Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Friday, May 25, 2012
Valid: May 26-30 (Saturday-Wednesday)
Summary:
Saturday through Monday air quality will reach high moderate levels. The best chance for
Code Orange ozone will be Monday and Tuesday. Southerly transport on Saturday and Sunday
will limit ozone levels, timing of pre-frontal convection will be the key forecast issue on Tuesday.
Discussion:
There is good agreement among the NAM, GFS, and ECMWF through the period.
The main disagreement is the timing of a front that will pass through early Wednesday although the ECMWF is a bit slower. All three models agree
on the location of the ridge and, in general, the movement of the "tropical system" off the SE coast. As usual, the GFS remains the wetter solution.
The critical weather factor affecting the air quality forecast will be
the tropical system (94L) that is expected to drift northward early in
the medium range period. It will bring onshore winds from Saturday into Sunday,
particularly for the southern mid-Atlantic region, but they could extend into
the PHL area. The main impact will be the transport of relatively cleaner maritime
tropical air onshore.
Saturday, onshore winds are expected at low levels, however transport aloft
will be from the west. At this time, ozone levels at SNP remain steady in the
lower 50's ppbv. PM concentrations at SNP and Piney Run are rising slightly to the good/moderate threshold suggesting that there is more sulfate than NOx in this mix.
This regional load of pollutants will assure at least moderate air
quality on Saturday.
Light winds, primarily from the south to southeast, with morning fog, on Saturday.
Skies will clear by late morning and precipitation is unlikely. These factors
affect air quality in different directions. Morning fog and light winds will allow
PM concentrations to rise in the morning but will retard ozone formation. Sunny
skies will increase ozone but maritime air will provide lower concentrations of
ozone and PM precursors. The early numerical model forecast runs give low ozone for Saturday with the exception of the NOAA model which is higher in the PHL area. With no unambiguous signal for high ozone potential, we expect moderate air quality for both ozone and PM.
Sunday, winds will be primarily onshore for the region, which will work to keep PM
in the good range. However, mostly clear skies will be conducive to moderate ozone
levels. By Monday, winds will veer southwest and temperatures will
reach 90 degrees in the mid-Atlantic. Low level transport along the I-95 Corridor
is likely to include an air mass higher in PM and ozone and PM precusors. Both ozone
and PM concentrations are expected to rise on Monday with a possibility of scattered
Code Orange ozone levels. Still a lot of uncertainty with respect to Monday's forecast.
For the entire holiday weekend, local emissions will be uncertain. Motor vehicle emissions
will be higher Friday and Monday, especially along I-95 and the beach routes but urban emissions will be lower. It is difficult to determine the effect on peak pollutant concentrations
but we expect Monday afternoon to be high in emissions.
Tuesday remains questionable due to the timing of pre-frontal mesoscale convection.
The GFS predicts precipitation ahead of the front as early as 12 UTC Tuesday with
significant rainfall continuing through Wednesday. If this plays out, it will keep PM and ozone
levels in the good range. The frontal passage is expected Wednesday morning with a
cleaner air mass in its wake.
-Bunavage/Wiles/Ryan
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Thursday, May 24, 2012
Valid: May 25-29 (Friday-Tuesday)
Summary:
Good air quality with broken clouds and a chance for rain on Friday. A chance for an
extended poor air quality event this weekend, with moderate to USG (unhealthy for sensitive
groups) ozone concentraions particularly from Saturday to Monday. PM concentrations will reach moderate levels Saturday and Sunday. Tuesday will be a pre-frontal case with a continuing chance for scattered poor air quality.
Discussion:
Overall, there is good agreement and consistency between the NAM and GFS forecasts
with the ECMWF remaining the outlier as to the strength of the upper level ridge. The NAM and GFS both build the ridge into the mid-Atlantic by Saturday while the ECMWF
continues to be the weaker solution, keeping the ridge further south due to
a strong eastern Canadian low suppressing northward movement.
