Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
101 am CDT Friday may 22 2015
Short term...(this evening through friday)
issued at 406 PM CDT Thursday may 21 2015
The main focus of the short term will be precipitation chances for
Friday and temperatures.
In the synoptic analysis...an upper level trough is positioned over
Quebec while an additional trough is located across the Desert
Southwest. A very weak low amplitude ridge existed over the southern
Central Plains this morning. At the surface...high pressure is
dominate across much of the Central Plains...while low pressure is
forming along the Front Range of The Rockies.
As the upper level trough across the Desert Southwest swings
northeast across the Central Plains...a weak upper level disturbance
will slide through the forecast area overnight and into Friday.
Model solutions indicate precipitation chances should begin across
the southwest by early morning...roughly 9 to 12z Friday
morning...continuing to spread northwest throughout the day. While
rain is certainly expected across much of the area through the
morning hours...questions remain about the extent of rain through
the afternoon. Lowered ceilings throughout the day and drying out in
upper levels suggest rain changing over to drizzle by afternoon. As
the surface low approaches from the west...a tightened pressure
gradient will aide in increasing southeast winds across the forecast
area. Not looking to see much sun on Friday...which will help keep
temperatures down. Might even need to go a bit lower...as most model
solutions are colder than guidance.
Long term...(friday night through thursday)
issued at 406 PM CDT Thursday may 21 2015
Not much change in the overall large-scale expectations of this
6-day stretch from yesterday...as "unsettled/fairly active/troughy"
are definitely the operative terms. Literally every single one of
these 12 forecast periods features at least a modest 20-30 percent
chance of showers/thunderstorms. Of course...it's hopefully common
sense to most folks that it won's actually rain at every given
location every single day/night...but this type of weather pattern
makes it pretty much impossible to rule out any given time frame
from having at least a slight chance of rain. Right away to kick
off the Memorial Day weekend...Saturday and probably most of
Sunday are looking quite cloudy...and even if there is not
legitimate shower/thunderstorm activity happening...pesky light
drizzle could put a damper on outdoor activities.
Fortunately...there are no "obvious" time frames that appear to
carry a legitimate threat of severe storms yet...but even as early
as late Saturday afternoon/evening suppose a few stronger storms
with small hail/gusty winds cannot be totally ruled out mainly in
southwestern zones. Given all the uncertainties/complexities in
this active weather pattern...it's certainly not out of the
question that a few days next week could bring at least a marginal
severe storm risk as temperatures/dewpoints rise and instability
increases...but at this point it is impossible to pinpoint this
potential with any confidence. As a result...will just need to
keep evaluating any upcoming potential for severe storms a few
days at a time as things draw nearer. Flooding-wise...see separate
section below for some of the latest trends on the Platte River
situation. However...other parts of the County Warning Area may also become prone
to at least some minor flooding issues if a few of these various
rain chances pan out and produce appreciable amounts.
Temperature-wise...a gradual warming trend is still anticipated
over the course of these 6 days...with the current forecast
calling for highs only in the 60s for most of the County Warning Area on Saturday
into Sunday...before rebounding back into the 70s most of next
week. Meanwhile...overnight lows should hold up well into the 50s
on most nights...as it's now highly likely that any risk of
frost/freeze has breathed its last gasp for the Spring. There is
some uncertainty however mainly with the high temperature
forecasts...as there is a possibility that days such as Saturday-
Sunday could trend cooler under widespread cloud cover (maybe
some areas stuck in the 50s?)...while days next week such as
Wednesday-Thursday could possibly end up warming well into the 80s
in some areas per some model guidance.
With the main points covered...here is a quick look at some
daily/nightly details in 12-24 hour blocks.
Friday evening/night...although most of the County Warning Area will probably not
see "significant" rainfall during the night...it is looking more
and more likely that this will be a cloudy/dreary/drizzly
night...and likely with at least some light/patchy fog as well.
While large scale forcing is relatively weak with the County Warning Area in
between shortwave disturbances in prevailing southwesterly flow
aloft...low level moisture/saturation looks to be fairly
significant...making a ripe environment for at least some
drizzle. Kept probability of precipitation in "likely" territory County Warning Area-wide as odds are most
places will experience wetness of some kind...whether it be from
drizzle or legit heavier showers. Despite meager elevated
instability...cannot rule out a few rumbles of thunder mainly in
the southwestern 1/2 of the County Warning Area. Otherwise at the surface...steady
southeast breezes of 10+ miles per hour should persist through the night.
