Area Forecast Discussion


Area Forecast Discussion National Weather Service Indianapolis IN 429 PM EDT Wed Jun 14 2017

.UPDATE… Aviation section updated


.SYNOPSIS… Issued at 150 PM EDT Wed Jun 14 2017

A warm front is forecast to cross Indiana from the southwest overnight and Thursday. Next our weather will come under control of high pressure covering most of the United States east of the Mississippi.

Things should get more active next week. A cold front is predicted to arrive over the Hoosier state late Sunday or Monday. We can expect high pressure for Tuesday, and another cold front Wednesday.


.NEAR TERM (Tonight and Thursday)…

Issued at 150 PM EDT Wed Jun 14 2017

The main issue is thunderstorm timing.

The models agree POPS should be high into Thursday as a warm front passes. Lack of shear means organization and hence predictability will be limited.

Some chance to be needed in the forecast most of the time. Activity may be greatest 04Z-15Z, when there is rough agreement on positive advection of wet bulb temperatures into the CWA. Confidence about this is low.

Considering recent history and that precipitable water is well above normal, heavy rain needs to be mentioned. Guidance temperatures are close. Consensus should produce a forecast accurate to within 1-2 degrees.


.SHORT TERM (Thursday night through Saturday)…

Issued at 150 PM EDT Wed Jun 14 2017

The forecast problem is POPs.

Not much can be confidently forecast except that Thursday night should be dry. The models agree Indiana will be under warm, humid air. Forcing from well defined systems should be lacking, resulting in what used to be called ‘air mass’ storms. The consensus forecast will work as well as anything. For the most part that means chance POPS.

Sky cover will be affected both by diurnal trends and weak disturbances. Overall we should be partly cloudy.

Consensus temperatures should be accurate to within 1-2 degrees in a relatively easy to forecast summer pattern.


.LONG TERM /Saturday night through Wednesday/…

Issued at 221 PM EDT Wed Jun 14 2017

Strongest of short waves troughs and associated cold front will be approaching our area by Saturday night and moving through central Indiana Sunday. This will likely provide our best chance for most areas to get some rainfall. The only limiting factor may be front and storm timing where these may come through western counties early morning when air is typically most stable.

All models develop decent precipitation by Sunday afternoon appears reasonable with good dynamics, very unstable air, and triggering cold front to aid lift. This may also be most favorable time for severe weather outside of pulse severe today.

As upper low pressure progresses across southern Canada, surface high pressure will build into our region from the northwest bringing cooler and less humid weather for several days. Another short wave trough will drop SE across central Canada early next week and sweep an additional surface trough and threat for showers or storms Tuesday night and Wednesday.

Blend of model temperatures appears reasonable and was followed. After above normal temperatures into Sunday, a return to slightly below normal temperatures for a day Tuesday before settling back towards normal midweek next week.


.AVIATION /Discussion for the 142100Z IND taf Update/…

VFR Conditions continue. As Storms continues to develop west of the Wabash…VCTS and periodic TSRA will be expected…especially after 00Z. Brief MVFR Conditions will be possible with any storm that strikes a TAF site. HRRR suggests best chances for TSRA at IND will be after 00Z….however confidence on specific timing remains low.

Previous Discussion Below

(Discussion for 141800Z TAFs)…

Issued at 1208 PM EDT Wed Jun 14 2017

Thunderstorms are the main issue.

Most sites will experience storms as a warm front passes tonight and Thursday. Within storms there should be LIFR in heavy rain and strong gusts. It is not possible to be confident about timing, but VCTS will be used to indicate periods of greatest threat.

Between storms, expect VFR with south or southwest winds around 10 knots. Given storms will be relatively short-lived, these conditions should actually prevail most of the time.