The critical weather factor affecting the air quality forecast will be
the tropical system (94L) that is expected to drift northward early in
the medium range period. There is disagreement between the models as to
how far the 'tropical system' pushes north, but for now
we will continue to follow the GFS which keeps it slightly further south.
The NAM appears to be a outlier in placing the center of the low further to the
northwest. The ECMWF is consistent with the GFS.
The position of the low will likely affect the southern mid-Atlantic and
its effects may be felt as far north as PHL. The main impact will be the
transport of relatively cleaner maritime tropical air onshore.
Continued clouds and scattered rain on Friday is expected with a frontal passage
overnight and into Saturday morning. This should keep PM and ozone concentrations
in the good range on Friday.
Saturday remains a difficult forecast although the models have been transitioning to
a strong onshore flow pattern that may limit peak ozone concentrations.
Clear skies on Saturday with possible onshore winds should keep PM in the good range
for the southern mid-Atlantic. Stronger onshore winds are expected according to the NAM
solution. However westerly transport aloft will bring moderate PM for the
rest of the region. Ozone is the primary focus for Saturday with concentrations
expected to reach upper moderate levels. If the coastal low weakens, and westerly
transport dominates, then Code Orange ozone is not out of the question.
Sunday and Monday pose similar forecast issues. The persistence of onshore winds, as is likely to be the case Saturday, will be the primary issue. The GFS back trajectories suggest continued on shore flow in the boundary layer through Monday. Second, convection will be an issue both days, particularly in the northern mid-Atlantic. Very warm temperatures will support Code Orange ozone but the transport and convection issues make it a 50/50 proposition at this time.
Tuesday will be a pre-frontal case. The medium range forecast models typically are too aggressive pushing frontal boundaries eastward in summer so a threat of poor air
quality remains into Tuesday.
-Wiles/Bunavage/Ryan
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Wednesday, May 23, 2012
Valid: May 24-28 (Thursday-Monday)
Summary:
Good air quality with clouds and rain on Thursday. A chance for an
extended poor air quality event this weekend, with Code Orange ozone perhaps
as early as Saturday but more likely Sunday-Monday.
Discussion:
In general, good agreement and consistency with the forecast models. This
lead to good confidence in the air quality forecast through Friday but lower
confidence through the weekend.
The main disagreement between the weather models is the timing and strength of the incoming
ridge. The NAM (and SREF) are most aggressive building the ridge into
the mid-Atlantic while the GFS is slightly slower. The ECMWF is a bit of a outlier with
a strong eastern Canada low suppressing the northward movement of the ridge.
Overall, the NAM provides the highest ozone solution while the ECMWF is the cleanest.
For now, we will generally follow the GFS solution.
Continued clouds and scattered rain on Thursday with winds slowly becoming southerly
and picking up speed late in the day. Air quality will be good through the region
with PM likely the leading pollutant on this day.
By Friday ridging is dominant in the region and precipitation and cloud cover become
more scattered, with the GFS having the wetter solution. Winds will also have more of
a southerly component. PM and ozone concentrations will likely rise but should still
remain in the good range.
Saturday is the forecast day of most interest. There are differences between the models in
the strength of the upper level ridge and this implies that the track of likely mesoscale
convection may or may not be displaced north of the mid-Atlantic. Expect quickly rising
ozone concentrations Saturday with a chance of isolated Code Orange peaks. PM will rise
as well due to high dew points and westerly transport aloft but is likely to stay in the
moderate range.
Chances of convection will be the key forecast issue on Sunday. Otherwise conditions are
conducive to high ozone and PM. Monday looks to be the worst day in the period. Temperatures should
reach around 90 degrees Fahrenheit throughout the region, and the direction of transport
will be primarily from the west, which promotes rising PM and ozone concentrations. Ozone will also
rise due to clear skies.
One last fly in the ointment is the location and strength of the possible tropical system
(now Invest 94L) expected to be east of Florida later this week. The southern mid-Atlantic
may see sustained low level onshore winds at the periphery of this system which will lead
to much cleaner conditions.
