Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Omaha/valley NE
1117 PM CST Wednesday Dec 11 2013
Aviation...06z tafs for kofk...klnk and koma.
VFR conditions are forecast through Thursday evening. Passing thin
high clouds and south to southwest winds less than 10kt should
Previous discussion... /issued 316 PM CST Wednesday Dec 11 2013/
Short term...tonight through Saturday
WV imagery this afternoon depicting an amplified ridge off the West Coast
with a broad downstream trough over the eastern Continental U.S.. at the surface...with
widespread snow cover along with cold high pressure centered in southeastern
Nebraska...temperatures were struggling to climb above the single digits.
Models are in good agreement large scale trough will for the most part
remain in control over the Continental U.S. Heading into this weekend.
Appears that a short reprieve from the cold temperatures are in store
Thursday when aforementioned surface high slides east allowing
backside southerly warm air advection. Highs will be a bit tricky where narrow
salient of no snow cover is in close proximity to
Antelope/Boone/Platte counties. Given expected warm air advection...feel
confident enough to push maximum highs in those counties to the upper
Meanwhile...500mb height falls around 100m are prognosticated to spread across
the plains Thursday night/Friday along with next Arctic airmass
plunging into the lower 48.
Ecm/CMC/GFS all advertise area of snow activity developing by
Friday mainly over NE Kansas within area of increasing low/middle layer
transverse ageostrophic lift along axis of boundary layer baroclinic
zone. Upper divg associated with rrq of northern stream jet stream
aiding with large scale ascent. At this point...appears that most
likely time frame for any accumulating snowfall will occur Friday
afternoon/evening and be focus generally east of the line from about
Montgomery to Jefferson counties. Given that the County Warning Area will be on
the outer bioundary of best forcing...suspect that any
accumulations will top out around an inch.
On Sat...subsidence prevails as deepening cold air advection continues spreading
Long term...Saturday evening through Wednesday
Dry weather will be the rule during this forecast period. A couple
different shortwaves will track well north of our area on Sunday and
Monday...yielding light snow showers north of our area into
South Dakota into Minnesota. Precipitation aside long range guidance
supports a warming trend as middle-upper level flow turns zonal by
Tuesday. The degree of warming though is in question as solutions
vary how much the airmass will warm and for how long. For now will
continue to show a warming trend in the extended forecast with highs
reaching into the 40s by Wednesday. Overall confidence in the going
temperature forecast beyond Sunday and especially by Tuesday is low.
As an example the projected high using the European model suggests
highs near 50 on Wednesday while the GFS suggests highs in the middle
20s to low 30s. This difference is hinged on the placement of a
downstream trough which the GFS/Canadian models place over the upper
Great Lakes...allowing for an earlier re-introduction to the cold
air. At the same time the European model (ecmwf) depicts this feature well downstream
over the eastern Seaboard...keeping the cold air in Canada. Once
this feature is better resolved by the models confidence in the
extended forecast will improve.