textproduct: Raleigh

WHAT HAS CHANGED

As of 220 AM Saturday...

* No significant changes to the weekend storm system, with continued high confidence in light to moderate rain areawide.

KEY MESSAGES

As of 220 AM Saturday...

1) Confidence remains high in widespread and mostly beneficial rainfall this weekend, mainly Sun into early Mon morning, although isolated street flooding is still possible.

2) Temperatures climbing above normal Tuesday through Friday with mostly dry weather this week.

DISCUSSION

As of 220 AM Saturday...

KEY MESSAGE 1... Confidence remains high in widespread and mostly beneficial rainfall this weekend, mainly Sun into early Mon morning, although isolated street flooding is still possible.

Synoptic overview: Models and ensemble systems continue to agree fairly well on the speed and amplitude of the mid level low and shortwave trough now tracking E over the Srn AZ border, taking it E across TX through this evening, into the Mid South and Deep South through Sun evening, and off the Southeast coast Mon. At the surface, high pressure analyzed over the Mid Atlantic and E Carolinas will shift SE off the Carolina coast tonight, setting the stage for in situ cold-air damming development Sun morning as the incoming lift and moisture flux generate precip and a cool stable pool over the Piedmont. Models agree on this surface pattern evolution, featuring a strong primary surface low moving from AR east to AL/GS Sat night to Sun night, then as the CAD/wedge front edges NW into SE sections of central NC, the secondary low will form and deepen along the CAD/wedge front over the eastern Carolinas.

Rainfall: Agreement is quite good among the deterministic models and ensemble members in a solid area of rain spreading in from the W, with forcing for ascent fueled in part by mid level height falls, vigorous upper divergence, and strong/deep moist upglide at 285K- 310K. Moisture should be deep and plentiful, with PW still likely to peak at 225-250% of normal as a plume of high integrated vapor transport spreads from the Gulf NE into NC. The timing of the rain still looks on track, with patchy light rain moving into the western forecast area very late tonight, followed by precip picking up and becoming steady areawide through much of Sun, peaking in the afternoon and evening before a W-to-E departure late Sun night into early Mon, with the early Mon rain chances mainly confined to our E half. Storm total rainfall is still expected to be generally 1-2 inches, with probabilities of storm total amounts over 1" holding at 50%-65% over much of the Piedmont, where the peak moist upglide should occur as the nose of a projected 35-45 kt SSW low level jet focuses along the sloping wedge front and enhances lift. In addition, as dewpoints in the warm sector (SE of the wedge front) are poised to rise into the 50s, we may see pockets of weak surface- based convection that could boost rainfall rates locally, mainly across the SE CWA. Given our current severe to extreme drought conditions and paucity of rainfall across the area lately, this rain will be largely welcome and beneficial. But brief heavier rain rates over more urban or poor drainage areas could still lead to isolated areas of street flooding.

Where this forecast could deviate: If the mid level low remains very strong and tracks well to our S with a preceding band of convection tracking across the Deep South into S GA and FL and off the GA/FL coast, this has the potential to rob NC of the greatest moisture transport and could result in a suppression of the higher rain totals to our S and a reduction in expected rainfall amounts in our area. While this probability is low, we've seen this scenario before, so it will be worth watching for.

Temps: With confidence increasing that we'll be in an in situ CAD event, Sun highs remain a bit lower than most guidance in the NW CWA and slightly higher in the SE CWA. Expect a range from the upper 40s in the NW and near the VA border, to the low 60s SE, with a tight gradient somewhere in between. Further adjustments and refinements to Sun max temps are likely as we get closer to the event. -GIH

KEY MESSAGE 2: Temperatures climbing above normal Tuesday through Friday with mostly dry weather this week.

Weak northwesterly flow aloft will prevail across the area early in the week in the wake of Sunday's departing storm system. However it will gradually become more zonal Tuesday and especially by Wednesday. At the surface, this will translate into high pressure settling over NC, then shifting offshore Wednesday through Friday. Return southerly flow each day will promote a noteworthy warmup with highs easily climbing into the 60s and 70s each afternoon from Tuesday through Friday. Some spots in the Sandhills/southern Coastal Plain could make a run at the mid/upper 70s by the end of the week.

Within the broad zonal flow aloft, a series of fast moving shortwave troughs are forecast to sweep from the Great Lakes into the Mid Atlantic with one wave on Wednesday and another Friday/Saturday. The majority of the 100 member grand ensemble keep these waves and any associated precip well north of NC although a few solutions suggest a stray shower may be possible late in the weekend.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 610 AM Saturday...

Confidence remains high that central NC terminals will have VFR conditions through the next 24 hours, albeit with increasing clouds. Skies will be fair for much of today with just high thin clouds, although a deck of bkn to ovc clouds based at 15-18 thsd ft AGL will spread in from the W starting late afternoon through this evening, with overcast bases dropping to 6-9 thsd ft AGL overnight. No vsby restrictions. Sfc winds will be nearly calm through mid morning, then from the SW at 6-10 kts during the day, and from the S or SSW after nightfall under 5 kts.

Outlook beyond 12z Sun: A W to E trend to sub-VFR conditions is likely Sun morning, with sub-VFR conditions persisting with periods of rain through Sun night. A period of low level wind shear can't be ruled out Sun into Sun evening, mainly at INT/GSO/RDU. Rain should taper off at western terminals late Sun night but may last into mid morning Mon at RWI/FAY. VFR conditions will return late Mon morning, although gusty NE winds will hold through the rest of Mon areawide. VFR conditions should prevail from late Mon through Wed. -GIH

RAH WATCHES/WARNINGS/ADVISORIES

None.