textproduct: Raleigh

WHAT HAS CHANGED

As of 225 PM Thursday...

* Confidence is increasing in the timing of early-week backdoor cold front, which favors warmer temps continuing through Mon. Additionally, rain chances Mon/Mon night have come down a bit.

KEY MESSAGES

As of 225 PM Thursday...

1) While Sat/Sat night still looks mostly dry, we're seeing some potential for an isolated shower or storm in the SW CWA, which will bear watching.

2) A backdoor front is expected to push south through the area Mon afternoon. Model spread with timing remains elevated, but has improved. Rain chances and amounts are trending lower.

DISCUSSION

As of 225 PM Thursday...

KEY MESSAGE 1... While Sat/Sat night still looks mostly dry, we're seeing some potential for an isolated shower or storm in the SW CWA, which will bear watching.

While today's deep mid level trough along the Eastern Seaboard shifts gradually offshore through early Sat, the strong anticyclone over the Desert Southwest will slowly weaken and begin to flatten. This will allow mid level perturbations riding atop the ridge to dive SE toward our area, one of which will track through the Mid Atlantic region late Fri night into early Sat morning, bringing a chance for brief light showers over our far NE sections. This flow will also include another weak shortwave trough which tracks SE over the Mid South and Southeast Sat aftn/evening and which shows good timing and amplification agreement among the deterministic models and ensemble members. A pocket of elevated PW (~150-200% of normal) does accompany this feature, and spot forecast soundings from a few deterministic models do show sufficient moisture through a deep enough layer to support a few showers and isolated storms reaching our SW, along with a few hundred J/kg of CAPE. The weak low level wind field and northwest mid-upper flow is less favorable for substantial convection coverage, and the NBM mean remains largely dry in this period. But this potential bears watching, considering that there may be outdoor activities taking place on this spring weekend evening.

KEY MESSAGE 2... A backdoor front is expected to push south through the area Mon afternoon. Model spread with timing remains elevated, but has improved. Rain chances and amounts are trending lower.

Our next significant weather feature is a backdoor cold front that will be moving southward through the Mid Atlantic region and Carolinas early next week. A mid level polar low is expected to drift southward over Canada starting this weekend, and shortwave energy initially sheared within fast WNW flow across the central US/Canada border is expected to dive across the Great Lakes/ Northeast/Canadian Maritimes through Tue, propelling the backdoor front southward. Model differences regarding speed and amplitude of this shortwave trough have been responsible in part for the vast model spread among ensemble suites (including the NBM, LREF, and AIGEFS) regarding frontal timing, and this spread has had the most noteworthy sensible ramifications on the temps Sun night through Mon night, including 18z Mon ensemble 2m temp spreads as much as 30-40 degrees F (10th to 90th percentiles) on the earlier model runs from Tue/Wed. As model consensus has improved, though, confidence has grown in a cold front passage through NC most likely to take place during the early to mid afternoon Mon, although the ECMWF and its ensemble mean remains on the faster end of solutions. This timing would allow for at least some heating Mon and a longer duration in the warm sector, although clouds and gradual late-day onset of CAA should result in temps down a bit from the very warm Sun highs (expected to be in the 80s to near 90 areawide), down to the mid 70s to low 80s. Regarding pops, most models do show an uptick in PW to 200-225% of normal in NC Mon morning, just ahead of the mean mid level trough axis, along with marginal forcing for ascent. But this earlier-in-the-day timing would not be favorable for taking advantage of any prefrontal heating and potential instability that might boost ascent and hence raise the coverage and intensity of any convection, despite having favorable deep layer bulk shear of 35-45 kts. Recent guidance also shows the steeper mid level lapse rates in the 7.5-8.0 C/km range (sourced from Sun's EML over the Plains) passing through Mon morning, also a timing not well-aligned with peak heating. Given the drying westerly or WNW component to the low- mid level flow, as well as the limited Gulf-source moisture tap due to the E-to-W surface ridge across the Gulf/FL/Bahamas, lower coverage overall with lighter amounts is expected with frontal passage, and pops will be no greater than 25-30%. Will keep monitoring trends, though, in case the front slows, allowing for more heating and better temporal alignment of the shear, CAPE, and lapse rates aloft.

Temps will drop post-front to the mid 30s to low 40s Mon night, followed by highs Tue in the mid 50s to low 60s. The progressive nature of this trough over the NW Atlantic will allow for a quick temp modification as we head through mid-late week, though.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 700 PM Thursday...

24 hour TAF period: High confidence dry, VFR conditions will prevail through the TAF period. High clouds will move in from the NW quickly around 18Z Fri, becoming overcast at 8-15 kft by the end of the TAF period. Winds will be calm to light and variable overnight, then become mainly swly on Fri, with gusts of 15-20 kts at KINT, KGSO, and KRDU during the aft/eve.

Outlook: There is a chance of light rain Friday late eve/night, highest probability at KRWI, however VFR conditions should prevail. Showers will be possible at all terminals Monday aft/eve as a cold front moves NW-SE across central NC. Winds may be gusty with the cold front.

RAH WATCHES/WARNINGS/ADVISORIES

None.