Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
710 PM EDT Friday Aug 29 2014
Previous discussion... /issued 340 PM EDT Friday Aug 29 2014/
Short term /tonight through Saturday night/...
short term models consistent with increasing rain chances this
weekend after a long...dry week. Anomalously strong upper level
ridge continues to remain in place over the southeastern Atlantic
coastline...but an eastward shift in the ridge will expose the
region to perturbations in the synoptic flow. For now...models
continue to advertise a gradual increase in cloud coverage and
moisture from the southwest Saturday and upper level shortwave
expected to move into the Tennessee and Ohio valleys looks to dampen
somewhat as it tracks just north of the state. This positioning
should keep the majority of any associated energy outside the County Warning Area.
Anticipate much of the precipitation activity to be diurnally
driven and orographically enhanced...with the best chances between 1
and 10 PM Saturday afternoon. Models appear to continue the trend on
backing off on extended periods of widespread rainfall...with
coverage being slightly more limited. As a result...have dropped
likely wording with the probability of precipitation...but have continued with good chance
through Saturday afternoon. Expect high precipitation efficiency
with abnormally high precipitable waters ...and although quantitative precipitation forecast is expected to be 0.5
inches or less through early Sunday morning...locally heavier
rainfall amounts can be expected. MLCAPES look to be marginal...and
do not anticipate intense storm development.
Have gone with a blend of temperatures for Saturday and Sunday
morning. With the high still in place...but with rain in the
forecast...temperatures will be warmer than normal Saturday...but
slightly cooler than today.
Low level moisture remains in place into the extended period...and
an additional 0.5 to 1 inch of rain can be expected from Sunday to
Long term /Sunday through Friday/...
no changes made to the extended forecast. Models in a little
better agreement as the long term period begins with vorticity maximum
lingering over the Tennessee Valley as upper ridge holds over the
southern part of the state. This vorticity maximum is more strung out
providing little lift on the European model (ecmwf) but more potent with distinct
trough noted on latest GFS. Regardless...precipitable water values
will be high...on the order of 1.8 to 2.2 inches which should be
sufficient for likely probability of precipitation to the north where shortwave energy
resides and Middle Range chance to the south. There is a distinct
area of middle level dry air noted on the European model (ecmwf) which could lead to
reduced probability of precipitation for the northern half of the forecast area despite
aforementioned energy but will need a few more runs to confirm
before getting fully onboard with this solution.
Into early and middle week...the Euro is definitely more aggressive in
build middle and upper ridge back over the area and limiting probability of precipitation.
For now have gone with a blend of this drier solution and the
slightly wetter GFS which suppresses ridge to the south while
strung out vorticity maximum provides focus for convection. This yields
generally low to Middle Range chance probability of precipitation for the remainder of the
extended portion. With upper ridge in place...should see some
increase in maximum temperatures although guidance not especially bullish on
this aspect. Will need to monitor to see if they trend upward with
future runs but would not be surprised to see some middle 90s by Tuesday
VFR conditions expected through the overnight and for the most part
on Saturday. Surface winds becoming light and variable or light
south-southeast tonight. Potential for VFR ceilings later tonight or during the day
Saturday with chances for showers and thunderstorms increasing.
Winds will vary around south for atl Saturday.
//Atl confidence...00z update...
high confidence on all elements through tonight.
Low confidence for ceilings...wind direction and impacts from
thunderstorms on Saturday.
Preliminary point temps/pops...
Athens 67 92 70 91 / 10 30 30 50
Atlanta 72 90 72 88 / 10 40 40 50
Blairsville 63 85 66 83 / 10 40 40 60
Cartersville 67 91 70 89 / 10 50 50 60
Columbus 73 93 74 92 / 10 50 40 40
Gainesville 69 89 71 87 / 10 40 40 60
Macon 69 94 71 92 / 10 30 30 40
Rome 66 91 70 90 / 10 50 40 60
Peachtree City 66 90 69 90 / 10 50 40 50
Vidalia 72 94 73 92 / 10 30 20 40