textproduct: Raleigh

WHAT HAS CHANGED

As of 200 AM Saturday...

* Increasing chances for light rain in most areas of central NC today

* High confidence in widespread rain late tonight through midday Sun, with perhaps a brief changeover to snow in our far NE zones Sun evening.

KEY MESSAGES

As of 200 AM Saturday...

1) Widespread very light to light rain is expected through early afternoon with localized areas of moderate rain possible.

2) Widespread rain late tonight into midday Sunday, followed by a brief changeover to some snow in the far NE sections of central NC early Sunday evening.

3) Strong and gusty winds Sunday evening and Monday morning through Monday afternoon between 30 and 45 mph.

4) Temperatures look to rise above normal on Wednesday, until a frontal system late week looks to drop temperatures back to near normal.

DISCUSSION

As of 200 AM Saturday...

KEY MESSAGE 1... Widespread very light to light rain is expected through early afternoon with localized areas of moderate rain possible.

A dryline is slowly working its way southeastward through the forecast area with surface dew points in the 20s to 30s in its wake and 50s to 60s to its east. This will prime the forecast area to develop an insitu CAD as light to moderate rain diabatically cools the boundary layer. Primary forcing mechanism will be a shallow sloping boundary over NC with the primary surface baroclinic boundary draped across southeast TX, through the Southeast, and off the SC coast. Moderate moist-isentropic ascent along the 295-305K surface (roughly 800-650mb layer) will promote scattered to widespread light rain. The HRRR and the REFS members have thus far been handling the ongoing rain over the TN Valley the best and would result in trace amounts to 0.2" in most locations. Localized moderate precipitation with locally enhanced rain-rates from perturbations within the moist west-southwesterly flow aloft may result in a narrow corridor of up to 0.5".

High temperatures today will have a high bust potential with a 10-15 degree range between the 10-90th percentile from the latest run of the blend of models. Latest official forecast ranges from mid 50s to mid 60s (NE to south and west).

KEY MESSAGE 2... Widespread rain late tonight into midday Sunday, followed by a brief changeover to some snow in the far NE sections of central NC early Sunday evening.

A vigorous storm system is set to develop tonight through Sun and bring unsettled weather to the region. A pair of shortwaves seen on water vapor imagery, one presently over MT and another over western KS, will merge and deepen to a vigorous upper-low over the lower OH valley and southern Mid-Atlantic region Sun into Sun night, before rapidly deepening further offshore of the Mid-Atlantic Mon morning and afternoon. At the surface, model and ensemble/AI guidance are in pretty good agreement that a surface low will develop along the stalled frontal zone off the NC coast Sun morning and rapidly deepen Sun night into Monday to perhaps sub-970 mb.

Impressive height falls and DPVA along and ahead of the deepening trough will aid widespread rain starting mainly late tonight into about mid/late morning to early afternoon Sun. Isentropic ascent and some divergence with a jet streak in VA should allow for precipitation to blossom late tonight, especially after midnight. As the upper low digs into SW VA and western NC Sun afternoon, a dry slot will overspread most of central NC. As such, rain may come to an end briefly by the mid to late morning hours, earliest across the west. However, once the upper-low tracks further ESE along the VA/NC border early Sun evening, a wrap-around deformation band is expected to develop for areas mainly along and east of the Triangle, roughly between 2 and 8 pm. The high-res HREF depicts this quite well based on the synoptic pattern. Expected precipitation amounts based on high-res and ensemble guidance ranges from 0.3 to 0.6 inches via the median from west to east, to upwards of 0.75 inches in the NE Piedmont and northern Coastal Plain. High end amounts are up to an inch, again highest in our NE counties, with low-end amounts in our western zones of 0.2 to 0.4 inches of liquid.

