Rainy Monday and ???
01/16/2011 11:00
The great thaw continues Sunday with sun at times and highs near 50. Rain moves in Monday morning and will continue through Tuesday evening. What snow and ice doesn’t melt today will certainly be taken care of by the rain. Hothlanta is quickly returning to just plain old Atlanta.
But will it stay that way? Hmmmm....
Despite many folks (myself include) thinking the later half of January could see a warm up, it seems that winter isn’t ready to throw us a break. Arctic returns for late week with a CHANCE for... you guessed it! Snow...
Here is the end of the forecast period for Atlanta from the NWS:
Thursday Night: A chance of rain and snow showers. Mostly cloudy, with a low around 23. Chance of precipitation is 30%.
Friday: A slight chance of flurries. Partly sunny, with a high near 33.
Friday Night: Mostly clear, with a low around 20.
* * *
And here is the longterm forecast discussion from Peachtree City (Atlanta) NWS. There is a lot of jargon that I’ve tried to define below for those that ask.
/ISSUED 645 AM EST SUN JAN 16 2011/
...
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
ANOTHER ARCTIC SURGE APPEARS DESTINED FOR THE SE U.S. DURING THIS
PERIOD. THE POLAR VORTEX WILL DEEPEN SIGNIFICANTLY WED-THU IN THE
WAKE OF THE SHORT TERM SYSTEM. AN ARCTIC HIGH WILL QUICKLY DROP SE
FROM SC CANADA TOWARD THE SE U.S. IN THE DEEPENING NW FLOW THU-FRI.
SUFFICIENT FORCING APPEARS EVIDENT WITH THE DRIVING UPPER SHORT WAVE
THU-THU NIGHT TO SUPPORT -SHRA. HOWEVER...THE ECMWF QPF OF 1.0-1.5
INCH APPEARS WAY OVERDONE GIVEN THAT DEEPER MOISTURE HAS BEEN
REMOVED BY THE INITIAL EARLY WEEK SYSTEM. PREFER LIGHTER QPF
DEPICTED BY THE GFS FOR THIS PERIOD. STRONG CAA AND OROGRAPHIC
LIFTING PROVIDE A CLASSIC SETUP FOR -SHSN IN THE NE MOUNTAINS. THIS
IS CONSISTENT WITH EARLIER THINKING FOR THESE PERIODS. AN INCH OR SO
OF SNOW CERTAINLY NOT OUT OF THE QUESTION FOR THE NE MOUNTAINS WITH
THIS SCENARIO. THE ARCTIC HIGH WILL SETTLE ACROSS THE SE STATES
EARLY SAT...THEN MODIFY AND DRIFT EAST BY SUN AS THE UPPER FLOW
REMAINS RELATIVELY PROGRESSIVE WITHIN THE MEAN EASTERN U.S. TROUGH.
THERE REMAINS CONSIDERABLE UNCERTAINTY BEYOND THIS WITH RESPECT TO
POTENTIAL SOUTHERN STREAM SHORT WAVES EARLY THE FOLLOWING WEEK. WITH
A REMNANT ARCTIC AIR MASS ACROSS THE REGION...ANY SUCH SYSTEMS COULD
BRING MORE WINTER WX TO THE AREA AND WILL NEED TO BE WATCHED
CAREFULLY. IN ADDITION...THE 00Z ECMWF HAS JUST COME IN WITH A
COMPLETELY DIFFERENT SOLUTION FROM THE 12Z RUN...SHOWING A
WARMER...BUT STILL WITH SOME WINTER WX POTENTIAL DURING THE LATER
PORTION OF THE EXTENDED. FOR CONSISTENCY...WILL REMAIN WITH THE MORE
CONSISTENT RUN-TO-RUN GFS SOLUTION FOR THE EXTENDED PERIODS AND NOT
MENTION ANY WINTER WX OTHER THAN THE -SHSN N GA THU NIGHT/FRI
MORNING.
MEX MOS COMES IN COLDER WITH EACH RUN FOR THE FRI-SAT
PERIOD...CONSISTENT WITH EARLIER THINKING. THE SOURCE REGION OF THE
LATE WEEK AIR MASS EMANATES FROM A VERY COLD AIR MASS CURRENTLY
LOCATED ACROSS SIBERIA. 850MB TEMPS ARE STILL PROGGED TO APPROACH
-40C ACROSS SE CANADA LATE IN THE WEEK...WITH -16C PUSHING INTO N GA
FRI. ANALOGOUS TO SIMILAR EVENTS...E.G...12 DEC 2010...THIS WOULD
EQUATE TO HIGHS 25 TO 30 N GA AND 35 TO 40 CENTRAL GA
FRI...RECOVERING DURING THE WEEKEND BUT REMAINING BELOW NORMAL. WILL
LEAN TOWARD THE COLDEST MEMBERS OF THE DETERMINISTIC GUIDANCE FOR
THESE PERIODS.
