Previous Day
Mostly a down day for the with a few strong storms to NE of Phoenix. The WRFNAM predicted a strong outflow into the east side of Phoenix which did not materialize. The WRFNAM had a bit too much activity while the WRFGFS didn't have quite enough.
Initializations
There are scattered mid level clouds around western Arizona and eastern Arizona. The eastern Arizona clouds seem to be forming due to mid level ascent perhaps from outflow from the large MCS in Sonora last night or more likely, on the nose of the 500mb jet across SE Arizona into NM. In any case, the trend is for mostly clearing skies. The RR may actually be a bit too cloudy over the northern part of the domain.
No obvious cyclonic circulations present over or near Arizona. A closed cyclonic circulation is present over the south end of the GofC which was initialized too far to the north in the RR.
The WRFNAM has large wet bias from Hermosillo up into SE Arizona and then over into NM. Large enough that I think it may impact the forecasts. The 6Z NAM is much better as are the 12 GFS and RR. The Guaymas sounding is not to blame for the NAM errors. The 6z WRFNAM and 12Z WRFGFS/RR appear to be well initialized and any of these can be used with confidence today. As all runs over the past day are quite similar, forecast confidence is high.
Day 1, July 29
A very unusual situation is present across much of the state where the combination of factors is about perfect for a major severe weather outbreak. A surge has begun with dewpoints in the mid 70-degree range over SW Arizona and 80F at Puerto Penasco. IPW has also responded as Yuma has increased to 45mm. Normally the first day of a surge brings higher moisture and cooler PBL temperatures, capping the lower deserts. This surge is weaker thus not cooling the PBL very much.
Moisture continues to be advected over the state during the day with IPW increasing slightly in most areas except for NE Arizona and far SE Arizona where there is moderate dry air advection occurring due to low-level easterly winds. At this point, Tucson is located on the wet side of this line. It is likely this boundary will be the initiation for deep convection over SE Arizona.
An impressive 500mb jet is present at 12Z from Tucson back towards west Texas as well as some cooling with temperatures around -7C over Arizona. The wind speeds are highest over southern Arizona this afternoon with 20 to 25 knots. Central Arizona has good ENE flow at 15 knots. Very favorable speed and direction for moving storms off the rim towards Maricopa/Pinal/Pima counties.
What is truly impressive, and a bit scary is the amount of CAPE present this afternoon. These are the largest CAPE values I've seen in a long time. With the combination of heating and steering flow, this is about as good as it gets; a perfect storm. Afternoon values over the lower deserts are from 1500 J/Kg to around 3000. All of the 12Z runs are similar. Looking at the 6Z runs as a sanity check, the WRFNAM is a bit drier and has somewhat less CAPE. However, even here, values are as high as 2000 J/Kg during the afternoon.
Deep convection takes it's time forming and doesn't really get going until late afternoon over the higher terrain. Both the WRFRR and WRFNAM have strong/severe storms to the east of Phoenix and developing over eastern Pima county around 5pm while the WRFGFS holds off by another hour or two.
I took the middle of the road skew-t for the Tucson area. Over 1500 J/Kg of CAPE, but the low-level easterly flow is close. At this point, most likely the strong to severe storms will be over the west and northwest parts of the city. All of Tucson is at risk. As in Phoenix, a deep mixed layer will be very favorable for strong/severe outflow winds. Last night's soundings had around 2000 J/Kg of DCAPE which is probably similar to the amount today. Excellent wind profile as 20 knot easterly winds in the mid level along with upper NW winds, blowing the anvils away from the storm motion.
Very, very strong outflows are produced by the storms with wind speeds about as high as I've ever seen. I'm running one of the 12Z runs with an alternative PBL scheme to double check the wind speeds as the operational PBL scheme may be over predicting wind speeds. Model wind speeds have been as high as 50 knots. Using a conservative gust factor, gusts could be above 70 knots.
This is a serious situation for Phoenix. All runs have between 1500-3000 J/Kg of CAPE by late afternoon with the WRFGFS at the high end. Mixing ratio is from 11-12 g/kg. Steering flow is a bit weaker, but still OK with very optimal NE flow. Inflow is a bit weak but that isn't going to matter with such strong outflows and outflow intersections occurring in Pinal and Maricopa counties.
Strong to severe outflow winds blow through Phoenix around 6-9pm followed by strong to severe storms with very heavy rain, 2 inches/hour and continued high winds.
