Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Hastings NE
635 am CDT Tuesday Aug 4 2015

Short term...(today and tonight)
issued at 355 am CDT Tuesday Aug 4 2015

Radar and satellite imagery show activity ongoing on both the northern
and southern sides of the County Warning Area early this morning. Thunderstorms
across portions of Kansas are being driven by an upper level shortwave
disturbance sliding out of southern Colorado...aided by an increased low level jet. To
the W/NW...satellite imagery shows another disturbance over
portions of southern Wyoming/northern Colorado...which will be the player behind
weather across our area through the short term period. To the
N/NE...currently the County Warning Area is barely outside of a line of
thunderstorms extending from wcentral South Dakota into NC Nebraska and into northern
MO...set up along a line of middle level convergence/increased
isentropic lift. Will keep some probability of precipitation going early this
morning...though models generally keep the brunt of the activity
in the general vicinity it is now...cant completely rule out the
north/NE getting precipitation. At the surface...most of the County Warning Area sits with Erly
winds...with a stationary boundary draped from western Nebraska into NC Kansas
and into central MO. Some models suggest the potential for fog
this morning near that will insert a mention of
patchy fog across the south...but will be keeping a close eye on
observation to see how low visibilities actually get...and will adjust the
forecast as necessary.

Through the rest of the short term period today and
mentioned above...the primary concern revolves around that
shortwave disturbance and accompanying southeastward extending
trough axis shifting east out of southern Wyoming/northern Colorado. Models are in OK
agreement showing that the activity affecting northern/eastern Nebraska being
the main focus through the first half of the morning or so...with
attention turning more toward the west/southwestern portions of the area with
time as the disturbance shifts further east. The surface boundary
currently over far southern portions of the County Warning Area looks to creep
northward today as low pressure deepens some over the High
Plains...but even within 6-12 hours...models still have some
differences with just how far north it actually gets. It may end
up remaining closer to the NE/Kansas state line...with some showing it
pushing into northern portions of the County Warning Area.

The best chances for thunderstorm activity looks to come as we
approach/pass the midday hours...continuing into the
evening/overnight period. Because models suggest that just about
anywhere in the County Warning Area could see thunderstorms...either near the surface
boundary and/or near the main middle level trough axis...have 50 probability of precipitation
in place County Warning Area-wide this afternoon/evening. Concern for severe
thunderstorms models havent changed much showing the
potential for at least modest instability to be in place across
the area...but there are some differences across the area looking
at deeper layer shear. Models are in pretty good agreement showing
the better shear values setting up across roughly the southwestern half of
the County Warning Area /pushing 40kts depending on the model/...further northeast
model values struggle to get above 20 kts early on. That southwestern half
sits in the Storm Prediction Center day 1 slight risk area...the remainder of the area
sits in the marginal risk area.

This evening/tonight...models are in good agreement showing the
disturbance itself sliding east across the area...and the
continued lift aided by an increased low level jet will keep thunderstorm
chances going.

Long term...(wednesday through monday)
issued at 355 am CDT Tuesday Aug 4 2015

A messy upper level pattern is expected through the extended
periods as several disturbances make their way across the
intermountain west bringing multiple chances for precipitation to
the local area. The weak ridge of high pressure across the
southwest is eventually expected to strengthen towards the middle
of next week...potentially building into the central and northern
plains and thence diminishing thunderstorm chances while
increasing temperatures....but plenty of time for subsequent model
runs to continue to push this drier period father out into the
future. In the meantime...seasonable temperatures with near daily
chances for thunderstorms are expected...with these showers and
thunderstorms primarily dependent on timing/location of passing

Starting off Wednesday...expect the local area to be on the tail
end of an upper level low rounding the top of the ridge to our
southwest...with thunderstorm chances eventually diminishing from
west to east through the afternoon hours. While there will still
be some elevated instability to work with during the evening and
overnight hours...with the lack of any significant trigger...think
Wednesday night will be dry. This dry period will be short the next upper level disturbance approaching
from the west reaches the local area. While there are timing
differences amongst models...with plenty of instability expected
by Thursday will not take much to forcing to
initiate thunderstorms. This instability...combined with modest
0-6km shear values...could lead to a few organized thunderstorms
capable of producing strong wind gusts and marginally severe
hail...but as of this time...the forecast area is not outlooked
for severe weather from the Storm Prediction Center on Thursday.

Thereafter...near daily chances for thunderstorms will continue
across the local area...although they will remain scattered in
nature...and not all areas will see precipitation on a daily
basis. As hinted earlier...could see a pattern change late in
the extended periods...but confidence of this is low...and think
it is reasonable to expect near seasonable temperatures through
the upcoming weekend and into next week...with scattered
thunderstorms around from time to time.


Aviation...(for the 12z kgri/kear tafs through 12z Wednesday morning)
issued at 627 am CDT Tuesday Aug 4 2015

Certainly not a clear-cut forecast for this taf period...and
confidence is low. An area of low level stratus draped across
portions of the area is bringing MVFR to LIFR conditions to the
terminals...kear is more solidly in the stratus vs kgri which
appears to be more on the fringe of the lowest ceilings. Kear
also continues to see visibilities near 1/2sm at times...which
could linger for another hour or two. Kept any mention of ts out
of the taf for this morning...but will be keeping a close eye on
the activity ongoing across NC Nebraska into eastern Nebraska. For the most part
it has been drifting E/se...but there are some models that suggest
the potential is there for it to push further S this morning.
Better chances for ts activity looks to come this
afternoon/evening as the main upper level disturbance starts to
move onto the Central Plains. At this point kept the mention as
thunderstorms in the vicinity due to uncertainty with exactly where things will develop.
Outflow from activity to the north is resulting in a brief switch
to more northeasterly winds this morning...but the prevailing
direction through the day is expected to be E/serly.


Gid watches/warnings/advisories...


Short term...adp
long term...Rossi

National Weather Service Glossary of Abbreviations