Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
645 am EST sun Feb 1 2015
Previous discussion... /issued 413 am EST sun Feb 1 2015/
.Light snow remains possible for mountains but accumulations
.Thunderstorms now possible western and southern sections
Short term /today through Monday/...
high pressure now centered just offshore the Carolinas allowing
for a return flow over the local area. Thus far this has only
resulted in a slight increase in low level moisture and not low
clouds. Instead...middle and upper levels continue to dominate with
abundant cloud cover the result of a strong southern branch to the
jet from the eastern Pacific through Mexico and Texas and into the
deep south. Have been seeing returns on regional radar pretty much
all night but nothing reaching the ground dewpoints remaining in
the 20s to lower 30s at best across the area.
For today...impulse in middle level flow for the northern sections
will act to moisten the atmosphere below but at least through middle
morning expect continued virga from a mainly middle cloud deck. More
substantial impulse moves in from Alabama this afternoon and by
this time all areas will be conducive to seeing light rain as
dewpoints rise into the lower to middle 40s. Between 18z and
00z...continued moisture increase and lift from embedded
shortwaves in mean flow...not to mention adiabatic Omega
influences is enough to warrant categorical probability of precipitation in the grids.
With further northward progression of synoptic features with this
system the past few days...seeing locally a response in the surge
of dewpoints late this evening into the overnight hours. Now
seeing middle 50s to around 60 degree values moving all the way up to
Rome and extending across the metropolitan and all of middle Georgia.
Given abundance of cloud cover and precipitation...not sure how much
actual surface cape we will be able to generate but strong
isentropic flow may be able to allow for at least some elevated
convection and have added thunder to a good portion of the area
with this issuance. Further south from Columbus to Macon...higher
likelihood of surface based instability but should be weak in
nature. 925mb winds increase to 45 to 50 kts Sun night into Monday
morning over these same areas so concerned there could be some
strong damaging winds over these areas despite the apparent lack
of instability. Will need to be watched closely as helicity values
are also sufficient for an isolated spinup ahead of the main line
should enhanced instability be realized.
With the system further north...we also see that the snow
potential has decreased with this run. There is still an
opportunity for much of the higher elevations to see a brief
switchover and for some accumulating snow over the NE
mountains...but chances and amounts are less. Will generally go
with a half an inch or less over the higher elevations of the NE
mountains for now but cannot completely rule out isolated higher
amounts at the highest peaks. Of more concern is the rapid drop in
temperatures as precipitation exits. Brasstown Bald model Cobb shows temperatures
dropping from 44 to 25 in just 2 hours as precipitation hangs on. Feel
this could be the case across much of the extreme northern tier
higher elevations and black ice will once again be of concern.
Winds will help as they gust all night so should be a fairly short
lived event for most.
Long term /Monday night through Saturday/...
following the active short term period...high pressure returns to
the area Tuesday. Models continue to delay the onset of the
precipitation Wednesday...and have largely backed off on
introducing probability of precipitation to the area until late Wednesday. European model (ecmwf) and GFS
solutions continue to flip-flop and so have tried to avoid siding
with one model or the other...and have gone with more of an
overall blend...trending towards the previous forecast.
Temperatures Thursday and Friday mornings will be cold enough to
support wintry precipitation as moisture remains across the state. For
now...Thursday morning chances look to be isolated to the north
Georgia mountains...while Friday morning chances extend a wintry
mix into the Atlanta metropolitan area. Uncertainty with this system is
still very high and expect this forecast to change somewhat as middle
12z update... tranquil start to the taf period but things will
changing quickly ahead of the next approaching cold front. Low
level moisture will be the first thing on the increase with MVFR
deck moving in from south to north through middle morning so
affecting mcn and csg first and then the atl sites. -Ra and IFR
ceilings in the offing for the afternoon with visibility dropping as well to
around 2sm at most sites. Winds shift with front getting nearer
around 05z to the SW and increasing to 12 kts with low end gusts
possible as well.
//Atl confidence...12z update...
medium on MVFR ceiling timing.
High on remaining elements.
Preliminary point temps/pops...
Athens 57 46 47 25 / 40 100 40 0
Atlanta 56 41 42 27 / 70 100 40 0
Blairsville 46 36 39 22 / 70 100 40 0
Cartersville 55 39 41 23 / 80 100 30 0
Columbus 63 47 48 28 / 60 100 20 0
Gainesville 51 41 43 26 / 70 100 40 0
Macon 65 51 52 26 / 30 90 40 0
Rome 54 38 41 22 / 80 100 20 0
Peachtree City 59 43 45 24 / 60 100 30 0
Vidalia 67 54 57 32 / 20 60 40 5