-Ryan/Bunavage/Wiles
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Tuesday, May 22, 2012
Valid: May 23-27 (Wednesday-Sunday)
Summary:
Good air quality with clouds and rain through Thursday. A chance for an
extended poor air quality event, primarily ozone, over the weekend although
considerable uncertainty in the forecast models past Friday.
Discussion:
Good agreement and consistency with the forecast models through Thursday but
quite a bit of disagreement beginning Friday. The model differences could have
profound impacts on air quality. Good confidence in the air quality forecast through
Friday but low confidence through the weekend.
Continued clouds and rain through Thursday with winds slowly becoming southerly.
Air quality will be good through the region with PM likely the leading pollutant
both days.
The forecast uncertainties begin on Friday. The NAM 0600 UTC run develops a
"tropical looking" system off the Florida Atlantic coast. This, in turn, drives
stronger onshore winds for the southern mid-Atlantic and retards the onset of
warm air from the west. At this time, the NAM is an outlier with respect to the
location and strength of this circulation although all models have some kind of
inverted trough off the east coast at this time.
The GFS is the high ozone model for later in the period. A large upper level ridge
will nose into the mid-Atlantic by Saturday and remain in place through the holiday
weekend. The ECMWF does have a ridge but it does not push as far north as the GFS.
To be on the safe side, we will follow the GFS forecast for now. In that scenario,
ozone concentrations will rise significantly on Saturday as transport direction
shifts west and surface high pressure sits over the mid-Atlantic with a hint of a
lee trough developing.
The GFS continues ozone conducive weather through the Memorial Day weekend although
holiday emissions are always difficult to determine. Increases in PM concentrations will lag
ozone by ~ 48 hours with highest PM expected late in the weekend. Best chance of Code Orange ozone will be in the Sunday-Tuesday period (Saturday is still uncertain) with PM highest Monday-Tuesday.
-Ryan/Bunavage/Wiles
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Monday, May 21, 2012
Valid: May 22-26 (Tuesday-Saturday)
Summary:
Good air quality through Thursday with clouds and rain likely. An upper
level ridge builds in for the weekend. This ridge bears watching but, for now,
looks to support only moderate air quality.
Discussion:
Reasonably good agreement between the forecast models with some differences
arising late in the period. The HPC considers the ECMWF to be an outlier by
day 5 (Saturday). The key forecast issue for our purposes is the strength and
location of an upper level ridge building in over the weekend.
An upper level closed low will be over the SE and mid-Atlantic through the short
range with clouds and afternoon rain for most locations. Winds will be onshore, becoming
more southerly later in the week. The combination of maritime air and cloud cover will
keep ozone and PM in the good range through Thursday.
For the coming holiday weekend, there are some differences in the forecast models. The GFS builds a strong ridge to our west and this is an ozone-conducive weather pattern. However, temperatures are expected to remain in the mid-80's F so that Code Orange conditions do not appear likely at this time. The ECMWF appears to be an outlier bringing a strong back door front to the region by Saturday.
-Ryan/Bunavage/Wiles
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Friday, May 18, 2012
Valid: May 19-23 (Saturday-Wednesday)
Summary:
Primarily onshore flow through the period with good to low moderate air quality.
Highest concentrations in the western mid-Atlantic. Considerable uncertainty
in the weather forecast after Sunday with a trend to cloudier and wetter
conditions.
Discussion:
Forecast model consensus breaks down pretty quickly after Saturday so only limited confidence in the weather portion of the forecast. For air quality concerns, the difference is
limited to the good/moderate threshold.
A weak "Rex block" develops over the weekend with high pressure aloft over New England
and low pressure near HAT. The main difference in the forecast models is the track of
the surface low associated with this pattern. The GFS is a bit of an outlier and this
discussion relies mainly on the NAM and ECMWF forecasts which bring the low from HAT along the coast to near CT by Tuesday. This is a cloudier and wetter forecast which will
mean lower pollutant concentrations overall.
In general, air quality will be in the good range along and east of I-95 through the
period as low level winds will be primarily onshore. Higher concentrations are expected
west (downwind) of the I-95 Corridor. Highest concentrations are likely on Saturday
with sunny skies and light easterly winds. Winds increase with cloud cover late on
Sunday then rain likely both Monday and Tuesday.
-Ryan
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Monday, May 14, 2012
Valid: May 15-19 (Tuesday-Saturday)
On Web: http://www.personal.psu.edu/wfr1/blogs/AQF/
Summary:
Good air quality through Thursday then rising ozone concentrations Friday and
Saturday as high pressure stalls over the region.
Discussion:
The forecast models differ on the timing of the end of this precipitation event,
but are otherwise in reasonable agreement so confidence in the weather portion of the
medium range forecast is good. The main uncertainty for air quality will be the
timing of air mass modification late in the period as high pressure stalls overhead.
For Tuesday, rain continues with periods of heavy rain likely during the day. Ozone will
remain quite low and PM will be in the good range as well. There are differences of opinion, as
noted above, on the timing of the end of the rainfall with predictions varying from Tuesday evening
to Wednesday morning. I tend to side with slower frontal passage in this case and therefore rain
and clouds lingering well into Wednesday with good air quality.
Drier air will definitely be in place by Thursday with sunny skies and northwest winds. This air mass
will be initially quite clean so good air quality continues. High pressure settles over the mid-Atlantic
by Friday and remains in place through the weekend. Temperatures will remain relatively cool, however, mainly
in the mid-70's F. Ozone is likely to reach the moderate range late Friday and continue into Saturday.
The dry air mass will limit PM formation so particles will remain in the good range through Saturday.
Ryan
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Saturday, May 12, 2012
Valid: May 13-17 (Sunday-Thursday)
On Web: http://www.personal.psu.edu/wfr1/blogs/AQF/
Summary:
Rain and low pollutant levels late Sunday to early Tuesday with dry Canadian air arriving Wednesday.
A slight threat of poor air quality next weekend.
Discussion:
Reasonable agreement in the forecast models today at least with respect to air quality
relevant features. There are the usual differences regarding timing, amount and extent of
precipitation in the Sunday-Tuesday period.
Little chance of poor air quality through the medium range. Ozone will likely peak today with
clouds arriving from the west on Sunday. PM will likely peak tomorrow as dew point rise and
southerly flow fills in.
Rain likely from late Sunday west through Tuesday morning east. This will keep ozone and PM
in the good range with PM likely the lead pollutant.
A Canadian air mass drops in behind the front on Wednesday, the next chance for moderate air
quality will be Thursday for ozone.
Looking further down the road, the next chance for high pollutant concentrations is next
weekend.
Ryan
Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Monday, April 30, 2012
Valid: May 1-5 (Tuesday-Saturday)
On Web: http://www.personal.psu.edu/wfr1/blogs/AQF/
Summary:
Good air quality begins the week with moderate concentrations likely as early as Thursday as
a summer-like Bermuda High moves into the southeastern US.
Discussion:
A warm front near ROA at this time will move north to central NJ by Tuesday morning
then stall and oscillate back and forth over the mid-Atlantic through the remainder
of the work week. A weak cold front arrives Saturday.
The forecast models are in good agreement on the evolution of the large scale pattern this
week but differ in the daily placement of the stalled frontal boundary and therefore on the
chances of rain and clouds for any specific area. This leads to higher uncertainty in the
ozone forecast compared to the PM forecast.
Temperatures in the 70's F (near normal) for Tuesday and Wednesday along with a mix of clouds
will keep ozone in the good range. Westerly transport aloft, and increasing humidity
late Tuesday, will push particle concentrations higher with a chance of scattered moderate concentrations
on Wednesday.
Summer-like weather Thursday and Friday with temperatures in the 80's F will bring moderate
air quality. With rain and cloud cover forecasts still uncertain, the leading pollutant is likely
to be PM. Moderate air quality is likely to linger into Saturday, particularly for PM, but cold air advection later in the
day will limit any increase.
Ryan
12.3 at the Clinton monitor.
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