South Ops Weather - 2021

[anvilhead]

Forecast models indicate a surface low pressure developing off of the Oregon coast early next week. The track of this surface low will determine how far south rainfall occurs on the 9th/10th November. Models have trended drier. After the surface low makes landfall, the trough will quickly dig into the midwest, and high pressure will build in. A Santa Ana wind sequence should kick off. At this time it appears that the ridging will drive the offshore winds as the trough axis is a bit far east, none-the-less offshore winds, unseasonably warm temperatures, and low humidity should be expected for middle November.

The active jet stream across the Pacific NW will likely begin to shift east as we head for December, which would open the door for inside sliders, outside sliders, and large swings between cold and hot weather. Precipitation could be very limited for Southern CA during the next month.

[anvilhead]

Expect a high degree of drying for Southern Operations area. North and East flow below strong ridging for this time of year will set up a situation where temperatures could be 10-20 degrees above normal from Wednesday-Saturday. Winds speeds do not seem to be strong at this time due to the ridge primarily driving the gradients, however locally elevated fire weather conditions are expected.

The big story to watch here is the compounded drying impacts on fuels as we enter about a week of hot temperatures. This will set the stage for fuel receptivity.
It’s a bit early but I am closely monitoring would could be a powerful Santa Ana wind event between 11-18-11-21 time frame. It is likely that ridging will give way to strong and sharp troughing in the Great Basin which would bring the conditions possible for strong cold air advection upper level support driven Santa Ana winds.

Stay tuned for further updates as the week of the longest lunar eclipse in the 21st century could be quite eventful.

[Flyron]

San Diego County Current Wx Data:
https://sdgeweather.com/

[Flyron]

[anvilhead]

The multi-model consensus is that a moderate Santa Ana wind event is likely to occur on Sunday the 21st.

[anvilhead]

Santa Ana winds continue. Another trough of low pressure will drop into the Great Basin Wednesday and a cut off low will pinch off over Northern Baja CA. This will provide some decent upper level support. Gradients should be stronger out of the north on Wednesday and stronger out of the east on Thursday.

The NAM peaks offshore gradients at LAX-DAG -8.1 and LAX-BFL at -4 for a peak average of -6. Assuming this is half a millibar overdone we are on track for a moderate strength Santa Ana wind event, with extremely low relative humidity, temperatures much above average, and a moderate duration.

Plan for red flag staffing on Thanksgiving.

The risk of large fire is compounded due to one of the busiest travel days of the year. There is a 25% chance the event could reach high wind warning level. Let us hope that the only Turkey smoked over the next few days is the one in the oven.

Looking ahead… the GFS was showing out in DUNE-land a potential monstrous ice storm across the midwest to start December. Let us watch this over the Thanksgiving for potential offshore wind implications in early December and be thankful for the men and women who continue to allow us to do these forecasts from our cozy homes while they risk everything to keep us safe.

Happy harvest days and feasts to all.

From NWS Los Angeles AFD

[FireCapt]

NWS LA: 9:30am

Offshore gradients to the N and E are fcst to peak at an impressive -9.4 mb LAX-DAG and -4.5 mb LAX-BFL at 12Z Thu. There will also be good cold air advection and upper level support for strong and gusty NE winds to affect much of VTU/L.A. Counties Wed night and Thanksgiving Day. 950 mb winds are forecast by the NAM to peak around 60 kt Thu morning, and to around 50 to 55 kt at 850 mb in the L.A. County mtns late Wed night into Thu morning. Surface wind gusts of 30 to 50 mph will be widespread, with damaging gusts up to 60 mph or more possible in the foothills and mtns. A High Wind Watch may be needed for this event for the higher mtns of VTU/L.A. Counties and the Santa Clarita Vly for Wed night and Thu.

Humidities will drop to between 8 and 15 percent on Wednesday, then likely lower into the 2 to 8 percent range by Thursday and Friday, which is very dry, along with very poor overnight recoveries. High temperatures will generally be in the 70s on Wednesday, and warm to the mid 70s to mid 80s Thursday and Friday. As such, Red Flag conditions are very likely for most of Los Angeles and Ventura Counties Wednesday and Thanksgiving Thursday, with a chance of continuing through Friday. The current Fire Weather Watches will likely be upgraded to Red Flag Warnings by Tuesday. Elevated to brief critical conditions will continue over Santa Barbara and San Luis Obispo Counties, but the chance for Red Flags are minimal.

