PBZ issues Area Forecast Discussion (AFD) at Nov 9, 2:58 AM EST712
FXUS61 KPBZ 090758
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
258 AM EST Sat Nov 9 2024
.SYNOPSIS...
Dry weather is expected through Saturday. Low pressure will
support widespread rainfall Sunday into Monday. Uncertainty
increase into next week with possible rain chances returning by
mid-week.
&&
.NEAR TERM /THROUGH TODAY/...
KEY MESSAGES:
- Overnight lows right around normal.
- Dry start to the weekend with above-normal temperatures.
-------------------------------------------------------------------
The cold air advection behind the front is more of a north to
northeast flow currently and so far has not exactly switched to
the northwest yet. This will keep the stratocumulus deck from
developing. It remains to be seen whether the layer will
develop but the NBM is showing less than 20% for a layer to
develop. Thus, will likely be dealing with cooler temps and less
cloud cover through dawn.
Upper ridge axis shifts overhead on Saturday and amplifies
downstream of a closed low across the Plains. Warm advection aloft
with the building ridge atop easterly surface wind will push 850 mb
temperatures to 8-12C, higher southwest and lower northeast, which
will push highs again a couple degrees above normal. Still dry low
levels and localized downsloping effects off of the ridges will
allow for dew points to mix out again in the afternoon and minRH
values down to the upper 20/low 30 percent range. Lesser wind
gusts should preclude widespread fire weather concerns, but
conditions will warrant monitoring and a SPS has been issued for
the PA counties. Clouds increase late Saturday as deep layer
moisture ramps up ahead of approaching low pressure.
&&
.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- High confidence in widespread wetting rainfall on Sunday.
-------------------------------------------------------------------
Warm advection will keep overnight lows in the upper 30s-low
40s. Deep southwest flow will provide a strong pull of Gulf and
remnant Rafael moisture on Sunday with integrated vapor
transport values 2-4 SD above normal and ensemble mean
precipitable water near 1.3" which is near the daily maximum
value. As low pressure lifts through the Great Lakes region,
widespread rainfall is expected to arrive in the morning hours.
The most steady rain likely comes Sunday afternoon as an 850 mb
jet encroaches and enhances low level convergence. Current
ensemble probability for a wetting rain (at least 0.10") is very
high at 95-100% areawide. Similarly, at least 0.25" is 90+%
with a 60-80% chance of a half an inch. The higher end (90th
percentile) of the goal posts has continued to sit around an
inch and is likely contingent on capitalization of whatever
marginal instability can develop; instability likely won't be
surface-based given the low-level warm advection regime, so any
severe weather threat is low. The system will be progressive
overall, but wouldn't rule out some localized totals nearer to
the 75th-90th percentile in some of the maximized higher
rainfall rates.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Low confidence rain chances for the beginning of the week.
- Better rain chances come mid-week but still some uncertainty.-
- Highs a few degrees above normal.
-------------------------------------------------------------------
Some showers may linger into Monday behind departing low pressure as
a weak secondary trough moves through, but ensemble clusters suggest
increasing uncertainty with the upper level pattern to start out
next week as an additional upper wave follows quickly behind the
original one from Sunday. Some clusters merge these waves while
others favor a flatter, more progressive pattern. A slower departure
would favor cooler temperatures and lingering precip chances through
Monday night while a faster pattern favors warmer, drier conditions.
Overall consensus is that high pressure and upper ridging briefly
return which favors still above normal temperatures through mid-
week. Another better chance for rain may come sometime Wednesday
into Thursday with another round of low pressure, but significant
differences among the ensembles suggests a low confidence forecast
by this point.
&&
.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions will prevail through the TAF period with light
winds gradually veering from northerly to easterly through the
morning. High/mid clouds will push into the area Saturday night
in advance of the next system.
.Outlook...
Rain and restrictions will likely overspread the region after
12Z Sunday.
A passing cold front early Monday will decrease the potential
for rain. However, restrictions may linger into late Monday
morning due to residual low-level moisture and cold advection.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB/Shallenberger
NEAR TERM...MLB/Shallenberger
SHORT TERM...MLB/Shallenberger
LONG TERM...MLB/Shallenberger
AVIATION...Rackley/88
Source:
PBZ issues Area Forecast Discussion (AFD) at Nov 9, 2:58 AM EST---------------
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