Area Forecast Discussion
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264 FXUS61 KPBZ 231039 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 539 AM EST Fri Feb 23 2018 .SYNOPSIS... Periodic rain chances will continue through Sunday. Conditions should be dry for the beginning of the work week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Moisture surging back northward is spreading light rain back into the area. With southerly flow developing, temperatures are slowly climbing, save for the eastern slopes of the Laurel Highlands where a favorable cold air damming scenario continues to play out. The observation at Oakland, MD shows 32 degrees and there are certainly locations in the deeper hollows that will remain much cooler with the easterly flow. For this reason, will keep the Winter Weather Advisory continuing through the mid-morning hours as freezing drizzle continues to be a threat. Fog/drizzle will continue along our eastern periphery through mid-morning, when the flow finally veers southerly. Elsewhere, light rain chances will increase through the early morning hours, but rain totals are expected to be light in the void of organized lift between waves. The next wave of appreciable rain will arrive with the warm front lifting back to our north with timing centered around midday. Hi-res models try to sneak in a few convective elements along the southern flank of rain, a claim further bolstered by NAM/RAP soundings showing skinny SB CAPE in the MGW area. While strong thunderstorms are not expected, some thunderstorms are not out of the question, which could produce a little more efficient rainfall in those areas. All told, looking at another half to full inch of rain for many locations today. Models differ slightly on the latitudinal focus for this rain, but most of it should fall through the central portion of the local forecast area. Without question, the Areal Flood Watch will continue seemingly in perpetuity. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... A brief lull in steady precipitation will once again play out late tonight into early Saturday morning as one low pulls away and temporarily disrupts the stream of moisture and lift. A remnant surface boundary will be splayed west to east just to our south. This will serve as the focus for renewed shower activity Saturday as moist advection matures through the Ohio Valley and overruns the boundary. Another half to full inch of rain is expected from I-80 south through the daylight hours. Strong southerly flow will creep the stationary front a little further north, directly over the forecast area. Rounds of efficient showers will carry into Sunday morning as the surface low deepens into Midwest. Unfortunately, the current track of the low sets up the inflection point over the Upper Ohio Valley, keeping us in steady moderate to heavy rain, with few breaks in the action Saturday night. Bolstered by an intensifying low- level jet, deepening warm cloud depths and almost certain record PWAT values, rain rates should be more than enough to overwhelm already saturated soils. Areal flooding extending to the creeks, streams, and eventually the mainstem rivers is generally expected at this point. Rain totals from 12z this morning through midday Sunday will be on the order of 2-3" and could locally go higher. Finally by Sunday afternoon, enough westerly push behind the cold front will shunt rain showers to our east, leading to a much needed dry end to the wet weekend. Temperatures will remain above-average through at least the weekend. && .LONG TERM /MONDAY THROUGH THURSDAY/... Considerable agreement across models in showing high pressure building into the region for the start of the new work week. At this point, Monday, Tuesday and Wednesday morning look dry with the high in place. The only "fly in the ointment" would be if the southeastern CONUS ridge is able to re-establish and push the southern moisture stream back northward, bringing additional rain to our southeastern zones Monday. Will opt to downplay this scenario as operational models tend to favor the previous solution. Another system is poised to impact the area by the middle to late part of next week. Models have a system approaching from the southwest before shearing out near us, and evolving quite differently. Will keep PoPs general for this time period. Temperatures will remain above-average through the middle of the week, with a potential cooldown coming near next weekend. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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Most terminals remain under IFR/LIFR ceiling/visibility conditions as moisture remains trapped underneath a stout inversion aloft. MGW/LBE remain the exceptions early on as they take advantage of downslope flow. Rain will overspread the region through the morning, with widespread IFR/low MVFR conditions continuing through the day. Some modest ceiling improvement is possible this afternoon. Precipitation will taper off once again during the evening, but mostly IFR or LIFR ceiling restrictions will continue through the rest of the TAF period. OUTLOOK... Restrictions are expected to continue with a Saturday warm front, and a Sunday cold front.
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&& .HYDROLOGY... Numerous forecast points are already at action stages across the region. Pittsburgh is already over 21 feet. 3 successive disturbances over the next 72 hours will drop rainfall amounts ranging from 1.50 to 4.50 inches across the region. River Flood watches will likely be expanded across the region. With QPF, we expect river flooding to be widespread by 00Z/25 February. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flood Watch through Sunday evening for MDZ001. Winter Weather Advisory until 10 AM EST this morning for MDZ001. OH...Flood Watch through Sunday evening for OHZ039>041-048>050- 057>059-068-069. PA...Flood Watch through Sunday evening for PAZ007>009-013>016- 020>023-029-031-073>076. WV...Flood Watch through Sunday evening for WVZ001>004-012-021- 509>514. && $$

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