Scientific Forecaster Discussion
fxus63 kind 221650
Area forecast discussion
National Weather Service Indianapolis in
1250 PM EDT sun Oct 22 2017
the aviation section has been updated below.
issued at 314 am EDT sun Oct 22 2017
A slow moving frontal system will impact the area beginning later
today, bringing showers to the area. A secondary low pressure
system developing along the front will prolong these precipitation
chances into the early portion of the week, along with a large
upper level low pressure that will drop into the Great Lakes early
to mid week. Temperatures will turn sharply cooler during this
Near term /this afternoon/...
Issued at 945 am EDT sun Oct 22 2017
Surface analysis late this morning shows southerly flow in place
across Indiana as a cold front was found near the Mississippi
River valley. Radar mosaics show sct light rain showers across
the Illinois...streaming northward. Water vapor imagery shows a
deep trough over the Central Plains...allowing Gulf moisture to
stream into the Mississippi and Ohio valleys.
Hrrr suggests dry weather to persist through at least
18z...before pushing some isolated to scattered bands of
precipitation across central Indiana by mid to late afternoon.
Forecast soundings continue to show a gradual increase in moisture
as the day progresses as the front and associated strong forcing
arrives from the west. Thus will continue a gradual ramp up of
pops after 18z. Best chances for precipitation should hold off
until near 00z...arriving in the western parts of the state late
in the day.
Given the expected increase in cloud cover yet warm air
advection...have trended highs only slightly higher than the
forecast builder blend.
Short term /tonight through Tuesday night/...
issued at 314 am EDT sun Oct 22 2017
Models differ on handling of developing secondary system, and
highest pops will progress across the area tonight with the front.
The boundary will slow further as this secondary system develops,
and the exact location of this will determine placement of the
highest precipitation chances. Will carry a gradient of shower
chances across the area from east to west Monday and Monday night
as the secondary system moves through the region, and from
north/northeast to south/southwest Tuesday Onward as the large
upper low drops into the Great Lakes.
Consensus temperatures are generally in the ballpark and only
required minor adjustment. Temperatures in the wake of the front
and as the upper low drops into the area will turn sharply cooler,
with highs in the 50s and lows in the 30s by the end of the short
Long term /Wednesday through Saturday night/...
Issued at 345 am EDT sun Oct 22 2017
Models are in agreement in regard to lingering rain showers
(mainly ne) Wednesday as an upper low drops into the Ohio Valley
from the Great Lakes region. However, high pressure will quickly
strengthen over the upper Midwest by Wednesday evening. So, dry
conditions will return through Thursday night. After that, focus
then turns to the next frontal system late in the week. Its
associated cold front will bring additional rain chances to
central Indiana on Friday, and the trailing upper low will keep
rain in the forecast through the weekend.
Below normal temperatures through the period will result in a
frost threat around mid-week that will have to be monitored.
Daytime highs will only be in the upper 40s/low 50s on Wednesday
with lows in the upper 30s that night. There will be a weak warm-
up on Thursday, but temperatures will quickly drop again for the
Aviation /discussion for the 22/18z taf issuance/...
issued at 1250 PM EDT sun Oct 22 2017
Good confidence in VFR conditions through 00z tonight, but then
increasing chances of MVFR and possibly IFR conditions 00-03z and
beyond as showers overspread the terminals. The showers will become
less prevalent at the western airports after 12z Monday. Overall,
confidence in trends is good, but exact timing is not.
South and southwest winds to over 10 knots but gusting to 25 to 28
knots will decrease to 10 knots or less 21z-22z shift to northwest
behind the cold front that should reach laf and huf near 02z but the
other sites not until after 12z Monday.