Area Forecast Discussion
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FXUS62 KRAH 252335
Area Forecast Discussion
National Weather Service Raleigh NC
735 PM EDT TUE OCT 25 2016
Cool high pressure will extend into our region from the north
through Wednesday night, before shifting offshore early Thursday. A
cold front will move into the area from the northwest Thursday night.
.NEAR TERM /through tonight/...
As of 735 PM Tuesday...
Strong high pressure centered well to our north (SW of Hudson Bay)
at 1036+ mb extended south and southeast deep into Florida tonight.
Very dry air was in place over our region and this will be the
case tonight and Wednesday with the high in place. Surface dew points
have come up since sunset a few degrees into the 40s, except 30s NW.
Surface temperatures fall quickly into the lower to mid 50s soon
after sunset and this trend will continue. The only cloudiness
was associated with the stronger mid/upper NW flow aloft extending
from the upper Midwest to the Tennesse and Ohio Valley regions. Most
of these clouds were high clouds and were evaporating as they
encounter the ridging over the eastern seaboard. Any cirrus overnight
should be scattered and thin resulting in no worse than mostly clear
skies. Since winds will go calm the temperatures will fall rapidly
as mentioned above. Some mixing of the dry air just above the
boundary layer will aid in lowering the near surface dew points
as the temperatures fall. Expect lows of 35-42 by daybreak, with
some scattered frost possible in the low-lying areas around
our normally cold spots (including the Roxboro, Louisburg, Rural Hall,
and the Yadkin River valley as well). However, the frost is not expected
to be enough to damage plants/crops that are still yet to be harvested.
A Warning will not be needed at this time. We will add wording in the
Hazardous Weather Outlook to indicate more in the way of mid 30s in the
rural areas of the Piedmont. No other changes at this time.
.SHORT TERM /Wednesday through Thursday night/...
As of 240 PM Tuesday...
The axis of the weak shortwave ridge will shift eastward over the
Southeast states Wed, as the axis of the Canadian-source surface
ridge begins to shift east and off the East Coast. Expect another
mostly sunny day with below-normal thicknesses indicating highs in
the mid-upper 60s. Milder lows expected Wed night as the return flow
around 925-850 mb anticyclones starts to draw low level moisture
into the area, advecting first into the western CWA. Lows from mid
40s NE to upper 40s and around 50 far south and west. A fast-moving
and strengthening shortwave swinging ESE through the Great Lakes and
Northeast Thu/Thu night will help draw a front into NC from the NNW,
likely not arriving until late Thu night. Have low confidence in our
area receiving any significant precip, considering that the
vorticity will be shearing through the mid level trough axis as it
passes through, the upper divergence will be minor and mostly to our
north, and PW is projected slightly lower than what the models
showed yesterday. That said, forecast soundings do show some
marginal instability late in the day into the evening, although
surface dewpoints may not get quite high enough for anything more
than an isolated storm or two. Will stick with low chance pops (20-
35%), higher north and lower south, from mid afternoon through the
evening, with the isolated thunder risk confined to the north. Warm
sector highs Thu in the 70s. Thu night lows in the 50s, as the front
will be delayed until late and may not work much more southward than
the northern sections of NC prior to daybreak Fri. -GIH
.LONG TERM /Friday through Tuesday/...
As of 315 PM Tuesday...
The long term period will feature a generally west to northwesterly
upper level flow which would support dry conditions, fair weather,
and near to above normal temperature regime for the extended range.
A single northern stream short wave trough moves across the Great
Lakes and Northeast late in the weekend with a dry frontal passage
Sunday night. Have adjusted max temperatures upward on Saturday and
more significantly on Sunday as thickness values by 12Z Sunday
morning increase to 1385 to 1390m. Latest ECMWF ensemble guidance
product for RDU has operational maxes on Sat/Sun of 80/83 with
warmest ensemble member on Sunday at 85 an the 50th percentile at
.AVIATION /18Z Tuesday through Sunday/...
As of 145 PM Tuesday...
High confidence in continued VFR conditions through the next 24
hours, as surface high pressure extends into the area from the
north. With deep dry air in place, very few clouds are expected,
primarily confined to high thin clouds spreading in from the
northwest. Surface winds will be light and variable under 6 kts
Looking beyond 18z Wednesday: With one exception, VFR conditions
will remain dominant for the rest of the week and into the weekend.
The exception will be late Wed night through Thu morning, as we get
into a mild flow from the south or southwest which will bring a
period of sub-VFR (likely MVFR, with brief early-morning IFR
possible) stratus, and potentially some daybreak fog. The chance for
MVFR cigs will hold into late Thu afternoon and Thu evening as a few
showers and isolated storms pass through the area ahead of a cool
front pushing in from the north-northwest. MVFR cigs may linger near
FAY through late Thu night. Then, high pressure will build in both
at the surface and aloft, leading to mostly dry weather and VFR
conditions Fri through the weekend. -GIH