Scientific Forecaster Discussion
fxus62 kffc 182345
Area forecast discussion...updated for aviation
National Weather Service Peachtree City Georgia
735 PM EDT Thu Jul 18 2019
Short term /tonight through Friday night/...
To begin the short term period, a 500 mb longwave trough is
positioned over the Atlantic coast, promoting northwesterly flow
aloft on the backside of the trough. At the surface, a weak surface
trough remains in place into central Georgia. Showers and
thunderstorms are ongoing across the forecast area, focused along a
southeastward moving shortwave embedded within the upper level
northwesterly flow and the surface trough. The highest convective
coverage is currently located near the Atlanta Metro area and on an
east-West Line across central Georgia from near Columbus to Macon.
Additional diurnally driven convection is furthermore possible
throughout the remainder of the afternoon and into the evening.
In typical July fashion, the atmosphere will remain very moist and
unstable through the period. Precipitable water values range from
1.75 to 2 inches this afternoon and will increase to over 2 inches
on Friday. As a result, heavy rain is to be expected with any
convective activity that occurs. Widespread flooding concerns are
not anticipated, but if localized flooding is nonetheless possible
if cells train over the same area or if slow-moving cells remain
over a location for a prolonged amount of time. Furthermore, while
convection will diminish in coverage with the loss of diurnal
heating, the deep moisture could allow for some thunderstorms to
remain well into the night tonight and tomorrow night.
Good instability is in place this afternoon, with MLCAPE
values of 2000-2500 j/kg, along with SBCAPE of 3000-3500 j/kg and
dcape of 750-100 j/kg. While mid-level lapse rates are progged to be
marginal at around 6 to 6.5 c/km , it is possible that the shortwave
dropping southeastward through the area could enhance the lapse
rates higher than anticipated. Mid-level lapse rates are anticipated
to be slightly steeper tomorrow. As a result of these factors, it is
possible that a several storms each day could become strong,
producing gusty winds, frequent lightning, and heavy rainfall. An
isolated severe thunderstorm cannot be ruled out, as well, with
damaging wind gusts being the primary hazard.
High temperatures across central Georgia will be 3-5 degrees above
climatological normals this afternoon, in the upper 90s. Dewpoints
in the upper 60s and low 70s across the area will contribute to heat
index values between 100 and 104 across east and central Georgia,
but it does not appear that heat advisory criteria will be met this
afternoon. Higher coverage of convection and cloud coverage are more
likely to keep temperatures in check across the area tomorrow. High
temperatures tomorrow are thus expected to be near average across
the area, mainly in the low 90s. Dewpoints, however, will also be
higher across the area, leading to heat index values over 100 and
approaching 105 in some areas. These heat indices will need to be
monitored in ensuing forecasts as only a minor increase in
temperatures or dewpoints could lead to heat advisory criteria being
Long term /Saturday through Thursday/...
Guidance has been very consistent over the preceding days, and
therefore, only minor tweeks have been made to the long term
forecast. The previous long term forecast discussion continues to be
valid and is provided below...
Previous discussion... /issued 337 am EDT Thu Jul 18 2019/
The long term portion of the forecast begins late on Friday with
high pressure situated just to the west/northwest of the local area
with an area of lower pressure in the vicinity of the southeast that
will persist through the weekend. Models are showing differences in
location, but overall impacts will be similar through the fist half
of the extended with plenty of moisture in the lower levels of the
atmosphere. This will allow for chances for showers and
thunderstorms daily with the best chances/coverage in the afternoons
and evenings. At this point, have included likely pops across much
of the area on Saturday and chance pops across the area on Sunday
with an area of likely pops across the northern tier. With moisture
continuing to advect into the area, higher coverage of showers and
storms is expected to continue on Monday as well. Likely pops have
been included across the northwestern portions of the area with
chance pops elsewhere.
By late Monday to Tuesday, a front will push into the area
continuing to enhance chances for rainfall across the area and
dropping temperatures to just below seasonal norms. As that front
approaches and enters the area, pwats are expected to rise to around
2 inches increasing the potential for heavy rain. Likely pops have
been included for Monday through Wednesday in the afternoons and
evenings with the highest pops across northern portions of the area
before spreading southward as the days go on.
High temperatures through the weekend are closer to seasonal norms
with cooling trend after the weekend through the first half of the
work week. Overall, high temps are expected to be in the mid-80s to
mid-90s. Overnight low temperatures through the extended will be in
the mid 60s to mid 70s.
convection is on a diminishing trend but could linger for another
few hours. Expect storms should be mostly gone by 06z. VFR expected
through the period with afternoon cumulus developing tomorrow in the
040-050 range. Some scattered MVFR possible toward sunrise mainly
kmcn-kcsg. Winds should stay on the west side throughout...except
light and variable overnight.
//Atl confidence...00z update...
medium confidence on morning MVFR.
High confidence on all other elements.
Preliminary point temps/pops...
Athens 74 93 73 92 / 30 50 40 50
Atlanta 75 91 74 89 / 30 60 40 60
Blairsville 67 86 68 84 / 20 50 30 60
Cartersville 73 91 73 89 / 30 50 30 60
Columbus 76 92 74 91 / 30 60 30 60
Gainesville 73 90 73 88 / 30 50 30 50
Macon 75 94 73 93 / 30 60 40 50
Rome 72 92 73 90 / 30 50 30 60
Peachtree City 74 91 73 90 / 30 60 40 60
Vidalia 75 95 75 94 / 30 50 30 40