Scientific Forecaster Discussion
fxus63 koax 172322
Area forecast discussion
National Weather Service Omaha/valley NE
522 PM CST sun Nov 17 2019
..updated aviation forecast discussion...
issued at 315 PM CST sun Nov 17 2019
The main forecast concerns are precipitation chances, amounts and
precipitation type for Wednesday into Thursday. Potential rain
amounts of 0.25 to 0.75 are possible, mostly southeast of a line
from Columbus to Onawa.
Also there is some potential for a rain/sleet/freezing rain mix
after midnight tonight into mid morning Monday. The event
tonight/Monday looks like low amounts and mostly from northeast NE
into west central Iowa.
Short term...tonight through Wednesday morning.
A fairly strong mid level trough extended from western Ontario
down to the OK/Texas border earlier today. This had 12 hour height
falls of up to 110 meters (noted at koax and kmpx) at 500 mb at
12z. Another area of height falls was pushing eastward into
Low clouds will continue to decrease late this afternoon and this
evening in our eastern counties, while mid and high clouds
thicken from west to east later tonight. This could bring some
light mixed precipitation to parts of the area. Chances are
highest from northeast NE into western Iowa. Will include some
mention of this in the severe weather potential statement.
Otherwise the rest of this period, from Monday afternoon into
Wednesday morning, looks mainly dry. It also looks fairly mild.
For Monday, highs should range from upper 40s and lower 50s in
western Iowa to the lower 60s from Neligh, Albion and Columbus
toward Seward, Lincoln and Beatrice. Temperatures should be
slightly warmer Tuesday. Cooler air will start to filter into
northeast NE on Wednesday.
Long term...Wednesday afternoon through Sunday.
There is fairly good model agreement on the large scale pattern at
the beginning of this period. Differences start to develop after
that though. The 12z runs of the GFS and European model (ecmwf) are in better
agreement with the timing and strength of the shortwave in the
northern stream across the northern plains and upper Midwest, but
there are some differences with the surface pattern and moisture.
Expect rain/rain showers to develop across at least parts of
southeast NE and southwest Iowa by late Wednesday afternoon. There
also should be some elevated instability (in this case, parcels
lifted from around 850 mb) across southeast NE by evening, as
noted in 12z GFS forecast soundings. Rain amounts Wednesday
afternoon should be less than a tenth of an inch, with the
heaviest amounts currently expected Wednesday night. Forecast
soundings show the Omaha and Lincoln areas staying warm enough for
mainly rain, with a mix possible just before precipitation ends 4
am to 7 am Thursday. Based on current timing, we expect the
precipitation to possibly linger in western Iowa Thursday morning
but end before daybreak Thursday in all of eastern NE. Snow
amounts (at least for now) look to be possibly an inch or two,
generally confined to northeast NE. We will monitor to see if
colder air tries to intrude in faster, which could change the
precipitation type sooner or farther south.
High temperatures Wednesday ahead of the cold front should reach
the upper 50s and lower 60s, with 50s behind the front. Thursday
should be the coolest day of the week (highs in the upper 30s and
lower 40s) then expect temperatures to slowly moderate into the
weekend back to at or slightly above normal. There is quite a bit
of model variance as we get to the weekend in regards to
precipitation chances. The European model (ecmwf) brings a system into the area by
Friday night, while the GFS is dry.
Aviation...(for the 00z tafs through 00z Monday evening)
issued at 520 PM CST sun Nov 17 2019
VFR conditions are expected through the forecast cycle. High
clouds will continue to spread east across the region overnight
and thicken but still remain VFR. Surface winds will remain light.