Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
1216 PM CST Friday Mar 7 2014
Short term...(today and tonight)
issued at 441 am CST Friday Mar 7 2014
The biggest challenge in the short term will be chances of
precipitation today determining potential precipitation type and
amounts today and night.
A cold front is entering the County Warning Area early this morning in advance of a
middle-upper level trough approaching from the Rocky Mountains. I
actually ticked up highs today as cold air advection will not be
particularly strong until evening. That being said...confidence is
not all that high as we could have quite the temperature gradient.
As for precipitation chances...ensembles suggest measurable
precipitation is likely...but numerical models are indicating this
would be very light. Synoptic lift is weak and frontogenetic forcing
is absent for the most part. The 06z NAM just pulled out the rug
from under US and left US high and dry for the entire event...after
being the most promising numerical model for precipitation. This is
likely a result of the best synoptic lift remaining southwest of the
County Warning Area...with divergent q vectors between 500 mb and 300 mb confirming
this. The rear right quadrant of the jet to the northeast may wind
up being a little too far to the northeast to be of much
consequence...but I did leave slightly higher amounts for snow in
the northeast and southwest...closer to where there will be somewhat
better lift. Most of the precipitation should fall toward evening
when we are more likely to get snow...but still...precipitation
amounts are expected to be so low that this should not be much
consequence...except for perhaps a brief reduction in visibility.
For temperatures...I followed closer to bcconsraw and for
precipitation chances I like the sref data from ensembles.
Long term...(saturday through thursday)
issued at 441 am CST Friday Mar 7 2014
Pattern: a western USA ridge/eastern USA trough will dictate the weather through Thursday
3/13. For Sat-Tuesday this pattern will be low amplitude...but
thereafter in the 5-10 day period it will become highly amplified.
This supports continuing dry weather with temperatures at or above normal. There
are signs of a pattern change in the ec/GFS ensembles over the central
Pacific in the 10-15 day period /Mar 16-21/. If this holds it would
result in a western USA trough and possibly the first thunderstorms of the season
followed by colder temperatures.
Aloft: the trough associated with fri's weather will sag through Sat followed
by low amplitude ridging developing over the plains sun-Mon. A
Pacific origin trough will move through Tuesday and as it migrates into the
eastern USA...the flow will amplify putting the Central Plains in northwest flow.
Surface: northern plains high pressure will drop S across the forecast area Sat
and into the Southern Plains Sat night. That puts US in the warm sector
as a pair of lows tracks along the US-canadaian border. A prefrontal
trough will move through Monday as the second low moves into the Great
Lakes. The cold front will follow Monday night. High pressure builds in
Wednesday-Thursday as a substantial winter storm develops over the eastern USA.
The daily details...
Sat: the day probably starts with substantial high clouds per
multi-model vertical cross sections...then decreasing clouds. There
could be a little light snow that lingers over north-central Kansas...but any
threat for accumulate will be over.
Highs will be a touch cooler than normal...especially from Highway 281
east. Otherwise...they are largely continuity with the previous forecast...
except over Dawson County where they were nudged into the low 50s.
Sun-Mon: looking very very nice with Sunday the breezier of the two
days. These will be the best days out of the next 7. Patches of
cirrostratus will begin spilling over the ridge sun and continuing
into Monday. Nonetheless...we are expecting Monday to be the warmest day
so far this year. Believe it or not we actually have to make it past
the highs of Jan 19th. It/S doable. Highs were raised 3-4f above
As forecasters we usually are not warm enough in these situations.
Dont be surprised if the forecast ends up warmer than we are currently
indicating. That being said we will have to deal with a substantial
amount of cirrostratus. I am certain we are not high enough on cloud
cover...but we trended it upward.
Fire wx: we need to keep an eye on dewpoints sun. Breezy SW winds
could transport drier dewpoints than now forecast into the area. That
would result in near critical fire danger. Forecast dewpoints were
trended down using a blend of the 00z/06z NAM and the 00z mosguide.
Cold frontal passage roughly 12am-12pm Tuesday.
Uncertainty increases Tuesday. We are sure of the frontal passage and
trough moving through. However...there are indications that part of the
trough will try to cut-off from the mean flow from a time...probably
in vicinity of the 4-corners. The Gem/GFS/ec all handle this and the
threat of precipitation differently. The last two runs of the ec are the
deepest with neutral tilt while the GFS/ec have a broader positive
Tue: for now suffice to say windy and cooler. Windy especially if
the ec is right with its 993 mb low heading out of Texas into the Tennessee
Valley. The 12z/6 ec is actually deeper with a 988 low by the time
it gets to Tennessee.
For continued mention of a chance of rain/snow.
Given the northwest flow pattern if precipitation occurs at all it will be light/
minor. 00z GFS ensembles only have a 10-20% chance for 0.10" from
12z/Tue-12z/Wed. The ec ensembles have a 20-40% chance for .10" and
a 10% chance for .25". We could see something a little more
substantial if the ec is correct.
Temperatures Tuesday-Wednesday will be knocked down...but just back to normal
Thu: high pressure drifts S putting the forecast area back into the warm
sector as a low tracks across southern Canada. So temperatures will warm back
into the 50s.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1216 PM CST Friday Mar 7 2014
The taf will begin with VFR conditions...but will turn to MVFR
conditions around sunset for low ceilings and visibility
restrictions during snowfall. Wind speeds will be breezy from the
north behind a cold front which passed through the region earlier
today. Speeds will range between 15 and 25 knots...and will be
pretty consistent until around midnight. The period of snowfall
now appears to be brief...with a window of opportunity between a
couple hours. The timing of the snow is in question...so a tempo
group was used to illustrate this uncertainty. Any snowfall
accumulation will be less than an inch. VFR conditions will return
to the terminal around midnight.