Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Hastings NE
525 PM CST Sat Dec 27 2014

Short term...(this evening through sunday)
issued at 250 PM CST Sat Dec 27 2014

The short term will be rather quiet compared to yesterday. We have a
recap of yesterdays snow event posted to our webpage and social
media please feel free to read over that
information for a general overview of the event.

A surface high has slid in over the region from the west. Clear
skies and light winds are now in place...and this will be the case
for a majority of the short term period. Eventually...the surface
high will continue to slide eastward...and the wind speeds should
become more southwesterly. Middle to high level clouds will eventually
move back into the area from the northwest tomorrow around 18z.

Lows tonight will be in the single digits for most of the area...but
areas across our southeastern counties may be as warm as about 10 to
12 degrees for lows. Highs for tomorrow afternoon will range between
25 and about 37 degrees...with a majority of the outlook area under
snow cover struggling to get above 32 degrees.

Long term...(sunday night through saturday)
issued at 250 PM CST Sat Dec 27 2014

Guidance suggests quasi-zonal to southwesterly upper tropospheric
flow...near 30000ft above ground level...will be noted over the central Continental U.S. To
start the long-term forecast period at 00z Monday. A strengthening
upper tropospheric longwave trough axis from the northern plains
into the west-central Continental U.S. Is expected to help maintain quasi-zonal
flow over our area until the trough axis approaches and clears our
area next Friday or Saturday. A little lower through the
troposphere...closer to 20000ft above ground level...a subtle short wave trough
axis is expected move southeast from the northern rockies starting
Sunday night...and clearing our area Monday into Monday evening.

Guidance continues to suggest DPVA and tropospheric moisture...along
with meager thermal advection...ahead of the aforementioned short
wave trough axis will be supportive of precipitation production
across much of our area Sunday night into Monday...and perhaps for a
time Monday evening. An overall lack in Omega should then promote
dry conditions Tuesday through Thursday...before the approaching
longwave trough axis provides another chance at precipitation Friday
and Saturday. Given all this...went ahead with 20-40% probability of precipitation across
much of the County Warning Area Sunday night through Monday evening...and then 20-
30% probability of precipitation across much of the area Friday into Friday night. Forecast
proximity soundings from across the County Warning Area...per the NAM and
operational GFS...suggest the lower troposphere will remain
supportive of snow Sunday night through Monday evening...and again
Friday into Friday night.

Taking an average of the NAM...operational GFS and ec provides
liquid precipitation amounts a few hundredths of an inch across our around 0.20" across our north 06z Monday through 06z
Tuesday. A blend of the NAM and operational GFS also suggests snow-
water ratios will start in the 12-15:1 range at 06z Monday...but
will increase into the 16-20:1 range by 06z Tuesday...which lines up
pretty well with wpc/westward guidance. Taking these factors into
consideration would provide 1-3 inches of fresh snow across our County Warning Area
06z Monday through 06z Tuesday. That said...there are some
potentially complicating factors which need to be considered. This
really is a subtle short much in fact model data only
shows it near 700mb...with little if any indication of the wave at
500mb or higher. is typical with most clipper
systems...the true magnitude of thermal advection and resultant
Omega really is in question and thus...its hard to say if the ~0.20"
liquid precipitation being suggested across our north will be
realized. Based on wpc/westward appears wpc agrees and
given all this...opted to cut the aforementioned liquid
precipitation amounts by as much as half and as a result...the
current liquid precipitation forecast 06z Monday through 06z Tuesday
stands at a few hundredths of an inch across our
around 0.10" across our north. Assuming the aforementioned snow-
water ratios provides storm-total snow accumulation of around a half
inch across our almost two inches across our north 06z
Monday through 06z Tuesday. This essentially doubles the snowfall
forecast for much of the County Warning Area compared to the inherited
forecast...but does not yet go as high as model guidance. Obviously
this will need to be closely monitored through the next couple
days...should it appear higher liquid precipitation amounts will be
realized thus resulting in greater snow accumulation.

In addition to the increasing barometric pressure
gradient Post-frontal passage will likely promote a strong boundary-layer wind
field across our area Monday into Monday night...sustained at 15-
20kts with locally higher gusts. This could certainly create
periodic visibility restriction in blowing snow and as a
result...will go ahead and mention such conditions in the severe weather potential statement.

Other than the potential for snowfall Sunday night through Monday
evening...the biggest weather impact across the area will likely
reside with the potential for very cold temperature readings as an
Arctic air mass infiltrates the area starting Monday. Even though
highs in the teens and 20s are currently forecast for Monday...highs
will likely struggle to break out of the single digits and low teens
on Tuesday. Thankfully...a warming trend is then expected Wednesday
through Saturday as highs climb back into the 20s and 30s by late
next week. Lows Sunday night will likely bottom out in the teens for
most locations...but are then expected to plummet into the single
digits above and below zero Monday night and Tuesday night. Some
recovery into the single digits and teens above zero are then
expected Wednesday night Onward. At this time it also appears
apparent temperature values of -10 to -20 will be possible Tuesday
morning and Wednesday morning across much of the area and given
this...will go ahead and continue a mention of such conditions in
the severe weather potential statement.


Aviation...(for the 00z kgri/kear tafs through 00z Sunday evening)
issued at 523 PM CST Sat Dec 27 2014

VFR conditions are expected at both terminals through the period
with light westerly winds and only passing middle/high level clouds
tomorrow afternoon ahead of an approaching upper level disturbance
expected on Monday.


Gid watches/warnings/advisories...


Short term...Guerrero
long term...Bryant

National Weather Service Glossary of Abbreviations