Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
539 FXUS61 KPBZ 261636 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1236 PM EDT Wed Jun 26 2024 .SYNOPSIS... Thunderstorms capable of producing damaging wind and localized flooding are expected this afternoon and evening ahead of a cold front. Dry and seasonable weather will return Thursday, with rising temperature expected Friday. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Strong to severe storms are expected between 1pm to 8pm. Damaging winds will be the main threat. An isolated tornadoes and hail as large as a quarter can`t be ruled out. - Storm Prediction Center (SPC) has expanded the Slight Risk for severe weather across the region, and Weather Prediction Center (WPC) has continued the Marginal risk for flooding. ------------------------------------------------------------------- 11am Update: Weak vorticity advection from the lower Ohio River Valley will continue to provide enough ascent within a weakly unstable (elevated) environment to push areas of light rain and low probability thunderstorms into southeast Ohio over the next two hours. PoP forecast has been updated to account for this feature; the expectation/focus remains on this afternoon with convection firing along/near Lake Erie and moving SE. The lower OH movement isn`t expected to disrupt storm evolution off the lakes, but that isn`t 100 percent confident. The rest of the daytime scenario is discussed below. Rest of the Discussion... An well-organized upper shortwave trough is expected to drop southeast from the western Great Lakes today and cross the Upper Ohio River Valley region through tonight, pushing through a surface cold front. Ahead of this feature, moist advection is helping to create a storm environment featuring above 90th percentile PWAT values, 30-40kts of effective shear, and between 1000-2000 J/kb SBCAPE (the latter two increasing towards those values by the afternoon). The resulting chemistry of the large- scale synoptic pattern and meso setup should feature fairly widespread thunderstorm development initiatilizing near the cold front along Lake Erie and traversing ESE between 1pm to 10pm EDT. Environment and model-supported outlooks favor a damaging wind and localized flooding threat for the stronger, more organized thunderstorms (that will attempt to be more line/QLCS oriented); however, lower probabilities still exist for large hail (due to for deep updrafts) and a tornado (lower LCL heights and modest sfc-1km shear). Shower and thunderstorm activity is likely to weaken late tonight as surface instability wanes along with the passage of the cold front. Much of the severe threat should subside by 10pm EDT while lingering post-frontal showers and convective stratiform rain regions exit the higher terrain of WV by early Thursday morning. Dry air and residual mixing of a NW post- frontal wind should mitigate morning fog risk, but residual boundary layer moisture in river valleys (favoring locations SE of Pittsburgh) could have patchy fog development. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... KEY MESSAGES: - Dry weather returns. - Temperature rises above normal again Friday. ------------------------------------------------------------------- Cool, dry northwest flow will develop Thursday as high pressure builds in from the northwest. Residual moisture and delay in subsidence is likely to allow for lingering stratocu Thursday morning that turns into scattered to occasionally broken afternoon cumulus. Cold advection and cloud cover will result in more seasonable afternoon temperature while post-frontal mixing may support NW wind gusts around 20 mph. The surface high will shift over New England by Friday as heights aloft rise ahead of the next upper level shortwave trough. Positioning of the high will support weak warm, moist advection amid mostly clear skies to raise area temperature about 5 degrees above the daily average. Broad ascent may increase mid to high level clouds and even low probability showers Friday night as weak perturbations ahead of the main upper level trough axis. && .LONG TERM /SATURDAY THROUGH TUESDAY/... KEY MESSAGES: - Shower and thunderstorm chances return Saturday into Sunday with the next low pressure system. - Low probabilities exist for a damaging wind and flooding threat with these thunderstorms. ------------------------------------------------------------------- Broad ascent within warm, moist southwesterly flow ahead of the main upper level trough axis will support increasing shower and thunderstorm probabilties starting early Saturday morning. Arrival of a more notable embedded shortwave and the surface cold front Saturday afternoon and evening is likely to help concentrate convective activity (currently favoring NW PA) and spreading it southeast through Sunday morning. Variation in storm timing and environment remains large due to differences in upper trough depth/timing as well as convective evolution prior to its (and cold fronts) arrival. Latest analysis suggests a low probability risk for damaging wind (mean values currently show 30-40kts of 0-6km shear) and localized flooding (tall-skinny CAPE values around 1500 J/kg with PWATs approaching daily maxima). Will mention threat in HWO and monitor evolving forecasts for this period. Dry weather and seasonable temperature is likely by late Sunday into Monday as the upper trough axis moves east and high pressure builds in from the western Great Lakes. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... A broken band of rain showers is currently tracking across the state of Ohio along a low-level jet. Impacts have only been noted to visibility at terminal for a brief period. Restrictions appear promising to start between 20Z and 03Z, as convection develops along a frontal boundary near Lake Erie and a shortwave ejects southeast; TEMPO groups continue for all sites with scattered coverage. Strong to severe wind (40mph to 65mph) gusts could be observed with passing downdrafts and hail up to the size of quarters could also develop in isolated storms between 20Z to 00Z. Probability of thunderstorms rapidly decreases after 04Z (MGW/LBE/DUJ will likely be the last to be impacted) as the trough ventures east. MVFR is expected as the thunderstorms end, with a period of showers. IFR is likely (LIFR possible) overnight with low level moisture in place. Restrictions in stratus/fog are possible with all sites; TEMPOS will be added in the afternoon update. .Outlook... VFR is then expected through Friday under high pressure. Restriction are possible Friday night with a crossing warm front. Restrictions are likely Saturday and Saturday night with showers and thunderstorms ahead of and along a crossing cold front. VFR returns Sunday under high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...WM/Hefferan