FINALLY...16 DAY RUN OF GFS SHOWS VERY PERSISTENT DEEP POLAR VORTEX
AND DEEP TROUGH REMAINING ACROSS THE EASTERN U.S. THROUGH THE END OF
THE MONTH. OVERALL THIS WILL SUPPORT CONTINUED BELOW TO WELL BELOW
NORMAL TEMPS AND AT LEAST SOME THREAT OF WINTER PCPN DURING THIS
PERIOD AS REPEATED SURGES OF ARCTIC/CANADIAN AIR SPILL WELL
SOUTHWARD ACROSS THE EASTERN U.S.
WX = Weather, but you should know that by now!
SHRA = Showers of Rain / Rain Showers
SHSN = Showers of Snow / Snow Showers
PCPN = Precipitation
GFS = Global Forecast System (Main US based global weather forecast model)
ECMWF = European Centre for Medium-Range Weather Forecasts (aka European Weather Model/“The Euro”)
QPF = Quantitative Precipitation Forecast - How much liquid (or frozen precip if melted down)
CAA = Cold Air Advection - (Advection: the transfer of heat or matter by the flow of a fluid, esp. horizontally in the atmosphere or the sea.)
OROGRAPHIC LIFTING - air is pushed up by mountains
SHORT WAVES - Think of it like energy impulses that could cause precip
SOUTHERN STREAM - Upper level winds that push those SHORT WAVES along. “Southern branch of jet stream”
12Z - Model run for 12:00pm UTC (London Time). 00Z would be midnight UTC. 18Z would be 6pm UTC and so on...
MOS - Model Output Statistics
MEX MOS - Basically the extended forecast MOS for the GFS
DETERMINISTIC GUIDANCE - it’s jargon, but in the context above, it helps to replace it with “model solution sets”
Those definitions are as quick as I can make them, and some are oversimplified. If you REALLY want to know/understand, then check this site out:
WEATHER PREDICTION EDUCATION
I’ll leave POLAR VORTEX, TROUGH, 850MB TEMPS, and whatever else for you to look up there. Hope this helps!
But will it stay that way? Hmmmm....
Despite many folks (myself include) thinking the later half of January could see a warm up, it seems that winter isn’t ready to throw us a break. Arctic returns for late week with a CHANCE for... you guessed it! Snow...
Here is the end of the forecast period for Atlanta from the NWS:
Thursday Night: A chance of rain and snow showers. Mostly cloudy, with a low around 23. Chance of precipitation is 30%.
Friday: A slight chance of flurries. Partly sunny, with a high near 33.
Friday Night: Mostly clear, with a low around 20.
* * *
And here is the longterm forecast discussion from Peachtree City (Atlanta) NWS. There is a lot of jargon that I’ve tried to define below for those that ask.
/ISSUED 645 AM EST SUN JAN 16 2011/
...
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
ANOTHER ARCTIC SURGE APPEARS DESTINED FOR THE SE U.S. DURING THIS
PERIOD. THE POLAR VORTEX WILL DEEPEN SIGNIFICANTLY WED-THU IN THE
WAKE OF THE SHORT TERM SYSTEM. AN ARCTIC HIGH WILL QUICKLY DROP SE
FROM SC CANADA TOWARD THE SE U.S. IN THE DEEPENING NW FLOW THU-FRI.
SUFFICIENT FORCING APPEARS EVIDENT WITH THE DRIVING UPPER SHORT WAVE
THU-THU NIGHT TO SUPPORT -SHRA. HOWEVER...THE ECMWF QPF OF 1.0-1.5
INCH APPEARS WAY OVERDONE GIVEN THAT DEEPER MOISTURE HAS BEEN
REMOVED BY THE INITIAL EARLY WEEK SYSTEM. PREFER LIGHTER QPF
DEPICTED BY THE GFS FOR THIS PERIOD. STRONG CAA AND OROGRAPHIC
LIFTING PROVIDE A CLASSIC SETUP FOR -SHSN IN THE NE MOUNTAINS. THIS
IS CONSISTENT WITH EARLIER THINKING FOR THESE PERIODS. AN INCH OR SO
OF SNOW CERTAINLY NOT OUT OF THE QUESTION FOR THE NE MOUNTAINS WITH
THIS SCENARIO. THE ARCTIC HIGH WILL SETTLE ACROSS THE SE STATES
EARLY SAT...THEN MODIFY AND DRIFT EAST BY SUN AS THE UPPER FLOW
REMAINS RELATIVELY PROGRESSIVE WITHIN THE MEAN EASTERN U.S. TROUGH.
