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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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401 FXUS61 KPBZ 091940 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 340 PM EDT Tue Jul 9 2024 .SYNOPSIS... Dry weather continues through most of Tuesday ahead of the remnants of Hurricane Beryl that will bring showers and thunderstorms to the area overnight tonight and tomorrow. Some may pose a damaging wind and tornado risk. Tuesday and Wednesday will be the hottest days of the week with heat indices approaching 100 degrees. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Hot and humid with heat indices nearing or topping 100 degrees. - Marginal Risk (1/5) for severe overnight Tuesday night in eastern Ohio and northwest Pennsylvania. ------------------------------------------------------------------- Cirrus coverage will thicken ahead of the remnants of Beryl with increasing moisture aloft in southwest flow. Said southwest flow will also promote additional warm advection and hi res ensemble mean 850 mb temperatures climb up to 21C. Weak moisture advection will keep dew points steady if not rising slightly through the afternoon. This will result in heat indices climbing to near or just touching 100 degrees, especially in the urban areas. The warm, moist airmass will continue into Tuesday night providing little relief with a 70- 90% chance of lows >70F primarily south of I-80. Should the cirrus coverage be thinner than currently forecast, it`s possible that Heat Advisory criteria may be reached, but that is a lower probability solution. Regardless, those who are sensitive to heat should take extra precautions and remember to check on those who are at risk for heat illnesses. A Marginal Risk (1/5) for severe has been introduced for a small sliver of our eastern Ohio counties and extending into northwest PA as a warm front lifts north through the Ohio Valley late tonight. Wind and few tornadoes would be the primary threat; that said, the majority of forecast soundings from the CAMs suggest a stable surface given the poor diurnal timing. Dynamics won`t be an issue as plenty of low level shear will be present as Beryl gets closer, but the chance of a storm rooting at the surface and subsequently posing a wind or tornado threat is low probability. Otherwise, we should see a limited severe threat with mid level lapse rates not all that favorable and limited deep layer instability as moisture increases through the depth of the column. In addition, the warm, moist airmass will continue tonight, providing little relief with a 70-90% chance of lows >70F and a 40- 50% chance of >75F. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... KEY MESSAGES: - Remnants of Beryl track near the area beginning on Wednesday. - Dry slot will prohibit widespread rain but scattered thunderstorms possible. - Slight Risk (1/5) of severe for far northeastern areas and Marginal Risk (1/5) for Pittsburgh and east. - Hot with heat indices in the upper 90s to near 100. ------------------------------------------------------------------- The remnants of Beryl approach and impact the area starting on Wednesday. Ensembles have now resolved to better agreement on a dry slotting solution that will significantly reduce rainfall chances and amounts across most of the area. Latest NBM and HREF probabilities for even >0.5" by Wednesday night are only ~50% north of I-80 (~25% at PIT) coincident with the intrusion of a remarkably sharp dry slot (ensemble mean 500 mb RH values drop from the 80% range to single digits in 3-6 hours); coverage is very likely going to take on a scattered, convective nature. Can`t rule out some very localized hydrology concerns in the far northern part of our CWA, but confidence on this is rapidly decreasing and thus the Slight Risk for excessive rainfall has been removed in favor of a Marginal Risk from I-80 and north. We may even raise heat concerns on Wednesday, especially south and east of Pittsburgh, as low level moisture surges with dew points into the low to mid 70s. and MaxTs in the low 90s. Highs could jog a degree or two either direction if cloud cover manifests a bit more widespread or clearer than currently forecast, but trends are toward clearer. Mixing and tapping into a 30-40 kt wind at 850 mb may result in gusts up to 30 mph at times. For the severe threat, the points of interest will be the continued northward moving warm front that brought a conditional severe threat overnight Tuesday night, how long the area remains in the open warm sector ahead of a surface trough/surge of very dry mid level air, and additional development along said "boundary." The first possible severe risk could be focused along the warm front as it continues its