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585
FXUS61 KPBZ 100913
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
513 AM EDT Thu Jul 10 2025

.SYNOPSIS...
A typical warm and moist summer airmass will remain in place
this week and allow scattered afternoon and evening
thunderstorms to develop over the Upper Ohio River Valley each
day. Thunderstorm chances will be a bit higher this weekend as a
weak cold front sags into the area from the Great Lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
KEY MESSAGES:
- Patchy dense fog lifting this morning.
- Isolated showers and thunderstorms.
- Main threats are wind and flash flooding.
- Patchy fog possible again tonight.
---------------------------------------------------------------

A stabilized airmass is noted near and north of a stalled surface
boundary across eastern OH to southwestern PA. The airmass is
currently characterized by cool temps and dew points in the mid to
upper 60s. Areas of low visibility have been reported at various
airports across the region along with satellite confirming areas of
fog. Areas of patchy fog will lift with diurnal heating by 8AM/9AM.

An upper level trough over the eastern Great Lakes will bring moist
and unstable environment to the region. This results in diurnal
thunderstorms that are isolated in nature and poorly organized. With
the upper level flow weakening, these storms are expected to be slow
moving in nature. Precipitable water values are forecast around
1.5" which will be high enough to support locally heavy rain.
With the slow-moving storms and the moisture, there is the
possibility for localized areas of flash flooding.

Mid levels are forecast to be drier today. With some additional
DCAPE, there is a slightly higher potential for wet microbursts.
Strong wind is possible with thunderstorms today.

After sunset, the probability for showers and storms will
significantly decrease. With the moisture expected to remain
stationary, there is a chance for patchy fog to develop again
tonight.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
KEY MESSAGES:
- Weak troughs moving along northern edge of subtropical high
  will support scattered diurnal thunderstorm development
- Low probability of severe and flash flooding at any one point but
  a couple spots could see significant weather each day
- Temperatures a bit above normal with a gradual warming trend
  peaking out on Saturday around 90F
----------------------------------------------------------------

Upper High Centered over Southwestern US as it often does in
summer with subtropical ridge over the southern part of CONUS.
Westerlies continue to stay over the northern states with a
tendency for troughing over the Great Lakes. This results in a
seasonably moist and unstable airmass with daily rounds of
diurnal thunderstorms that will be poorly organized with weak
shear. In fact Corfidi upstream MCS motion vectors become light
and variable for the rest of the weak so expect slow moving
storms that will produce heavy rainfall. Precipitable Water
values around 1.5" will not be excessive but will be high enough
to support locally heavy rain given the slow storm motions.

Mid levels become a lot drier tomorrow so a bit more DCAPE in
profiles and a slightly higher potential for wet microbursts on
Thursday.

Overall not much organization for the thunderstorms and
coverage will be scattered with very sparse coverage of heavy
rainfall and damaging winds each day. A difficult situation to
message because it is likely that only 1-2 locations each day
are impacted by significant weather. Many spots will be dry each
day and it is difficult more than 6-12 hours in advance to get
your arms around where the chances for impacts will be higher.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Weak front brings better chance of thunderstorms Sunday
- Not much cooling with temperatures remaining about 5 degrees
  above normal
-------------------------------------------------------------------

Not a lot of change to the pattern and, even with weak summer
flow regime, a good bit of spread on the timing and intensity
of weak troughs drifting through the Ohio Valley and Great Lakes
areas.

Looks like best shot for a weak front to enhance thunderstorm
chances will be on Sunday. NCAR AI severe probabilities based on
ECMWFE are highest on Sunday and that seems reasonable. Would
also be a higher threat of heavy rain and flash flooding that
day as Precipitable Water values increase from about 1.5" to the
1.75-2.00" range.

Pattern for Monday thru Wednesday becomes a bit more complex
and uncertain as we could see a series of weak trough/ridge
couplets. Certainly could be a dry day or two in that time range
but not much confidence at this time.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
Patchy fog development currently observed across the region has
potential to become more widespread by sunrise based off latest
forecast soundings showing MRI values favoring fog over stratus
and crossover temperatures dipping down to between -3 to -5F
based off TDs during max mixing yesterday afternoon. Latest
ensembles/blends show a 20-50% chance of IFR vis restrictions
in general between 4 and 8AM this morning, and nealy identical
probabilities for MVFR vis restrictions. So at appears to be an
all or nothing situation, and will make amendments to current
TAFs early prior to sunrise once it becomes more apparent which
scenario plays out.

Any fog is likely to dissipate quickly around mid-morning
with a broad return to VFR conditions. Storms are possible
after 18z and will present as more scattered in coverage. Timing
will be difficult to pin down with development potentially off
of Lake Erie`s lake breeze initially, with subsequent initiation
driven by storm outflow. Any showers/storms could bring brief
heavy rainfall and gusty wind. PROB30 was included at all sites
for now, pending refined mesoanalysis later this morning, which
could help identify targeted areas and timing.

Outlook...
A weakly forced but warm/humid environment is favored through
the end of the week that will allow for intermittent periods of
showers/thunderstorms. Confidence is likely to be lower on
timing various rounds of precipitation as well as the resultant
cig/vsby impacts they could have during the morning hours.

More significant upper-level and surface boundary movement
appears to arrive over the weekend, which will create a better
focused period for convection and restriction development.

&&

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

&&

$$

SYNOPSIS...Craven
NEAR TERM...Lupo
SHORT TERM...Craven
LONG TERM...Craven
AVIATION...88