Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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034 FXUS62 KRAH 231943 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 330 PM EDT Sun Apr 23 2017 .SYNOPSIS... A strong mid and upper level storm system will move slowly east from the Tennessee Valley into the Carolina`s through Tuesday. A surface low pressure will track from Georgia east to the Carolina coast through Tuesday. && .NEAR TERM /Tonight through Monday/... As of 330 PM Sunday... Flood Watch through 800 AM Tuesday... For the rest of the afternoon and evening... Periods of rain will continue through the evening across most of the area. Widespread rain will continue across our western and northern zones of the Piedmont. Hourly rates are in the 0.05 to 0.10 range in these areas are not expected to produce any significant or widespread type flooding issues through the evening. However, these rains will wet and in many cases begin to saturate the soil. This will prime the area for runoff when the heavier rainfall rates develop from the west later tonight. We will maintain 100 POP in the west and north, with 70 (likely) POP in the southern tier of counties where the current radar trends are in a lull there. Temperatures will be in the 50s west and north, with readings falling into the 50s south. Concerning the Flood Watch through 800 am Tuesday... The main flood threat is expected to develop into our region from the west tonight. The latest models are in good overall agreement in depicting entire positively tilted mid/upper low over middle TN to slowly track ESE through the TN valley to over northern GA later tonight and Monday, evolving into a negatively tilted system aloft with time. Strong mid level lift is forecast to arrive over much of southern and western areas later today and tonight, then in the east on Monday. The negatively tilted system will tap very deep moisture which will be pulled NW from the Gulf Stream and western Atlantic into northern SC and much of NC. This surge of moisture will be forced to lift over the cool stable dome - north of the stationary boundary across our region. The result will be increasing rainfall rates with heavy rain likely to spread eastward into our western Piedmont late tonight, then progress slowly east through the Piedmont, Sandhills, and Coastal Plain Monday and Monday night. It is still a bit too early to pin point where flooding will occur; however, it appears that the western and southern part of central NC may end up the most likely location for widespread type flooding. Storm totals are still expected to range between 3 and 5 inches, with locally 6+ inches possible. Just about any area could see the 6+ inches in the current watch area and we will continue the Flood Watch for all zones. The main time frame for flooding will be Monday through Tuesday morning. The heaviest rain should end early to mid day Tuesday. General meteorological and sensible weather discussion: Driven by the 1022+ mb surface high pressure that was nosing down into our region from PA/NY, strong CAA with the low level NE wind had overspread all our region. The cold front has made it well south into South Carolina. All of our region including even the SE Coastal Plain is on the cool side of the boundary. Temperatures were a good 30 degrees colder today than this time on Saturday. Readings were in the 40s NW ranging into the 50s elsewhere. Rain was widespread over the western half of NC west and south through the Tennessee Valley and northern GA. Rain continued to overspread areas along and NW of a line from Albemarle to Raleigh and Roanoke Rapids. This covers all the Piedmont and portions of the northern Sandhills and northern Coastal Plain. Rainfall thus far has been generally 0.50 to 1.50 inches in the west with between 0.25 and 0.50 east - locally 1+ inches. This is just about as expected thus far. The maximum rain thus far has been in a SW to NE corridor from the Mountains along the northern tier of NC and southern VA where 1 to locally 4 inches has been observed. The rainfall thus far has simply wet down the dry ground as many areas had received only 50 to 75 percent of normal precipitation in the past 1 to 2 months before this rain even began. The latest models support the ongoing forecast and reflect the current radar and satellite trends very well. Strong layer lift is forecast to develop east to cover much of southern and western areas tonight, then slowly move east over all of NC, especially strong over the southern zones Monday and Monday night. The negatively tilted system will tap very deep moisture which will be pulled NW from the Gulf Stream and western Atlantic into northern SC and much of NC. Thus, the heavy rain with storm totals of 3 to 5 inches still appears likely if not probable, with 6+ inches possible. The possibility of thunderstorms may exist, mainly over the Sandhills and SE Coastal Plain late Monday and Monday night as the warm sector may penetrate these areas. This occurs as the low pressure tracks east and the warm front tries to nudge inland. The front may be able to reach into portions of our SE zones and if so, there would be a risk of a brief tornado with any storms that develop near or along the boundary. Cool temperatures in the 50s tonight will warm only into the mid 50s to mid 60s Monday, except near 70 SE. Lows Monday night will hold in the 50s NW and range to the mid 60s SE. && .SHORT TERM /Monday night through Tuesday/... As of 330 PM Sunday... The threat of flooding will continue with heavy rain gradually tapering off from the west Monday night into Tuesday morning. The severe threat should end as the low pressure and cold front shift offshore early Tuesday. Rain will continue over much of the eastern half of the region through at least mid day as the low tracks up the coast. Cloudiness and northerly low level flow will keep many areas in the upper 50s and 60s Tuesday, with the warmest readings in the SW, where some clearing may take place. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... As of 330 PM EDT Sunday... A short wave ridge will quickly move across our region Tue Night through Thu night, resulting in dry warming weather during this time. Highs Wed and Thu in the 80s and lows in the upper 50s to lower 60s. A weak short wave in the sw flow is progged to move across the area early Fri. Will include a slight chance pop for daytime Fri. Otherwise, the ridge over the se is progged to amplify over the weekend, keeping the precip-makers to our north and west, and an above normal airmass over our area. Highs in the upper 80s and lows in the mid 60s during this time. && .AVIATION /18Z Sunday through Friday/... As of 145 PM Sunday... IFR to LIFR CIGS with MVFR VSBYS in rain and fog are expected through the TAF period. Period of heavy rain will occur at KINT/KGSO tonight, then all areas Monday and Monday night. The rain should begin to taper to drizzle on Tuesday. However, low CIGS and VSBYS below MVFR range should continue through 12z/Tuesday. Cigs should rise gradually to MVFR areawide Tue as the mid level low slowly departs the area, then trend to VFR Tue night lasting through Fri with a drier air mass. && .HYDROLOGY... As of 300 PM Sunday... ...A Flood Watch is in effect through 800 AM Tuesday... Flooding of creeks and small streams is expected to begin later today and tonight as the ground saturates and the rainfall becomes heavier. This is expected to occur over the western Piedmont, including the Triad region first, then shift east with time (later tonight and Monday) to bring the threat across all areas. River flooding will become more likely on Monday and could linger into midweek. Based on our expected rainfall distribution at this time, the Haw river would be particularly prone to minor flooding above Lake Jordan, but any of the mainstem rivers could reach minor to flood stage, especially given just a bit more rain than currently forecast. On a positive note, we were on the cusp of drought conditions due to rainfall deficits over the late winter and spring, so this event will turn that around and possibly eliminate much of a drought threat for the rest of the spring season. && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043- 073>078-083>086-088-089. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Badgett LONG TERM...np AVIATION...Badgett HYDROLOGY...MLM

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