northward trek through the area in the morning and parks north of the PA/NY border. This would be in the very early morning hours of Wednesday and pose a conditional tornado threat if any storms can fire along it. This might be the timeframe of the most potent atmosphere we see as low level flow veers and 0-1 SRH values rise above 150 m2/s2, but, CAMs show very little interest in convective initiation and any that does might not be surface based anyway. Our better chance for development looks to come in the wake of the warm front during our couple hour residence time in the warm sector during the mid to late morning hours just ahead of the punch of bone dry mid level air. Plenty of shear will still be available and with a drier atmosphere, we`ll see more insolation, thus greater instability, and another shot at a conditional tornado and wind risk. Yet again though, CAMs are tame despite at least modest convergence along a trough and the nose of an 850 mb jet in eastern OH/western PA but rather favoring development later on across the ridges and quickly out of our area. If nothing develops ahead of the dry air intrusion, then our precipitation chances will rapidly cut off by late afternoon. Nevertheless, SPC has maintained a larger area of a Marginal Risk (1/5) and a Slight Risk (2/5) that only covers Forest and Venango Counties. && .LONG TERM /FRIDAY THROUGH TUESDAY/... KEY MESSAGES: - Temperatures rebound to close out the week with scattered showers. - More active pattern may return by late weekend. ------------------------------------------------------------------- After Beryl`s departure, ensembles linger the remnant upper trough across the Great Lakes into Thursday while ridging off the East Coast tries to nudge westward. Moisture and troughing may result in continued shower chances into Thursday, especially in the ridges. It`s not until Friday into Saturday that the consensus is for the trough to begin to shift out of the area, but this remains on the lower confidence side and some showers may still linger especially in the eastern half of the area. Temperatures are favored to rebound back to or a few degrees above normal to close out the week into next weekend. By the beginning of next week, a northwest flow sets up over the area with a couple of disturbances set to impact the forecast area. Machine learning is hitting a large portion of the Plains, Mid-Atlantic, and Northeast for severe weather potential starting Sunday, but will have to wait for details to iron out better in the coming days. Slight chance PoPs have been introduced but confidence is low. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... High confidence in continuation of VFR through the TAF period under the influence of high pressure and weakening upper ridging. Mid to high level cloud decks have filled in as expected, with diurnal heating leading to a scattered cu field around 4-6kft also developing over portions of the area. The cu field will dissipate around sunset, but mid/high clouds will continue to thicken and gradually lower as the remnants of Beryl approach the Ohio Valley. A few isolated storms could develop along the lake breeze this evening, with little impact to area terminals except perhaps FKL (but confidence is too low to warrant including mention in TAFs at this time). Ensembles continue to favor low probability showers (30-40%) and thunderstorms (10-20%) associated with the approaching remnants of Beryl tonight into Wednesday. The best chances remain west of PIT (closer to the track of the surface low) and north of I-80 (closer to a warm front that will set up along the PA/NY state line). Any storms that form, especially late morning and early afternoon on Wednesday, will have potential to produce damaging wind gusts and possibly a few tornadoes. .Outlook... Ensembles favor a Hurricane Beryl track northwest of the region Wednesday, which would result in low probability precipitation and restriction chances that get lower the farther SE you are from the track. Residual showers on the backside of the general trough system may also linger Wednesday night into Thursday morning for eastern OH/northwest PA. Restriction potential increases during that time, with probabilities for MVFR cigs peaking around sunrise Thursday (09-15Z) at 50-70% near/north of the PIT area and 30-50% farther south. Ensembles favor VFR returning to the area Thursday afternoon and staying in place thereafter. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory until 8 PM EDT this evening for PAZ020-021-029- 031-073-075. OH...None. WV...Heat Advisory until 8 PM EDT this evening for WVZ003-004-012- 021-509. && $$ SYNOPSIS...MLB NEAR TERM...MLB/Shallenberger SHORT TERM...MLB/Shallenberger LONG TERM...MLB/Shallenberger AVIATION...Cermak/Frazier