Tuesday, December 04, 2012

There's a Storm Brewin' ?

11:10 AM Monday Update...  This is why you can't hang your hat on any particular model run when you're dealing with a long term forecast.  The latest version of the GFS is not as strong with the energy coming out of the southwestern United States next week and therefore develops a weaker surface low and moves it on through.  This model continues to show the potential for significant rainfall though with more than 1-2 inches or more.  Like I said in the earlier post, this will change several more times between now and then, but I thought I would just update you and show you why forecasting this based on a model that's run 4 times a day with 4 different solutions is impossible at this point.

The upper energy is pulling out of the southwest and isn't as impressive compared to earlier model runs.
Here's the surface chart showing the low moving through with heavy rain the big threat late next Monday into Tuesday.

The GFS run this morning shows 1-2 inches with higher amounts possible.  This will vary with each model run, but notice it has been consistent with the corridor right through the gut of Arkansas.

It finally appears the pattern is changing, but details are still to be sorted out.  I thought it would be by the middle of the month at the earliest, but it's coming a few days before that.  I don't hear many complaints about that though.

With all that said, this is more than likely going to happen next Monday, December 10th, so this is still very much considered the long range period and much can and will change. 

It's very tough to go from highs in the 70s to near 80 degrees in December to colder weather without something significant happening.  Without sounding like a President or politician, I hope we can do this peacefully.

However, the overnight run of the Global Forecasting System (GFS) stalls a strong boundary right through Arkansas with waves of rain on it this weekend.   The flow aloft is parallel to the front not allowing it to move.  A strong upper level storm system will dig into the southwestern United States.  Once THIS feature pulls out, strong surface low pressure will develop along the front and sweep it to the east.  

So here are the questions that remain in regards to the GFS solution:  where does the front stall? ( this will be the focus for the heaviest rainfall ).  Also, where does the surface low pressure develop?  How much instability develops ahead of the front?  How fast will this feature move?  As you can see, details are sketchy this far in advance.  If you believe the overnight run of the model, the biggest potential is heavy rainfall and some severe weather can't be ruled out.

Then there's the Euro model which offered a faster solution yesterday (Monday) blasting the system through here Sunday.  As I look at the new run Tuesday morning, it now looks more like the GFS so there is some agreement.  However, it does keep the front north of Arkansas most of the weekend, but brings it south Sunday night into Monday with rain (some heavy) with the surface low tracking right through Arkansas late Monday.  So there are still some differences, but they both agree on a significant storm system.

Both models agree temperatures will return to average behind the front or even below average!  FINALLY.

Here are the maps below which explain the set up.

This is the 00Z run of the GFS at 500 millibars.  Notice all the black lines running from southwest to northeast across the southern United States including Arkansas.  This upper level southwesterly flow is parallel to a surface front.  It's not conducive to much movement if any so the front COULD stall according to this scenario for awhile.  NOW, notice the big blob (for lack of better words) of red over the southwestern U.S.  This is a strong piece of upper level energy.   Smaller disturbances will be moving through this flow along the surface boundary and this could produce rounds of rain along the front wherever it's located.  Once this pulls out of the southwest, it will form low pressure along the front and sweep it to the east.  However, the questions remain:   when, where does the low develop, where is the surface front, and how fast?
This is the GFS early next Monday morning.  You can clearly see the green blobs, precipitation fields) along the stalled front from NE TX through AR into the Ohio River Valley.
By early Tuesday morning, look at the black closed line in western AR.  This is the surface low forming along the front in western AR.  This is what will push everything to the east and allow much colder air to move into Arkansas behind it.  Here are the questions that remain:  How much instability is there as this low forms?  This is at midnight Tuesday and would help reduce the instability due to overnight timing, but will that happen?  Also, will cloud cover and rain keep the instability in check.  According to this, I would keep an eye on the southeastern half of the state just along and south of the northeastward advancing low pressure.  If you take this literally, it's a heavy rain threat with some strong and possibly severe storms.  HOWEVER, details WILL change as we are still several days away from this happening.
This is the Euro run last night showing a slightly different scenario, but has come around to the slower timing of the GFS compared to Monday's run of this model.  The front is still just NW of the state late Sunday.  It's quite warm and breezy here, but the cold air is advancing southward.
The Euro late Monday really shows a strong surface low developing along the front in NW AR with a trailing cold front into Louisiana.  All the blue behind it is the colder air and the white line is the 32 degrees line.  This surface low and the timing of day (afternoon and evening) does raise concern for the threat for strong/severe storms depending on instability levels.  Plenty of rain and clouds ahead of it could reduce that, but AGAIN, it's so far out to know for sure.
In summary, there's a storm brewing next week which has potential to be a heavy rain maker and produce strong/severe storms.  Since this is still several days away, much will change as these are only computer models which are run several times a day and change just as much.  I'll keep you updated here, on facebook, twitter, and on Channel 7 News.


Will said...

Very true when it comes to relying on one model and one run of that model. IMO, Long Range forecasting should be based upon the trends of the differing models / ensembles and it appears that the longer range, (which is always horribly difficult to forecast) is definitely trending colder. Now, hopefully that is just not a function of climatology and that the models are actually looking at something that will produce the cold and snow that we are all wanting. As always I will be on the SnowBirdBob train and look at the snowman as half full rather than half empty. Canada is very cold with quite a bit more snow this year than last. Trends, Canadian cold and snow cover are all favorable and I believe to be conducive to a snowy, cold winter. As the great and powerful Snowbird always tells us---We Shall See.

Where is the Ninja to pour water on our Snowman??

Jason H said...

Hello again all. So far my December Outlook is looking great! We have some fun time ahead for Arkansas and the real battle will start next week! Looks like a chance of some HEAVY rain, and/or Severe storms next week....but thats not the fun part,its what "could" follow in the days after.......as allways, HOPE SNOW! Here is another copy of my December Outlook I did back on November 23rd......

December 1-10 Temps mostly at or above avg. Precip above avg with heavy rain/storms possible 2nd-3rd and again 9th or 10th. No frozen precip.

December 11-20 Temps above normal. Precip above normal with 2-3 rounds of rain/storms. Light frozen precip for Northern Arkansas around 12th-14th.

December 21-31 Temps at or below normal. Precip around or slightly above avg. Watch out for our first REAL cold blast and wintry storm from dates 25th-30th.

NOAA Winter Guidance