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
131 FXUS61 KPBZ 022323 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 723 PM EDT Tue Jul 2 2024 .SYNOPSIS... Shower and thunderstorm chances increase Wednesday evening through Friday with a series of upper level disturbances, with potential for convective lulls during the overnight periods. Expect well above normal temperature through the holiday weekend, with high probability for dry weather returning Saturday and Sunday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... KEY MESSAGES: - High pressure will maintain dry and seasonable weather through the overnight period. ------------------------------------------------------------------- Update... Only minor adjustments to the forecast based on current observations and near term model trends. Previous discussion... Dry and seasonable weather will persist through the rest of the evening as a 500mb ridge crosses overhead and the surface high positions along the east coast. A few cirrus clouds may cross overnight but are unlikely to alter area temperature much; the main driver of the rising low temperature is the column warm, moist advection as southwesterly flow increases. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... KEY MESSAGES: - Dry weather and seasonable warm weather expected for most of Wednesday. - Showers and thunderstorms possible Wednesday night and Thursday, with low probability threat of severe weather. ------------------------------------------------------------------- An upper level shortwave and decaying convective complex will approach the region from the west Wednesday morning as warm, moist advection persists. Subsidence and the prior dry air mass should result in dry weather and above normal temperature through the afternoon. That shortwave will traverse north of the region during the late afternoon to evening hours and push a decaying surface boundary east southeast, increasing shower and thunderstorm probabilities. The convective focus will be approximately between 20z-01z (4pm-9pm) across eastern OH where convection is likely to develop just ahead of the surface boundary. Environmental conditions supporting the SPC marginal risk for damaging wind includes mean SBCAPE around 1000-1500 J/kg, around 30kts effective shear (though potentially decreasing with event time as shortwave exits), and rapidly rising PWAT values (going above 90th percentiles). The threat remains conditional on a few factors: 1) the column moisture increase likely coincides with weaker lapse rates (equating to less intense updrafts); 2) the decaying front and north-bound shortwave are likely to offer limited support for initiation and upward growth; 3) there is potential for convection along the southwest flank of the front to fire earlier and cut off moist advection to the region (and/or limit instability with cirrus coverage). Overnight, isolated to scattered showers remain possible as the shortwave exits northeast and the front stalls generally along and south of I-70. Loss of heating should limit severe potential, with storms relying on elevated instability to continue through Thursday morning. The rest of the day Thursday features likely convection along/south of the boundary as additional weak shortwave cross within the WSW flow aloft. Localized flash flooding remains a concern given near-record PWAT values and near parallel upper flow with the surface boundary; however, marginal instability and weak lapse rates may limit maximization of rainfall rates. Thursday evening will see a downward trend in convective activity, with mostly isolated to scattered storms remain south of I-70. && .LONG TERM /FRIDAY THROUGH TUESDAY/... KEY MESSAGES: - More widespread storm coverage expected Friday, with non-zero hazardous weather threat. - High probability for dry weather and slightly above average temperature the rest of the weekend. ------------------------------------------------------------------- A better developed upper level shortwave trough will enter the lower Ohio River Valley Friday and promote broad jet-aided ascent for the forecast area. Northward lifting of the stationary boundary and eventual crossing of a surface cold front is likely to generate more widespread shower and thunderstorm coverage Friday afternoon and evening. Environmental conditions remain variable amongst ensemble models but mean SBCABE around 1000 J/kg, PWAT above 90th percentile, and 30-40kts 0-6km shear suggest potential for hazardous weather in the form of damaging wind and flash flooding. Long range patters suggest troughing will persist over the Central Plains, leaving the Upper Ohio River Valley within weak southwest flow (and likely within a dry slot). There is fairly high confidence in dry weather and slightly above normal temperature occurring Saturday through Monday until the next low pressure system potentially crosses Tuesday. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/... VFR is expected through most of Wednesday as an upper ridge moves east across the region. Wind should veer to the SW after sunrise, with a few gusts up to 20kt. A shortwave trough will approach the Upper Ohio Valley region late Wednesday afternoon and evening. Scattered showers and thunderstorms are expected to develop in advance of the trough. The coverage and timing remain in question, with the most favorable instability for storms expected just to the west of the area. Included a VCTS mention for now in the tafs with uncertainty remaining. .Outlook... VFR is expected through Wednesday. A slow moving front is expected to persist across the region Wednesday night through Friday, bringing showers, thunderstorms and associated restrictions back to the area through the end of the week. A cold front will maintain showers, thunderstorms and ocnl restrictions Friday night/early Saturday. VFR should return Sunday under high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...WM/Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...WM