textproduct: Raleigh

WHAT HAS CHANGED

* Continued downward trend in rain chances Sunday night/Monday, but increasing confidence in some rain mid to late next week.

KEY MESSAGES

As of 250 PM Thursday...

1) Well-above-normal temperatures expected on Friday.

2) Very light, non-accumulating rain, is possible Sunday night into Monday. There is a much better chance for accumulating rainfall from mid to late next week.

DISCUSSION

As of 250 PM Thursday...

KEY MESSAGE 1... Well-above-normal temperatures expected on Friday.

Ridging aloft will briefly build over the Midwest on Friday ahead of a shortwave moving through the SW US. A backdoor sold front will be to our north and poised to push through the area Friday night with cool high pressure to follow. Ahead of the front and downstream of the ridging, thicknesses are correspondingly forecast to rise 20m from thus morning to Friday morning, suggesting upper 70s to lower 80s. Most MOS is a degree or two higher than the NBM, and will leave toward MOS in a slightly amplified pattern, with highs of 80- 83. These values were 10-15 degrees above normal but 2-3 degrees below record values.

KEY MESSAGE 2... Very light, non-accumulating rain, is possible Sunday night into Monday. There is a much better chance for accumulating rainfall from mid to late next week.

A shortwave associated with the remnants of Tropical Storm Vance which is currently just south of Baja California will amplify as it moves NE into the Southern Plains on Saturday, then track into the Southeast US on Sunday/Monday. While it will result in widespread mid-level cloud cover during this time, by the time the system gets this far east, any precipitation looks to have a hard time reaching the ground. This is due to fairly dry air in the low levels from surface high pressure extending down the Eastern Seaboard behind Friday night's cold frontal passage. Deterministic and ensemble guidance has trended to a mostly dry solution, keeping the deeper moisture pinned to near the Gulf Coast and FL. Only about 10-20% of ECM/GFS/CMC ensemble members depict any measurable precipitation over central NC on Sunday night/Monday, and the ones that do are very light. So POPs have again trended downward and are now below the slight chance range.

Meanwhile, a deep mid/upper trough is forecast to progress from the Western US on Sunday to the MS Valley on Wednesday and Thursday, likely closing off into a low as it does so. At the surface, a cyclone will develop and deepen over the Central Plains as a weaker secondary low potentially develops over the Southern Plains and lower MS Valley. An associated strong cold front will move east across these areas as well. As the high to our NE moves away during this time, it will be replaced by deep moist southerly flow ahead of the aforementioned frontal system. The timing and degree of phasing that occurs between the northern and southern stream pieces of energy over the Western US will have a big impact on the timing and strength of the system as it moves east, and that is still highly uncertain at this time. However, ensemble guidance is in much better agreement that we will at least receive some precipitation from mid to late week, particularly on Thursday. Deterministic guidance is generally wetter than the ensembles, but even ensemble means indicate close to an inch of rain is possible on average. Severe weather can't be ruled out given the strong deep-layer flow, but still too early to pinpoint exactly where that will be, and instability looks fairly marginal at this time.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 740 PM Thursday...

24 hour TAF period: While VFR conditions should largely prevail through the next 24 hours, there is still a signal for some shallow LIFR/VLIFR fog, primarily at KRWI, KFAY and perhaps KRDU between 08Z and 14Z Fri. Given the uncertainty have kept vsbys MVFR and cigs sct, but if latest hi-res guidance trends continue those lower restrictions may be noted in the next TAF issuance. Winds should be calm to light and variable through tonight, then become nly around 5 kts Fri aft/eve.

Outlook: A backdoor cold front will bring a more steady northeast wind Friday night into Saturday, with VFR conditions forecast through at least Sunday. There is a slight chance of a shower on Monday.

RAH WATCHES/WARNINGS/ADVISORIES

None.