Thursday, January 30, 2014

Winter Kicks Into High Gear

Over the past month, we have been completely dominated by the northern branch of the jet stream.  It has delivered numerous shots of cold air well down into the Gulf and this has cut off our main moisture supply.   On a side note, the continuous arctic air intrusions have cooled Gulf of Mexico surface temperatures and they are well below average.  As I have mentioned in previous posts, this may help squash any significant severe weather until later in the spring when those sea surface temperatures can recover.  I want to make it clear what I'm saying here.  We can still have severe weather, but significant outbreaks could be delayed this severe weather season much like last year.  Outside of the Botkinburg tornado in April, the only "outbreak" was late May.  On yet another side note, there is no official definition of "outbreak", but I think May 30th of last year did meet my criteria as more than a dozen tornadoes hit the Natural State.

Now the southern branch of the jet will get active starting next week with numerous precipitation chances.  At the same time, the northern branch will still be in a favorable position to deliver punches of cold air.  Ridging over Alaska will continue.  Many times you will hear it's warmer in Alaska than in the lower 48.  This is very normal in this type of pattern.  That's how the United States gets cold.  Rarely is it cold in both places at the same time. When Alaska is in the deep freeze, it usually stays bottled up there and we are flooded with milder Pacific air.  Anyway, the ridging up there continues and the transport (pump) for cold air will continue into the lower 48.

Now we have 3 systems to watch next week.  Mild air comes in through Saturday, then we get back into the cold air.  Waves of moisture will trek across the western and southern United States bringing numerous opportunities for precipitation.  This is wonderful news for the wildfire situation, but can be bad news for travel as winter weather chances will be on the increase. The cold air from the north and the moisture will first combine on Sunday.  This is a minor disturbance compared to the following one, but it can deliver some wintry weather, especially to northern Arkansas.  This will be the target area all week.  While winter weather will be possible further south, it's the north that will be more susceptible as the best cold air and moisture come together in that location.

The next and more significant disturbance arrives Tuesday into Wednesday.  The exact track of the low and the strength is crucial for precipitation types, but all will be likely across Arkansas during this 48 hour time period.  The further south the low tracks, the more likely frozen precipitation will be seen into central Arkansas, but the further north, just a cold rain.  This is still several days away so it's wayyyyyy too early to get specific.

The next system arrives Friday of next week.  The models show a very cold solution and snow, but I'm extremely hesitant to go with that at this time.   It's possible, but once again, I think the north will be the favored area.  

I have maps below explaining EVERYTHING YOU NEED TO KNOW.

Cold air will continue to come in waves from the north with a moisture supply coming along the southern branch of the jet.  The combination of these two means precipitation chances will be on the increase, relief from the wildfire danger, and maybe some winter weather.

This is the overnight run of the Euro.  In these maps, it's important to know what the blue dashed line is called.  It's the "540 line".  Basically this is the rain/snow line.  Just south of this, there can be an area of ice where surface temperatures are cold enough.  The black closed line over Iowa, Missouri, and Illinois is a surface high from the northern jet delivering cold air.  The green and yellow blobs are precipitation amounts over the previous 6 hours.  There is a wave of energy producing this coming from the southern jet.  This is showing the chance for some frozen precipitation across northern AR Sunday afternoon and evening with a cold rain further south.  This is round #1

Here's the Euro valid next Tuesday as noon. Taking this literally (this WILL change) it's a cold rain for much of central and southern Arkansas.  The tiny black circle over SE AR is the surface low.  The further south this travels, the higher the chances for winter weather.  Further north, just rain.  This is indicating heavy amounts of precipitation which is good news for the wildfire situation. Traveling to the north?  This version of the Euro indicates MAJOR snow for north TX, OK, KS into Missouri.  The 540 line is north of AR, BUT remember, just south of that there will be icing concerns if temps support that at the surface.
And here are the surface temperatures Tuesday at noon.  The solid white line is the freezing line.  That's located from near Ft. Smith over to near Clinton up to NE AR.  This is an icing situation for that portion of the state while central and south have a cold rain.  As the low moves away Tuesday night into Wednesday morning, that freezing line will move south and there's at least some chance the rain will change to snow before ending for central and northern AR.  Maybe even further south.  AGAIN, THIS IS MANY DAYS AWAY AND SPECIFICS CAN AND WILL CHANGE.
Here's the next system arriving Friday Feb. 7th.  The low is in the Gulf allowing colder air into the state.  The 540 line is much further south implying this is snow across the north half and ice/rain across the south half.   I have serious doubts about this verifying.  The Euro in this time frame has been less than stellar. 

In summary, as always, when you're talking about a winter forecast this far out, things are going to change.  The track and strength of the low will be crucial.  The purpose of this post is to show you the possibilities.   This is ONLY 1 run of the operational Euro, the next run could show something completely different.  However, at this time, given the pattern, I feel confident there will be wintry weather in the state.  As I mentioned on twitter this morning, the brunt will be across the north.  It's still POSSIBLE further south.  I'll keep you updated. 

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