Area Forecast Discussion

WHAT HAS CHANGED

Flood Watch has been expanded 1 tier of counties further north. A Severe Thunderstorm Watch has been issued until 8pm for all of our OH, WV and PA counties south of a Beaver- Westmoreland line. Morning rain has soured some of our environment and shifted our focus a little further south, mainly along the I-70 corridor.

KEY MESSAGES

1) Enhanced Risk for severe weather on Tuesday; Slight Risk for Excessive Rainfall.

DISCUSSION

KEY MESSAGE 1... A large-scale area of low pressure is currently moving through central Ontario. Remnant showers and storms from overnight mesoscale convective systems (MCS) continue across the region early this morning in the unzipping warm sector. Morning convection has complicated but not eliminated our risk of severe weather across the region. It has also acted to raise our short term flood threat.

Our morning sounding only measured a PWAT of 1.32 but continued moisture advection from our west will look to advect PWATs near 1.9 inches (just below the daily maximum of 1.96 inches) across the region. This accompanied with a relatively high freezing level will allow for efficient warm rain processes in a very moist environment. Instantaneous rainfall rates up to 3-6 inches per hour seem possible but this will be tempered by shorter residence time of these rates owing to quick storm motions. With more progressive storms we have a higher chance of exceeding our 3 hour flash flood guidance more so than our 1 hour values likely requiring multiple rounds of storms. Morning rain is acting to set the table for flood issues later across a wider portion of the region and thus our Flash Flood Watch has expanded one tier of counties further north. The Flood Watch continues across the region through 11pm.

Several factors in our previous analysis remain true: we have a very intense (for July) left exit jet region overhead, dew points are in the low 70s and shear across the region is even over performing expectations with mesoscale analysis suggesting upwards of 50 knots available in the 0-6km layer. The locally lacking ingredient is instability due to widespread rain across the region this morning. However, a local lack of instability doesn't end our severe threat if we can produce instability to our west and advect storms into the region. This is likely the way our severe threat is shifting. If storms can form to our west and move into our incredibly strong dynamic environment then we still have a very high end severe threat on the table. If storms do not form west of us and move in then lower level storms can continue going forward and we may not realize the full potential of our environment for today. To this point there is a large area of clearing and Cu popping across IN and western OH. This activity is already even or south of Pittsburgh and any activity across our region from this likely focuses our severe threat Pittsburgh on south, especially along the I-70 corridor.

The amount of shear available in the environment points towards the possibility of Supercellular or QLCS structures. Each of these storm modes can bring damaging wind gusts and tornadoes. Morning rain has acted to locally lower LCLs nodding towards a possibly improving Tornado threat. Going along with this is drastically improving structure of our hodographs this afternoon especially I-70 on south and a noticeable uptick in our SIGTOR parameter. A Severe Thunderstorm Watch has been issued until 8pm for all of our OH and WV counties and all of our PA counties south of a Beaver- Westmoreland line.

Expect lingering showers and non-severe thunderstorms into early Wednesday before a cold front tracks through the region.

The potential for precipitation remain low through the remainder of the work week and into the weekend before showers and storms again look possible on Sunday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Showers and thunderstorms continue to cross the forecast area through the afternoon and evening. Much of the terminals east of ZZV will remain within MVFR and below conditions through the 22Z timeframe. Heavy downpours will cause vis at some terminals to drop below 1 mile. Have used mostly TEMPOs during the early part and some PRB30s to cover later convection.

The main threat of severe storms will likely be over by 23Z. The overnight tonight will expected to see left over showers and a few thunderstorms but with flight conditions remaining below IFR for most terminals due to low cigs.

Towards dawn, expect to see some development of some fog which could drop vis below 1 mile at times. Winds through the period will be from the southwest with some gusts up to 30 knots.

Outlook... There may be some MVFR cigs in the vicinity of DUJ/FKL early Thursday morning with cool northerly flow. Otherwise, VFR conditions will prevail under high pressure into Friday.

PBZ WATCHES / WARNINGS / ADVISORIES

PA...Flood Watch until 11 PM EDT this evening for PAZ014-020>022- 029-031-073>078. OH...Flood Watch until 11 PM EDT this evening for OHZ040-041-049- 050-058-059-068-069. WV...Flood Watch until 11 PM EDT this evening for WVZ001>004-012- 021-509>514.