Area Forecast Discussion
Issued by NWS Atlanta, GA
FXUS62 KFFC 302358
Area Forecast Discussion
National Weather Service Peachtree City GA
758 PM EDT Sun Apr 30 2017
Following collaboration with SPC, have canceled the Tornado Watch
ahead of the 8 PM expiration time. The leading edge has lost its
integrity as it moves into Georgia, and there now appears to be
little if any tornado risk.
The actual front remains back over Mississippi and still expect
another line to develop ahead of it as it moves through Alabama
overnight. This line is still expected to have more of a punch as
it moves into western Georgia before sunrise, and continue
eastward through the day. Overall there is still a moderate level
of uncertainty given the issues with model solution timing and
indication of available ingredients, particularly as they did not
have much of an indicator on this evening`s activity.
.PREV DISCUSSION... /Issued 342 PM EDT Sun Apr 30 2017/
SHORT TERM /Tonight through Monday Night/...
A deep closed low lifting out of the Rockies will be tracking to
the Great Lakes region through the remainder of the short term. An
associated cold front moving through the central CONUS will
eventually push through GA Monday. This system will spawn off two
main rounds of convection noted below.
A strong line of thunderstorms moving across Alabama will
continue to track eastward this afternoon/evening. This line is
pushing out ahead of the main front and is producing strong winds
and heavy rain with isolated tornadoes a possibility. Given this,
we have issued a Tornado Watch until 7pm this evening across
portions of NW GA. If the line holds together and the threats
continue, we may need to extend the watch in time and further west.
However, at this time, we feel that the line will be moving out
ahead of the main front/dynamics and into a more stable airmass. The
line should diminish as we go through the evening hours. There will
be a brief lull until the main line starts to redevelop along the
front across Alabama later tonight, eventually moving toward NW GA
by the early morning hours.
Timing of the main line is still a bit uncertain. However, based on
model consensus, the main line of showers/thunderstorms should
approach during the early morning hours across NW GA. The line will
continue to move east through the day Monday, exiting to the SE by
the evening hours. Anticipate showers/thunderstorms to approach and
move through the metro between 5am and 10am.
The overall extent of strong to severe thunderstorms looks marginal
as much of the upper level support/dynamics surge further to the
north. Weak to marginal parameters are expected, with 30 to 40kt
deep layer shear and CAPE values less than 1000J/kg. However, dew
points in the mid/upper 60s would result in higher MLCAPE. Also,
helicity will be fairly elevated right along the front lending to
the possibility of brief embedded tornadoes along the line. Like we
have seen with recent events, would not be surprised if there were
some discrete thunderstorms moving up from the south just ahead of
the line that may show characteristics of brief circulation. But the
overall coverage of severe thunderstorms should be fairly isolated.
The main impact from this system will be damaging winds, isolated
brief tornadoes, frequent lightning and heavy rain (leading to
localized flooding). Large hail will likely become more of an issue
as the line moves into central and eastern GA during the
afternoon hours with better instability and lapse rates.
Given the aforementioned variables (timing of the precipitation,
cloud coverage ahead of the system and marginal convective
parameters), current thinking is the strongest storms may be right
as the line moves into NW GA and across central/eastern GA later in
Strong gusty winds ahead and just along the front can be expected.
We have placed the far northern counties within a Wind Advisory from
8pm this evening through 4pm Monday. Winds of 15 to 25 MPH with
gusts upwards of 45 MPH at the highest elevations can be expected.
As the front moves out of the area Monday afternoon, clearing will
commence with cooler air moving into the region by the evening.
Winds will also diminish through the overnight hours.
LONG TERM /Tuesday through Sunday/...
No changes have been made to the long term. The location of the
upper low on Friday and Friday night differs a bit between the
ECMWF and the GFS...also the GFS is showing more wrap around
moisture into the state. For now...have left the pops alone for
Friday. Previous discussion follows below.
Previous...130 AM EDT Sun Apr 30 2017
LONG TERM /Monday Night through Saturday/...
Cold front will be exiting the CWFA at the very beginning of the
long term period. High pressure will briefly build across the area
on Tuesday, but begin shifting offshore by early Wednesday as the
next low pressure/frontal system moves into the central US. A second
cold front is expected to impact the CWFA Thursday, with high
pressure building in for the weekend.
Any lingering showers and thunderstorms Monday night should move out
of the area and diminish by early Tuesday morning. A dry period with
near to slightly above normal high temps is expected Tuesday through
Wednesday. Good moisture begins returning on Wednesday ahead of the
next system, but most areas should remain dry through the day
Wednesday. This is a slight change from previous forecasts.
Precip chances begin to increase Wednesday night ahead of the front.
Thursday and Thursday night should be pretty wet with on/off shra
and tsra for most of the period. The models have been pretty
consistent with bringing a line of shra/tsra through on Thursday.
There is definitely some potential for strong to severe
thunderstorms as this system moves through the area. It`s too early
to call what the coverage of storms will be, but instability
parameters and forcing along the front/in the mid levels are lining
up. In addition, the potential for locally heavy rainfall exists.
Cooler temperatures are expected behind the front...and for now...a
pleasant weekend is on tap.
Showers and isolated thunderstorms will continue to move towards
the Atlanta-area TAF sites through late evening, with an overall
diminishing trend. The main concern will be the threat of severe
storms beginning before sunrise, and continuing into the early
afternoon hours. Best time period for storms in the Atlanta area
will be 09-16z, with MVFR cigs/vsbys expected ahead and within the
convection. Quickly improving conditions are expected behind the
line of storms, with VFR after 18z. Expect SW gusty winds through
the day with speeds of 10-15kt and gusts to 25kt. Winds will shift
to the W in the afternoon.
//ATL Confidence...00Z Update...
High Confidence on wind speed and direction.
Medium on all other elements.
.PRELIMINARY POINT TEMPS/POPS...
Athens 68 75 53 78 / 50 70 10 5
Atlanta 66 74 55 78 / 70 70 10 5
Blairsville 63 70 48 72 / 70 70 10 5
Cartersville 63 75 51 77 / 70 70 10 5
Columbus 68 77 55 82 / 70 70 10 5
Gainesville 66 73 53 76 / 70 70 10 5
Macon 69 77 52 82 / 40 60 20 5
Rome 62 75 51 78 / 70 70 5 5
Peachtree City 65 75 51 79 / 70 70 10 5
Vidalia 70 84 57 83 / 30 60 30 10
Wind Advisory until 4 PM EDT Monday for the following zones: