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September Discobs 2023


George BM
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:axe:

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Heading out of the Labor Day holiday weekend, conditions remain
seasonably hot with legitimate opportunities to break daily
temperature records. An expansive ridge encompasses the entire
eastern U.S. with little downstream movement as an upper low remains
parked south of Nova Scotia. This particular upper low will contain
the post-tropical remains of Idalia. Looking toward the middle to
latter portions of next week, an upstream trough should eventually
erode the persistent ridge across the northeastern U.S. This
ultimately favors a pattern change and a return of shower and
thunderstorm chances.

For Tuesday and Wednesday, 850-mb temperatures are forecast to rise
into the 22 to 24C range. Given deep mixing, dry adiabatic profiles
within this layer would support highs well into the 90s, locally
approaching 100 degrees. The 00Z GEFS and 18Z EPS ensemble
probabilities show around a 50 percent chance at a triple digit
reading somewhere between the Blue Ridge and I-95. Skies should
generally remain devoid of clouds given the ridge. One wild card in
this pattern is the humidity which will dictate how high heat
indices become. For now, modest rises in dew points should hoist
heat index values into the 97 to 102 degree range. While this would
fall short of local Heat Advisory criteria, those outdoors should
take the necessary precautions to mitigate any heat-related
illnesses. This would include taking shade breaks, wearing light
clothing, and staying hydrated with plenty of water. Of course, do
not leave anyone, including pets, inside a locked vehicle.
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6 hours ago, yoda said:

:axe:

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Heading out of the Labor Day holiday weekend, conditions remain
seasonably hot with legitimate opportunities to break daily
temperature records. An expansive ridge encompasses the entire
eastern U.S. with little downstream movement as an upper low remains
parked south of Nova Scotia. This particular upper low will contain
the post-tropical remains of Idalia. Looking toward the middle to
latter portions of next week, an upstream trough should eventually
erode the persistent ridge across the northeastern U.S. This
ultimately favors a pattern change and a return of shower and
thunderstorm chances.

For Tuesday and Wednesday, 850-mb temperatures are forecast to rise
into the 22 to 24C range. Given deep mixing, dry adiabatic profiles
within this layer would support highs well into the 90s, locally
approaching 100 degrees. The 00Z GEFS and 18Z EPS ensemble
probabilities show around a 50 percent chance at a triple digit
reading somewhere between the Blue Ridge and I-95. Skies should
generally remain devoid of clouds given the ridge. One wild card in
this pattern is the humidity which will dictate how high heat
indices become. For now, modest rises in dew points should hoist
heat index values into the 97 to 102 degree range. While this would
fall short of local Heat Advisory criteria, those outdoors should
take the necessary precautions to mitigate any heat-related
illnesses. This would include taking shade breaks, wearing light
clothing, and staying hydrated with plenty of water. Of course, do
not leave anyone, including pets, inside a locked vehicle.

Will be interesting to see whether IAD can eclipse the monthly record of 99F, and set a new latest date for a maximum of 100F or better. The current record is August 27, 1987, when it reached exactly 100F.

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3 hours ago, MN Transplant said:

The GFS is broken.  The NAM's 95ish makes more sense.

Not sure what the core issue is, but the GFS seems to be depicting air that is quite dry compared to reality under these anomalous h5 ridges lately. Noticed this with the recent central US heat wave, where in some cases it had dewpoints in the upper 30s-low 40s. That will contribute to notable error in the advertised high temps due to the specific heat capacity difference.

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