PBZ issues Area Forecast Discussion (AFD) at Mar 4, 3:13 PM EST684
FXUS61 KPBZ 042013
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
313 PM EST Tue Mar 4 2025
.SYNOPSIS...
Dry with above average temperatures today. Rain returns later
tonight with thunderstorms and gusty winds possible on
Wednesday. Rain will change to snow Wednesday night and Thursday
with colder air filtering in. Periodic rain and snow chances
continue through the weekend.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:
- Dry and warm weather today with highs in the 50s/60s.
- Mild with clouds increasing tonight.
-------------------------------------------------------------------
Intruding drier mid level air with rising heights has allowed clouds
to scatter out nicely this afternoon providing a beautiful
early March day with temperatures well into the 60s across the
board. Aiding in highs tapping into the mid 60s is mixing into a
very dry boundary layer offsetting the moisture advection in
gusty southerly flow at times. Leaned toward the NBM95th
percentile for highs today, which is still underdoing temps in
some spots, and NBM10th percentile for dew points capturing the
dry and warm trend today on an otherwise cold biased NBM.
With those lower dew points and afternoon mixing, minimum RH values
are forecast to dip into the 25-30% range this afternoon across
southwest PA and northern WV. Southerly wind will gust up to 15-20
mph through the day today, and 10 hour fuel moistures are as low as
10-15%. In collaboration with neighboring offices and state fire
partners, have issued an SPS for those areas through 23z tonight.
Clouds will be on the increase tonight as deep layer southerly flow
increases moisture ahead of approaching low pressure. Warm advection
will keep highs mild in the 40s and 50s.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Dynamic system brings rain, strong wind, and potential for severe
weather Wednesday.
- Slight Risk (2/5) for severe.
- Rain changes to snow Wednesday night into Thursday.
--------------------------------------------------------------------
Aforementioned low pressure will cross out of the southern Plains
and through the Great Lakes Wednesday as a deep upper trough ejects
out of the Rockies and crosses the eastern CONUS through the same
timeframe. We will start to see effects locally from this system
beginning very early Wednesday morning.
The first hazard to discuss is wind. This will be a very dynamic
system. Strong pressure falls are expected tonight in a
south/southeast flow regime as low pressure nears, with near 15 mb
height falls from Wednesday morning through Wednesday afternoon.
Simultaneously, the surface pressure gradient will tighten rapidly
as the low approaches. This setup should result in a period
downsloping enhanced gusts on top of the gradient and mixing on
the western side of the ridges. Strongest gusts will be across
eastern Tucker County, WV, where a Wind Advisory is in effect
from 7pm tonight through 7pm Wednesday. HREF and NBM prob 24
hour max gust probabilities for >46 mph are both at 100% in
eastern Tucker County and roughly 50% for >58 mph. There is less
certainty in how this will translate to the ridges/Laurels
farther north. Latest NBM and HREF probs still are more hesitant
up there, and there may not be a period of prolonged favored
direction for downslope effects, so have kept the wind headline
as is. In the lowlands, the probs of >40 mph are anywhere from
50-90%. There is even some signal for advisory criteria there,
but this may be stemming from convective related gusts as
opposed to synoptically driven. Regardless, it will be a very
windy day across the area.
The next hazard is the rain and severe potential. Strong moisture
advection with surface pressure and height falls as low pressure
nears will result in rain moving into the area after midnight
tonight. Moisture flux will increase PWAT values to 1.0-1.1".
Enhanced convergence on the nose of an 850 mb jet, meager elevated
instability above a WAA-driven inversion, and warm cloud depths to
~10kft will support a period of steady rain in the morning hours.
