Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 310550
Area Forecast Discussion
National Weather Service Raleigh NC
150 AM EDT SUN JUL 31 2016
An upper level trough will cross the Northeast and Mid-Atlantic
states through Monday, and then will slowly drifting offshore by
Wednesday. A cold front will gradually approach our area from
the northwest before stalling over the region early in the work week.
.NEAR TERM /THROUGH TONIGHT/...
As of 930 PM Saturday...
A couple of intense supercells affected the northern CWA earlier
this evening, including one deep cell with tornadic signatures.
While those storms lost strength quickly within poor mid level lapse
rates and other cells stayed rather weak, the environment over the
northeast CWA and all of eastern NC remains supportive of strong
convection for a couple more hours. Favorable factors include
lingering elevated instability with MUCAPE of 1500-2000 J/kg
(although CINH has grown since sunset) and good low level shear (20+
kt 0-1 km), which have helped push the SCP values to 1-2. Upper
divergence, albeit weak, is also providing larger scale support for
lift, and deep layer effective shear is decent at 25-30 kts. Despite
the stabilizing column, we should maintain small elevated
instability through the night, within high PW well over 2.0". Will
hold onto scattered pops east / isolated west for storms for another
couple of hours before trending down to just isolated showers
areawide overnight, a trend indicated by the latest CAM runs. Have
nudged lows upward slightly based on trends and high-res guidance to
Earlier discussion as of 250 PM Saturday: Scattered showers and
tstms have developed as expected across central NC, invof of the
Piedmont trough, and to our west over and just east of the
mountains. Aloft, SW flow persists across our area on the east side
of a broad trough centered over the Ohio and Mississippi valleys.
For the rest of this afternoon into this evening, the aforementioned
showers and tstms will move east across our CWA, but given the
scattered nature, not all locations will see rain, so for now will
keep pops capped at 50%, implying the scattered coverage. As for
storm intensity, latest mesoanalysis shows plenty of instability, esp
from the US-1 corridor eastward, but shear is pretty weak, so look
for mostly pulse storms, with perhaps some modest clustering north
and northeast of Raleigh where the effective shear is the highest in
our CWA. Given the instability, an isolated severe cell (wind or
hail the main threats) can`t be ruled out, but given the weak shear,
any severe cells won`t remain severe very long. Again, the best
chance for a strong or severe cells will be north and northeast of
Raleigh closer to the better shear.
Look for shower/storm activity to wind down around midnight, with the
remainder of the night partly cloudy. With little or no pattern or
airmass change, will lean toward persistence for temps. Low`s
tonight in the mid 70s.
.SHORT TERM /Sunday through Sunday night/...
As of 250 PM Saturday...
Sunday will start off much like today, with PC skies and isolated
showers or sprinkles perhaps lingering on old outflow boundaries.
Like today, isolated-to-scattered showers and tstms are expected to
develop invof of the Piedmont trough during the early-to-mid
afternoon. Then during the early evening, guidance is suggesting
that a broken band of thunderstorms, first having formed over the
mountains, will move east across our CWA. This band of tstms may
have a little better coverage since it will be supported by a
shortwave embedded in the SW flow. That shortwave is currently
moving across the central plains. Despite this upper support, 0-6km
shear is still progged to be aob 25 kt. So once again, most storms
should remain below severe limits, but an isolated severe cell
or two still can`t be ruled out given the instability.
Speaking of instability, temps and dew points on Sunday will be
similar to today, given that the airmass will have changed little.
However, with slightly increased shower/storm coverage, our
confidence of hitting heat advisory criteria in our eastern counties
is not particularly high. For now, will forecast highs in the lower
90s and heat indices around 100. Nevertheless, it will still be
uncomfortably hot, so folks need to continue exercising the heat
precautions that we`ve been advertising.
.LONG TERM /Tuesday through Saturday/...
-- Changed Discussion --As of 145 AM Sunday...
Broad troughing aloft will prevail over the Carolinas and Mid-
Atlantic early next week, transitioning to NW flow aloft mid-week as
an upper level ridge re-strengthens over the lower MS river valley
and Deep South, followed by ridging aloft mid/late next week as the
aforementioned ridge builds E/NE over the Carolinas and Mid-Atlantic.
With the above in mind, expect near normal temperatures early next
week with temperatures rising above normal mid/late week as the
aforementioned ridge builds over the region. With broad troughing
aloft, expect near or above-normal chances for convection becoming
somewhat more ambiguous in NW flow aloft by mid-week, then falling
below normal (dry perhaps) late-week as the ridge builds over the
region. With central NC situated on the southern periphery of the
westerlies and eventually a period of NW flow aloft, a potential for
organized severe weather may exist early to mid-week if small
amplitude waves and/or upstream convection /MCVs/ progress
into/across the region, particularly near peak heating. -Vincent
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.AVIATION /00Z Sunday through Thursday/...
As of 730 PM Saturday...
24-Hour TAF period: Scattered showers and thunderstorms will locally
reduce cigs and vsbys to MVFR or IFR category. Otherwise, expect VFR
conditions and light and variable winds for the rest of the evening
and overnight. Expect variable gusts around 20 kts near storms
and/or thunderstorm outflows. Storms should dissipate after sunset.
Similar conditions will prevail Sunday, with slightly higher chances
for showers/storms resulting in gusty winds and locally reduced cigs
Looking ahead: Similar conditions through Tuesday with scattered
afternoon/evening tstms and associated reduced flight conditions.
Patchy morning fog possible as well. During the mid-week period, we
may see decreased daily shower/storm chances as slightly drier air
moves in the from the north. -NP