Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 300744
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
335 AM EDT Sun Apr 30 2017

.SYNOPSIS...
Bermuda high pressure will extend across the Southeastern states
today. A cold front will approach the Appalachians tonight, then
cross the region late Monday afternoon through Monday evening. Warm
high pressure will build in from the southwest Tuesday through
Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 320 AM Sunday...

Little change required to the near term forecast.

Another warm day in store for much of central NC though high
temperatures will average about 3 degrees cooler compared to highs
observed on Saturday. The slightly lower max temps can be attributed
to the potential for morning stratus to linger longer than Saturday,
reducing the amount of insolation for the first part of the day,
especially across the Piedmont, and to a weakening of the mid-upper
level ridge. Highs should range from the lower 80s across the nw
Piedmont to the mid-upper 80s elsewhere. While an isolated shower
cannot be ruled out, primarily across the western Piedmont, coverage
expected to be too limited to mention a PoP at this time.

A mature cyclone over the central U.S. will lift slowly newd
tonight. The approach of this system coupled with an area of high
pressure anchored offshore will tighten the pressure gradient over
central NC, especially after 06Z, resulting in a steady sly sfc wind
overnight. This sly flow will maintain a warm moist low level air
mass, leading to the development of a low cloud deck overnight. The
cloud cover along with a steady sly flow will maintain warm
overnight temperatures in the mid-upper 60s.

&&

.SHORT TERM /Monday and Monday night/...
As of 335 AM Sunday...

A cold front associated with the mature cyclone lifting newd across
the upper Midwest Monday will approach from the west late in the day
and cross central NC late Monday night. The air mass ahead of the
front will become convectively unstable with MLCAPE values off of
the GFS in the 500-1000J/Kg range (and this model is typically too
stable in this type of set-up). Meanwhile adequate shear for
organized convection will be in place thanks to a low level jet
around 40-45kts crossing overhead Monday afternoon. The latest
convective allowing models suggest isolated-scattered
showers/isolated t-storms crossing the Piedmont late Monday morning
through early afternoon, with an increasing threat for a broken line
of organized convection crossing the Piedmont late Monday afternoon-
Monday evening, and into the coastal plain and Sandhills Monday
evening-Monday night. At this time, a few strong/severe storms will
be possible, primarily across the Piedmont due to the favorable
timing of late afternoon when low level instability is maximized.
Appears the main severe weather threats with the stronger storms
will be large hail and damaging straightline winds.

Breezy south-sw winds will occur ahead of the front Monday afternoon
with gusts 25-30 mph probable across the region.

High temperatures Monday dependent upon shower extend in the late
morning-early afternoon and thickness of cloud cover. Feel fairly
confident that locations along and east of highway 1 will reach the
low-0mid 80s due to later arrival of showers. Favor max temps in the
west in the upper 70s-lower 80s though if shower coverage is much
less than expected, high temps 80-84 will be more probable.

Bulk of showers and storms should be east of highway 1 by 03Z, and
exit the coastal plain counties of central NC by 06Z-08Z. Cooler
more stable air will gradually filter into our region after 06Z,
though not likely reaching our eastern periphery until close to
daybreak. May see a 10 degree spread in the overnight temperatures,
ranging from the mid 50s in the west to the low-mid 60s along the I-
95 corridor.

&&

.LONG TERM /Tuesday through Saturday/...
As of 315 AM Saturday...

Tue/Tue night: A strong mid level low will track from the northern
Great Lakes NE over E Canada as it fills Tue/Tue night. The surface
front will be pushing off the NC coast early Tue, with falling lapse
rates, much drier air, and a shift in low to mid level flow to
westerly by Tue night. A very dry and stable column, with weak mild
high pressure building in from the SW, will ensure plenty of
sunshine and good mixing. Thicknesses start out slightly below
normal, countered by strong heating, and expect near-normal highs of
75-81, with a WSW breeze. Passage of a weak mid level perturbation
Tue night should bring some high cloudiness, but otherwise expect
fair skies and lows in the lower-mid 50s.

