Area forecast discussion
National Weather Service Hastings NE
1230 PM CDT Thursday may 23 2013
Update...
issued at 655 am CDT Thursday may 23 2013
Overall...forecast for today still looks on track from earlier
issuance...and made only a few minor tweaks to the first few
hours. Broken band of sprinkles/light rain continues to push eastward
into the far southwestern County Warning Area at this time. Based on upstream
observation...still feel that legitimate measurable rain will be tough to
come by with this activity...and thus have maintained wording as
only sprinkles. Day shift will have to keep an eye on the areal
coverage of this light precipitation however...as current forecast has it
confined southwest of a Lexington-Beloit line. Otherwise...the
combination of extensive low stratus and incoming middle clouds could
delay temperature rises a bit this morning...but still thinking increasing
afternoon sun should get all areas up around 70 eventually.
&&
Short term...(today and tonight)
issued at 515 am CDT Thursday may 23 2013
This 24 hours Marks the very beginning stages of the more
active/stormy weather pattern that will ramp up heading into the
Holiday weekend. Like last night...low level stratus trends are
presenting a challenge mainly during the first 6 hours. Precipitation-
wise...have introduced sprinkles into southwest zones this
morning...and overall made little notable change to overnight
showers/storm chances...which should not be overly widespread.
Also made only minor tweaks to temperatures today/tonight.
08z objective Central Plains surface analysis is highlighted by
the southward extension of a rather strong 1032+ millibar high
centered well to the north over central Canada...with pressures to
around 1018mb as far south as the local County Warning Area. This high is driving
steady north breezes generally 5-15 miles per hour early this morning...with
locally higher gusts. Aloft...water vapor imagery and short term
model data depict the departing middle level low that brought the
light rain to eastern areas 24 hours ago now well off to the east
in the Great Lakes region...while well upstream to the west an
expansive 500mb closed low continues churning over or/WA. In
between these lows...a ridge axis extends north-south through The
Heart of the nation...with its axis aligned through western
portions of neb/KS. 11-3.9 micron satellite imagery confirms that
in fact the stratus that eroded northward across much of the County Warning Area
on Wednesday has sunk back southward overnight...with the majority
of the County Warning Area sitting under a roughly 1500 feet cloud deck. Earlier in
the night...there were hints at a few automated stations such as
Ord that brief sprinkle/drizzle might have fallen...but otherwise
the County Warning Area has remained dry thus far...with overnight low temperatures
likely ending up between 45-50 nearly all areas. Looking just to
the west...a classic northwest-southeast band of middle level Theta-E
advection evident on both the 700mb and 310k surface is driving a
surprisingly healthy area of light rain showers over mainly
northwest Kansas/northeast Colorado...with a more organized area of
thunderstorms developing along this same zone of lift much farther
south over OK.
Heading into the daytime hours...the most immediate issue is to
what extent the light rain showers to the west will hold together
as the middle level corridor of lift continues edging eastward toward
the County Warning Area. Given that this forcing should continue weakening a bit
as it spreads east this morning...and also given a considerable
amount of dry air noted below 600mb on forecast soundings...think
the odds of legitimate measurable rain affecting more than a tiny
fraction of the western County Warning Area this morning is quite low. That being
said...went ahead and introduced a sprinkle mention to a
previously rain-free forecast through middle-day for areas generally
southwest of a Lexington-Beloit line...with seemingly little risk
for even sprinkles for the Tri-Cities and points North/East.
Although this sort of setup often produces at least a rogue
lightning strike or two...even elevated instability is essentially
non-existent over the County Warning Area this morning so will not go the
thunderstorm Route. As for the middle/upper level story today...the
aforementioned ridge axis will amplify a bit over the Central
Plains today...resulting in rising heights. At the
surface...winds will be on the increase a bit and transition from
northerly to easterly due to the combination of high pressure to
the north drifting east...and also decent pressure falls to the
west as a fairly strong surface low ramps up over Wyoming. This
afternoon...steady easterly breezes around 15 miles per hour with gusts into
the 20-25 miles per hour range will be in place...strongest west of Highway
281. As for the evolution of sky cover today...will again lean
toward the latest rap/hrrr low cloud/relative humidity
fields...which suggests a fairly rapid scattering out/lifting of
low clouds through the middle-late morning hours...paving the way for
an afternoon that should average no worse than partly cloudy.
Assuming this all pans out as planned...temperatures should have no
problem making a decent rise...and have aimed highs between 68-72
degrees for nearly the entire County Warning Area...which is only slightly warmer
than previous in some spots. As for afternoon precipitation
chances...kept it dry as any convection should focus at least a
few counties off to the south and/or west.
