Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS62 KRAH 240140

National Weather Service Raleigh NC
940 PM EDT Wed Oct 23 2019

Cool and dry high pressure will build across the region through 
Thursday. A storm system will develop across the Deep South late 
Friday and move northeast across the Appalachians over the weekend 
before a cold front approaches the Carolinas from the west on 

As of 940 PM Wednesday...

Surface high pressure centered over southern MS/LS will build across 
the Carolinas tonight under weak height falls behind the departing 
upper trough.  The surface ridge will be centered across the 
northwestern half of the area, and winds have gone calm at most 
locations after sunset.  Strong radiational cooling will support 
lows in the upper 30s and lower 40s, with some mid 30s in rural area 
based local climatology for low-level thicknesses.  Seems like 
another night with a few hours of patchy frost night but not a 
widespread frost warranting an advisory.


As of 255 PM Wednesday...

High pressure will continue to migrate to the northeast on Thursday 
as the subtropical ridge builds a bit off the Southeast US.  The 
local airmass doesn't change much, however, with  the return flow 
induced warm advection low-level holding off until Thursday night 
and H10-H85 thicknesses only increasing about 10m.  Highs clouds 
spreading in from the south should also hold off until after sunset, 
so expect highs to be close to those recorded today given the loss 
of some some downslope component....68-73.

Forecast soundings show increased cloud cover from the south above 
12k ft Thursday night, with lower stratus across the western 
Piedmont late Thursday night, all in repsonse to increased southerly 
flow out ahead of the amplifying trough over the southern plains. 
The NAM is much more aggressive with the stratus, enough so to squeak 
out some drizzle. This seems a bit overdone in the western Piedmont, 
so will just indicate the increasing cloud clover and temps falling 
more rapidly early on and then stabilizing through the night...mid 
40s north to lower 50s south.


As of 350 PM Wednesday...

As noted in previous shifts, forecast confidence during the long term 
period remains below normal although global models are becoming more 
similar for the late week and weekend but significant differences 
arise later in the period during the work week. 

The beginning of the period will feature a deepening central U.S. 
trough that closes off across the OK/TX region on Friday that 
gradually lifts northeast on Saturday and opens up as it moves into 
the Northeast on Sunday. A 592dm subtropical ridge extends into the 
the coastal region of the Southeast on Friday and early Saturday 
before relaxing. Surface cyclogenesis is expected to commence on 
Friday morning along the TX/LA coast with the cyclone moving 
northeast into the western TN and OH Valleys on Saturday and then 
into the Northeast late Sunday. A trailing cold front is expected to 
move across the central Appalachians late Sunday into Monday. NWP 
guidance has become more consistent the evolution of this pattern, 
especially through Sunday with timing and placement differences 
noted in the deterministic models between a faster EC that moves the 
front into central NC Sunday night and a slower GFS that keeps the 
front stalled near the Mountains.  

In terms of sensible weather, the guidance generally paints a similar 
picture into the weekend with the bulk of the precipitation threat 
expected for late Saturday night but especially/mainly on Sunday. Dry 
conditions are expected on Friday as a corridor of enhanced low-level 
moisture and isentropic lift shifts from eastern GA/SC into GA/AL and 
then into the TN and OH valleys by early Saturday. While clouds will 
be on the increase and some mist or sprinkles are possible on Friday 
morning, dry weather is expected. Highs will range in the upper 60s 
to lower 70s with mostly cloudy skies. The upper trough axis 
approaches on Saturday but the best forcing for ascent remains 
across western NC and into the TN/OH valleys. Can't rule out a light 
rain shower in the west or southwest but most locations on Saturday 
should be dry with highs again in the upper 60s to lower 70s. The 
threat of rain showers increases on Saturday night and Sunday as 
heights begin to fall, the surface front approaches and the as the 
warm sector becomes realized. Mainly slight chance PoPs late 
saturday afternoon in the west and across the area Saturday evening 
will increase overnight into the chance (around 50%) on Sunday 
afternoon. Highs on Sunday will be milder even with more cloud cover 
and scattered showers. Highs will range in the 70s. 

The pattern becomes more confused for the Monday through Wednesday 
period as the global models begin to show significant differences. 
Initially guidance differs in the placement and motion of the cold 
front that approaches the region on Sunday into Monday per the EC or 
drops into central NC by early Monday and stalls per the GFS. With 
the upper flow parallel to the front on Monday, don't expect a lot 
of eastward motion. Have included slight to low chance PoPs, 
especially near and south of the frontal zone on Monday into 
Tuesday. Then differences in the upper flow arise. The GFS providing 
a faster arriving short wave trough that moves across the OH Valley 
into the mid Atlantic on Tuesday with a longwave trough axis that 
reaches the East Coast by Wednesday night. Meanwhile the EC has a 
stronger southern stream flow which includes a closed low across the 
four corners region on Monday with a much slower eastward progress 
of the long wave trough which is still progged to be west of the 
Mississippi on Wednesday night. Given the uncertainty have opted to 
follow the WPC guidance which provides limited PoPs for late Monday 
into Tuesday with a slight increase on PoPs and coverage on 
Wednesday. Highs are expected to generally cool through the period 
with highs of 70 to 75 on Monday dropping to the mid 60s to lower 
70s on Wednesday. -Blaes


As of 725 PM Wednesday... 

High confidence of VFR conditions through the TAF period as surface 
high pressure builds across central NC. A shallow layer of moisture 
will advance into the southeastern terminals Thursday afternoon and 
may produce a period of SCT clouds at around 5kft, otherwise skies 
will be mainly clear with just a few wisps of cirrus. Mainly calm 
winds overnight will become light east and southeasterly at 5kts or 
less on Thursday afternoon. 

Outlook: Moisture will increase late Thursday into early Friday with 
some stratus possible at KFAY, KGSO, and KINT along with a veil of 
cirrus clouds across all of central NC. Otherwise, VFR conditions 
are expected into early Saturday. As a storm system develops and 
approaches, increasing clouds are expected on Saturday with 
increasing chances of adverse aviation conditions in showers and 
reduced CIGS and VSBYS late Saturday into Sunday that may continue 
into Monday. 




National Weather Service Glossary of Abbreviations