Area Forecast Discussion
Issued by NWS Atlanta, GA
FXUS62 KFFC 300558
Area Forecast Discussion
National Weather Service Peachtree City GA
158 AM EDT Thu Mar 30 2017
.PREV DISCUSSION... /issued 945 PM EDT Wed Mar 29 2017/
No changes planned for the forecast.
SHORT TERM /Tonight through Thursday Night/...
Old frontal boundary situated across south central GA should begin
to push northward tonight in response to a cold front moving into
the Mississippi River Valley. This old front should orient itself
almost north/south across the far eastern CWFA on by early Thursday.
The cold front should remain well west of the CWFA until later in
the day Thursday.
There are some timing differences with the cold frontal passage
between the NAM and GFS. This also shows up in our locally run
models, one based on the GFS and one based on the NAM. The GFS is
faster with the precip onset and fropa, while the NAM lags behind a
few hours. The ECWMF looks to be right smack in between the NAM
Isolated showers/thunderstorms are possible late this afternoon and
evening, but should diminish quickly with the loss of heating.
Thursday will be a little complicated, because the highest pops will
be centered around the two boundaries, the approaching front in the
west and the old stationary front across eastern GA. The middle part
of the CWFA will have the least amount of precip coverage for most
of Thursday. The chances for precip will begin to increase quickly
from the west late Thursday afternoon/early evening as convection
along and ahead of the cold front approaches the area.
Do think that scattered showers and thunderstorms will develop out
ahead of the main frontal boundary tomorrow afternoon during peak
heating. Lapse rates will be steep tomorrow afternoon and the some
surface instability will be present, so there is some potential for
strong/isolated severe storms tomorrow afternoon ahead of the main
show in the evening and overnight hours. The better potential for
strong/severe thunderstorms should be in the evening/overnight hours
with any convection along the front/squall line. Good mid level
support, steep lapse rates and decent shear will all be present.
Moderate surface instability will also be present.
LONG TERM /Friday through Wednesday/...
Fairly active pattern to continue through this long term period.
Short wave by Friday will be weakening/filling while traversing
east across the Ohio valley. Ridging aloft quick to build late
Friday and Saturday so above normal temps likely this weekend.
Upper ridge axis passes east of the state Sunday morning. Clouds
will increase ahead of next wave, which is much more amplified
with correspondingly slower forward speed and more substantial
rainfall and supportive of linear storm modes. This wave also
expected to follow more southern track than previous waves. 12Z
ECMWF a little deeper and slower with upper low than other 12Z
By the time the main forcing from this wave arrives Monday
morning, upper/sfc low already occluding and greatest instability
shifts south of CWA. As with this week`s system, CAD will be in
place over NE counties prior to onset of precip, further reducing
instability over north GA. Could see swath of heavy rain due in
this pattern as strong baroclinic zone will be in place and
associated isentropic lift also fairly strong and persistent.
Wouldn`t be surprised if later medium range model runs spit out
3-6 inches of rain if we can get higher PW air into the area. 12Z
GFS already indicating this kind of scenario. With long term
drought conditions firmly in place, we could certainly use this
amount of rainfall.
Wraparound precip associated with upper low will persist Tuesday.
Finally next vigorous broad/large upper low progged to track
further north over the central CONUS into the OH valley Wednesday.
And while forecasts this far out are unreliable, a track that far
north with strong mean flow in early April usually means
significantsevere weather likely. Again too far out to hang your
(or anyone`s) hat on but something to keep an eye on.
Guidance for this TAF set much less aggressive with the low level
moisture coming in from the Carolinas. It still arrives in AHN as
MVFR cigs this morning but should remain just east of the
remaining terminals. VFR cigs for most of today at the TAF sites
in advance of a storm system expected move through late this
afternoon into the evening and overnight hours. Timing will be
difficult to pinpoint with this system but for now have gone 04Z
for ATL and added some wind gusts to the Prob30 group. This Prob30
group will eventually transition to a TEMPO later today.
//ATL CONFIDENCE...06Z UPDATE...
Medium on TSRA timing.
High on remaining elements.
.PRELIMINARY POINT TEMPS/POPS...
Athens 79 60 75 52 / 40 90 70 10
Atlanta 80 59 73 53 / 40 90 40 5
Blairsville 71 54 66 47 / 40 90 50 10
Cartersville 79 57 73 50 / 40 80 20 5
Columbus 83 62 78 55 / 30 80 40 5
Gainesville 76 57 72 51 / 40 90 50 10
Macon 84 62 79 54 / 30 80 60 10
Rome 79 56 73 50 / 40 80 20 5
Peachtree City 81 58 75 51 / 40 90 40 5
Vidalia 85 64 82 58 / 40 50 60 10