Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
1048 am EDT Friday may 29 2015
have made some minor updates to the grids this morning. Based on
current radar trends and hi res models...cut back on probability of precipitation
initially this morning across the County Warning Area and into the early
afternoon and then again later this evening. Overall very little
change to 12 hour pop values though.
Other changes were basically just to account for hourly trends.
Short term /today through Saturday/...
axis of deeper moisture remains in the vicinity of western and
northern Georgia today. Models consistent in building the upper ridge
westward into the forecast area this afternoon into Saturday.
With drier and somewhat more stable air indicated across portions
of eastern Georgia...have confined probability of precipitation to the north and west today and
again Saturday. After loss of heating...much of the forecast
area should be dry overnight. Some moisture moving on shore Saturday
afternoon may be sea breeze influenced...so have included low probability of precipitation
for the extreme east central areas.
Guidance temperatures look reasonable and have stayed close.
Long term /Saturday night through Thursday/...
synopsis...00z GFS and European model (ecmwf) in general pattern agreement at the
beginning of the extended through midday Monday before differences
in the evolution of a cut off low over the southern Mississippi
Saturday and Sunday...mean trough that has been anchored over the
western US for the last month it seems begins shifting east into
the central US with ridging building across the West. Georgia will
remain under the influence of upper ridging centered off the East
Coast particularly Saturday and waning by late Sunday as the trough shifts
eastward along with a weak surface front. Best chances for rain on
the weekend will remain generally confined to far northwest Georgia Sat and
north and west of i85 on Sunday afternoon and evening. Look for
typical afternoon thunderstorms to develop across the
aforementioned regions each day.
Monday through Thursday...differences begin to appear on Monday
between the GFS and European model (ecmwf) over the evolution of a cutoff low as
energy rides over the developing western ridge into the base of
the fairly shallow trough centered over the MS river at that time.
Operational GFS wants to cut the low off over la which puts our
region on the moist flow side with a tap into a moisture plume
from the Caribbean by Wednesday and making for a much wetter week. The
European model (ecmwf) on the other hand delays the onset of cutting the low off
until the mean trough gets to around the 85th parallel and thus
centering the low over Florida. This difference puts our area on
the drier north side of the low middle to late week. GFS ensemble
resembles the operational GFS quite a bit more thus making the
European model (ecmwf) an outlier for now. Carrying above climatology probability of precipitation each day for
now that will likely need to be fine tuned each day for nuances as
confidence increases. Localized flood threat will certainly be on
The Table each day as precipitable water values...per the GFS...each day through
Thursday range from 1.50 to 1.75 inches across the region which
statistically is in the 90th percentile. Stay tuned to the
forecast for next week.
/issued 736 am EDT Friday may 29 2015/
IFR expected to improve to MVFR by middle morning. Improving
to VFR by afternoon. Mostly diurnal convection this afternoon for
mainly the northern taf sites...but should be less coverage than
yesterday. Winds will remain on the east side through the period.
Becoming 8 to 10kt after 14z.
//Atl confidence...12z update...
medium confidence on ceilings. High confidence remaining elements.
Preliminary point temps/pops...
Athens 85 65 86 67 / 20 10 20 20
Atlanta 83 67 84 69 / 30 10 20 10
Blairsville 78 60 79 62 / 40 30 20 20
Cartersville 84 64 85 66 / 40 20 20 20
Columbus 88 67 88 70 / 20 10 10 10
Gainesville 82 65 83 66 / 30 20 20 20
Macon 87 64 88 68 / 10 5 10 10
Rome 84 64 86 66 / 40 20 30 20
Peachtree City 85 63 86 65 / 20 10 10 10
Vidalia 88 68 87 69 / 10 5 30 10