Johns Creek, Georgia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

688
FXUS62 KFFC 101947
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
247 PM EST Sun Nov 10 2024



...Afternoon Area Forecast Discussion...

.SHORT TERM...
(This afternoon through Monday)
Issued at 244 PM EST Sun Nov 10 2024

Surface analysis shows a strong wedge in place across much of the
state. Precipitation in the form of light rain and drizzle has
fallen into the wedge this morning and early afternoon, helping to
reinforce it. With isentropic lift continuing to occur up and over
the wedge overnight, do not think much erosion will occur. In
addition, the BL winds will remain weak - another indication that
little, if any erosion will occur. Have had to blend in any cooler
guidance available use some manual adjustment downwards to get temps
anywhere near what is actually occurring. Did the same for overnight,
keeping most temps holding steady. A little fluctuation is possible
across the very southern tier of zones.

Also, have had to adjust the pops upwards for the areas of light
rain currently depicted on the radar. Pops for the first couple of
hours in the evening will be a bit higher than guidance to continue
depicting the high pop/low QPF pattern. Do think the light rain and
drizzle will become more patchy during the evening, but it will
continue into the overnight hours.

A frontal boundary will approach the NW portions of the state early
tomorrow morning. A weak line of shra/isold thunderstorms will be
possible across the northern CWA. Models do weaken any line of
shra/tsra as it approaches the metro area. (Any mid level forcing
moves well off to the north.) This seems reasonable and have trended
pops accordingly. However, will keep some small pops in the forecast
until the front clears the CWA.

Models are also indicating some potential for dense fog overnight.
There is definitely some potential, but could be inhibited by any
showers. Precip falling could temporarily improve any low vsbys.

NListemaa

&&

.LONG TERM...
(Tuesday morning through next Saturday)
Issued at 244 PM EST Sun Nov 10 2024

Key Messages:

  - Temperatures run 5-10 degrees above average for November on
    Tuesday.

  - Next shot of rain will be Wednesday night into Thursday. Models
    are some disagreement on amounts and extent. See below for a fun
    dive into the why and what it means.

  - Weekend looks to be a pleasant fall weekend with a
    little above average temperatures.

Forecast:

Long term picks up Tuesday with surface high pressure beginning to
slide into the area behind our current rain maker. No real
connection this far south with any true Arctic airmass with this
system (at least that hasn`t been heavily modified over time), so
the dropping dew points and sunshine will allow for temperatures to
be 5-10 degrees above average during the day. The core of this
surface high slides into the northeast and eastern Canada by
Wednesday. While it is pretty far to the north, the high is pretty
potent with forecast values in models approach 1040 mb in some
cases. Models are now in almost complete agreement on seeing a cold
air dam/wedge move into the area. Forecast highs continue to be
adjusted down in response, with most of north Georgia barely getting
into the 60s (and this may need even further refining given the
typical trends with these).

From this point, things get a bit more complicated. All guidance has
a few key features in place - the strong surface high over the
northeast, a strong shortwave moving through the Great Plains into
the midwest and Great Lakes, a remnant "slug" of tropical moisture
left over from Rafael, and a cut off low spinning over the northern
Atlantic. How all this interacts will have some big consequences on
the precipitation forecast. The surface high looks to be pretty
locked in place thanks to the cut off low remaining in place
Wednesday into Thursday across the guidance. This means the wedge is
likely going to hang on into Thursday morning. A surface low and
attendant cold front associated with the shortwave moving across the
midwest should be moving into the CWA overnight Wednesday into
Thursday as well. This feature looks to be a big part of the
differences across models, where the GFS suite is actually now a bit
different compared to other ensemble and deterministic guidance.

The GFS is a bit further north and less "sharp" with the shortwave
as it moves across the CONUS. This has big implications in a few
ways - first, better forcing remains to the north of the CWA,
limiting rainfall to what can be generated by isentropic processes
as moisture is brought over the top of the wedge and the front
moves in. Next, the front is positioned a bit more poleward and
more aligned with the zonal flow compared to other models,
limiting the forward movement and moisture pooling, weakening the
temperature gradient, and generally making lift a bit more
difficult. Last is where the remnants of the tropical system in
the Gulf matter - the GFS/GEFS doesn`t seem to tap into the
leftover moisture from that system as well as the other models.
Put all of this together, and the GFS is definitely much drier
than what some other models and ensembles are showing.

As for the forecast grids, have upped PoPs a bit compared to the
previous forecast, and if the trend continues, expect to see it
happen again into the future. Also linger them a bit longer into
Thursday, especially into eastern Georgia to account for a system
that may push a bit further into the CWA compared to previous
forecast output. Current forecast amounts are in the half and inch
to inch range across the CWA, though these amounts could increase a
little bit if confidence continues to increase in a non-GFS
solution. Not expecting huge increases that would lead to flooding
or anything like that. Thunderstorm chances with this look very low.

After this, surface high pressure should slide in for the weekend.
This will keep us dry. Friday looks to be pretty seasonable overall,
with highs in the mid 60s across the north to near or just above 70
in central Georgia. Lows will fall into the 40s areawide. Going into
the weekend we see a very gradual warmup, with highs increasing only
a few degrees each day, which will put us just a bit above average.
Skies look to be clear, so may be a nice fall weekend to enjoy,
especially with winter just around the corner.

Lusk

&&

.AVIATION...
(18Z TAFS)
Issued at 1149 AM EST Sun Nov 10 2024

IFR/LIFR cigs likely for the remainder of the afternoon. Values
could bounce between 005-006 for the next several hours. Closer to
sunset, do think the cigs should drop to around 004 then go 003
for the overnight hours. Vsbys should oscillate between 2-5sm for
the remainder of the afternoon. Lower vsbys are expected overnight,
with some patchy fog less than a mile possible. Gradual
improvement in the cigs/vsbys by mid to late morning Monday.
Winds should shift around to the east around the same time as
cig/vsby improvements occur.

//ATL Confidence...18Z Update...
Med confidence all elements.
NListemaa

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          55  74  49  72 /  50  20   0   0
Atlanta         57  73  52  72 /  30  30   0   0
Blairsville     55  70  43  71 /  60  40   0   0
Cartersville    57  74  47  73 /  60  40   0   0
Columbus        65  79  56  77 /  30  20  10   0
Gainesville     53  73  50  71 /  40  40   0   0
Macon           62  78  54  75 /  40  20  10   0
Rome            58  75  47  72 /  80  40   0   0
Peachtree City  58  75  50  73 /  30  20  10   0
Vidalia         65  80  59  77 /  60  20  10   0

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...NListemaa
LONG TERM....Lusk
AVIATION...NListemaa