textproduct: Raleigh

WHAT HAS CHANGED

* Have bumped today's highs downward slightly from the Triangle south and east, where confidence in widespread rain is high. Otherwise, no major changes.

KEY MESSAGES

As of 310 AM Saturday...

1) Unseasonably cool today, with a high chance of wetting rainfall over all but the NW.

2) Temps will trend above normal Mon into Wed, ahead of a cold front that may bring strong storms by Thu.

3) Marginal fire concerns Monday and Tuesday within a dry and increasingly gusty airmass.

DISCUSSION

As of 310 AM Saturday..

KEY MESSAGE 1... Unseasonably cool today, with a high chance of wetting rainfall over all but the NW.

Today's forecast remains largely on track, with increasing confidence in a solid area of rain spreading over mainly our SE half. A weak surface cold front pushing SE through the area currently will merge with an existing stronger cold front snaking from the N Gulf across N FL and just off the Southeast/Carolina coast, and this front will waver a bit but mostly hold in place today as a series of surface lows tracks along the front, all while a cooler air mass begins to move in from the NW and W. (This synoptic setup is similar to a typical wintertime pattern in the Carolinas, although with warmer temperatures.) The occurrence of rain today is a near certainty for areas SE of the Triangle, where PW values are projected to be above normal today and where light rain is already approaching from the SW, according to regional composite radar imagery. But a couple of factors will keep rainfall amounts to a half inch or less over all but the far SE CWA (MEB/FAY/CTZ/GSB): Over much of the area, somewhat dry air in the very low levels combined with modest and elevated moist upglide, marginal PW just a bit above normal, and an overall lack of convective elements should limit rain rates. We're already seeing this upstream with the northern area of the rain shield producing rates of just a few hundredths per hour. Over our far SE CWA, however, where moisture will be deeper with a shallower sub-cloud layer beneath stronger upper divergence to help force ascent, rainfall totals today are expected to reach three-quarters to just over one inch. These totals are in line with the most likely scenario from the latest HREF and LREF suites. Pops are expected to be highest between 12z and 19z. Models are in good agreement on moving precip out of our NE in the early afternoon and out of our SE during the early evening hours.

Temps are expected to be quite cool today, within several degrees of record-cool daytime highs at RDU and especially FAY (see climate section below). The Triad area, which will have the potential for a little late-afternoon partial sunshine, should reach the low-mid 60s, however from the Triangle to the S and E, highs are most likely to range from the mid 50s to around 60, given the widespread precip and clouds.

KEY MESSAGE 2... Temps will trend above normal Mon into Wed, ahead of a cold front that may bring strong storms by Thu.

No major changes have been noted in the extended next week, with the two main points being temperatures trending above normal and watching our next weather system late in the week.

With respect to temperatures, cool high pressure from Sunday shifts off the coast Monday, allowing return flow to set in for much of next week. Highs will largely hover above normal, starting out in the upper 70s Monday and reaching the low to middle 80s Tuesday through Thursday. Some upper 80s are possible midweek with low-level thicknesses rising to around 1400m.

In regards to the late-week system, ensemble spread remains large with a cold frontal passage sometime late Wednesday or Thursday. Aloft, this spread seems to stem from the potential interaction or phasing of a northern stream trough with a southern closed low during the early to middle part of next week. These differences will not be resolved until the systems can be better sampled. But as of now, most ensemble cluster solutions support the best chance of showers and storms late Wednesday or Thursday, with the front moving through by early Friday. Given the ensemble spread, the AI convective guidance is not as clear cut as it was yesterday, but still includes some probabilities for a severe threat late Wed or Thu. If conditions can align, the front will certainly have favorable shear and instability to support scattered showers and storms during this time, but uncertainty is still too large.

KEY MESSAGE 3... Marginal fire concerns Monday and Tuesday within a dry and increasingly gusty airmass.

As high pressure shifts offshore next week, return southwest flow takes shape across central NC. In the low-levels, the 925-mb flow will range from 20-25 kt within a more pronounced pressure gradient. As happens quite often in these regimes during the springtime, the moisture return is initially slow to recover. Dewpoints are expected to mix out into the low to middle 40s over the Piedmont Mon and Tue. During this time as well, south-southwest winds may gust in the 15- 25 mph range, perhaps 25-30 mph over the western Piedmont on Tue. While the latest forecast indicates that conditions should remain below IFD criteria, the worst-case scenario shows that it also cannot be entirely ruled out. The most favorable fire danger may be across the western Piedmont, which may see little if any rain from this Saturday's system.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

As of 220 AM Saturday...

Adverse aviation conditions are likely early this morning through much of this afternoon over S and E terminals, as widespread rain moves through southern and eastern NC, associated with surface low pressure tracking from the Gulf coast to the NE across the Southeast coast. FAY will see the poorest conditions, with sporadic MVFR cigs becoming more solidly MVFR after 09z with rain spreading in, and several hours of IFR cigs and vsbys are possible 15z-19z. RDU and RWI will be slightly better, as the rain that moves in will be lighter, and mostly VFR cigs are expected but may become MVFR for a time between 13z and 19z. INT/GSO are likely to see just very light rain at most, with VFR cigs prevailing. The low will push off the NC coast late today through early evening, resulting in a W to E ending of rain through the last 6 hours of the TAF valid period, and cigs are expected to trend to VFR areawide after 20z-22z at RDU/RWI and after 02z at FAY. Surface winds will be mostly under 10 kts from the N or NE.

Looking beyond 06z Sun, VFR conditions should dominate through at least early Wed, under the influence of high pressure. As this high moves further offshore, a warm and moist southwest flow ahead of an approaching cold front will bring increasing chances for sub-VFR conditions and scattered to numerous showers and storms, starting Wed evening.

CLIMATE

Record Low Maximum Temperatures:

May 2: KRDU: 53/1939 KFAY: 61/1963

RAH WATCHES/WARNINGS/ADVISORIES

None.