Area forecast discussion
National Weather Service Hastings NE
421 am CDT Wednesday Jun 19 2013
..above normal uncertainty continues as we grapple with thunderstorm
potential with minimal forcing...
Short term...(today and tonight)
issued at 421 am CDT Wednesday Jun 19 2013
Aloft: the ridge over The Rockies 24 hours ago was shifting east onto the
plains as a potent -2 Standard deviation closed low was moving
onshore into the Pacific northwest. The ridge axis will remain over the plains
through tonight as the low swings into western Montana by daybreak Thursday.
24 hours ago we were wondering if the modeled shortwave trough forecast to move
through today was legit or solely an artifact of model-generated thunderstorms.
WV does indeed confirm the presence of a subtle pv anomaly/shortwave
trough over Colorado. This appears to be the leading trough associated with
the new long wave trough/closed low moving into the Pacific northwest.
Sfc: high pressure was over the Great Lakes and will gradually slide east
through tonight. Meanwhile...the pressure gradient will increase as a Lee trough
develops. A Pacific cool front will continue pressing east through the
intermountain west. In addition...leftover boundaries from previous
thunderstorm activity linger.
Forecast confidence: average for temps/dwpts/winds...but very low for
clouds/thunderstorm chances and precipitation amounts.
Early this mrng: the remnants of Panhandle and eastern Colorado thunderstorm activity
have been drifting east. An impressive/expansive outflow boundary
emanated from the thunderstorms that moved through the gld area. This boundary
kicked off a couple pulse-type showers here and there around midngt.
Precipitation was been on the wane as it approached our north-central Kansas counties.
Today: expect skies turn M/sunny after debris clouds from overngt
thunderstorms dissipates/heads east. Dont have a good feel for precipitation potential.
A shower or thunderstorms could be possible at any time. Models indicate the
weak shortwave trough will move through 12z-18z. Thereafter would expect
subsidence to limit afternoon thunderstorm development.
General ridging aloft may also put a lid on thunderstorm development.
At 05z there appeared to be an mesoscale convective vortex associated with the dissipating
thunderstorm complex over gld...along with an outflow boundary heading east-northeast
around 30 kts. The mesoscale convective vortex is moving east-southeast around 22 kts and it should
enter Phillips/Rooks counties around 515 am and exit Jewell/Mitchell
counties by 915 am. So this feature will be too far east to play a role
in any subsequent thunderstorm development here.
The 25-35 knots low level jet will remain today due to the increasing pressure
gradient and the bl will mix into this. While it will be breezy
everywhere...areas west of Highway 281 will measure the highest gusts of
30-35 miles per hour. Could see an isolated g40 from lxn to Beaver City.
Tngt: the low level jet intensifies. There should be some thunderstorm development but
just no sure where.
Bottom line...cant entirely rule out a thunderstorm today or tonight but most
of the time it will be dry at most locations.
Temperatures today and tonight are based on a bias corrected blend of the
previous Gid forecast and 2m temperature guidance.
Long term...(thursday through tuesday)
issued at 421 am CDT Wednesday Jun 19 2013
Overview: a several day stretch of hot weather is on the way
beginning on Thursday as highs warm into the upper 80s to lower and
middle 90s. The brunt of the heat will be felt Friday through at least
the end of the forecast period on Tuesday with highs in the 90s each
day for most Nebraska zones and middle to upper 90s for Kansas zones.
The precipitation forecast is extremely challenging and of fairly
low confidence with only minor disturbances passing through and a
pattern that supports more hit and miss isolated convection rather
than any kind of widespread obvious rain makers.
Thursday...confidence in the chance of precipitation is lower than
would typically be expected in the day 2 time frame. The high res
00z European model (ecmwf) was unavailable to field offices and thus this forecast
was based primarily on NAM...WRF...and GFS models. The 06z NAM..00z
GFS...and some WRF members showed an mesoscale convective system moving across our area
Wednesday night that may linger into Thursday morning across our far
east. Will keep Thursday morning dry for now...but could certainly
see some probability of precipitation being added in the east if confidence in a long
lasting mesoscale convective system increases. Warmer air aloft at 700mb then moves in
through the day on Thursday strengthening the cap. For the
afternoon...the 00z GFS is dry...but the 06z NAM tries to develop
convection across our eastern Nebraska counties despite 14 to 15c
cap at 700mb. We rarely get convection in our northeastern counties
with those kind of temperatures at 700mb. The NAM seems well over
done with quantitative precipitation forecast and thus will keep the afternoon dry due to cap.
However...will include a slight chance of thunderstorms for areas
along and north of Highway 92 for Thursday night due to increasing
low level jet nosing into this area. Best bet of nocturnal elevated
convection associated with the low level jet will be north of our
County Warning Area. Any thunderstorms that form would have the potential of
becoming strong to severe...given cape and shear environment...just
not very confident that we will even initiate any convection. The
warmup will begin with highs ranging from the upper 80s around Ord
to the middle 90s around Phillipsburg Kansas.
Friday through Saturday afternoon...temperatures at 700mb remain
toasty evidence of a strong cap. Consequently...most areas should be
dry. There may be a weak vorticity maximum or two that track through the
area...but the cap will be difficult to overcome. The only probability of precipitation in
the forecast during this period will be across our Kansas counties
to far southwestern Nebraska zones where convection sometimes can
overcome the cap on the High Plains due to significant heating and
then may slide into our area. Even so...this is a very low end 20
percent chance. The 06z NAM continues to look suspect given the
strong cap with convection Friday evening and thus it will not be
used at this time. It will be a hot period with highs in the 90s for
most locations Friday and Saturday...and that is more like middle to
upper 90s across Kansas.
Saturday night through Sunday night...the main upper trough over the
northern rockies will slide into the northern plains and send a surface
front into our forecast area. The best chance of storms will be well
north of our forecast area in association with the upper
system...but we could once again see at least a slight chance of
thunderstorms due to the flattening of the upper ridge...and surface
front in the area. The lack of strong upper forcing is the reason
for keeping the probability of precipitation fairly low.
Monday and Tuesday ... upper ridge will have flattened out...but
the primary track of short waves will be across the Dakotas.
Therefore...given the absence of any noteworthy synoptic systems
will keep these days dry for now...but can not completely rule out
the chance of a diurnally driven isolated thunderstorm or a stray
High Plains system moving in during the evening/overnight hours.
Temperatures should remain hot in the 90s.
&&
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1232 am CDT Wednesday Jun 19 2013
Rest of tngt: VFR with 20k feet cirrus ceilings from dissipating
upstream thunderstorms. Southeast winds will average less than 10 kts.
Wed: VFR with a very low probability for an IFR thunderstorm. Confidence
is not high enough to include in the taf at this time. South-southeast winds will gust
to around 26 kts.
Wednesday ngt: VFR. Thunderstorm chances are highly uncertain. The low level jet is forecast
to intensify which could provide a favorable environment for thunderstorms
to form. This could also result in low level wind shear beginning around 04z. Low level wind shear
is currently not in the taf due to it being a marginal threat.
Will convey to later shifts in case confidence increases.
Ceiling confidence: medium
visibility confidence: high
wind confidence: high except near any thunderstorms that might develop
weather confidence: low
&&
Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&
$$
Short term...halblaub
long term...wesely
aviation...halblaub
