textproduct: Raleigh

WHAT HAS CHANGED

* The forecast movement of Isaias has stabilized which continues to support in widespread showers increasing from the SW by late Saturday and continue into early Sunday. A few thunderstorms are possible early Sunday. Rapid clearing in the rear of the system is expected Sunday.

* Storm total rainfall amounts have also stabilized and are generally still expected in the range of 1 to 2 inches with locally higher amounts across the Coastal Plain and tucked up against the Blue Ridge foothills into the mountains.

KEY MESSAGES

As of 210 AM Thursday...

1) Above normal temperatures are expected through Friday.

2) The likelihood of unsettled weather and significant rain associated with Isaias continues to increase for late Saturday through early Sunday.

DISCUSSION

As of 210 AM Thursday...

KEY MESSAGE 1... Above normal temperatures are expected through Friday.

A moisture-starved cold front will move through the region tonight into early Friday. Ahead of the front, weak downslope winds and rising low-level thicknesses will propel afternoon highs some 6-10 degrees above normal in the lower to middle 80s.

Behind the front, cooler high pressure settles in Friday, gradually strengthening into Saturday over the Mid-Atlantic region. Northeast flow tomorrow will promote lower daytime highs but still a few degrees above average in the mid to upper 70s. Dewpoints will be a touch higher today, but drier air works in behind the front Friday for another comfortable afternoon as dewpoints drop into the 40s over most of central NC.

KEY MESSAGE 2... The likelihood of unsettled weather and significant rain associated with Isaias continues to increase for late Saturday through early Sunday. Rapid clearing in the rear of the system Sunday.

Tropical Storm Isaias is forecast to quickly strengthen into a hurricane on Thursday, move ashore on the northern Gulf Coast Friday night near MS/AL/western FL, with the system center turning NNW Saturday and Saturday night. This is a bit west of the previous track forecasts as once the system weakens over land, it will get pulled into the upper low over the mid-MS valley region then. Finally, the remnant low should turn NE through the OH Valley late in the weekend.

The timing of showers for central NC continues to focus on late Saturday into Saturday night and Sunday. We will likely have the large surface high shift east and off the New England coast Saturday night and Sunday as the tropical cyclone weakens to a depression and remnant low. As this occurs, showers are expected over the far southern and western areas that will likely set up a CAD event by Saturday night. A coastal front is expected along the SE US, and this will likely get pulled inland (NW) into SC and far SE NC on Saturday night. Central NC may have to rely on a secondary low pressure to form along this boundary for the most significant rain late Saturday night and Sunday morning. In an interesting twist, the NW Piedmont may again have a minimum in QPF with this event with the expected CAD in that region. The ESE upslope flow into the Blue Ridge should lead to a maximum there. And, the coastal front's secondary low should lead to a maximum of QPF over the Coastal Plain and maybe the eastern Piedmont. Overall, 0.5 to 1 inch storm totals in the NW Piedmont and 1-2 inches elsewhere.

Showers should taper off and end quickly on Sunday with the dry slot and the sinking/downslope flow in the rear of the system as it departs to our N-NE. Sunshine and warmth will likely return later Sunday.

AVIATION /06Z THURSDAY THROUGH MONDAY/

As of 1245 AM Thursday...

Mostly VFR conditions are expected to prevail at the TAF sites through the 24-hour period. The one exception is the potential for shallow ground fog at a few sites, namely INT/RWI and possibly FAY. The last few runs of some high-res guidance, namely the HRRR/RRFS/REFS, suggest this potential. Crossover temperatures are somewhat favorable near the middle 50s at INT, but low temperatures may just be shy of crossover. However, given clear skies, opted to introduce a brief MVFR restriction into Thu morning. We kept the same brief restriction at RWI based on persistence, though crossover temperatures may be somewhat less favorable as earlier shifts noted. Light winds will become west to northwest Thu afternoon at 5-8 kt. A few brief gusts to 15 kt are possible over the Triad terminals.

Outlook: Rain and flight restrictions, and cold air damming, are likely to develop across cntl NC late Sat into Sun. Although there remains timing/duration uncertainty of those impacts, the heaviest rain will probably taper off to lighter rain/mist/drizzle over the Piedmont on Sunday, where cold air damming will be most likely to continue. The CAD regime may be eroded by the passage of a warm/wedge front over parts of especially sern NC, including near FAY, where both a lifting/scattering to VFR and development of convective precipitation will be possible Sunday afternoon. Flight restrictions in CAD may remain over the Piedmont through Mon morning.

RAH WATCHES/WARNINGS/ADVISORIES

None.