Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Raleigh NC
1013 PM EDT Thursday Apr 24 2014

Synopsis...a warm front will push northward Friday morning ahead of
a cold front that will approach the area Friday night...bringing
unsettled weather to the region.


Near term /through Friday night/...
as of 1009 PM Thursday...

As of 2z high pressure has moved off of the NC coast and winds have
gone calm across much of the County Warning Area. In addition dewpoint recovery has
begun with 40s across the area and temperatures dropping into the lower 60s
and upper 50s. As the high moves away and a warm front lingers south
of the area...flow will gradually move from a more southeasterly
direction around the back side of the high to a southwesterly
direction ahead of the approaching cold frontal system that remains
back over the Mississippi Valley at this time. Until then expect
increasing chances of stratus...especially in the west where
moisture advection will arrive more quickly. While some of the
convective allowing models hint at some shower activity prior to
sunrise...confidence in this is very low due to the lack of moisture
at the current time. Any precipitation that does occur would be very
light at best and confined to the southwestern Piedmont. Low temperatures
in the upper 40s to middle 50s NE to SW. Previous discussion follows

Friday: the chances for showers and thunderstorms will increase
through the day Friday...from west to the warm front lifts
northward and a cold front approaches from the west. Models continue
to show good instability of 500-1500 j/kg and shear of 40-50 kts
Friday aft/eve. The Storm Prediction Center has upgraded much of the area to slight risk
for severe storms for tomorrow afternoon...with the main threats
expected to be hail and locally damaging winds. An isolated tornado
cannot be ruled out...should some differential heating boundaries to
set up early in the day. Forecast instability and cyclonically
curved forecast hodographs...with srh values in the 100-300 m2/s2
range would also support a low tornado threat. Otherwise...expect
southerly winds of 10-15 kts...gusting to around 20 kts and highs in
the middle to upper 70s during the day.

Friday night: as the cold front moves through and nocturnal
stabilization commences after sunset...should see showers and storms
move off to the east and wind speeds decreasing and veering to the
northwest. Clear skies and dry weather are expected by midnight for the
majority of central NC...and lows Friday night will be lowest in the
northwest...upper 40s...and highest where the frontal passage and clearing happen
later...middle 50s.


Short term /Saturday through Sunday night/...
as of 230 PM Thursday...

Forecast pattern during the period will feature a departing northern
stream shortwave trough early Saturday with a secondary trough
moving across the northeast Saturday night. A general northwest flow
aloft persists through the period. At the surface a weak and
progressive area of high pressure moves across the deep south on
Saturday and then off the southeast coast Saturday night as a back
door cold front drops into Virginia and northeast North Carolina
late Saturday night and early Sunday. The back door cold front will
be the main forecast problem during the period.

Guidance is consistent in advertising some great weather on Saturday
with a few periods of high clouds mix with a good deal of sunshine.
High temperatures will range between 78 across the northeast and 82
in the southwest. A light westerly wind at 5 to 10 miles per hour is expected
with a few gusts to 15 miles per hour during middle afternoon. Middle and high level
moisture will increase Saturday night with partly cloudy skies
expected. Lows should range in the lower to middle 50s.

Forecast confidence decreases on Sunday and Sunday night as the
latest set of guidance is a little bit more aggressive in bringing
the backdoor front into at least the northeast part of the on Sunday
County Warning Area. The NAM/GFS/ec all push the front into at least the northern
coastal plain after midnight Monday morning and then linger for most
of the day. Still not ready to fully commit to this scenario but
have lowered temperatures in the northern coastal plain for Sunday and
increased cloud cover a bit. Subsequent shifts will need to monitor
this and the forecast is likely to evolve over the coming days.
Highs are now forecast to range in the lower 70s across the
northeast and near 80 in the southwest. -Blaes


Long term /Monday through Thursday/...
as of 230 PM Thursday...

An unsettled weather period is expected beginning early next
week...likely persisting into the middle/late part of the week as a
blocking pattern sets up across the Continental U.S.. a strong system/cutoff
low that will likely be a big severe weather maker for the central
Continental U.S. Over the weekend/early next week....will slowly move eastward
affecting our area mostly likely starting Tuesday. Due to
significant model spread...there is still a lot to be worked out
with regard to the details of this system...therefore forecast
uncertainty remains high. Overall will continue to ramp up precipitation
chances late Monday... with the best time frame looking to be
Tuesday into Wednesday. Given the strength of the system and time of
year...severe weather and/or heavy rain will be a possibility...
although exactly when is tough to determine right now. Temperatures should
be near to slightly below normal...but will ultimately depend on the
amount/timing of clouds/precip.


Aviation /00z Friday through Tuesday/...
as of 820 PM Wednesday

24 hour taf period: we have high confidence of VFR conditions
continuing this evening into early Friday morning. Increasing
southerly low level flow will increase Friday morning in advance of
a cold front. This will likely lead to some sub-VFR ceilings by daybreak
and possibly some isolated to widely scattered showers along a
northward retreating warm front. The highest confidences in sub-VFR
conditions by around daybreak is expected to be in The Triad region
(kgso/kint)... where IFR/MVFR conditions will be possible (possibly
even brief lifr). Expect any sub-VFR ceilings that form across the area
will improve in a east to west fashion... with kgso/kint possibly
not returning to VFR until after a band of showers/storms cross the
region during the middle to late afternoon. With respect to the potential for
showers and storms... a strong to severe line of showers and storms
is expected to cross the area during the afternoon into the early
evening along and or in advance of a cold front. Sub-VFR conditions
with gusty winds will be possible with any showers/storms Friday
afternoon. Thus... have included a prob30 group for this time frame
to account for the threat. In addition... strengthening southerly to
southwesterly flow in advance of the cold front will allow sustained
winds to increase into the 12 to 20 miles per hour range in the afternoon...
with gusts of up to 25 miles per hour (maybe even 30 miles per hour late in the day)
possible. Expect the band of showers/storms will move to the east of
central NC by early Friday evening (generally by 00z)... with the
main cold front not moving through the area until late evening into
early Saturday morning.

Looking ahead: conditions should improve back to VFR behind the
front Friday night and into Saturday morning. Light winds and VFR
conditions will prevail for the weekend. Unsettled weather will
return again early next week...and will likely linger through middle-


Rah watches/warnings/advisories...



near term...Ellis/kc
short term...jb