A Real Halloween Scare - Sandy's Impact

There might be a real Halloween scare for the eastern portion of the country next week.  At this time, Hurricane Sandy has bloomed in the backyard of the Caribbean and is gaining strength quickly.

As of Wednesday, Sandy is a category one hurricane that is shredding through Jamaica.  Recent satellite and aircraft data suggests the hurricane is holding at 80 mph and will stay a weak hurricane for the time being.  As the cyclone ventures northward into the Western Atlantic will likely strengthen a massive system and could flirt with the Eastern coastline early next week.

Before Hurricane Sandy becomes a major headline, we'll watch a strong cold front venture into the Natural State late Thursday night.  This cold front will be a huge game changer for Arkansas and get us out of this warm, humid pattern we've enjoyed the last four days.  Once we're behind the front, we'll plummet to the 40's and 50's with a brisk wind out of the north.  Since the front will arrive a little sooner than expected it looks as though the Razorback game will dry this weekend.  Just make sure to bring the warm gear as you go out to tailgate.

While we suffer under the fall chill,  Hurricane Sandy will run into Bermuda, then an upper level low will enhance the cyclones development just before Halloween.  If all the cards fall into place, we could be looking a storm that could rival the "Perfect Storm" back in 1991.

                                  (European model showing Sandy slamming into New York next Monday)

The latest weather models paint a frightening picture of a deep cyclone producing extensive hurricane force winds around New York and Washington D.C. Besides massive power outages, extremly high waves, we'll be looking at major coastal flooding and possibly flight delays across a good portion of the country.

In other words, you might want to hold off on traveling to the Northeast next week.  It is going to be one nasty storm.

Wenesday Severe Weather Threat

 9 PM Update:

Main severe weather threat now pushing East out of Arkansas. Still a few isolated storms around through this evening, generally ending before Midnight.

 5:30 PM Update:

Tornado Watch issued until 2 AM for most of Arkansas. A tornado watch means conditions are favorable for storms that may produce a tornado

 3 PM Update:

Nothing showing up on radar in Arkansas as of 3PM. Storms are moving East through Missouri with wind damage reported around Springfield. Winds were estimated to 70 MPH. Storms will rapidly increase across Arkansas after 4 PM.

(Radar & Warnings at 3 PM)

12 PM Update:

Updated tornado probabilities from the Storm Prediction Center. Highest tornado threat for Eastern and Southeast Arkansas through this evening, although still a risk for Central Arkansas as storms begin to fire up.

(SPC Probability of a tornado within 25 miles of a given point - issued 1130AM Wed Oct 17)

Given the strong wind field expected to develop ahead of the cold front, an enhanced threat of strong to violent tornadoes is indicated mainly for Southeast Arkansas. Below is the area at greatest risk for EF2 or stronger tornadoes.

(SPC EF2+ tornado probability within 25 miles of a point exceeding 10%)

11 AM Update:

Storms still on track to take shape late this afternoon into this evening. Here is the latest high resolution computer model forecast for 6 PM today showing a line of storms rapidly intensifying over Central Arkansas.

(4km NAM simulated radar forecast for 6 PM Wed Oct 17 2012)

Wednesday Severe Weather Discussion:

A fast moving cold front will sweep into Arkansas Wednesday Afternoon bringing the risk of some strong to severe thunderstorms. Most of Wednesday will be dry, but storms will begin to fire up along the cold front by late afternoon. Storms should initiate around 4-5 PM and increase in coverage and intensity through the early evening.

 (Computer model projection for 5 PM Wed Oct 17 2012)

Storms will quickly intensify during the evening hours as they push across Central Arkansas. This will be the time frame for the greatest threat of severe storms mainly between 5 PM and 7 PM. 

(Computer model projection for 7 PM Wed Oct 17 2012)

The storms will organize into a line as they push Eastward through Eastern and Southeast Arkansas later in the evening. The main threat from the storms will be strong wind gusts, however, a brief large hail and tornado threat may take shape as the storms first begin to intensify over Central Arkansas.