[SIXONENINE]

See the below message from NWS San Diego, They are predicting higher winds than first thought due to expected Mountain Waves potentially forming. Top gusts could exceed 75 MPH.

From NWS
ECMWF ensemble guidance continues to support stronger winds for today and Thursday, diminishing into Friday. Guidance has trended upward in regards to wind speeds tonight into Thursday. Peak wind gusts could reach 65 to 75 mph, especially below the Cajon Pass and near the coastal foothills of the Santa Ana mountains. Peak gusts in San Diego county will be 55 to 65 mph. HiRes models show mountain waves surfacing tonight into Thursday, especially for Orange and southwestern San Bernardino Counties. It would not be surprising if there were some occasional very strong gusts downstream for the locations with the most consistently stronger winds, especially in portions of the Inland Empire. The greatest potential for damaging winds for those areas appears to be for tonight into Thursday morning. Winds will weaken by Thursday evening with weaker and more localized winds continuing into Friday.

[Twigpig]

Current observations 22:00PST.

[anvilhead]

LAX-DAG gradients peaked at -7 this morning, which is 2 MB off the WRF-NAM forecast. A lot of new leaves on the ground. Forecast models are in agreement that the upper level low off of the coast of Baja will move east and be replaced by ridging over head.

Surface high pressure will remain over the Great Basin and as the ridge builds overhead of Southern CA the pressure gradient should remain offshore. A piece of energy could spin into an upper level low off of the coast of Baja, albeit weaker than the present one. The conditions present through the next 5 days is conducive for weak offshore flow inland. Temperatures will increase into the 80’s.

I am continuing to monitor a potential ice storm event for the midwest between 12/3 to 12/10. In no way is it forecastable this far out but based on the timing of the event in synchronicity with other things occurring in the world this is a time frame that should be closely monitored for an extreme weather event. Santa Ana implications should become more clear in the next 96 hours.

No rain is forecasted the next 10 days, much of Southern CA had no rain in November.

[Flyron]

San Diego County Wx Obs:

https://weather.sdgeweather.com/

[LACoCB]

01-LFM-Summary-Fire-Danger-Zones-2021-2.pdf

these live fuel values were taken before the past 8 days of low humilities and warm temps

[sofr_bear]

Glad nothing significant happened in the last 48 hours. Also glad I have vacation coming up…used the a/c in my buggy yesterday.

[FireCapt]

[anvilhead]

Forecast models are in pretty good agreement for a Santa Ana wind signal around 12-6 to 12-8. There are cut off lows off of the coast of Baja that are complicating a consensus forecast. It will be a few more days before a strength and duration forecast can be confidently put together.

[ffviking]

Just curious anymore on that potential ice storm in the midwest areas?

[anvilhead]

There is too much model variation. The timing kickbacks are largely caused by cut off lows complicating the forecast. My intuition tells me that there is a very good chance of a high impact ice type event between the 8th and 12th though. I will bring in some supporting data for Santa Ana winds and that potential event in about 48 hours.

[FSFF]

“Winter is coming.”

[anvilhead]

Forecast models have backed off on the idea of a strong Santa Ana wind event for 12/6. There appears to be some good upper level support from the upper level low off of the coast of Baja CA, however the cold air advection in the great basin is not as strong and thus the strong ridge nosing off of the Pacific will likely drive the offshore wind event. Temperatures will be very warm, likely into the upper 80’s at the warmest locations due to compression heating.

The bigger picture here is the trough axis that will impart itself from Canada between 12-7 & 12-12. Forecast models are in agreement that it will be very very cold oriented… however the GFS and ECMWF disagree on location. The GFS wants to bring it into Southern CA for low elevation snow and rain while the ECMWF wants to sharpen it into the Great Basin and across the midwest for a snow and ice storm. The CMC is directly in the middle of these two solutions with an inside slider just clipping us.

Here is the important aspect: the strong ridge off of the Pacific will drive the offshore winds the next few days. The cut off low providing a weakness in the ridge will allow this brutally cold trough axis to extend south. Where/how fast the cut off low moves will determine where the trough axis sharpens. The brutally cold long wave trough will bring the potential for strong and gusty Santa Ana winds bearing it is in the form of an inside slider. I am leaning more towards dry weather with offshore winds despite NWS optimism for rain.

potential cold snap across the mid west as northerly flow drives cold air from Canada into the deep south

[Keestrokes]

Ah, to spray water on a windy, cold "Santa Ana’ at 0100. Who could ask for more… :slight smile: