Tuesday, October 21, 2014

Changes Coming to SPC Severe Weather Forecasts

If you follow severe weather, you know the Storm Prediction Center (SPC) issues daily forecasts that warn the public of possible severe weather. In an attempt to simplify these forecasts, SPC is making some changes to their outlooks starting Tuesday, October 22nd.

Here's a look at an old outlook issued by SPC. The severe threat is broken up into four categories:

1. See Text
2. Slight
3. Moderate
4. High

With the old outlooks, the "See Text" risk doesn't really convey a meaningful severe threat. The "Slight" risk also covers too large of a range when it comes to possible severe weather. SPC is hoping the new outlooks will solve these problems.

The new outlook breaks up the "See Text" risk into non-severe thunderstorms and a "Marginal" risk. The outlook also keeps the "Slight" risk, but adds an "Enhanced Slight" risk to help denote areas with a slightly higher severe threat. The "Moderate" and "High" risks will remain the same.

1. Marginal
2. Slight
3. Enhanced (Short for "Enhanced Slight")
4. Moderate
5. High
Here's what all the new categories mean statistically for a Day 1 Outlook:

General Thunderstorms
-10% or greater probability of non-severe or near severe thunderstorms.

- 2% or greater tornado probability, or
- 5% or greater severe hail or severe wind probability.

- 5% or greater tornado probability, or
- 15% or greater severe hail or severe wind probability.

- 10% or greater tornado probability, or
- 30% or greater severe hail or severe wind probability.

- 15% or greater tornado probability AND 10% or greater probability of an EF2+ tornado, or
- 30% or greater tornado probability, or
- 45% or greater severe wind probability AND 10% or greater probability of a wind gusts 75 mph or greater, or
- 45% or greater severe hail probability AND 10% or greater probability of hail 2 inches or greater in diameter, or - 60% or greater severe wind probability, or
- 60% or greater severe hail probability.

- 30% or greater tornado probability AND 10% or greater probability of an EF2+ tornado, or
- 45% or greater tornado probability, or
- 60% or greater severe wind probability AND a 10% or greater probability of a wind gust 75 mph or greater.

For a closer look at how SPC is changing the Day 1-3 Outlooks, click here.
To see how SPC is changing the Day 4-8 Outlooks, click here. -BA

Weather 101: How Clouds Affect Temps

Cloud cover is an important tool meteorologists look at when trying to determine both high temperatures during the day and low temperatures at night. So what's the relationship?

Think of clouds like a reflective blanket hanging in the atmosphere. It can either keep heat in at night or prevent heat from getting in during the day.

Tuesday Morning Lows
Tuesday was a perfect example of how cloud cover can affect temperatures. Eastern parts of the Stateline started off the day with cloudy skies, helping to keep morning lows in the lows 40s. Areas to our west that saw clearer skies also saw lows well into the 30s.

Tuesday Afternoon Highs
Heading into the afternoon, the cloud cover stuck around for the eastern portions of the viewing area. That kept highs in the low to mid 50s. Areas to the west that saw more sunshine warmed into the upper 50s.

With all of this in mind, be warned that everyone will have mostly clear skies in the forecast Tuesday night. That means we're expecting a chilly night ahead... bundle up! -BA

Back to the 70's? It's possible this weekend

The weather for the first couple weeks of October was kind of cool and definitely rainy.  This week, we've entered into a little more of a drier pattern with only a few opportunities for rainfall - Thursday and then again next Monday.  The dry weather will be nice for the local farmers as there were only two or three days that were suitable for getting out in the fields to finish the harvest last week.

To add to the drier pattern will be the warmth that is expected to arrive by the end of the week and for the weekend.  A pattern change in the jet stream will shift winds around to the southwest on Saturday which will give temperatures a nice boost back into the 60's, possibly even the 70's!  Winds will be strong on Sunday with gusts close to 30-35 mph, and this time of year you need a strong wind to get those kind of temperatures.  But hey, who's complaining.  Unfortunately, after next Monday we're back down to reality behind a cold front with temperatures falling back into the 50's.

