textproduct: Raleigh

WHAT HAS CHANGED

* Most guidance depict a continued downward trend in forecast rainfall amounts on Saturday.

KEY MESSAGES

As of 300 PM Friday...

1) Unseasonably cool, with a wetting rain (0.10" or greater) likely over all but the nw Piedmont on Saturday.

2) Below average temperatures on Sunday will moderate and become above average by Tuesday with a risk of showers and storms late Wednesday into Thursday with cooler weather for Friday.

3) Marginal fire weather concerns for Monday and Tuesday with a somewhat dry and increasingly gusty pattern.

DISCUSSION

As of 300 PM Friday..

KEY MESSAGE 1... Unseasonably cool, with a wetting rain (0.10" or greater) likely over all but the nw Piedmont on Saturday.

A positively-tilted mid/upr-level trough will amplify across the Plains and MS Valley tonight and across and offshore the Middle Atlantic Sat-Sat night, while a low-level frontal zone will strengthen and progress slowly across the nern Gulf and South Atlantic coasts. In the meantime, 850 mb-centered sly flow and warm, moist advection and lift, beneath the exit region of an energetic (~140 kt) srn stream upr-level jet, will progress across cntl and ern NC through this evening. The flow in the layer will then veer to wly and nwly into the aforementioned, strengthening frontal zone along the coast overnight.

The 850 mb-centered lift will continue to support the maintenance of patches of light rain this afternoon and evening across the Sandhills and Coastal Plain. Rain will then redevelop and become increasingly-widespread late tonight-Sat, as the positive tilt trough pivots ewd and causes the area of widespread rain now across the Gulf Coast states to buckle nwd and overspread cntl-ern NC. QPF has continued to trend lower across most guidance, with the nw edge of the precipitation shield likely to extend across the nw Piedmont. 50th percentile values from the GEPS, EPS and GEFS all depict ~0.01" at GSO, ~0.25" at RDU, and a spread of a third to three quarters of an inch at FAY. LREF and HREF probabilities of a wetting rain of at least a tenth of an inch are 60% or greater over all but the nw Piedmont, with similar probabilities of a quarter inch or greater from near Raleigh and points sewd.

It will also be quite cool Sat, with temperatures 10-20 F below average and likely to break the record low maximum of 61F at FAY. Late afternoon west to east clearing across the wrn Piedmont, and a general lack of rain and earlier diabatic cooling, may support low- mid 60s there, with 55-60 expected elsewhere. Continued west to east clearing Sat night will favor good radiational cooling conditions and lows in the upr 30s to mid 40s, and with the development of areas of fog and/or low stratus especially where earlier rain occurs.

KEY MESSAGE 2... Below average temperatures on Sunday will moderate and become above average by Tuesday with a risk of showers and storms late Wednesday into Thursday with cooler weather for Friday.

Cool high pressure and morning low-level thickness values in the 1320s will result in a chilly start to Sunday. Despite a good deal of sunshine highs will range in the mid to upper 60s, or about 6 to 12 degrees below average.

The surface high will quickly shift east, supporting the development of a return flow with moderating temperatures, a gradual increase in moisture as well as warm gusty afternoon winds. Highs on Monday and Tuesday should warm above average and range in the upper 70s to lower 80s. The mixing depth will increase and support gusty afternoon winds with gusts up to 20 to 25 mph on Monday and perhaps 30 mph on Tuesday, especially across the western and northern areas.

Northern and southern stream troughs across the Desert Southwest and Canadian Prairies early in the week will phase as they shift east across the central and eastern U.S. on Wednesday and Thursday. How these systems phase will impact the timing and pattern of precipitation and the evolution of a southeastward advancing cold front. Ensemble guidance is still varied with the timing of these systems with a tendency for the best chance of precipitation Thursday, especially the afternoon, while some guidance supports a more progressive pattern with precipitation chances on Wednesday afternoon and night. The mid and upper level flow is rather strong with 500mb winds across the southern Appalachians ranging from 80 to 90kts, supporting some deep-layer shear. A little more uncertain is the degree of destablization the the timing of any potential convection with dew points creeping into the upper 50s to lower 60s. As noted in the previous shifts, many of the AI severe convective guidance tools indicate the potential for some stronger storms late Wednesday or Thursday, but the signal isn't super robust at this time. Some much needed rain appears a good bet although average rainfall amounts will be light and range around or perhaps a little less than 0.25 inches. The chances of a more significant rain, more than a half inch, are less than 25%.

A northwest flow of cooler and drier air arrives late Thursday into Friday with cooler and drier weather expected. -Blaes

KEY MESSAGE 3... Marginal fire weather concerns for Monday and Tuesday with a somewhat dry and increasingly gusty pattern.

Surface high pressure across the eastern U.S. on Sunday shifts east and offshore on Monday before a return flow of more moist air moves into the region toward mid week. Expect RH values to end up a little lower than guidance with adjusted minimum RH values on Sunday bottoming out in the 25 to 30% range, just under or around 30% on Monday and around or just over 30% on Tuesday. While the RH is lowest earlier in the period, wind gusts will likely be somewhat limited on Sunday and but increase notably on Monday and especially Tuesday. Thus fire weather parameters do not line up optimally and while marginal fire danger concerns cannot be completely ruled out, the risk appears somewhat limited.

AVIATION /00Z SATURDAY THROUGH THURSDAY/

As of 745 PM Friday...

The approach of a mid and upr-level trough late tonight and early Saturday will cause an area of rain now across the Gulf Coast states to buckle nwd and overspread central NC by Saturday morning.

The rain will be very light, fleeting, and likely without flight restrictions at INT and GSO, whereas, it will be somewhat heavier and accompanied by MVFR to IFR restrictions at FAY, RWI, and RDU.

Outlook: Areas of fog and/or low stratus are expected in the south and east on Saturday night as the system exits and skies in the mid and upper levels clear out. Otherwise, a general trend to VFR is expected Sunday into next week. The next chance of showers is expected possibly late Thursday or Thursday night.

RAH WATCHES/WARNINGS/ADVISORIES

None.