Tuesday, February 24, 2015

You Want More Snow? Here It Comes




5PM Tuesday Update... Quick post to tell you about how sharp the snowfall gradient will be and how difficult it will be determining where that gradient sets up.  Snowfall amounts could vary greatly over a very short distance.  It's hypothetical for Conway to get none,  Little Rock to get and inch or two and Pine Bluff gets 6 inches or even more.  I'm not saying that's going to happen specifically, but just to illustrate how hard it will be to know exactly where this gradient sets up until the system arrives.  We're very confident southern Arkansas will get snow, but the northern extent is in question.  IT ALL HAS TO DO WITH THE TRACK OF THE LOW.

THE MIDDAY RUN OF THE NAM HAS AN INCREDIBLE DIFFERENCE IN SNOWFALL AMOUNTS OVER A SHORT DISTANCE.  IT HAS ALMOST NOTHING IN MAYFLOWER AND CONWAY WHILE IT BURIES JEFFERSON COUNTY WITH MORE THAN 6''.  LOOK AT THAT GRADIENT OVER LITTLE ROCK!  THIS IS JUST ONE MODEL.   COULD IT BE RIGHT?  SURE, BUT WHAT IF THE LOW TRACKS JUST 20-30 MILES NORTH?  JUST A SMALL ADJUSTMENT MEANS A HUGE DIFFERENCE BETWEEN THE HAVE AND HAVE NOTS. ALSO, THE NAM HAS A TENDENCY TO OVER FORECAST AMOUNTS LATELY.
AND THE GFS HAS THAT GRADIENT JUST A TAD FURTHER NORTH.  IT'S A HUGE DIFFERENCE WHICH AFFECTS A MAJOR POPULATED AREA... CENTRAL ARKANSAS.   STAY TUNED. 

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2PM Tuesday Update... The morning models continue a little northward trend with the NAM still the most aggressive and furthest north.  I still think areas along and south of I-40 have the best chance for accumulating snowfall Wednesday.  What about areas north of I-40?  You still have a chance due to the uncertainty with the track of the low.  There should be a heavy snow band and exactly where that sets up is also uncertain.  For more information, read the post below.  Here's the SCHOOL:CON index made early Tuesday afternoon.



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This is going to be a very tricky forecast for Wednesday.  The system coming through is more of a classic snow for Arkansas and the track of this area of low pressure is extremely critical.  I can't stress that enough.  This is a case where just a few miles can mean the difference between very little snow and several inches. It's a very difficult forecast at this point.

Let's rewind to last week for a moment.  The models had this hitting Arkansas with a big snow.  Then it took the system much further to the south.  Starting with yesterday's data, its trending back to the north and is now bringing snow back to the state.  What I just described has been the case for the past couple weeks.  The storm is there in the long range, it trends south, then comes back north once within 48 hours.  The NAM (North American Model) is leading the pack with this trend and the morning run of the GFS is catching up to it now.  I expect the Euro to do the same.

The snow Monday was forecast by the NAM to be around 5'' for the metro and I'm glad I didn't go with that scenario, however, the NAM did a great job showing the system and its placement.  So while I like the NAM, the amounts could be overdone a little.

As I alluded to above, the Wednesday storm system is much different than the Monday disturbance.  This is a much stronger area of low pressure aloft.   This large pocket of cold air in the upper levels will wipe out any mid level warming and that simply means most of the precipitation will fall in the form of snow.  However, there could be a little sleet during the onset.   Strong upward motion will cool the atmosphere and keep temperatures around freezing while it's snowing Wednesday.

The National Weather Service has a winter storm watch for the southern half of the state from Little Rock south.  I completely agree with that and think many counties will turn into a warning.  I also expect more counties to be added further north.  At this time, I think everyone south of a Waldron to Greenbrier to West Memphis line will be favored for snow.

Timing?  I think this starts early in the day for south Arkansas and mid morning for central Arkansas.  I have more on the timing below.

The following maps are from WeatherBell Analytics.  I'm mostly using the NAM.  Remember, this will NOT be perfect.  It's not a forecast.  I'm just showing you model information below.

SIMULATED RADAR AT 9AM WEDNESDAY
NOON WEDNESDAY
3PM WEDNESDAY
6PM WEDNESDAY



PLEASE DO NOT TAKE THIS LITERALLY.  IT'S ONLY A MODEL.  THE NAM IS VERY AGGRESSIVE THAN OTHER MODELS WITH AMOUNTS.  IT WAS WRONG ON AMOUNTS ON MONDAY TOO AND THEY WERE FAR LESS THAN IT FORECAST.  I THINK THIS MODEL HAS THE RIGHT IDEA WITH PLACEMENT OF SNOW HOWEVER




This is the Tuesday morning run of the GFS.  Now you see the forecasting problems with the track of the low.  The GFS is much further south, BUT has trended north.

3 comments:

Christopher Pipkin said...

Oh how great. My town is gonna miss it agian :(

Sue said...

Well, Todd, you are THE MAN! Pine Bluff was supposed to get snow yesterday...not one flake in my neighborhood, only alot of sleet! Not crazy about making up school days til the middle of June but enjoying the snow (sleet) days now! (as long as we keep power!)Bring on the SNOW!

Anonymous said...

One more victory dance for the North. Bury the south so they won't whine about no snowfall.