Historic Halloween storm to brew monster rainfall and howling winds

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Halloween 2013 fcst

More Tricks than Treats weather-wise for Halloween 2013

RAIN ARRIVES TONIGHT

Showers and thunderstorms will continue to work east this evening and spread across parts the state overnight.  The chance of a storm looks rather good as a warm front lifts north drawing warmer and more moist air with it.  The bulk of the rain tonight will fall over western and northwestern Indiana then increase pushing east toward sunrise.  This is the leading edge of the powerful autumn storm that arrives for Halloween.  Showers are expected into the city as early as 8 PM tonight and there could be thunderstorms in the area as well.  Below is a forecast from a High-resolution hourly computer at 8 PM.  Note all the rain in Illinois that moves in later in the night.

HRRR Weds night 10-30

Forecast Radar 8 PM Wednesday night

HISTORIC STORM

The storm will intensify – deepen tonight, with the central pressure dropping sharply as the storm encounters stronger upper air wind support.  The jet stream winds strengthen when there is a large temperature spread over a small geographical location.  We are on the front side of the storm – the warm side so the milder air will filter in during the overnight hours.  Rainfall for Thursday appears to be quite healthy and may easily shatter the record rainfall for the date.  Only 2 Halloweens have ever produced 1” of rain of more.  The wettest in 1941 with 1.30” and 1.09” in 1919.  It has been 40 years since a half-inch of rain fell on the Holiday.

MONSTER RAINFALL

The average off 7 computer models for rainfall here as nosed up to 1.46”  (up from .98” yesterday).  Locally heavy amounts are possible where thunderstorms are involved with a rainfall range of .85” to 2.19”.

Rainfall_Comparison

Rainfall Thursday could be enough to break the record for the date

HOWLING WINDS

With the storm strengthening (central pressure dropping) the winds will ramp up through the day.  As early as 8 AM Thursday wind gusts could top 30 miles per hour and are expected to grow through the day.  Wind gusts from noon on could top 40 miles per hours and peak after 8 PM as the cold front charges east from Illinois.  This front may create locally higher gusts over 50 miles per hour before exiting the state after midnight.  Below a projected wind gust forecast at 8 PM Thursday.

Wind Gust Forecast

Non-t-storm Wind Gust Forecast 8 PM Thursday

Non-thunderstorm wind gusts Thursday could cause local power outage.   This is an estimate of potential power outage off our in-house computer model through 12 AM Friday morning.

Power Outage

Computer estimated power outage forecast

SHOCKING STORMS?

There may be very limited lightning and thunder Thursday night but should one t-storm get going, it could briefly produce a local gust in excess of 58 mph – the criteria for severe thunderstorms.  This is the reason why the storm predication center has forecast a slight risk of storms here Thursday.  While a watch box may or may not be issued, it is possible a few thunderstorm warnings could come out.  A powerful jet stream roaring overhead could be tapped in by a thunderstorm and bring those winds down to the surface.  On the extreme end, a thunderstorm storm could briefly spin or rotate and briefly spin up a tornado.  We will monitor closely.

NAM Jet Stream FCST

Powerful 120 mph Jet stream 12 to fuel surface wind gusts Thursday

Day 2 Svr wx outlook

SPC Severe Weather Outlook Thursday

This will affect trick-or-treaters from southern Michigan to Houston Texas – roughly 41 million people.  Many cities and towns have moved the trick or treat times to Friday. A complete list of times is located here.