textproduct: Raleigh

WHAT HAS CHANGED

* No major changes to forecast thinking

KEY MESSAGES

As of 149 PM Saturday...

1) Rainfall ending from west to east this afternoon, with dry weather expected at all sites shortly after sunset. Unseasonably cool tonight.

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

3) A cold front could bring strong storms to the region Wednesday night into Thursday.

DISCUSSION

As of 149 PM Saturday..

KEY MESSAGE 1... Rainfall ending from west to east this afternoon, with dry weather expected at all sites shortly after sunset. Unseasonably cool tonight.

Early afternoon water vapor imagery reveals a broad plume of moisture across the southeastern CONUS while a quasi-stationary upper low remains in place over Quebec. At the surface, 12Z objective surface analysis placed the remnants of a cold front across the Coastal Plain and it still remains in this general area as of 17Z. Meanwhile, a series of weak surface lows continue to ride along this front, working in tandem with broad divergence aloft to produce the rainfall we've seen since the pre-dawn hours. Not surprisingly, the highest rainfall totals have been across the southern Coastal Plain where several spots have seen 0.30 to 0.40+" of rain. With several more hours of steady rain to come, a storm total forecast close to 0.50" seems more than reasonable for these spots. Naturally, there has been a sharp cutoff in precip amounts to the west which is reflected in observed amounts around 0.01 to 0.02" across the NW Piedmont since midnight.

The widespread rainfall and cloud cover has kept daytime temperatures well below normal for early May, so low that there is an increasingly likely chance that FAY will set a new record for coolest maximum temperature on this date. RDU's cool max temp record was also in jeopardy for a bit but is no longer threatened based on 16Z obs. See Climate section below for record specifics.

A clearly defined back edge to the precip is making its way into Forsyth and Davidson Co's as of 17z and outside of a few lingering sprinkles through mid afternoon, rainfall is rapidly coming to an end in those areas. There are increasing gaps in the stratiform precip area across central SC which is also well captured by the 12Z HREF and recent runs of the HRRR, suggesting that rain will taper off in the Triangle by mid/late afternoon, and perhaps just after 00Z across the Coastal Plain. While skies won't clear out entirely tonight, expect rapid clearing after sunset which will set the stage for an unseasonably cool night tonight. Widespread readings in the lower 40s will be common, although mid to upper 30s can't be ruled out in the normally cooler areas along the NC/VA border as well as portions of western Chatham/eastern Randolph.

The cooler than normal weather will persist into Sunday as well, with highs ranging from the lower 60s in the NE Coastal Plain to the lower 70s across the Sandhills.

KEY MESSAGE 2... Marginal fire concerns Monday and Tuesday within a dry and increasingly gusty airmass.

As the surface high moves eastward over the Atlantic early-mid next week, swly return flow into the area will increase. In the low- levels during the daytime, the 925-mb flow may range from 15-25 kts, highest across the west and north. 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 upr 30s to mid 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 where lowest dewpoints and highest winds are forecast.

Highs will moderate from near to above normal, starting out in the mid to upr 70s Monday and reaching the low to middle 80s by Wednesday. Some upper 80s are possible Wed, with low-level thicknesses rising to around 1400m.

KEY MESSAGE 3... A cold front could bring strong storms to the region Wednesday night into Thursday.

Medium-range guidance appears to be coming into a bit better agreement on arrival of precipitation to central NC, track/strength of the low, and fropa timing, however some variance remains and model spread increases with time beyond Wed.

Aloft, the longwave trough and embedded shortwave disturbances will generally swing ewd across the cntl and ern CONUS from Tue to Fri. As mentioned in the previous discussion, there is still some ensemble spread with this system, likely stemming 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. At the surface, a warm front in the form of increased low- level moisture will lift nwd across the area early Wed. The cold front approaching from the nw will stall as an area of low pressure lifts newd along it, progressing from the ARKLATEX on Wed aft to ern NY by Thu aft. The model disagreement increases on Thu wrt the low track and strength, as well as the ewd front progression. Generally, the front should move across the region Thu aft or eve, with cool high pressure ridging into the area as it moves across the Deep South/Southeast US in its wake.

Showers and storms could move into the area as early as Wed night, with the highest chances area-wide Thu morn into early aft. Earlier arrival of storm and extensive cloud cover would help limit the destabilization and potential for stronger storms Thu aft/eve. Will monitor this system over the coming days, but for now there is too much uncertainty to say with much confidence how things may unfold on Thu.

AVIATION /18Z SATURDAY THROUGH WEDNESDAY/

As of 130 PM Saturday...

TAF period: INT, GSO, and RDU have remained VFR so far today, and there is no reason to expect that any ceiling restrictions will develop at these three terminals as the shield of rain and low clouds with a coastal low continues to move to the east. With the greatest amount of moisture farther to the south and east, expect intermittent IFR ceilings at FAY as rain comes to an end, along with prevailing MVFR ceilings at both FAY and RWI. Rain will come to an end at these two sites before sunset with skies becoming mostly clear by midnight. For all five terminals, expect the wind to back from the northeast to the northwest this evening as the coastal low moves offshore and high pressure moves into the region from the west. Some gusts up to 15-20 kt are possible late Sunday morning, but confidence was not high enough to include this mention in the forecast.

Outlook: Dry VFR conditions are forecast through Tuesday night, at which point some restrictions and a chance of showers will enter the forecast at INT/GSO/RDU. Showers and restrictions will become more widespread at INT/GSO Wednesday night and at other terminals Thursday, along with a chance of thunderstorms.

CLIMATE

Record Low Maximum Temperatures:

May 2: KRDU: 53/1939 (this record is safe since RDU reached 54 at noon) KFAY: 61/1963

RAH WATCHES/WARNINGS/ADVISORIES

None.