textproduct: Raleigh

WHAT HAS CHANGED

As of 215 PM Thursday...

* Precipitation chances increased for Sunday, but rainfall amounts remain very low.

KEY MESSAGES

As of 215 PM Thursday...

1) Increased Fire Danger Statement remains in effect through this evening. A fire danger statement may be needed again Friday and Saturday.

2) An early season heat wave continues through Saturday.

3) A cold frontal passage on Sunday will bring scattered showers embedded within a stratiform rain band. Conditions turn cooler early next week with patchy frost possible Monday and Tuesday morning.

DISCUSSION

As of 215 PM Thursday...

KEY MESSAGE 1... Increased Fire Danger Statement remains in effect through this evening. A fire danger statement may likely be needed again Friday and Saturday.

An increased fire danger remains in effect for all of central NC through this evening, due to a combination of gusty winds, RH as low as 20-35 percent, and severe to extreme drought. A lee trough exists in place this afternoon and along with a tighter pressure gradient, is allowing for wind gusts to reach the 20-25 mph range. A few infrequent gusts to 30 mph are also possible. As temperatures climb into the upper 80s NW to low 90s elsewhere and dewpoints mix out into the upper 40s to low 50s, our RH levels will fall into critical territory.

On Friday, although winds are expected to be weaker with the passage of a mid-level shortwave and with a weaker pressure gradient, relative humidity levels will still dip into the 20s in most areas of central NC in a downslope NW flow regime. By Saturday, the pressure gradient tightens again with continued hot weather in the 90s, and another day of RH levels in the 20s. We are currently in coordination with NCFS on the need for a fire danger statement Friday and Saturday, and will follow up if conditions warrant.

KEY MESSAGE 2... An early season heat wave continues through Saturday.

The early season heat will continue through at least Saturday, ahead of a cold front slated to move through Sunday. Highs this afternoon will top out in the lower 90s in most areas under a prominent lee trough and tighter pressure gradient. The low- level thicknesses will approach values similar to Wed around 1418m, typical for July. Record high values today are likely to be tied or broken at GSO/RDU (see climate section for more details).

A shortwave passes overhead on Friday, with 60-70 dm height falls. However, moisture and instability is rather lacking. As such, rainfall chances are limited at best, with the most favored area to see a trace or a few hundredths of an inch of rain over the northern Piedmont to northern Coastal Plain. Mostly, this upper-level wave will bring some mid-level clouds, clearing out by late morning. The airmass is not as hot tomorrow, with thicknesses about 10 m lower. As such, highs may be a tad lower in the upper 80s to around 90, but this is still well above normal.

The hottest day of the stretch may end up being this Saturday as the pressure gradient tightens under a southwest flow, and low- level thicknesses approach 1420-1424 m. Highs in the lower 90s area-wide are expected, again getting close to record highs. Right now, FAY is most favored to break its record high of 93 set in 1941, but GSO/INT are certainly going to get close as well.

KEY MESSAGE 3... A cold frontal passage on Sunday will bring scattered showers embedded within a stratiform rain band. Conditions turn cooler early next week with patchy frost possible Monday and Tuesday morning.

The core of a northern stream trough shifting through the PacNW this afternoon will slide just south of the Hudson Bay Sat night with its trough axis expected to traverse the Mid-Atlantic and Northeast Sun/Sun night. The trailing cold front will be helped across the mountains and into the Carolinas by surface high pressure over the ArkLaTex region as it migrates into the Ohio Valley by Mon morning. The general consensus within the medium range guidance suggests the front will progress across central NC Sun morning into the early afternoon, which would be diurnally unfavorable for showers/storms without any elevated instability and stable/dry preceding air mass over the Carolinas. The bulk of the precip appears to come from anafrontal rain on the immediate backside of the front where low-lvl FGEN and 60m H5 height falls in 12 hrs overlap a narrow band of enhanced deep-layer moisture. Even so, disjointed lift and low resonance time over a given area will keep precip amount pretty meager (trace to 0.25").

Low-lvl thicknesses behind the front plummet nearly 100m and bring noticeably cooler and slightly below normal temperatures, a relief from the multiple days of unseasonably warm conditions. A weakening pressure gradient and clearing skies Mon morning may bring some patchy frost, mainly in isolated locations of the eastern Piedmont. A better chance for patchy to areas of frost will likely come on Tues morning with the surface high parked over the Mid-Atlantic coast into the Carolinas, resulting in a nearly optimal radiational cooling setup. Statistical guidance from the ECMWF and long-range GFS suggest 32 to 38 degrees will be common across the Piedmont and northern/central Coastal Plain. If this forecast pattern continues, then a Frost Advisory will likely be needed.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

As of 120 PM Thursday...

VFR conditions are expected to prevail through the 24 hour TAF period. Gusty southwest winds will continue through 23-00z before becoming light and variable. The LLJ will strengthen ahead of a trough and weak front tonight and result in marginal LLWS, primarily at RDU and RWI. Weakening and decaying convection along the front over the western Piedmont and Foothills may bring a very light shower, 5-8 kft cigs, and briefly gusty northwest winds to INT/GSO after midnight, but confidence is too low in any restrictions to include in the 18z TAFs.

Outlook: Northwest winds Fri will again veer to southwesterly by Sat ahead of an approaching cold front, progged to shift through central NC on Sun. Scattered showers, isolated lightning, and brief vsby restrictions will be possible along and behind the fropa. Immediately behind the front, northwest winds will become gusty, 25 to 35 kts, for several hours before relaxing Sun night into Mon morning.

CLIMATE

All-Time Records for April:

KGSO: 95 on 4/28/1915 KRDU: 95 on 4/23/1980 and 4/18/1896 KFAY: 96 on 4/12/1930

Record High Temperatures:

April 16: KGSO: 88/2002 KRDU: 92/1941 KFAY: 94/2006 April 17: KGSO: 90/1967 KRDU: 93/1896 KFAY: 92/1941 April 18: KGSO: 90/1976 KRDU: 95/1896 KFAY: 93/1941

Record High Minimum Temperatures:

April 16: KGSO: 66/2006 KRDU: 64/1912 KFAY: 69/1934 April 17: KGSO: 63/2002 KRDU: 67/1896 KFAY: 66/1921 April 18: KGSO: 66/1909 KRDU: 63/1941 KFAY: 67/2002

RAH WATCHES/WARNINGS/ADVISORIES

None.