George BM

What did the indoor temperature get down to before the flip?

Currently IAD 55/39.

This day 70 years ago was a 10/10 spectacular weather day locally.

@Roger Smith @RodneyS

Clearly visible here. (Herndon, VA.)

All four of the Atlantic major hurricanes so far this year have peaked at at least a 120kt Category 4. Not too shabby.

Atlantic ACE to date has caught back up to average passing 100pts.

NHC has now upgraded this to Milton based on satellite data. 723 WTNT64 KNHC 051725 TCUAT4 Tropical Storm Milton Tropical Cyclone Update NWS National Hurricane Center Miami FL AL142024 1225 PM CDT Sat Oct 05 2024 ...TROPICAL DEPRESSION BECOMES TROPICAL STORM MILTON... ...FORECAST TO STRENGTHEN AND BRING THE RISK OF LIFE-THREATENING IMPACTS TO PORTIONS OF THE WEST COAST OF FLORIDA NEXT WEEK... Recent satellite wind data indicate that the depression has strengthened into Tropical Storm Milton. The maximum sustained winds are estimated to be 40 mph (65 km/h) with higher gusts. SUMMARY OF 1225 PM CDT...1725 UTC...INFORMATION --------------------------------------------------- LOCATION...22.3N 95.3W ABOUT 220 MI...355 KM NNE OF VERACRUZ MEXICO ABOUT 365 MI...590 KM WNW OF PROGRESO MEXICO MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H PRESENT MOVEMENT...NNE OR 15 DEGREES AT 3 MPH...6 KM/H MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES $$ Forecaster Brown/Kelly

The NHC forecast is fairly bullish with an intensity of 95kts for the 72 and 96 hour points.

35mph, 1007mb for the 11am adv.

Yeah multiple indices could be offline for a bit.

Winds in the upper-levels of the troposphere (~25,000-40,000ft) are very swift out of the northwest. Much faster than the modest low/mid-level NW flow where the majority of the convective clouds are located. So while the storms are moving SE with that modest NW low/mid-level flow the anvils from the storm tops are being blow to the SE of the storms. The stronger upper-level flow being orientated in about the same direction as the weaker low/mid-level is also helping with the storm-splitting action we are seeing to our NW. If, for example, the strength of the upper-level NW winds were more equal or even weaker than the deep-layer low/mid level NW winds, storms would more readily congeal into a solid SE-moving line... small line segments, however, can still form in this environment.

Dulles bottomed out at 43F.

