FXUS62 KRAH 020728

Area Forecast Discussion
National Weather Service Raleigh NC
326 AM EDT SAT JUL 2 2016

A frontal boundary will become nearly stationary over central NC
Saturday through Monday.


As of 325 AM Saturday...

Today: Convection has developed this morning along a s/w disturbance
moving across the area in advance of a southward moving cold front.
While we do not anticipate any severe storms from this activity we
will see some heavy rain and gusty winds of up to 30 to 40 mph,
primarily across the Northeast Piedmont. The last few runs of the
HRRR and other hi-res guidance shows this activity decreasing in
coverage and intensity within a couple of hours though. However,
wherever this broken line finally falls apart we may see a lingering
outflow boundary that could along with a southward sinking weak cold
front serve as a focus for convective develop late this morning into
the afternoon today. The latest ARW and NNM show convection
developing across the southern half of our area by early to mid
afternoon today, then spreading via many outflow boundaries across
the CWA. With regard to a severe threat, the latest guidance
continues to show the best instability today across the southern
half of the area, with up to 1500-2000 J/KG of MLCAPE. However, the
best deep layer shear is expected to be across northern portions of
the area closer to the NC/VA border as the sub-tropical mid level
ridge ever so slightly nudges northward across the area. Thus, the
day 1 SPC convective outlook has all of central NC in a marginal
risk for severe storms today, with the main threat from damaging
wind gusts and marginally severe hail with the strongest storms.

More of a concern today may be from the potential for heavy rain
with scattered to numerous showers and storms expected by late this
afternoon into the evening as a weak surface front stalls across the
area, generally oriented from west to east and parallel to the
mid/upper level flow, along with PW`s of around 2 inches. While
widespread flash flooding is not expected due to the convective
nature of the showers and storms, we could see some training of
storms today and a localized flooding through, especially across
urban and poor drainage areas.

High temps today are expected to range from the mid to upper 80s
north to the lower 90s south.

Tonight: With the aforementioned stalled frontal zone across the area
tonight and the potential for weak disturbance aloft to track across
the area in the westerly flow, expect continued chances for periods
of showers and storms areawide (with the best chances perhaps across
the east/northeastern portion of the area). Low temps are expected
to range from the upper 60s north to the lower to mid 70s south.


As of 325 PM Friday...

Precip chances start to increase late Sat into Sat night. The
frontal zone is expected to sink a bit south and east across our
northern and western sections and sharpen up as mid level shortwave
energy streaks from the Midwest eastward across the OH valley and
mid-Atlantic region. This will provide a focus for pooling of low
level moisture over NC, with strengthening 925 mb moisture transport
and rising PW projected to peak at 1.8-2.0" Sat night. Deep layer
bulk shear will be increasing to 25-35 kts (best north) with the
southern edge of the westerlies just to our north, but mid level
lapse rates will be quite poor especially across the north, which
will greatly limit CAPE values and reduce the threat of strong or
severe storms particularly across the northern half. PW continues to
increase on most models Sat night especially along and just south of
the surface frontal zone, while shortwave energy zipping by just to
our north may provide a shot of weak but important dynamic lift over
the far northern CWA. Persistent storm clusters and training cells
should boost the threat for locally heavy rains and potential for
urban and small stream flooding as we head through late Sat and Sat
night. Will top out pops in the 50-60% range, mainly from the
Triangle north and east where the best combination of bulk shear,
deep moisture, and low level mass convergence will reside. Expect
highs of 87-93 Sat and lows of 67-73 Sat night. -GIH


As of 210 PM Friday...

Models are still in agreement regarding a frontal zone stalled out
over the area with deep westerly flow aloft that will allow for
several opportunities for convection on Sunday through Tuesday
afternoons during peak heating. CAPE values on some simulations have
come in around 1500 J/Kg or higher in the eastern half of the CWA.
In addition, bulk shear values of 20-30 kts were common with some
time periods coming in about 30 kts. This indicates that when
convection forms there is a chance for severe weather, in the form
of both hail and damaging winds. SPC has a marginal risk at the
moment for day 3 (Sunday). Forecast soundings look very wet through
the column so damaging winds would be in the form of wet
microbursts. With PW values above 2 inches, in the end it might be
the heavy rain threat that is greatest during this time period.
Especially with deep westerly flow aloft, there is a chance for
training of cells which will present a possible flash flood threat.
While all days and locations during this period will carry a threat
for unsettled weather, The best chances for stronger storms will be
in the eastern half of the CWA and the timing when conditions appear
to be best at this point on Sunday and Monday afternoon but the
addition of a 500 mb vort max moving through near the VA border may
add a little more forcing to the equation on Sunday afternoon.
Rainfall totals could easily eclipse a couple of inches if caught
underneath heavy or training thunderstorms. That being said some
places could see no rainfall given the convective nature of the
precipitation. It will continue to be warm with high temperatures in
the mid 80s Sunday and Monday and rising into the low 90s for
Tuesday afternoon.

After tuesday the deterministic models are a bit more low confidence
in that the GFS pushes the frontal zone through the area, keeping us
cooler, drier and more stable. On the other hand the ECMWF keeps the
front over the area and central NC in the warm, moist, unstable
atmosphere. At this time, trends have been to favor the ECMWF so
will keep pops in the forecast but will hedge a little drier than
previously forecast. Friday may be the driest day of the long term.
Temperature wise, with the ECMWF solution, highs will stay in the
low 90s but if the GFS solution becomes more favorable then
temperatures could turn out to be cooler.


.AVIATION /06Z Saturday through Wednesday/...
As of 230 AM Saturday...

24-hr TAF Period: A broken line of showers and storms are currently
moving across northern portions of central NC this morning, with
KRDU and KRWI having the best chance of seeing some the convection
and associated sub-VFR conditions. Expect the bulk of this
convection to be over by around 10-12Z or so. Otherwise, expect VFR
conditions will continue this morning outside of a brief period of
MVFR/IFR stratus/fog near daybreak. Scattered showers and storms are
expected to develop this afternoon into the evening along/near a
southward sinking cold front. Sub-VFR conditions, gusty wind and
possibly some hail will be possible with any storms that develop.

Looking Ahead: A relatively active upper level pattern will result
in little change in aviation conditions (i.e. similar to previous
days) through mid next week. -Vincent





SHORT TERM...Hartfield

NWS RAH Office Area Forecast Discussion