VFR. Southeast winds less than 10 kts.
Ceiling confidence: average
visibility confidence: average
wind confidence: average
weather confidence: average
&&
Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&
$$
Update...halblaub
short term...pfannkuch
long term...ado
aviation...halblaub
