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
230 FXUS61 KPBZ 082354 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 754 PM EDT Mon Jul 8 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 beginning Tuesday night. Tuesday and Wednesday will be the hottest days of the week with heat indices approaching 100 degrees. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... KEY MESSAGES: - Dry with lows 5-10 degrees above average. ------------------------------------------------------------------- High pressure will maintain dry weather through tonight, although high clouds will continue to stream across the region as moisture is drawn northeastward well ahead of the remnants of Hurricane Beryl. There is still a short window of opportunity for a stray orographically driven shower in the ridges, but development to this point has been off to our east, where it is largely expected to remain. Any remaining cumulus will dissipate with sunset, and we`ll be left with cirrus and a light to calm wind overnight. A warm and muggy night expected as southwest flow will continue to usher in moisture and weak warm advection combined with the cloud coverage will keep lows above normal in the upper 60s to low 70s in the urban areas. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... KEY MESSAGES: - Hot and humid Tuesday with heat indices nearing 100 degrees. - Marginal Risk (1/5) for severe overnight Tuesday night in eastern Ohio. ------------------------------------------------------------------- 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 as a warm front lifts north through the Ohio Valley late Tuesday night. A 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 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. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... KEY MESSAGES: - Remnants of Beryl track near the area beginning on Wednesday. - Still uncertainty with potential phasing with northern stream trough which will determine potential for severe and flooding concerns. - Temperatures rebound to close out the week with scattered showers. ------------------------------------------------------------------- The remnants of Beryl approach and impact the area starting on Wednesday. Primary uncertainty at this point comes from how Beryl phases with a northern stream trough. In terms of rainfall, a more phased solution would result in longer residence time and a stronger push of moisture providing amounts on the higher end of the wide distribution. Less phasing and quicker movement would provide less rainfall on the lower end of the distribution. Current NBM probabilities for >1" over a 48 hour period are highest to our west, north, and east (only ~30% at PIT) coincident with the potential intrusion of a dry slot dependent on the phasing of the low. Can`t rule out some hydrology concerns as we sit with uncertainty as the northern half of the area remains in a Slight Risk (2/4) for excessive rainfall and the rest of the area in a Marginal Risk (1/4). The driest solution could even potentially raise heat concerns on Wednesday if it comes to fruition, especially south and east of Pittsburgh, as moisture surges with dew points into the mid 70s. This is well represented by the NBM 10th/90th percentile spreads in MaxTs on Wednesday sitting at 78/93 respectively. For the severe threat, the track of the low again will play a big role. The points of interest will be a warm front, how long the area may remain in an open warm sector ahead of a cold front/surface trough, and, dependent on the low track, what type of environment we see. A possible severe risk could be focused along the warm front as it moves north and/or the cold front later in the day, though all of that will ultimately be dependent on the track of the low which, as stated, is still uncertain. Ample shear looks to be available as the CAMs now just start coming into play, so a solution with a more moist environment with low LCLs would indicate the necessity to watch for a tornado risk. The flip side would be a drier atmosphere --> more insolation --> more instability supporting a conditional wind/hail risk with diurnally driven convection. That said, a potential failure mode here with the drier environment could be an atmosphere that is simply too dry to convect in the first place. SPC has maintained the Marginal Risk (1/5) covering areas north of I-80. Still a good amount of questions remain as we await better agreement amongst the ensembles and a higher confidence forecast in which one will play out, but the array of potential solutions is narrowing. 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. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... VFR prevail for the TAF period with high confidence. Calm to light and variable winds will persist overnight. There is a very low chance of fog tonight (less than 10%) confided to river valley ports (FKL, HLG). Tomorrow, mixing will ensue and contribute to scatted to broken high-based (6kft-8kft) cumulus decks. Winds will accelerate and veer from south to west throughout the day. In the late afternoon period (4pm-8pm), there is a less than 15% chance of showers/storms in eastern Ohio and northwest Pennsylvania. Cumulus will dissolve after sunset and give way to mid-level broken decks as winds lighten and veer northerly. .Outlook... There is a 30% to 40% chance cigs south of Pittsburgh drop to MVFR in the 6am to 9am timeframe Wednesday morning with the remnants of Beryl. Chances increase to 50% to 70% north of Pittsburgh with rain/storms more likely. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...MLB NEAR TERM...MLB/CL SHORT TERM...MLB LONG TERM...MLB AVIATION...Milcarek