 Later in the evening, a squall line will rapidly push across Eastern and Southeast Arkansas. Most storms will likely exit the State by about 10 PM

(Computer model projection for 10 PM Wed Oct 17 2012)

The Storm Prediction Center has placed most of Central Arkansas under a SLIGHT risk for severe weather for Wednesday.

(Storm Prediction Center Day 2 Outlook for Wednesday Oct 17th - issued Tue Oct 16 1230PM)

Below is the severe threat associated with the storms for Wednesday evening. As the storms first begin to initiate there may be a few individual cells before the storms consolidate into a line. Given an environment of strong shear (changing wind speed/direction with height), these cells will begin to rotate leading to a hail/tornado threat. Once the storms organize into a line, strong straight line wind gusts will be the primary threat. Due to the fast movement of the cold front, flooding is unlikely

Although the severe threat will not last long due to the fast moving nature of the cold front, conditions will briefly come together for severe storms including tornadoes.  The front will also be associated with a strong jet stream moving into Arkansas Wednesday evening. At the same time, warm humid air will increase ahead of the front. The graphic below shows where the warm unstable air moves into an environment of strong upper level winds. 

(NAM model 250mb winds/Surface Based CAPE)

In addition, winds in the lower level of the atmosphere will be out of the South to Southwest while the winds aloft will be out of the West to Northwest. this creates the shear allowing for an environment in which storms can rotate. This is why there will be a brief tornado threat Wednesday evening as the storms begin to strengthen. 

Wednesday Evening Storms

A fast moving cold front will sweep into Arkansas Wednesday Afternoon bringing the risk of some strong to severe thunderstorms. Most of Wednesday will be dry, but storms will begin to fire up along the cold front by late afternoon. Storms should initiate around 4 PM and increase in coverage and intensity through the early evening.

(Computer model projection for 7 PM Wed Oct 17 2012)

The storms will organize into a line as they push Eastward through Eastern and Southeast Arkansas later in the evening. The main threat from the storms will be strong wind gusts, however, a brief large hail and tornado threat may take shape as the storms first begin to intensify over Central Arkansas. The main time frame for the greatest risk of severe weather for Central Arkansas will be between 4 PM and 8 PM, with the severe threat shifting into Eastern and Southeast Arkansas between 8PM and Midnight. The Storm Prediction Center has placed most of Central Arkansas under a SLIGHT risk for severe weather for Wednesday.

(Storm Prediction Center Day 3 Outlook for Wednesday Oct 17th - issued Mon Oct 15)

Well Hello Chilly Air

It's time to dust off those sweaters and long sleeves because a strong cold front is coming to town.

This is it like your run of the mill cold front either.  This is the kind of cold front that can turn the season around in a heart beat.  You can already make out from the image above that temperatures behind the front are struggling to reach the 40's and 50's up in the Dakotas.  That brisk, chilly air you see is aiming straight for Arkansas.

So you maybe asking yourself, when is it going to get here?  Judging by the latest trends and model data, the cold front should arrive sometime late Friday evening.  So you won't notice it on your way back from work tomorrow.  There is a chance though you might encounter a few showers and that chilly air while you're out for high school football games. If you head up north or west of Little Rock Friday evening then prepare yourself.

Once we fall behind the front Friday night, we'll have gusty winds  and you'll notice the refreshing cool air once you wake up for Saturday morning.  Speaking of which, Saturday overall looks wet and gloomy with temperatures not budging out of the 50's - Now that's a cold front for ya.  By Sunday, we'll see the sunshine come out but that will only boost temperatures close to 60 degrees.  Not to mention, next Monday morning looks downright cold and frosty with temperatures possibly reaching the upper 30's.

It goes without saying, this next front is going to be quite a change for us, so get those coats ready to go.

Not Feeling Like Fall

A warmer pattern shaping up this week as hotter temperatures and higher humidity return. The upper air pattern that featured a strong trough over the East has flattened out. allowing for the cooler temperatures to retreat North.

