Scientific Forecaster Discussion
fxus63 kind 141915
Area forecast discussion
National Weather Service Indianapolis in
215 PM EST Thu Dec 14 2017
the long term section has been updated below.
issued at 241 am EST Thu Dec 14 2017
Continued northwest flow aloft through the end of the week will keep
chilly temperatures across the area. Other than a few light snow
showers over northeast portions of central Indiana Friday...dry
weather is expected into Saturday. Upper ridging will expand into
the area over the weekend with warmer temperatures and by Sunday...a
chance for precipitation as an upper level wave tracks through the
Ohio Valley. High pressure will return with dry weather and
seasonable temperatures by late Monday and continue through the
middle of next week.
Near term /this afternoon/...
Issued at 951 am EST Thu Dec 14 2017
Satellite continues to show lingering cloud across the western
parts of central Indiana...streaming off of Lake Michigan.
Meanwhile high cloud was streaming from west to east in a mainly
zonal flow across Illinois and Indiana. Surface analysis shows
weak high pressure in place over Wisconsin and Iowa with northerly
surface flow streaming across Indiana.
Variable cloudiness will be expected this next several hours as
satellite shows plentiful cloud cover upstream with the flow
aloft. Again...some low cloud cannot be ruled out within the cool
north flow as forecast soundings suggest saturation from time to
time within the lower levels. Thus partly cloudy and cold will be
the way to go. Trimmed a few degrees off high from the forecast
builder to get closer to the lav on highs.
Short term /tonight through Saturday night/...
issued at 241 am EST Thu Dec 14 2017
Forecast challenges are largely focused on temperatures through the
period as predominantly benign weather is expected.
The upper level pattern across the country over the last 10 days or
so highlighted by the western ridge and eastern trough will finally
relax over the weekend as energy dives into a developing upper low
moving ashore over Southern California and baja Mexico by Saturday.
The Southeast Ridge will flex its muscle so to speak in response
with solid mid level height rises over the region by late Saturday.
This will result in southerly flow developing with a warming trend
for Saturday ahead of an approaching system poised to impact the
Ohio Valley on Sunday.
Prior to that transition taking place however...central Indiana and
the entire region will remain under the influence of the eastern
trough with yet one more wave aloft tracking through the Great Lakes
Friday before shifting off to the east as a deep upper low carves
out the trough over New England. Model trends remain further north
with the Friday system as a surface low rotates through the upper
Great Lakes before kicking east into Quebec on Saturday. Forcing
aloft remains displaced off to the north of the region with growing
confidence that this system has little if any impact on central
Indiana. Could see light snow showers and/or flurries graze
northeast counties during the day Friday as the upper wave passes
by...otherwise expect just an increase in clouds for much of the
Low level flow will back to southerly by early Saturday as surface
high pressure tracks into the southeast states. Model soundings and
relative humidity progs indicate more substantial drying and subsidence present on
Saturday with mostly clear skies developing for the Ohio Valley. The
approach of a weak frontal boundary Saturday night will encourage a
surge of moisture advection out of the Southern Plains and Gulf of
Mexico. Clouds will increase in response late Saturday night but any
precipitation will hold off until after daybreak Sunday.
Temps...undercut guidance temperatures tonight as cold advection
persists. Trended closer to cooler met guidance for Friday with
greater cloud coverage likely stunting temperature rises. The
arrival of warm advection...increased sunshine and southerly flow on
Saturday should ensure temperatures closer to the higher mavmos with
the entire area rising into the 40s. Utilized a model blend for lows
Friday and Saturday nights.
Long term /Sunday night through Thursday/...
Issued at 215 PM EST Thu Dec 14 2017
European model (ecmwf) shows an active period continuing on Sunday night through
Tuesday morning...with dry weather returning for the middle of
European model (ecmwf) shows a broad upper trough over the upper Midwest sagging
southward across Indiana on Sunday night into Monday. This trough
pattern is expected to persist unto Tuesday...allowing a few weak
upper level disturbances pass within the flow. Meanwhile in the
lower levels...a weak low pressure system will push through the
Great Lakes on Sunday night before broad cyclonic flow remains in
place. Thus chances for precip during this period appear
reasonable from forecast builder.
Dry weather should return by Tuesday afternoon through Thursday as
high pressure builds across the Ohio Valley.
Aviation /discussion for the 141800z tafs/...
Issued at 1228 PM EST Thu Dec 14 2017
VFR conditions are expected this taf period.
Surface high pressure over the upper Midwest is expected to drift
across Indiana into the Ohio Valley during this period. Meanwhile
a short wave aloft is expected to push across Indiana overnight.
Moisture for this system will be quite limited and no precip is
expected. More dry air and subsidence is expected to arrive in the
wake of the trough on Friday.
Thus will expect VFR conditions and mainly just some passing
high clouds during this taf period.