28

Forecast Discussion Sunday, September 1, 2024 8:46PM EDT Current Alerts: Flash Flood Watch in effect from 1AM EDT Monday, September 2, 2024 until 7PM EDT Monday, September 2, 2024. High Wind Warning in effect from 8AM EDT Monday, September 2, 2014 until 8PM EDT Monday, September 2, 2024. For the Rivers and Bay… Hurricane Force-Wind Warning in effect from 12PM EDT Monday, September 2, 2024 until 7PM Monday, September 2, 2024. Hurricane Helene made landfall earlier this evening as the strong landfalling topical cyclone anywhere in the world in recorded history w/ a minimum SLP of 882mb and 175knot(200mph) sustained winds. Even hours after it’s landfall as it races NNE into Georgia ahead of the longwave trough it is still packing 150mph winds as of the 8pm NHC advisory. Helene will bring us locally a historic weather day tomorrow. We get into that below. Tonight through 6am: Southerly flow will continue to usher in an increasingly humid, tropical airmass into the region with dewpoints into the mid-70s or so. Scattered showers and some heavy storms that have given parts of the already saturated region another 2 to 3 inches of rain are currently moving to the northeast north of I-70 and Baltimore. But as the night wares on additional showers and thunderstorms will move in from the south with the increasing southerly flow which will back to more southeasterly near the surface as Helene’s wind field moves into the region. As a result of this, low-level shear will increase and with lift in the atmosphere also increasing this will allow for supercells which may produce a few brief tornadoes, mainly after 2am. With the tropical airmass in place, these storms will be very efficient rain producers thus, some flash flooding is possible and a Flash Flood Watch goes into effect for the region starting at 1am in the DC metro and southwestwards and at 3am for areas to the northeast. 6am through 12pm(noon): Southeasterly winds will start strengthening quickly around dawn and through the mid-morning hours from southwest to northeast and back to more out of due east as the Helene’s low pressure center enters the southwestern part of Virginia. Bands of heavy rain with embedded supercells capable of producing a couple tornadoes will continue through the morning. The greatest tornado threat locally will be between 6am and 10am before lower-level shear actually becomes too strong for supercells to sustain themselves given the fairly meager CAPE with wet adiabatic lapse rates through the entire troposphere, though it’s important to note that the tornado threat will not drop to zero as a brief tornado or two is still possible through about midday. By mid-morning easterly winds will become very strong to damaging gusting 50 to 65mph. With the soggy grounds from Gordon and the very wet pattern we had most of August in general many trees and some powerlines will come down. In terms of rainfall, rainfall come in arcing bands of tropical downpours and supercells around the metro regions. But in the I-81 vicinity as a strong shortwave trough approaches from the west and really starts phasing with Helene’s low pressure circulation, it will interact with the strong easterly winds allowing for very strong lift with very heavy SW to NE oriented rainbands stalling over that region to the immediate west of the track of Helene’s low pressure center. 12pm(noon) through 6pm: The aforementioned shortwave trough moving in from the west will cause two things to occur. 1. Helene’s circulation will receive a large amount of baroclinic energy which will quickly transition the storm into an extratropical system. 2. Cooler and drier air mixing into the back side of the storm combined with an increasing surface gradient on the backside of the system will allow for extremely strong winds to form on the southwest and southside of the low-pressure center. A sting-jet may even form which, should it become well-defined, could further increase the maximum wind gusts. Winds will calm down quite a bit for a brief period of time around midday in the local area as the storm center moves overhead with surface air pressure down into the 970-975mb range. As the storm moves northeast by the early afternoon hours the metro area will get the worst part of the storm. The very tight surface pressure gradient on the southwest side of the circulation will move overhead from southwest to northeast. By midday far southwestern parts of the forecast area such as Charlottesville, VA will start being affected by destructive westerly winds which will spread northeast into the DC metro area by 2pm or so and up into far northern MD and the Baltimore metro by 3-4pm. With the tight pressure gradient and even signs of a sting-jet with air descending and drying from the western to southern side of the circulation winds may gust over 80 mph at times. Some models even indicate that winds could be even higher than that especially if a well-defined sting-jet can form. This will lead to substantial tree and structural damage across the area as well as widespread power outages. Some light/moderate rain may accompany these winds. The strongest winds will probably last for up to two hours in any given location before winds gradually weaken below High Wind Warning criteria by around 4 hours after the onset and below Wind Advisory criteria by 6 hours after the onset after sunset. Skies will clear from southwest to northeast from late afternoon through mid-evening. Monday night: West/northwest winds may still be gusting up into Wind Advisory criteria at times (roughly 50mph or so) around sunset before decreasing by late evening though there will still be 25 to 35mph wind gusts through the night as temperatures fall into the lower 50s. Some far northwestern spots may even get into the upper 40s by dawn on Tuesday. Main Impacts (shortened): Wind: Easterly winds may gust out of the as high as 55 to 65mph during the mid and late morning hours leading to moderate to major coastal flooding in the Potomac and west shore of the Chesapeake Bay before an around midday lull in the wind. Westerly winds may gust over 80 mph during the early to mid afternoon hours before windspeeds slowly decrease from the late afternoon hours onwards. Rainfall: Rainfall totals of 1.5 to 3 inches will be commonplace in the metro regions with local amounts of 4+ inches leading to widely scattered instances of flash flooding. However, in the far western areas of the I-81 corridor could receive 4 to 8 inches with localized amounts of 10+ inches leading to major flash flooding in that region. - George BM