      (Upper pattern Monday night showing a more zonal, or West to East, flow)

This pattern will allow a warm front to push through the State, bringing in much warmer air from the Southern Plains Tuesday

The front will stay to our North through the middle of the week, keeping showers mainly North of the Arkansas border. 

Temperatures will remain well above normal with highs in the upper 80s through the week, although well shy of record highs. 

Rain chances increase toward the end of the week as the front to our North begins to shift South by Friday.

Arctic Ice Hits Record Minimum

The Arctic ice sheet reached a record low minimum extent this season according to The National Snow & Ice Data Center. The ice sheet shrunk to about 3.4 Million kilometers, which is roughly HALF of the long term average minimum extent. Below is the extent of the Arctic ice sheet as measured by satellites for a 5 day average ending September 18th.

The white area represents actual ice cover and the orange line represents the long term average extent. The long term average minimum extent is around 6.7 million square km and the previous record minimum ice extent is around 4.1 million square km set in 2007. The graph below compares 2012 ice extent to the average and to 2007.

The minimum Arctic ice extent is typically set in mid September, when conditions become cold enough that refreezing begins. This new record is part of a longer term trend of less Summer ice extent.

The 5 years with the smallest minimum ice extent have all occurred since 2007. Note that the 2012 minimum ice extent is well below any of the other years, falling below 4 million square km for the first time since measurements began. Satellite measurements have been used to estimate ice extent since 1979.
It is important to note that loss of ice extent has NOT been observed in the Antarctic. As a matter of fact, ice coverage there has actually increased somewhat as a whole.

The blue line represents Arctic ice extent, while Antarctic ice coverage is represented in red.
According to scientists at the National Snow and Ice Data Center, climate models have shown the Arctic becoming completely free of ice during the Summer by 2050, however the observed rate of ice decline is actually much faster than what the models suggest. This suggests that Summer Arctic ice may disappear within the next decade. Such a drastic change in ice extent will very like have significant climate impacts for much of North America. It is not known, however, specifically what those impacts would be.

2012 Fall Preview

WOW! Today's weather has to be one of best this year - temperatures are in the 70's, the sky is crystal clear and the humidity levels are perfect.  It's simply amazing outside.  You could say this weather is a nice preview of the fall season.

With that thought in mind, what does the meteorology community think about the fall season ahead? Well, let's find out.

When it comes to a season forecast, we typically turn to the CPC, or the Climatology Prediction Center.  Obviously their forecast comes with a clear disclaimer that these are just forecasts and they need be taken with a grain of salt.  Nonetheless, they are intriguing and are the most relible at depicting monthly forecasts in this day and age. So here goes...

According to the CPC, we can look forward to a slightly above normal temperatures in Arkansas during the next few months.  When I look at the climatology data for the state that equates to thermometers running anywhere from the low 90's to the mid 70's during October afternoons with overnight lows occasionally dipping to the 40's.  As for November that means temperatures will generally hang out in the 70's with major dips into the 60's-50's occurring in the second half of the month.

Rain predictions for the fall season aren't that appealing.  When you look at the image above, you can make out the normal precipitation amounts expected in Arkansas and most of the U.S.  In other words, the CPC expects 4-9" in the next few months.  More of the precipitation is anticipated to occur along the gulf coast.

            (Sea Surface Temperatures anomalies late August show a spike of warmer than normal Pacific Ocean water)

If you were wondering, these predictions aren't just computer generated.  These forecasts are heavily weighted on ENSO phases.  The latest ENSO analysis shows that an El-Nĩno phase is expected to ramp up very soon.  At the moment, the CPC thinks this transition to an El-Nĩno will have a greater impact on the winter months rather than the months of fall.  That is usually the case when it comes to climatology in our country.

Only time will tell how accurate these forecasts become.  For now we'll keep these ideas in the back of our minds.  All we can hope for is a wet and pleasant fall season ahead.