


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
046 FXUS61 KPBZ 181906 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 306 PM EDT Fri Jul 18 2025 .SYNOPSIS... A stalled boundary across the southern part of the area will continue to provide a heavy rainfall threat this evening, mainly south of I-70. Additional chances for flash flooding, as well as at least isolated severe storms, will occur this weekend as a warm front lifts through Saturday, and a cold front passes Sunday. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - A stalled boundary will be a focus of a heavy rainfall threat, mainly south of I-70, with lighter rain to the north - Fog development is likely overnight in areas that get heavy rain today. --------------------------------------------------------------- A boundary remains stalled in the general vicinity of the Mason-Dixon Line through tonight. Crossing perturbations in the quasi-zonal mid-level flow have fostered more of a stratiform rain to the north of the boundary, and more of a convective nature to the south, in an area with 1000-2000 J/kg of surface- based CAPE and precipitable water values in the 1.9 to 2.0 inch range. There has already been some training of showers in the area of the ongoing Flood Watch, and this potential will continue into this evening. HREF maximum rainfall potential suggest pockets of 2-3 inches of rainfall through this evening is possible, which represents a flooding risk, especially if it falls on ground that is more saturated from previous rain. In contrast, the risk of severe thunderstorms appears quite low. The high PWAT and skinny CAPE profiles suggests that updrafts will be relatively weak, and DCAPE levels remain relatively low. Cannot totally rule out a wind gust or two in Tucker County and vicinity, where higher CAPE and effective shear may support enough storm organization for a wind threat. Much of the activity will begin to weaken after sunset, with only scattered/isolated activity in the ridges by 06Z as instability diurnally decreases. Lingering low-level moisture and daytime rain will led to some fog develop tonight, especially over the ridges and locations in WV that received the heavier totals. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... KEY MESSAGES: - The front likely returns north on Saturday, bringing a risk of heavy rain and flooding at least to areas south and west of Pittsburgh. - A more isolated flooding threat is possible Sunday with a cold frontal passage. - Severe potential for Saturday and Sunday, with damaging wind gusts being the most likely threat. ---------------------------------------------------------------- The boundary will begin to lift northward across the region again on Saturday, as a shortwave trough crosses the Middle/Upper Ohio Valley, and as surface low pressure crosses the Upper Midwest into Lower Michigan by 00Z Sunday. Trends in the CAMs suggest later timing for the bulk of the precipitation, more towards the very late afternoon and evening. Model soundings are suggesting some mid-level warm air/capping that may inhibit convection until the shortwave arrives later in the day. This late-day convection may arrive in the form of a weakening MCS in Ohio, at a time when instability may be diurnally decreasing. SPC has pulled the day 2 slight risk a bit further west, essentially out of the forecast area, while maintaining a marginal risk over areas north and west of MGW. This seems reasonable, as increasing low- level flow and 20-30 knots of deep shear may support storm clusters capable of damaging wind gusts mainly, with a lesser risk of large hail. The flooding risk still exists as well given the likelihood of PWATs rising above the 90th percentile once again by later Saturday/Saturday night, with soundings supporting warm rain processes especially in eastern Ohio. Interestingly, HREF probabilities of greater than an inch of rain over 24 hours are fairly suppressed through Saturday night, maximizing in the 30-50% range west of the Ohio River and south of I-70. While the best flood risk may exist to the southwest of Pittsburgh through tomorrow night, think that these probabilities may be a bit underdone. While storm motions will be higher, the potential for heavy rates and an already saturated ground will keep the flood risk elevated. Sunday will feature a cold frontal passage as the Michigan surface low tracks into New England. Ensembles suggest a severe threat perhaps as early as the late morning hours and into the afternoon, with potential for 1000-1500 J/kg of surface-based CAPE overlapping with 30-40 knots of deep shear, mainly from Pittsburgh on south. This supports the day 3 marginal risk in this area from SPC for mainly a wind threat. The flooding risk will likely be confined to areas where east-west training may occur ahead of the advancing front. && .LONG TERM /MONDAY THROUGH FRIDAY/... KEY MESSAGES: - Building high pressure aloft may provide relatively dry weather early next week. - Heat and humidity begin to increase during the middle part of the week. - Shower/thunderstorm chances increase Thursday and Friday. ------------------------------------------------------------------- There is good confidence among the ensembles that strong ridging builds over the Mississippi Valley and into the eastern CONUS next week. Along with crossing high pressure to our north, a mainly dry pattern appears to extend into Tuesday, and possibly into Wednesday, with the potential for subsidence/warm air aloft to suppress convection. Of course, this will also lead to above- normal temperatures. NBM probabilities of 90+ highs increase to 40-70% over much of the area by Wednesday, and then 50-80% on Thursday. Combined with high dewpoints, heat risk is set to rise by the end of the forecast period. Shortwaves riding the top of the ridge may begin to suppress heights slightly by the Thursday/Friday period. This could lead to better rain chances during this period. Longer-range machine learning guidance suggests an uptick in severe storm potential as well, which makes sense given the amount of instability/moisture that may be available. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Crossing moisture on a shortwave today will continue to allow a mixed bag of restrictions, with VFR generally more likely in the north, and IFR more likely in the south with lower cloud bases and more intense rain near a stationary front. In tracking with trends, we expect a decrease in shower coverage into the evening, with some more convection possible in the periphery of the front. For this reason, a VCTS was maintained in the MGW TAF with convection tied to the PA/WV border just north. Nearly all area ports experienced at least some rain today, which will be followed by only a sct/bkn deck and allow some cooling overnight. With calm winds and moisture, at least every port has the chance to see fog or low stratus. While point probabilities of dense fog are generally 20% to 40%, these may be under-doing potential given the amount of daytime rain. The lowest vis was noted for the most susceptible ports, and ones that saw the most rain today. Some clearing is expected beyond daybreak, through cig lifting may be slower for southern ports (notably MGW, ZZV, and HLG) with probability of MVFR cigs through 16Z >50%. Another round of afternoon storms is possible as a warm front lifts north, but coverage should remain isolated, if any, into the daytime hours Saturday. Outlook... A chance of showers/storms is possible overnight Saturday on a prefrontal trough, through chances of rain and gusty winds have decreased since the last update. The actual cold front passage Sunday will allow additional late-morning to afternoon storm chances including, and south of, PIT. Dry weather returns early next week before more rain chances mid-to-late week. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...Flood Watch until 1 AM EDT Saturday for OHZ057-058-068-069. WV...Flood Watch until 1 AM EDT Saturday for WVZ012-021-509>514. && $$ SYNOPSIS...CL NEAR TERM...CL SHORT TERM...CL LONG TERM...CL AVIATION...Milcarek