The period of heaviest, steadiest rain will be pre-dawn through 8am
for western PA, then through 1pm for the ridges. A brief reprieve
from the rain and some sunshine by early afternoon Wednesday should
allow for some destabilization ahead of the cold front which,
coupled with strong upper jet support and deep-layer shear, may
support strong to severe thunderstorms during the afternoon
hours. HREF probs for SBCAPE >500 J/kg peak around 50% with 0-6
km shear in the 40-50 knot range. Of concern for a low end
tornado risk would be if we get a developing broken line of
showers/storms and how much CAPE is packed into the lowest 0-3
km, as well as any segments oriented more northwest to southeast
to capitalize on line normal low level shear. While the morning
rain and cloud cover may suggest a lower severe potential, it's
also possible that the result will be a lowering of LCLs given
increased surface moisture, though the couple hours of
scattering and mixing could offset that effect and will have to
monitor in the mesoanalysis timeframe there. The 12z suite of
CAMs are mostly suggesting an afternoon timeframe but still exhibit
some disagreement on the extent and location of redevelopment.
The highest risk will be across western PA. Damaging wind
remains the greatest threat, but hail and an isolated tornado
cannot be ruled out. SPC has maintained the Slight Risk (2/5)
for most of the area.
NBM 25th to 75th PQPF range is roughly 0.50-1.00" in most of the
CWA, with roughly 0.75-1.50" in the PA ridges. While convection may
enhance rainfall rates and bear watching, not expecting any
significant hydrologic impacts from this event given the 1 hour, 3
hour, and 6 hour flash flood guidance values ~1.25", 1.75", and
2" respectively.
Strong post-frontal cold advection Wednesday night will drop 850 mb
temperatures from roughly +5C to -10C with rain showers
changing to snow showers. Typical upslope enhancement into the
ridges will result in 1-3" of snow there through Thursday, and
light amounts are expected in the lowlands. Antecedent very warm
air should preclude efficient accumulation, but the highest
amounts will be in the WV ridges.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- Dry weather on Friday.
- Rain and snow chances Friday night and Saturday.
- Near seasonable temperatures with warming early next week.
-------------------------------------------------------------------
High pressure is favored to build into the area Thursday nigh which
will shut off any lingering snow showers. This will keep the area
dry on Friday with seasonable temperatures. A weak impulse passing
through the Ohio Valley could then bring rain/snow showers Friday
night into Saturday, but marginal temperatures at this time look to
point toward low end accumulation potential.
Considerable uncertainty remains in how a second system evolves on
Sunday, as most of the guidance has a relatively modest trough and a
potential for snow showers. GEFS remains the deeper/colder (outlier)
solution, with likely more realistic depictions by the EPS/CMCE.
Regardless, it is certainly still too early to jump on any
deterministic band wagons that have recently appeared.
Strong signals continue for height rises early next week, signaling
quiet weather and warming temperatures.
&&
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
VFR continues through the afternoon and into the overnight with mid
and high level clouds passing through the region as flat ridging
crests over the top of us. Afternoon mixing under largely clear
skies has led to isolated gusts between 12-20KTs.
Rain approaches from the west overnight and overspreads all
terminals by sunrise Wednesday. MVFR probabilities begin to rise by
06z Wed for most terminals, except for LBE and MGW which show strong
signs of downslope winds helping to keep clouds at bay. MVFR probs
begin to dip again as quickly as they came by late morning as the
initial press of rain clears and skies follow suit allowing for some
clearing during the middle of the day. Unsurprisingly FKL/DUJ both
sport the highest probabilities of IFR. These probabilities climb
above 40% near 10z and remain elevated through midday.
There remains a chance for thunderstorms during the afternoon,
especially if more of the area can achieve clearing. These storms
bring a slight risk of producing damaging winds. At this time these
storms have been included in a PROB30 group for PIT in the extended
TAF period but this risk will be present at most TAF sites tomorrow
afternoon.
LLWS concerns pick up late tonight with all terminals sporting LLWS
by 03z as the nose of a 40KT low-level jet presses into the region.
These concerns begin to taper Wednesday morning as SFC gusts are
unleashed.
Outlook...
Rain transitions to snow Thursday as the cold front
sweeps the area and temperatures plummet. Snow tapers late Thursday,
giving way to VFR Thursday night. Precip and restrictions can return
with another disturbance on Friday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...Wind Advisory from 7 PM this evening to 7 PM EST Wednesday for
WVZ514.
&&
$$
SYNOPSIS...Rackley/MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...Rackley/MLB
AVIATION...AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Mar 4, 3:13 PM EST---------------
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