textproduct: Raleigh

WHAT HAS CHANGED

As of 110 PM Saturday...

* Confidence is increasing in a multi-day early-season heat wave next week.

KEY MESSAGES

As of 110 PM Saturday...

1) A backdoor cold front moves in tonight. We cannot rule out a low- end threat of a few widely isolated storms between 4 and 10 pm.

2) Fire weather concerns will persist through next week, with continued dry weather.

3) Dangerous heat wave possible next week, with several consecutive very hot days. Near record temperatures possible Tue through Sat.

DISCUSSION

As of 110 PM Saturday...

KEY MESSAGE 1... A backdoor cold front moves in tonight. We cannot rule out a low-end threat of a few widely isolated storms between 4 and 10 pm.

A cold front draped over the lower OH valley and Mid-Atlantic states will push through in backdoor fashion tonight into early Sun. Cool high pressure of around 1032 mb over the Great Lakes will slide into New England by Sun morning, aiding the front to push south and west from SE VA and NE NC tonight and overnight.

Ahead of the front, a pre-frontal trough will pass through during the day, with winds being out of the north most of the afternoon. The airmass will continue to warm from Fri, with low-level thicknesses around 1390m, supportive of low/mid 80s for most of central NC. This is about 10-15 degrees above normal.

A weak area low pressure appears to develop this afternoon near the Charlotte area ahead of the backdoor front. As that happens, it may aid some pooling/convergence of moisture across the Piedmont, Triad, and Triangle for areas along/south of I-40/I-85 and US-64. In this region is where several HREF members are indicating some weak instability on the order of 500 J/kg, in an environment of 20-25 kt of northwesterly deep shear. Moisture is limited with PW's near normal and there appears to be a capping inversion in place. Nevertheless, several CAM solutions do indicate a few widely isolated showers or storms developing initially along the Triad and progressing south and east between 4 and 10 pm, before dissipating over the southern Piedmont and Sandhills. Confidence on this developing given sub-optimal conditions is low. However, cannot fully rule it out with fairly steep 0-3 km lapse rates. If a shower or storm can manage to form, it could feed on some modest DCAPE and inverted-V profiles seen in forecast soundings for some brief 20-30 kt gustiness with their outflow. We opted to introduce 20-percent shower/storm chances in the aforementioned area given the setup. As the front moves through, we could see some gusts from the east of 15- 18 kt within the tighter pressure gradient and cold advection.

KEY MESSAGE 2... Fire weather concerns will persist through next week, with continued dry weather.

Very dry conditions will persist through next week. Winds are projected to hold below criteria for red flag warnings, as gusts should peak at around 15 mph with infrequent afternoon gusts up to 20 mph. But fuels remain extremely dry, and little to no rain is expected in the region through the next several days, with minimum RH values forecast to be in the 2530% range Tue through Fri. National forestry officials are indicating a moderate to high risk for significant fire potential early next week, highest from the NC mountains through the western Piedmont. A statewide burn ban remains in effect for all of NC until further notice. All burning, including with previously-issued permits, is prohibited.

KEY MESSAGE 3... Dangerous heat wave possible next week, with several consecutive very hot days. Near record temperatures possible Tue through Sat.

Concern is increasing regarding the potential for a dangerous early- season heat wave across the Carolinas next week. Mid level ridging now over Mexico and the Gulf will steadily build and amplify across the Southeast states through next week as a Bermuda surface ridge remains in place, deflecting most fronts and precipitation systems to our W and N and keeping us generally dry under strong subsidence. Daily low level thicknesses are forecast to be well above normal by as much as 50 m into next Sat. Periods of clouds remain possible, including on Fri when deterministic models take a weak Baja-source shortwave trough across the region. But, overall, sunshine will be abundant, contributing to high heat stress and near record temps (see climate section below), with highs as much as 15 to 25 degrees above normal. The chance for several days of widespread 90s over central NC is increasing, and the latest NBM's 75th percentile for highs at RDU is 95-100 degrees F every day Wed-Sat. These successive days of perhaps unprecedented heat may be dangerous for all populations but particularly for those without adequate cooling and those working or exercising outdoors.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 600 AM Saturday...

There is high confidence in VFR conditions to start the TAF period. A backdoor cold front will move in later today and tonight as cool high pressure settles across the Mid-Atlantic states. Ahead of the front, several CAM solutions are indicating a low-end threat of some showers and a widely isolated storm or two. Instability is weak, but cannot fully rule out this threat given some moisture pooling along the westward moving frontal zone. The best chance based on the HREF ensemble would be at GSO, INT, and RDU in the hours of 20-24z. For now, given low confidence, kept PROB30 groups. As the front moves through, winds from the north will shift out of the east late tonight into Sunday morning, with some brief gusts of 15-18 kt upon passage. Moisture pooling along the front and weak upslope will favor the chance of MVFR stratus at GSO/INT early Sun morning. Stratus cannot be ruled out at RDU/FAY but confidence is too low to include at these terminals.

Outlook: Morning stratus is possible Mon in a return flow regime, most favored at GSO/INT and RDU. VFR should otherwise prevail through midweek.

CLIMATE

Record High Temperatures:

April 11: KFAY: 90/2001

April 13: KGSO: 88/1930 KRDU: 89/1922

April 14: KGSO: 90/1922 KRDU: 91/1941 KFAY: 93/1922

April 15: KGSO: 90/2006 KRDU: 92/1941 KFAY: 95/2006

April 16: KGSO: 88/2002 KRDU: 92/1941 KFAY: 94/2006

April 17: KGSO: 90/1967 KRDU: 93/1896 KFAY: 92/1941

Record High Minimum Temperatures:

April 13: KGSO: 61/2019 KRDU: 66/1930

April 15: KGSO: 65/2006 KRDU: 64/1993

April 16: KGSO: 66/2006 KRDU: 64/1912 KFAY: 69/1934

April 17: KGSO: 63/2002 KRDU: 67/1896 KFAY: 66/1921

RAH WATCHES/WARNINGS/ADVISORIES

None.