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Area forecast discussion 
National Weather Service Amarillo Texas
1104 PM CST Thursday Dec 18 2014

for the 06z tafs...MVFR to IFR ceilings across the Oklahoma and
Texas panhandles are expected to remain through much of Friday
morning. However....fog has been slow to develop. Have kept mention
of IFR fog in taf sites though confidence is waning that visibilities
will drop that low. IFR to MVFR stratus deck will remain into the
afternoon before slowly scattering out middle-late day. Confidence is
not high enough to add in precipitation at this time...and should
mainly be confined east of the taf sites today.



Previous discussion... /issued 248 PM CST Thursday Dec 18 2014/


Primary weather impacts during the next seven days will be in the
short term with precipitation chances tonight and potential for fog
once again. Main adjustment to the forecast was to try and be more
deterministic with precipitation type overnight although that
remains a challenge given marginal thermal profiles for frozen
precipitation in model forecast soundings. Initial concerns are fog
potential later tonight as low level flow becomes more easterly and
strengthens. Moisture over southwest Oklahoma and western North
Texas will advect westward and upslope. Have included areas of fog
in the grids. Locally dense fog will again be possible.

WV loop and 500 mb rap analysis clearly showed a shortwave trough
over eastern Arizona moving eastward. Short term models are in good
agreement on the timing and strength of this wave as it moves toward
West Texas tonight and crosses the region tomorrow morning. The
period of best Omega/saturation in the dedritic growth zone will be
after about 03z in the west spreading eastward overnight and lasting
through about 15z in the east. Just below the dgz is a layer of dry
air that will take some time to saturate thus delaying the onset of
precipitation until closer to midnight in the west/central and after
midnight in the east. The biggest challenge for conveying sensible
weather in this forecast will be the temperature profile. At least
short range models agrees fairly well. The depth of the above
freezing wet bulb temperatures is sufficient for all rain across
most of the area...especially the far southeast. Have trended
precipitation type to more rain as a result. Increased quantitative precipitation forecast slightly
in the far southeast.

Quite a bit of uncertainty develops by early next week and continues
throughout the extended period. Very powerful Pacific jet noses into
the central rockies by Monday east of a significant mean ridge over
the eastern Pacific. A very strong trough has been shown to develop
over the eastern United States. This should happen by around
Christmas evening or Christmas day but medium range models struggle with
how it evolves early/middle week once Pacific jet moves into the
central Continental U.S.. new 12z emcwf is quicker with developing a closed low
while the GFS is more pronounced with individual shortwaves
traversing the deepening upper trough. The GFS becomes deeper by
Wednesday with more substantial height rises on its west side over
the plains. Exact implications for US are unclear. Will need to
watch the potential for a downsloping warming/wind event on Monday.
GFS/mex depict this now. European model (ecmwf) is more expansive with height falls
over the central Continental U.S. Given its more consolidated/sprawling
solution with less distinct shortwaves embedded within. GFS
soundings show deep mixing into an area of strong flow aloft which
raises some concern of near advisory criteria winds if this solution
verifies. Otherwise did not deviate from medium range consensus. Any
precipitation in the extended should be insignificant...and
difficult to time given model differences.


Previous discussion... /issued 1142 am CST Thursday Dec 18 2014/

for the 18z tafs...the main weather elements for this forecast cycle will
be low clouds and episodes of fog. Fog is slowly eroding at the taf
sites and should continue to do so early this afternoon. IFR ceilings
will gradualy and temporarily lift into the MVFR category as well.
Expect the return of IFR ceilings and areas of fog again late tonight
into Friday morning. A fast moving upper level storm system will
graze the region tonight and early Friday...and may bring some
sprinkles...light rain showers...flurries...or very light snow.
However...the chance of precipitation is not very have
opted to omit from the terminal forecasts at this time.



Ama watches/warnings/advisories...




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