As the deformation band develops over our NE zones, there will be a narrow, roughly 3-5 hour window, when precipitation will overlap with strong cold advection. At this time, temperature profiles in our NE zones will support a period of sloppy wet snow on the tail end of the event, mainly between 3 and 7 pm. Given the vigorous nature to the system, it is not out of the realm of possibility that a light accumulation of snow could occur by Sunday evening before exiting. Wet bulb temperatures appear to only get into the middle 30s, but precip rates could overcome this to favor a light accumulation mainly on elevated/grassy surfaces. The favored area for this would be Norlina to Enfield to Scotland Neck and NE to Halifax and Roanoke Rapids. The LREF probabilities of a dusting is 50-60 percent in this region and about 30-40 percent for a half inch of snow. Again, marginal wet-bulb temps and warm ground would limit impacts, but certainly reduced visibilities are possible. All precipitation comes to an end Sun night as lows tumble into the upper 20s to around 30 degrees.

KEY MESSAGE 3... Strong and gusty winds Sunday evening and Monday morning through Monday afternoon between 30 and 45 mph

As the surface low deepens off the coast Sunday night and Monday, strong cold advection will combine with a tightened pressure gradient and strong winds in the low-levels of 30-50 kt. WNW winds Sun evening will be quite brisk between 35 and 45 mph, strongest during the mid to late evening hours. These gusts could briefly reach Wind Advisory criteria for portions of the area. Winds may slack off a tad overnight into Mon morning, but pick back up again Mon afternoon as the flow continues to remain elevated. Gusts on Mon could range from 25-35 mph, before tapering off Monday night as cold high pressure settles into the region. Our highs Mon and Tue will be some 10-12 degrees below normal in the 40s, with lows Mon night well into the 20s for most areas. Depending on how much rain falls, the gusty winds, low RH dipping into the upper 20s could favor a slight fire danger Mon afternoon.

KEY MESSAGE 4... Temperatures look to rise above normal on Wednesday, until a frontal system late week looks to drop temperatures back to near normal.

Temperatures are expected to jump back above normal on Wednesday as surface high pressure shifts off the southeast coast, allowing surface winds to shift to southerly over central NC. This should allow maximum temperatures to jump back into the mid 50s to low 60s Wednesday afternoon and increase further on Thursday into the low to upper 60s. This is up to 10 degrees above normal for this time of year. The next chance for rain will be Thursday into Friday as a cold front looks to move through the region. Continued high model spread leads to low confidence in the timing of rain and rainfall totals. However, ensemble guidance is showing overall low rainfall totals, with the 50th percentile of the GEFS showing less than 0.1 inch of rain over the region and the European ensemble showing between 0.25-0.5 inch of rain. Regardless of rain amounts, the front looks to bring temperatures back near or slightly above normal on Friday as high pressure starts to build back in over the region.

AVIATION /11Z SATURDAY THROUGH WEDNESDAY/

As of 610 AM Saturday...

Mid-level generated rain and associated cloud layer will continue to spread eastward across the forecast area this morning. Expect mostly likely rain with VFR vsby, but brief reduction to MVFR will be possible at nearly all terminals; prob30s and tempos were used to capture the most likely timing. Onset timing of sub-VFR cigs is highly uncertain and could be as early as after the cessation of precipitation at the northern terminals. Opted for a more optimistic forecast with the 12z forecast and introduced IFR flight category when the more steady light/moderate rain is also expected, mainly after 06z.

Outlook: Towards sunrise, a northwest wind shift will develop as an area of low pressure rapidly deepens off the NC coast, initially affecting the Triad terminals. This wind shift will not only bring marginally gusty winds, but should act to improve conditions to at least MVFR. A return to VFR is expected from west to east Sun afternoon through the late evening. As low-level clouds clear, northwest winds are expected to increase after 18z to 25-35 kts and continue until around midnight. Post frontal low-level turbulence is expected even after surface gustiness ceases. Wind gusts increases once again on Mon when light to moderate low-level turbulence is likely. VFR conditions are likely through Wed.

RAH WATCHES/WARNINGS/ADVISORIES

None.