Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
700 PM CDT Wednesday Sep 17 2014
Short term...(this evening through thursday)
issued at 253 PM CDT Wednesday Sep 17 2014
Focus is on the potential for fog and thunderstorm development tonight.
The pattern aloft featured an upper ridge axis over The Rockies...a
trough moving into the West Coast...weakening Odile lifting into
southern Arizona/nm and northwest flow across the Central Plains. Temperatures have
been on the increase this afternoon once stratus finally eroded across
our southern zones...with readings averaging in the upper 70s to
The first part of tonight is looking uneventful...however after
dark...chances for thunderstorms increase as energy translates east of
The Rockies onto the plains and middle level warm air advection increases aided by a
strengthening low level jet. A narrow moisture axis is expected to
develop along our western zones and in easterly low level flow with
light winds...expect low clouds to again develop toward daybreak.
Models are pretty robust with low visibility forecasts in fog and have went
with more areas vs patchy fog development. Will need to monitor
visibility trends through the evening but especially overnight as some
areas may see dense fog. How low visibilities drop will also be dependent
upon on quickly winds transition from easterly to
southeast/southerly Thursday morning with wind speeds picking up
by middle/late morning. Based on stratus/fog timing earlier
today...the visibility improvement was more toward 14z so went with
similar timing for Thursday. There is still some concern on how much
of this will be fog vs thunderstorm vs drizzle and have left drizzle out
due to having probability of precipitation in there for storms. If storms go...a strong
storm capable of producing nickel hail size hail due to presence
of instability of 1500 j/kg and 40kts of shear.
Thursday is complicated due to how long stratus will hold and if it
holds through much of the day...it will have an impact on temperatures.
Have went with a more pessimistic forecast as models hold onto
low level moisture into the afternoon and have lowered maximum temperatures and
increased cloud cover.
Long term...(thursday night through wednesday)
issued at 253 PM CDT Wednesday Sep 17 2014
Pattern: the next two weeks are looking very dry here...primarily
once we get past Sat. That does not mean it won't rain...just that
conditions generally will be unfavorable for decent rainfall and the
probability will be high for a long stretch with no rain. Multi-day
500 mb ensemble means from NCEP/ECMWF/MSC/jma all indicate high
predictability in a NE Pacific trough/western USA ridge with northwest flow here
over the plains. While this is a dry pattern...it will be
wonderfully warm at times as we tussle between the last vestiges of
Summer and oncoming autumn. There will be potential for a 90f day or
two in the Tri-Cities.
Aloft: the ridge currently over the western USA will advance east over the
plains by 00z/Friday as the low off California moves inland. Significant
amplification will take place over North America this weekend as heights
fall over the NE Pacific. This will send another serious spell of
below normal chill next week. The ridge will remain overhead Friday but
becomes quashed Sat as the longwave trough digs over the eastern USA. The
western USA ridge will be shoved temporarily east into the central USA next
Tue-Wed...along with the embedded low that will moves inland in the
west tomorrow. This low will be a forecast problem and could contribute to
a day or two of much below normal chill.
Another complication will be the remnants of Odile /currently moving
Surface: eastern USA high pressure will lose its influence over the region
as a cold front sags across Canada and the northern USA Fri-Sat. This
front will slip through here Sat night. Canadian high pressure will then
build in sun-Tuesday as it presses southeast into the eastern USA.
The daily details...
Thursday night: a mild night. Breezy at times. We have seen a lot of fall-
like chill this month. Temperatures will be the warmest in a week for sure
and possibly all the way back to Sep 3rd.
Fri: warm sector. Sunny/breezy and very warm just ahead of the
approaching Lee-side trough. This will be the warmest day we've seen
in over a week. Not out of the question one of the Tri-Cities could
briefly touch 90f for an hour. Best chance at Kearney. Can't rule
out a very late afternoon thunderstorm north of Nebraska Highway 92 as the front eases in
from the north.
Used a 50-50 blend of the mav and 4km NAM 2m dewpoints for 21z as
they have been consistently verifying best and our dewpoint
performance has been low at 57 hours.
Friday night: shortwave trough with the Lee-side trough and approaching
front will result in scattered clusters of thunderstorms...primarily after
midnight. MUCAPE 1000-2000 j/kg. Effective deep layer shear 40-50
kts. This could result in strong-severe thunderstorms. Probably not
widespread and confidence is only average.
Sat: some thunderstorms or thunderstorm clusters will probably linger as the
shortwave trough departs. Some help via the remnants of Odile could
occur over parts of Kansas. This activity /even if it does not make it
into our north-central Kansas counties/ could put a significant cap on temperatures.
Not sure we have this handled properly yet. Back to normal on the
temperatures...except this possible snag.
Sun: sunny and very nice with light winds. Temperatures near normal.
Mon: sunny with temperatures dropping cooler than normal but still very
Tuesday-Wed: warm sector with a warm front developing over the region.
Clusters of low level jet warm air advection-driven thunderstorms. Temperatures highly dependent upon cloud
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 658 PM CDT Wednesday Sep 17 2014
The biggest issue will be visibility and ceilings overnight into
early morning Thursday. Most numerical models are pointing toward
reduced visibility to some degree...and since much of the area
fogged up last night...it is even likely more will develop