Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Peachtree City Georgia
305 PM EDT Thursday Apr 24 2014
Short term /tonight through Friday night/...
models in decent agreement with progression and strength of
shortwave tracking across the Ohio and Tennessee valleys late
tonight into Friday and a relatively weak cold front pushing across
the County Warning Area. Moisture is rather limited and mainly confined to the
northern portion of the area...along with the stronger dynamics.
Best chance for any strong storms will be in the far northwest
portion of the area near 09-12z as consensus among the models
brings about 400 j/kg of MUCAPE coupled with near 25 kts of 0-1km
bulk shear...50-60 kts 0-6km bulk...and helicity of 150-200 in 0-1km
layer. While the shear values are supportive...the main limiting
factor for severe potential is the low instability in the
morning. Cannot rule out a few strong storms with gusty winds and cloud-to-ground
lightning as main threats /timing and coverage also supportive based
on local WRF solution/. While instability increases by Friday
afternoon...the best dynamics and moisture will be on the decrease
so only sparse coverage and slight chance for showers and
thunderstorms will trend into early afternoon across north Georgia and
possible weak redevelopment along the actual front. System should be
on the exit and some clearing occurring by middle afternoon for much of
the area. Quantitative precipitation forecast only about a quarter to third of an inch though higher
amounts possible with any storm development.
For temperatures...went a little higher than guidance based on recent
trends. Looking to have overnight lows about 10 degrees above normal
ahead of front tonight but could be tricky with timing of cloud
coverage. Have included some patchy fog in central Georgia based on
resultant relative humidity values and low end winds.
Long term /Saturday through Thursday/...
extended forecast looks to be on track given the latest model
runs. Have made minor edits through the entire package to refresh
current thinking...generally with slight adjustments to
temperatures...dew points and winds. More significant updates were
made to Monday afternoon through late Tuesday probability of precipitation and quantitative precipitation forecast with
the next big rain maker. GFS continues to advertise seemingly
unrealistic quantitative precipitation forecast amounts...with north Georgia blanketed with
anywhere between 3.5-4.5 inches for the 48-hour period ending
early Wednesday. European model (ecmwf) seems more reasonable...but still holding
on to widespread 1-2 with isolated 3 inch amounts. Have updated
probability of precipitation to show 1.5-2 inch quantitative precipitation forecast across north Georgia and 1-1.5 inches
for middle Georgia for Monday night through early Wednesday. Have
pushed probability of precipitation into the likely category for Tuesday...and modeled
convective available potential energy still look to support likely thunder mention. Previous
discussion is included below.
/issued 405 am EDT Thursday Apr 24 2014/
frontal system that moves through in the short term will exit the
state Friday night as high pressure moves back in from the northwest.
This ridge will bring in a drier airmass and keep north and
central Georgia precipitation free through Sunday night. The next
frontal system to affect the state begins developing as an
unorganized area of low pressure over the Front Range Friday
night. This area of low pressure deepens into a tight closed low
and moves east into the plains states by Monday morning. Its
trailing cold front finally pushes into northwest Georgia Monday night/Tuesday
morning. Instability and moisture increase with the front so
looking for showers and thunderstorms Tuesday and Wednesday. Temperatures
looking more like Summer with highs mainly in the 80s. Lows will
be in the 50s and 60s.
VFR conditions with scattered near 6 kft this afternoon...then ceilings on
increase overnight but staying mainly 4-5 kft with MVFR possible
for most sites 12z-18z Friday as front passes. Best precipitation chances
staying north of the taf sites in early morning as chance too low
to include mention for taf. Winds initially southeast swinging SW after
near 09z Friday with magnitudes increasing to near 10-12 kts
gusting 18-20 kts after 15z Friday.
//Atl confidence...18z update...
medium on ceilings.
High on all else.
Preliminary point temps/pops...
Athens 59 80 52 84 / 20 30 0 5
Atlanta 61 78 55 81 / 20 20 0 5
Blairsville 53 74 45 80 / 60 60 5 5
Cartersville 59 76 49 82 / 30 30 5 5
Columbus 62 80 57 83 / 10 10 0 5
Gainesville 59 76 53 81 / 40 40 5 5
Macon 60 82 54 85 / 10 10 0 5
Rome 58 77 48 85 / 50 30 5 5
Peachtree City 58 79 50 82 / 20 20 0 0
Vidalia 63 85 60 84 / 10 10 0 5