Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
504 PM CST Wednesday Dec 11 2013
Short term...(this evening through thursday)
issued at 315 PM CST Wednesday Dec 11 2013
Tonight and Thursday. Temperatures trend up heading
into Thursday. The pattern aloft featured northwest flow across the
interior Continental U.S. With ridging in the Pacific northwest and a closed
upper low in the southwest Continental U.S.. at the surface...a cold 1040mb
surface high was centered in southeast Nebraska.
The surface ridge axis will continue to slide southeast tonight
and return flow of southwesterly winds will set up across our region.
Heights rise heading into Thursday as the upper trough from the
Hudson Bay to the Great Lakes region shifts eastward and the
Pacific northwest ridging breaks down and translates east as well.
The airmass across the Central Plains moderates quite a bit with
850 mb temperatures rising about 7 or 8c compared to today.
With the forecast remaining dry the main focus is on temperatures.
In clear skies...and good radiating conditions tonight we are
still looking at lows in the single digits for the most part...due
in part to the snow on the ground. We continue to maintain a
fairly significant swath of snow across the southeast part of our Nebraska
counties and across northern areas in NC Kansas. Temperatures are
expected to drop off during the evening but may steady/vary during
the night with warm air advection. On Thursday...snow free areas should see high
temperatures above seasonal normals in the low/middle 40s. Areas with snow
are expected to rise above freezing into the middle 30s...which will
work at eroding the Snow Field especially on the edges. For
Thursday highs have followed close to previous forecast which
depicts the snow/snow free areas well. The NAM is holding onto too
much snow at initialization today and did not use for this
Long term...(thursday night through wednesday)
issued at 315 PM CST Wednesday Dec 11 2013
After Sat the bitter cold releases its grip and we will enjoy above
normal temperatures sun through possibly Wednesday with 1 or 2 days of much above
normal /ie departure of at least 10f/. No rain or snow is foreseen
through next Wednesday.
Pattern: the eastern Pacific oscillation /epo/ will spike positive Monday
12/16...with the Pacific North America /pna/ pattern becoming neutral.
Both indices are forecast to turn negative by Friday 12/20. This initially
results in below normal heights over Alaska with above normal heights
over the east Pacific into the western USA...supportive of the an extended
break from the excessive cold next week. It remains debatable how
much the cold will ease. Do temperatures return to near normal or do they
go above? For sure the core of the coldest air will miss the region
into the Great Lakes and Midwest. With northwest flow continuing the parade
of Alberta clippers to our north...the downsloping flow in their warm
sectors argues for above normal. But the associated cold fronts
could put a cap on temperatures. My general sense is temperatures will be fairly
close to normal with just a day or two of much above normal temperatures.
The trough currently ejecting out of Russia and into northwest Pacific will
eventually force the semi-permanent central Pacific Ridge to begin
amplifying over the east Pacific next Wednesday. This will force another dump of
bitter cold into the the region via Alaska and cross polar flow...with a
trough developing. So it is looking like another blast of frigid
Aloft: the longwaves are in a period of transition after being
locked into a western USA trough/eastern USA ridge the last 2 weeks. The
reconfiguration discussed above will result in a temporary evolution
to a western USA ridge/eastern USA trough. A pair of shortwave troughs will
combine and move through Fri-Sat. Then northwest flow becomes established through
Tuesday. Heights will then begin falling over the west next Wednesday.
The 06z and 12z GFS did not contribute to this forecast beginning next
Tuesday. Those runs turn the northwest flow cyclonic...bringing the next push
of Arctic air in here early. The GFS ensemble mean agrees with the
ec and its ensemble mean that northwest flow will become more anticyclonic
which delays the arrival of the Arctic air until later next week.
Surface: a cold front will extend from the Great Lakes to along the
northern Nebraska border and the northwest into Alberta. This front will be drawn S
through the forecast area Friday as low pressure develops over Texas and heads east. A
very weak low will race from Montana-South Dakota to Lake Superior Sat. Sun remains
uncertain. Does the associated cold front back door into neb? The
GFS/ec say no. The next much stronger low will eject across the
Canadian prairies and this suggests the front will stall and then
head back east as a warm front. The cold front associated with the
stronger Canadian low will move through here late Monday. High pressure slides
through Tuesday with the warm sector developing Wednesday as the next low heads
along the US-Canada border.
Hazards: nothing envisioned at this time.
The daily details...
Thursday night: mostly clear...but high clouds will begin invading from
the S and northwest. There is uncertainty on these southern clouds. The GFS is
much heavier with relative humidity above 500 mb while the Gem/ec/NAM have nothing.
If the GFS is wrong than low temperatures will not be cold enough S and east
of the Tri-Cities.
Fri: cold air advection in the GFS/ec leads to saturation in the
low-levels. Skies could eventually become cloudy...capping temperatures
from reaching their maximum potential. Temperatures below normal.
Sat: cloudy to start then clearing as the upper trough departs. Temperatures
Sun: considerable uncertainty due to the position of the front. We
have indicated the warmest temperatures /40s/ S and west of the Tri-Cities.
But there is potential to be very warm. Believe the bias corrected
Gem will verify with highs 45-55f...warmest west of Highway 281.
Mon: mostly sunny with temperatures possibly as warm as Sunday.
Tuesday-Wed: warm sector. Sunny. And with the preference of the ec and
its ensemble mean...believe there is significant upside potential in
temperatures. Forecast temperatures may bust too cold by 10-15f. The forecast has highs of
40-50f but the look of the ec suggests highs in the 50s and possibly
Thursday 12/19-21: keeping an eye on potential for more bitter cold to
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 504 PM CST Wednesday Dec 11 2013
VFR conditions to continue through the next 24 hours.
A fairly light surface wind...generally in the 8-10kt range...will
persist from the southwest during the taf period. An
intensification of the wind field just above the boundary
layer...likely nearing 40kts...may promote a period of low level
wind shear at gri tonight and such has been maintained in the taf
02-07z. Little in the way of cloud cover will be observed and
visibility restriction is not expected at gri through the next 24