Thursday, October 16, 2014

U.S. Winter Outlook: A repeat of last year?

Mike Halpert, Acting Director of the Climate Prediction Center, says it's unlikely that we'll see the cold pattern take place this winter like we did last winter, but cold snaps are likely.  After all, it is winter and there will be cold.

He also says what made last winter so memorable was not the cold outbreaks, although those were extreme at times, but the persistent pattern through the entire winter.  Meaning once we got past the December/January time frame, there was no break down of the cold.  The cold continued into the middle of March!  And looking ahead to this winter there, at this time, appears to be no signals that suggest this type of persistent pattern taking hold once again.

Photo: NOAA
Photo: NOAA
El Nino, which is an ocean-atmospheric phenomenon in the Tropical Pacific that affects global weather patterns, could still develop this upcoming winter.  Right now, this has not taken place but Climate Prediction Center forecasters do expect a weaker El Nino episode to develop within the next month or two.  Unfortunately, unlike with stronger El Nino episodes, a weaker one offers little help in trying to determine the winter outlook.  So the current outlook is more consistent with an El Nino event, but the probabilities are just a bit lower.

While there are no strong signals as to whether temperatures over the three month winter period will swing above or below average, it does appear that there is a slightly higher probability of a drier than normal pattern across the Great Lakes.

Bottom line with this forecast is this, seasonal forecasts are a young and evolving science with many different tools, both new and old, forecasters use.  While El Nino and La Nina events are something that can influence the weather across the U.S., we also have to look at other atmospheric circulations and phenomena that, at this time, are still evolving in trying to understand.  Looking ahead, there will be cold and snow this winter - that's a given.  But the probability of having the extreme cold like we did last year is unlikely. 

Tuesday, October 14, 2014

Rainfall from Monday and expected rainfall for today

Rainfall totals ranged anywhere between half an inch to two inches Monday evening.  Today's rainfall won't be quite as much, but I wouldn't be surprised if another half an inch to three quarters inch of rain fell by this evening.

Showers have already begun to overspread early this morning and will remain scattered through Noon.  Low pressure moving out of west-central Illinois will pull closer to north-central Illinois by this afternoon.  As it does, a few breaks in the cloud cover could help fuel some isolated thunderstorms into the early afternoon.  Severe weather isn't anticipated, but if storms were to develop stronger wind gusts could be possible.

Spooky scenes from out of this world

NASA's Goddard Space Flight Center
Even the sun is getting into the Halloween spirit!  Back on the 8th of October, the sun showed its more 'spooky' side with brighter spots that look like a grinning pumpkin.  NASA says the active regions of the sun appear brighter because those are the areas that emit more light and energy.  They indicate an intense and complex set of magnetic fields around the sun's atmosphere, known as the corona.

Monday, October 13, 2014

Monday weather update: Severe weather stays south, heavy rainfall likely north

A significant severe weather event will likely unfold across Arkansas, Mississippi, Kentucky, Louisiana and southeast Missouri this morning and afternoon.  An ongoing line of severe thunderstorms has already produced at least one tornado in Arkansas this morning with one confirmed fatality.  Severe weather this afternoon will remain in the middle and lower Mississippi River Valley closer tied to a strong cold front and low pressure system.  Further north, heavy rainfall will become a concern this afternoon and evening for northern Illinois and southern Wisconsin. 

Skies will remain cloudy through the morning and early afternoon for the Stateline with the threat for rain increasing after 2pm.  Showers with embedded thunderstorms continue to lift north and will reach the Quad Cities between 11am and Noon, and the I-88 corridor around 2pm.  While these thunderstorms are not expected to be severe, heavy rainfall into the evening will be likely.  Drier air wrapping in on the backside of the low could cut off some of the rainfall overnight, but additional showers are likely through mid-day Tuesday.  Through Wednesday morning, one to two inches of rain will be possible.