For the tonight period...00z-12z...little overall change in
thinking from previous forecasts. In the middle-upper levels...fairly
weak quasi-zonal flow continues across the Central Plains within
the ridge axis...while off to the west a lead shortwave trough
ejects northeast across Wyoming/Montana along the southeast side of the
parent Pacific northwest low. As the night wears on...another more
vigorous batch of middle level Theta-E advection will veer eastward
across western/central portions of Nebraska/Kansas. Slightly
lower in the column...a decent southerly 850mb low level jet will
strengthen to 30-45kt late in the night mainly along the far
western edge of the County Warning Area and points west. Needless to say...models
vary on how much quantitative precipitation forecast they generate over the County Warning Area tonight...with
some such as the NAM and even 4km WRF-nmm showing little if
anything going on locally...with better chances focused west.
However...given the decent middle level Theta-E advection and
forecast of 200 + j/kg of elevated MUCAPE in the 850-700mb layer
forecast into parts of the County Warning Area after midnight...and higher values
to around 1000 j/kg in the far western counties...kept fairly
modest 20-30 probability of precipitation going especially for the 09z-12z time
frame...while keeping the entire evening time frame rain-free.
Relegated these storm chances west of an Ord-Hastings-Beloit line
through sunrise...with chances in eastern counties holding off
until the Friday daytime period. Although not expecting any severe
storms late tonight...certainly cannot rule out some small hail
especially in the far western fringes of the County Warning Area. Could also see
renewed low stratus development as low level winds turn more
southeasterly. Surface breezes of 10-15 miles per hour will prevail through
the night...and made only minor changes to low temperatures with most
areas bottoming out within a few degrees either side of 50.
Long term...(friday through wednesday)
issued at 515 am CDT Thursday may 23 2013
The weather pattern will become more active in these extended periods.
On Friday...an upper level ridge axis will be in place across the
Central Plains in between an upper low in the Pacific northwest and
an upper low/trough along the eastern Continental U.S.. a warm frontal
boundary lifts east/NE across the Central Plains during the day and in
warm air advection/Theta-E advection...showers and thunderstorms are expected to develop
and spread east/northeast Friday/Friday night. Due to anticipated
precipitation and cloud cover on Friday...have lowered high temperatures a few
degrees. Instability parameters indicate convective available potential energy increasing to 1000
j/kg with some higher instability potential greater than this
possible across our western zones...and effective shear is prognosticated
around 30kts. Could see a few strong/severe storms by Friday
afternoon/evening and more so into Friday night...as low level jet increases.
Models suggest additional convective potential along High Plains
Friday night in vicinity of surface low/dry line which may then roll across
our region overnight.
On Saturday...flow aloft will be southwesterly as ridge axis shifts
eastward...while at the surface...low pressure should settle along the
High Plains with two potential surface low centers developing...one in
eastern Wyoming/Montana and another to the south across western Kansas. Warm
frontal boundary looks to settle near the Nebraska/Kansas start line with much
greater instability expected with convective available potential energy in excess of 3000 j/kg as
moisture pools along the boundary...and again decent shear is
prognosticated around 30kts...especially across Nebraska which increases
overnight with nocturnal jet. Warm middle level temperatures could may inhibit
convection to the west along the dry line...however warm front looks
to become active and if storms fire in vicinity of front...conditions
are favorable for severe weather. Convective potential continues
into Saturday night mainly across Nebraska north of front on nose of 50kt
low level jet.
Through the remainder of the Memorial Day Holiday
weekend...Sunday/Monday...convective potential continues in
southwest flow aloft as shortwave energy lifts across the plains and
interacts with low level boundaries. Timing/location of best precipitation chances
will be refined with time. This being said...the weather pattern
does look active with potential for severe weather and decent
rainfall/precipitation is possible for several days in increased
moisture...and precipitable water values increase to between an inch
and an inch and a half.
By middle week...extended models begin to diverge in handling of
trough/upper low across the western Continental U.S. And due to model
differences...did not deviate much from extended init.
&&
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1230 PM CDT Thursday may 23 2013
MVFR conditions to continue at kgri through 19z or so...with VFR
conditions forecast 19-10z...and then another round of MVFR
conditions to finish the taf period.
Stratus across the area continues erode at this hour and visible
satellite imagery indicates it will not be long before kgri also
scatters out. Went ahead with an MVFR ceiling through 19z as a
result. VFR conditions are then expected through the rest of the
day and much of tonight. Closer to sunrise Friday however...low
level Theta-E advection from the southeast will promote stratus
development across much of the region...including kgri. Most
guidance suggests an MVFR ceiling will be realized by sunrise
Friday...although some guidance does suggest the ceiling may drop
to IFR levels. For now will side with the majority of guidance and
forecast an MVFR ceiling...but future shifts will want to continue
monitoring for the possible insertion of an IFR ceiling in future
tafs. There is also a low chance of thunderstorm activity...along
with measurable rainfall...at kgri 12-18z...but the probability of
such activity being realized is too low for insertion into the taf
at this time. The surface wind will transition from the
east/northeast to more of a southeasterly direction during the taf
period...sustained generally in the 10-15kt range. Visibility
restriction is not expected at kgri through the next 24 hours.
&&
Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&
$$
Update...pfannkuch
short term...pfannkuch
long term...Fay
aviation...Bryant