THERE REMAINS CONSIDERABLE UNCERTAINTY BEYOND THIS WITH RESPECT TO
POTENTIAL SOUTHERN STREAM SHORT WAVES EARLY THE FOLLOWING WEEK. WITH
A REMNANT ARCTIC AIR MASS ACROSS THE REGION...ANY SUCH SYSTEMS COULD
BRING MORE WINTER WX TO THE AREA AND WILL NEED TO BE WATCHED
CAREFULLY. IN ADDITION...THE 00Z ECMWF HAS JUST COME IN WITH A
COMPLETELY DIFFERENT SOLUTION FROM THE 12Z RUN...SHOWING A
WARMER...BUT STILL WITH SOME WINTER WX POTENTIAL DURING THE LATER
PORTION OF THE EXTENDED. FOR CONSISTENCY...WILL REMAIN WITH THE MORE
CONSISTENT RUN-TO-RUN GFS SOLUTION FOR THE EXTENDED PERIODS AND NOT
MENTION ANY WINTER WX OTHER THAN THE -SHSN N GA THU NIGHT/FRI
MORNING.
MEX MOS COMES IN COLDER WITH EACH RUN FOR THE FRI-SAT
PERIOD...CONSISTENT WITH EARLIER THINKING. THE SOURCE REGION OF THE
LATE WEEK AIR MASS EMANATES FROM A VERY COLD AIR MASS CURRENTLY
LOCATED ACROSS SIBERIA. 850MB TEMPS ARE STILL PROGGED TO APPROACH
-40C ACROSS SE CANADA LATE IN THE WEEK...WITH -16C PUSHING INTO N GA
FRI. ANALOGOUS TO SIMILAR EVENTS...E.G...12 DEC 2010...THIS WOULD
EQUATE TO HIGHS 25 TO 30 N GA AND 35 TO 40 CENTRAL GA
FRI...RECOVERING DURING THE WEEKEND BUT REMAINING BELOW NORMAL. WILL
LEAN TOWARD THE COLDEST MEMBERS OF THE DETERMINISTIC GUIDANCE FOR
THESE PERIODS.
FINALLY...16 DAY RUN OF GFS SHOWS VERY PERSISTENT DEEP POLAR VORTEX
AND DEEP TROUGH REMAINING ACROSS THE EASTERN U.S. THROUGH THE END OF
THE MONTH. OVERALL THIS WILL SUPPORT CONTINUED BELOW TO WELL BELOW
NORMAL TEMPS AND AT LEAST SOME THREAT OF WINTER PCPN DURING THIS
PERIOD AS REPEATED SURGES OF ARCTIC/CANADIAN AIR SPILL WELL
SOUTHWARD ACROSS THE EASTERN U.S.
WX = Weather, but you should know that by now!
SHRA = Showers of Rain / Rain Showers
SHSN = Showers of Snow / Snow Showers
PCPN = Precipitation
GFS = Global Forecast System (Main US based global weather forecast model)
ECMWF = European Centre for Medium-Range Weather Forecasts (aka European Weather Model/“The Euro”)
QPF = Quantitative Precipitation Forecast - How much liquid (or frozen precip if melted down)
CAA = Cold Air Advection - (Advection: the transfer of heat or matter by the flow of a fluid, esp. horizontally in the atmosphere or the sea.)
OROGRAPHIC LIFTING - air is pushed up by mountains
SHORT WAVES - Think of it like energy impulses that could cause precip
SOUTHERN STREAM - Upper level winds that push those SHORT WAVES along. “Southern branch of jet stream”
12Z - Model run for 12:00pm UTC (London Time). 00Z would be midnight UTC. 18Z would be 6pm UTC and so on...
MOS - Model Output Statistics
MEX MOS - Basically the extended forecast MOS for the GFS
DETERMINISTIC GUIDANCE - it’s jargon, but in the context above, it helps to replace it with “model solution sets”
Those definitions are as quick as I can make them, and some are oversimplified. If you REALLY want to know/understand, then check this site out:
WEATHER PREDICTION EDUCATION
I’ll leave POLAR VORTEX, TROUGH, 850MB TEMPS, and whatever else for you to look up there. Hope this helps!