Wed/Wed night: By midweek, the fairly flat and westerly steering
flow across the SE quarter of the CONUS will give way to a deep
digging longwave trough over the Southern Plains, resulting in a
backing of our mid level flow to SSW and an increased number of weak
waves traversing the area. The most pronounced of these waves moves
NE across W NC Wed night, helping to moisten the column above 600 mb
overnight and foster a trend to mostly cloudy skies west, partly
cloudy east. At the surface, a diffuse frontal zone is expected to
dip southward into the Mid-Atlantic region but stay to our north as
the weak surface high pressure drifts overhead and offshore, keeping
NC within a light mainly southerly flow Wed night. Models continue
to slow the progression of any prefrontal warm advection showers Wed
night, although I still think isentropic and terrain-influenced
upglide is possible near the mountains/foothills Wed night,
resulting from a light but long-fetch low level Atlantic inflow, so
have retained a slight chance of light showers over the far W
Piedmont Wed night. Expect slightly warmer temps Wed, especially S,
with highs of 77-83. Warm lows Sat night with the increase in
clouds, 58-62.

Thu-Sat: The weather becomes much more active, but forecast
confidence in the details plummets. The GFS shows the aforementioned
digging longwave trough cutting off over the mid and lower Miss
Valley then drifting eastward over the Mid South and Gulf/Southeast
states through Sat, before becoming phased with a northern stream
trough and shifting east and offshore as a deeply amplified trough
along the East Coast on Sun. The ECMWF, on the other hand, keeps its
southern stream trough more open and nearly phased with the northern
stream as it progresses more quickly over the E CONUS Thu-Sat. Both
models have vacillated in recent runs between a more closed/slower/
deeper system and more open/faster one, and the GEFS mean is
actually closer to the ECMWF than the GFS, thus confidence is lower
than usual. But both operational models do focus the greatest chance
of showers/storms Thu-Fri, so will place the highest pops then, with
a lower chance Sat with expectations of the longwave trough axis
either shifting overhead or just to our east as we head into the
weekend. The risk of strong to severe storms appears to be greatest
Thu afternoon/evening on the ECMWF and Fri on the GFS, with both
showing DPVA ahead of the trough, focused upper divergence, mid
level height falls, and strong deep layer shear, although potential
instability may be marginal with mid level warming ahead of the
longwave trough. Will monitor and wait for models to come into
better agreement on timing. Expect warm highs in the low 70s to near
80 Thu, trending down to cooler than normal temps for Fri/Sat. -GIH

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 145 AM Sunday...

Widespread IFR/low end MVFR ceilings will develop over central NC
after 08Z and likely persist through much of the morning hours.
Ceilings should lift dissipate in the 15Z-18Z time frame with a
scattered cumulus cloud field highly probable this afternoon. Any
showers that occur will be very isolated and limited to the
Yadkin/Pee Dee River Valley.

Low stratus expected to once again envelope most of central NC after
05Z Monday and linger into the first half of Monday morning. An
approaching cold front will increase the threat for a few showers in
the western Piedmont by late Monday morning. Showers and a few
thunderstorms will increase in coverage across central NC Monday
afternoon and Monday evening as the cold front is in our vicinity.
MVFR ceilings/visibility highly probable in proximity to the heavier
showers and storms. Proceeding the front, sfc winds will be gusty
out of the south-southwest with gusts 25-30 mph probable Monday
afternoon.  The showers and storms should exit the coastal plain
counties of central NC shortly after midnight.

VFR conditions anticipated behind the cold front Tuesday into
Wednesday. Another low pressure system will approach from the west-
southwest by Thursday, increasing the risk for sub VFR ceilings and
scattered showers.


&&

.Climate...

Daily Record High Minimum Temperatures

April 30 /
Greensboro... 64 (1970)
Raleigh.......65 (2014)

May 1 /
Greensboro... 65 (2012)
Raleigh.......67 (2012)

The all time April Monthly Record High Minimum Temperatures

Greensboro... 68 set April 14, 1912 - then tied on April 23, 1920
and April 27, 2011.

Raleigh.......71 set on April 14, 1922 - then tied on April 25,
1925.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...Hartfield
AVIATION...WSS
CLIMATE...Badgett



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