textproduct: Raleigh

WHAT HAS CHANGED

As of 1240 AM Monday...

* Thursday is trending drier with increased chances Saturday and Sunday for precipitation.

KEY MESSAGES

As of 1240 AM Monday...

1) Trending warmer by Tuesday with a chance of rain Wednesday

2) High temperatures across central NC will fall back to below average on Thursday and then well below average on Friday.

3) Uncertainty in the evolution weather systems for Friday through Sunday is high, although ensembles suggest precipitation on Friday into Saturday is likely to limited and light with a better signal for a more significant precipitation event on Sunday. Precipitation type is uncertain with a tremendous range in the pattern and locations of cyclogenesis.

DISCUSSION

As of 1240 AM Monday...

Key Message 1: Trending warmer by Tuesday with a chance of rain Wednesday

Early morning satellite imagery and surface obs show quite a bit of cloud cover stretching from the lower Great Lakes across the mountains and into the western Piedmont of NC. While this has managed to keep temps in the lower 30s in those areas this morning, temps elsewhere have had no problem dropping into the 20s, teens, and even lower teens near the NC/VA border.

Today will begin a gradual warmup across the area, although afternoon highs will still be well below normal with highs in the upper 30s in the north and in the low/mid 40s in the south. It's not until the flow aloft becomes more zonal on Tuesday and surface high pressure migrates offshore that we see the real warm advection start in earnest. Look for afternoon highs to range from the upper 50s in the north to the mid 60s across the Sandhills/southern Coastal Plain. These will be some of the warmest temperatures we've seen across the area in nearly a month, although they will be short lived.

Meanwhile, a weak wave will sweep through the area on Wednesday. The overwhelming majority of EC/GFS/Canadian cluster groupings suggest the need for a chance mention of precip across the area Wednesday, with the highest probabilities (30-40 percent) generally along and south of US-64, with lesser values (15-30 percent) to the north. Rainfall amounts should be light, only a few hundredths of an inch, tapering off in the wake of the wave Wednesday night. Even the 90th percentile QPF during this period only looks to be a tenth of an inch or less. Given cloud cover and precip, temps won't be quite as mild although afternoon highs should still be in the mid 50s to mid 60s. Post-frontal cold advection behind this wave will bring about the end of the short lived warmup, with overnight lows Thursday morning bottoming out in the low to mid 30s. At this point it would appear precip should be over and done with well before any sub- freezing temperatures arrive.

Key Message 2: High temperatures across central NC will fall back to below average on Thursday and then well below average on Friday.

Following the passage of a cold front on Wednesday, a colder airmass initially centered over the northern Great Lakes and Ontario will extend into the region for Thursday and persist into Friday and Saturday. Highs on Friday and Saturday are likely to range in the 40s to around 50.

Key Message 3: Uncertainty in the evolution weather systems for Friday through Sunday is high, although ensembles suggest precipitation on Friday into Saturday is likely to limited and light with a better signal for a more significant precipitation event on Sunday. Precipitation type is uncertain with a tremendous range in the pattern and locations of cyclogenesis.

The upper-level pattern on Thursday into Friday will be dominated by a northwest flow that will be dominated by a northern stream short wave likely to dive southeast across the region on Friday into early Saturday bringing a risk of light precipitation. With a weakening area of high pressure to the north and marginal surface temperatures some wintry precipitation is possible, but ensemble probabilities note that QPF amounts for this system would likely range less than a tenth of an inch.

Behind the exiting northern stream short wave, the flow will become more zonal and disturbed with a southern stream trough moving across the Deep South on Saturday and a weaker northern stream. This will likely result a period of dry and fair weather before the next weather system.

As the southern stream upper trough moves east, surface cyclogenesis is expected across the eastern U.S. and Southeast. Examining individual ensemble members shows the surface cyclone positioned on Sunday afternoon all over the place anywhere from MI to the GA coast and with a mix of Miller B and Miller A patterns providing no real confidence in any real forecast details. It appears though that the system on Sunday is apt to be the wettest feature of the week and most impactful. Given a weakening surface high over the Northeast of modest intensity, there is the potential for some CAD but it is unclear how strong and potentially impactful it will be. The airmass across the region appears cold enough at this point for at the potential for at least some short lived wintry precipitation but marginal temperatures and a greater chance of an inland track suggests moderating temperatures would limit the wintry precipitation totals and impact.

One other item of note, given the timing and placement differences in the systems affecting the region on Friday through Sunday, the NBM guidance and our forecast will likely continue to contain a longer period of at least "chance" PoPs through much of this period as PoPs are smeared and smoothed when in reality there will be a period with no precipitation, perhaps on Saturday and not a 3-day washout.

AVIATION /06Z MONDAY THROUGH FRIDAY/

As of 1240 AM Monday...

24 hour TAF period: High confidence in VFR conditions. Some mid level clouds are currently passing near or south of various terminals, and after a period of clearing overnight, additional mid level clouds will stream across the area during the daytime. With high pressure over central North Carolina, winds are currently light and variable, and will eventually take on a southerly component around 5 kt this afternoon.

Outlook: Ground fog could possibly develop around daybreak Tuesday, and there will be a chance of rain and restrictions at all sites on Wednesday. There will be another chance for rain/restrictions on Friday. Other than these three events, dry VFR conditions are expected to prevail.

RAH WATCHES/WARNINGS/ADVISORIES

None.