Sunrise 6:13 AM   Sunset 8:18 PM Moonrise 2:56 AM   Moonset 2:07 PM

  Print   HELP   Reset   Save   Recall

FXUS61 KPBZ 030743 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 343 AM EDT Fri May 3 2024

SYNOPSIS
Dry and unseasonably warm weather precedes increasing precipitation chances Friday afternoon and continuing through the weekend. Cooler, but still above average, temperatures prevail Saturday and Sunday with warm and unsettled weather continuing into next week.

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- Showers and thunderstorms Friday afternoon and evening.
- Temperatures well above average approaching a few records.
-------------------------------------------------------------------

High pressure will retreat off to the east as a disturbance approaches from the west. Cirrus coverage will thicken and lower through the morning with increasing upper level moisture. Forecast soundings suggest another day similar to Thursday with a quickly breaking nocturnal inversion and a dry boundary layer allowing for mixing up to nearly 700 mb. The 850 mb ridge will gradually shift to the east and allow for warm advection in southwesterly flow to bring layer temperatures up to 15-16C across the area by afternoon, suggesting that high temperature will achieve the mid to upper 80s despite the cirrus. A couple sites have the potential to approach record highs (see climate section). Some lingering uncertainty in ensemble cloud coverage with suggestions for periods of scattering as cirrus push to the east lends potential for additional insolation to push temperatures up even a degree or two higher than currently forecast. This also could aid in a bit more destabilization ahead of showers and thunderstorms expected to develop by afternoon.

Indications are that showers and storms pop after 17z despite copious low level dry air (LCLs 6-8kft) as convective temperatures are met and a shortwave moves through, though weak net height rises through the day are expected. Mean hi res ensemble CAPE has increased in the latest run with 600-900 J/kg; conditional on potential scattering of clouds, the 75th percentile is up to 1400 J/kg. Most guidance suggests that warm mid-levels will suppress updrafts with an equilibrium level below about 500mb. Latest CAMs suggest that the best shot for deeper convection may be across eastern Ohio where slightly less warmth and moisture in the mid-levels may allow for greater vertical growth. Even if the higher end of the instability spectrum is achieved, weak cloud bearing layer flow will present a moderate CAPE/low shear environment likely more favorable of gusty wind with brief heavy downpours. PWATs will be pushing 1.5" and upwind propagation vectors around 10 knots despite practically no low level jet suggest this potential. HRRR probs for >0.5"/hr rates reach up to around 60% by evening. As a result, the Weather Prediction Center has our area in a Marginal Risk (1/5) for excessive rainfall on Friday.

Record low max temperatures may be broken Friday night with persistent cloud cover not allowing for radiative cooling.
Convection is favored to wane as instability is lost and the upper wave departs. Nonetheless, scattered showers will continue overnight.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
KEY MESSAGES:

- Unsettled pattern remains with rain chances continuing through Sunday. Thunder possible on Sunday.
- Temperatures drop, but still remain above normal.
-------------------------------------------------------------------

Come Saturday, there is some suggestion the trough progression will come to a halt and allow rain to persist ahead of it being reinforced by approaching low pressure and additional shortwave support arriving from the south. The positioning of the trough will have a great influence on the weekend weather. No significant changes to the forecast for Saturday as instability looks limited to the western side of the stalled boundary/trough with a 50-60% of >500 J/kg while elsewhere plenty of low to mid level warm air will cap the environment. Total rainfall Saturday is favored in the half to three quarters of an inch range.

There is good agreement the trough finally pulls through by Sunday. An area of maximized precipitation ahead of or just along the trough axis is favored, as is a greater chance for more instability to work with. Ensemble probability for CAPE >500 J/kg reaches 70-80% Sunday, but with a good amount of clouds around and a low probability of any scattering. Still, with a bit better dynamics in play and marginal instability, a few thunderstorms accompanying the trough appear possible. Most likely total precipitation amounts Friday night - Sunday night sit around 1.0-1.3", but the 90th percentile exceeds 2" primarily across the WV panhandle and western PA resultant of some convective enhancement along the aforementioned trough.
This does not raise any flooding concerns for now, but may warrant watching if the higher end becomes more likely.

Thick cloud coverage through the weekend will hold temperatures in check, but still above average, in the 70s.

LONG TERM /MONDAY THROUGH THURSDAY/
KEY MESSAGES:

- Rain chances continue into early next week but more uncertainty lends lower confidence.
- Temperatures favored to remain above normal.
-------------------------------------------------------------------

After a brief lull in the precip late Sunday night into early Monday morning as flat upper ridging slides through and surface high pressure meanders on by, rain chances again increase. Seeing some better ensemble agreement for Monday with shortwave low pressure approaching from the southwest but weakening as the responsible upper wave flattens out. High pressure to the north should keep the highest precipitation chances south of I-70. Much more ensemble spread comes into play after Monday primarily with the progression of the upper pattern as ridging tries to develop but a deep upper low across the Dakotas throws shortwave energy to the east and tries to break the ridge down. A warm front likely lifts through sometime Tuesday into Wednesday increasing rain chances again, but with uncertainty in the strength and positioning of the ridge, timing and precipitation amounts remain low confidence at this time.

AVIATION /08Z FRIDAY THROUGH TUESDAY/
VFR conditions through most of the day, with high clouds increasing this morning and mid clouds this afternoon.
Scattered showers and thunderstorms are expected to develop late this afternoon and evening. Expect locally lower ceilings and visibilities, lightning, and possibly some gusty winds to accompany any stronger storms. The probability that a storm will hit any particular port is low at this time so will use prob30 to cover the convection threat. Activity should dissipate with the loss of sunlight. Lower clouds are possible late tonight.

Outlook
Restriction potential continue through Saturday, then again early next week as multiple disturbances cross the region.

CLIMATE
Some record highs may be approached on Friday as well as record lows on Saturday. (* denotes current forecast temperature exceeds value)

5/3 Record High Year Pittsburgh 95 1887 Wheeling 90 1942 Morgantown 88* 1965, 2012 New Philadelphia 89 2012 Zanesville 91 1938 Dubois 84 2012

5/4 Record Low Year Pittsburgh 65 1938 Wheeling 63 1931, 1939, 1941 Morgantown 63 2021 New Philadelphia 60* 2012 Zanesville 65 1902 Dubois N/A N/A

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...None.

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Pittsburgh, PA,