Turner Downs Forecast Discussion

FXUS62 KRAH 230733

Area Forecast Discussion
National Weather Service Raleigh NC
330 AM EDT Tue Apr 23 2019

Weak high pressure will extend across central NC today, then drift
offshore tonight.  A weak cold front will drop into our region late
Wednesday into Wednesday night, then retreat northward as a warm
front Thursday. A cold front will approach from the west late
Thursday, bringing us a good chance of showers and storms on Friday.


As of 313 AM Tuesday...

Main weather story today will be the big warm up. S/w ridging aloft
coupled with a sfc high centered to our south will warm the column
due to the west-southwest flow and associated subsidence. This
warning will result in 850mb temperatures warming 5-6 degrees C
today. This will translate to afternoon temperatures in the low-mid
80s. Expect sunny skies for most of the day with a few strands of
cirrus probable later today, primarily across the northern counties.

Tonight, the s/w ridge will weaken/become broader, backing upper
level winds to a more wly direction and advect high level moisture
into our region. This should lead to increasing mid/high level
clouds, again mostly across the north. A northern stream s/w exiting
the Great Lakes and advancing into New England will drag a sfc cold
front toward the NC/VA border by early Wednesday. The sfc high
drifting east and the approach of the sfc cold front will maintain a
light sly sfc wind through the night. The combination of the light
sfc wind and increasing cloudiness will result in mild overnight
temperatures. Minimum temperatures tonight expected to be in the
upper 50s-lower 60s.


As of 313 AM Tuesday...

Near/short term model has come into better agreement for Wednesday
with the broad mid/upper level ridge maintaining a presence over our
region. This feature and its associated wly flow aloft will cause
the sfc front to lose its southward momentum, causing the front to
slowly drift swd into central NC late Wednesday into Wednesday
night. The GFS has come more in line with the drier ECMWF. Forecast
soundings depict layers of marginal moisture with anemic lift.
Still, cannot rule out the potential for a stray shower or two
during max heating so will retain the slight chance PoPs across the
northern counties though even this minimal PoP may be too high.

The warmth we attain today will continue into Wednesday, though
areas of cloudiness across the northern Piedmont may be opaque
enough to block put the sun at times. This may lead to highs
Wednesday near or slightly below highs reached this afternoon.
Across the remainder of central NC, highs Wednesday will be a degree
or two warmer. Potential for a few places across the south to warm
into the upper 80s.

The sfc front expected to stall across our region Wednesday night.
Weak confluence along this feature will cause low level moisture to
pool, possibly leading to a few pockets of fog or low clouds.
Otherwise, the depth of the moisture and the lift do not appear
sufficient enough to generate precipitation. Continued abnormally
mild with overnight temperatures in the upper 50s-lower 60s.


As of 330 AM Tuesday...

A brief period of mid level ridging early in the work-week will
swiftly transition back into a broad scale troughing regime late
week. This will allow the more progressive northern stream to come
into better sync with southern stream energy progressing east
through the Gulf Coast States. At the surface, Bermuda high pressure
will slide further offshore allowing a weak WAA regime to establish
across the Coastal Plain of the Carolinas with a stalled front
draped near the VA/NC border. This front will return north as
southerly flow strengthens Thursday afternoon, allowing for ample
heating to occur across central NC on Thursday. With 850mb temps
nearing 15 degrees C, have continued to trend afternoon highs up on
Thursday, with middle 80s likely across most of the CWA. Mid to
upper-level clouds will build gradually through the day, with
precipitation chances arriving late Thursday/pre-dawn Friday as a
southern stream disturbance gets a bit agitated and interacts with a
southeastward ejecting northern stream shortwave crossing the Great
Lakes. While the timing of the system (near/around peak heating) and
the presence of decently strong forcing would favor thunderstorm
development, the lack of good instability and less than impressive
shear values should limit thunderstorm development/intensity quite
drastically on Friday afternoon and evening.

Cooler and quieter high pressure settles in on Saturday with a
weaker shortwave trough expected to drag a cold front through
central NC Sunday afternoon/evening, possibly introducing a few
additional showers and storms. Uncertainty grows quite drastically
here, with the GFS model stalling the front over central NC for
several periods early next week, while the ECMWF keeps the boundary
north of central NC, keeping conditions clear and pleasant into
early next work-week.


As of 130 AM Tuesday...

There is a high likelihood that VFR will prevail across central NC
through Wednesday afternoon. The exception will be pockets of MVFR
fog early this morning, primarily across the southern Piedmont and
the Sandhills. Any fog that develop will lift and dissipate by 12Z.
Surface winds through Wednesday afternoon will generally be south
southwest less than 10 knots.

VFR parameters expected through most of the outlook period. A weak
cold front will drop into central NC from the north Wednesday night
then lift back to the north as a warm front Thursday. While
cloudiness and a few showers are possible with the front,
ceilings/visibilities are expected to remain VFR. There is a threat
for sub VFR ceilings late Thursday night into Friday as sly flow
advects moisture into the lower half of the atmosphere, possibly
producing areas of stratus. A cold front approaching from the west
will increase the risk for scattered showers and a few t-storms
Friday. The front should exit our region Friday night with a good
probability that VFR parameters will occur late Friday night into





NWS RAH Office Area Forecast Discussion