Saturday daytime/night: barring some pretty big changes in model
trends...this is unfortunately looking like a rather damp/dreary
start to the Holiday weekend. Various small-scale middle level
disturbances will continue to impinge on the Central Plains from
the southwest...as a parent larger scale trough remains anchored
over The Rockies. There is a good chance that widespread low level
cloud cover will stick around through this time...with a
continuation of drizzle/patchy fog from Friday night likely into
at least the morning hours. There could also be some hit-and-miss
thunderstorms embedded within areas of passing showers as
well...although agree with Storm Prediction Center that any marginal threat of strong
to severe storms during the afternoon/evening should largely
remain at least 50-100 miles west and/or south of the County Warning Area. As
earlier stated...highs temperatures aimed into the middle 60s could be
Sunday daytime/night: not a whole lot of change in the pattern
with pieces of the central rockies middle/upper trough continuing to
lift across the Central Plains. There are hints that the day may
not be quite as drizzly/gloomy as Saturday looks...but that's no
guarantee either. With a bit stronger upper forcing...the
potential for a few strong to possibly marginally severe storms
may increase...but this will be very dependent on
destabilization...which could be severely hampered. Highs are
aimed into the upper 60s/low 70s...but again this will probably
depend on at least a little sun breaking out.
Monday Memorial Day daytime/night: the main weekend low pressure
system starts to lift eastward and potentially out of the Central
Plains...but there is absolutely no way that either the day or
night can be "guaranteed dry" yet...and 20-50 probability of precipitation continue
through the period. The day is certainly not looking like a true
"washout" though despite these rain chances.
Tuesday daytime/night: per the latest European model (ecmwf) solution...this 24
hours may hold some hope of staying mainly dry...but because the
latest GFS solution brings additional energy into the Central
Plains cannot go with a dry forecast and have mainly 20-30 percent
probability of precipitation.
Wednesday daytime/night: although middle-upper flow is looking
relatively weak...even the European model (ecmwf) solution brings the next pieces
of energy into the Central Plains from yet another western Continental U.S.
Trough during this time...along with warmer air at the surface.
Could see at least isolated strong/severe storm potential around
this time frame...but nothing that looks very widespread.
Thursday daytime: the broad western Continental U.S. Trough continues
shifting slowly east...keeping modest shower/thunderstorm chances
going strong for the local area.
Aviation...(for the 00z kgri/kear tafs through 00z Friday evening)
issued at 612 PM CDT Thursday may 21 2015
A middle level low lifting north out of eastern Colorado will spread
plenty of low/middle level stratus and light showers and drizzle
across the region later this morning. Expect VFR conditions to
prevail through the morning hours...with ceilings slowly lowering to
MVFR levels by mid-day. May also see some MVFR visibilities in -dz and
br...as well as some IFR ceilings...but opted to keep VFR visibility and
MVFR ceilings for the time being. Otherwise...expect the pressure
gradient to tighten during the morning hours...resulting in breezy
southerly winds expected to become more southeast late in the day.
issued at 406 PM CDT Thursday may 21 2015
Not much change in the Platte River flooding situation since
yesterday...as the the same two Platte River Flood Warning
segments that we have had out for several days now continue...one
generally covering The Reach of the river from Gothenburg-
Lexington...and the other covering the stretch from near Kearney-
Doniphan. Known impacts remain minor. Based on the latest observed
gauge trends and the latest forecasts from Missouri Basin river
forecast center (mbrfc)...the river near Cozad may be slipping
just below flood stage within the next 12-24 hours...but could
also hover right at the flood stage of 6.5 feet for a time as
well. Farther east at the Kearney gauge...the river remains
solidly above the minor flood stage of 6.0 feet...and may very
well remain so for several more days despite a slow falling trend
that is expected to commence Friday night into Saturday.
Meanwhile...at the official Grand Island gauge along The Hall-
Hamilton County line...the river is still not expected to breach
minor flood stage of 6.5 feet...but could come very close this
weekend with a forecasted crest of 6.4 feet.
In closing...although any Platte River flooding within mainly the
western half of our County Warning Area is expected to remain minor...there
continues to be plenty of uncertainty regarding exactly when the
river will solidly drop back below official flood stages at
various locations...especially if parts of the basin see
appreciable rainfall during the next several days. Stay tuned to
the latest flood warnings/statements.