Models differ on the details of location and timing. In general it looks like a MCS forms and moves WSW.
Strong to severe winds are possible all the way to Yuma during the night.
While I have not shown any figures from the 0Z runs, they should be relatively good since yesterday was a very suppressed day. The agreement among the full time-lagged ensemble is extraordinary for severe winds, though the details of when and where, along with how much precipitation is of course harder to pin down.
Day 2 will follow later once I catch my breath.
Mostly a down day for the with a few strong storms to NE of Phoenix. The WRFNAM predicted a strong outflow into the east side of Phoenix which did not materialize. The WRFNAM had a bit too much activity while the WRFGFS didn't have quite enough.
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| WRFNAM |
Initializations
There are scattered mid level clouds around western Arizona and eastern Arizona. The eastern Arizona clouds seem to be forming due to mid level ascent perhaps from outflow from the large MCS in Sonora last night or more likely, on the nose of the 500mb jet across SE Arizona into NM. In any case, the trend is for mostly clearing skies. The RR may actually be a bit too cloudy over the northern part of the domain.
No obvious cyclonic circulations present over or near Arizona. A closed cyclonic circulation is present over the south end of the GofC which was initialized too far to the north in the RR.
The WRFNAM has large wet bias from Hermosillo up into SE Arizona and then over into NM. Large enough that I think it may impact the forecasts. The 6Z NAM is much better as are the 12 GFS and RR. The Guaymas sounding is not to blame for the NAM errors. The 6z WRFNAM and 12Z WRFGFS/RR appear to be well initialized and any of these can be used with confidence today. As all runs over the past day are quite similar, forecast confidence is high.
Day 1, July 29
A very unusual situation is present across much of the state where the combination of factors is about perfect for a major severe weather outbreak. A surge has begun with dewpoints in the mid 70-degree range over SW Arizona and 80F at Puerto Penasco. IPW has also responded as Yuma has increased to 45mm. Normally the first day of a surge brings higher moisture and cooler PBL temperatures, capping the lower deserts. This surge is weaker thus not cooling the PBL very much.
Moisture continues to be advected over the state during the day with IPW increasing slightly in most areas except for NE Arizona and far SE Arizona where there is moderate dry air advection occurring due to low-level easterly winds. At this point, Tucson is located on the wet side of this line. It is likely this boundary will be the initiation for deep convection over SE Arizona.
An impressive 500mb jet is present at 12Z from Tucson back towards west Texas as well as some cooling with temperatures around -7C over Arizona. The wind speeds are highest over southern Arizona this afternoon with 20 to 25 knots. Central Arizona has good ENE flow at 15 knots. Very favorable speed and direction for moving storms off the rim towards Maricopa/Pinal/Pima counties.
What is truly impressive, and a bit scary is the amount of CAPE present this afternoon. These are the largest CAPE values I've seen in a long time. With the combination of heating and steering flow, this is about as good as it gets; a perfect storm. Afternoon values over the lower deserts are from 1500 J/Kg to around 3000. All of the 12Z runs are similar. Looking at the 6Z runs as a sanity check, the WRFNAM is a bit drier and has somewhat less CAPE. However, even here, values are as high as 2000 J/Kg during the afternoon.
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| WRFGFS |
Deep convection takes it's time forming and doesn't really get going until late afternoon over the higher terrain. Both the WRFRR and WRFNAM have strong/severe storms to the east of Phoenix and developing over eastern Pima county around 5pm while the WRFGFS holds off by another hour or two.
I took the middle of the road skew-t for the Tucson area. Over 1500 J/Kg of CAPE, but the low-level easterly flow is close. At this point, most likely the strong to severe storms will be over the west and northwest parts of the city. All of Tucson is at risk. As in Phoenix, a deep mixed layer will be very favorable for strong/severe outflow winds. Last night's soundings had around 2000 J/Kg of DCAPE which is probably similar to the amount today. Excellent wind profile as 20 knot easterly winds in the mid level along with upper NW winds, blowing the anvils away from the storm motion.
Very, very strong outflows are produced by the storms with wind speeds about as high as I've ever seen. I'm running one of the 12Z runs with an alternative PBL scheme to double check the wind speeds as the operational PBL scheme may be over predicting wind speeds. Model wind speeds have been as high as 50 knots. Using a conservative gust factor, gusts could be above 70 knots.
This is a serious situation for Phoenix. All runs have between 1500-3000 J/Kg of CAPE by late afternoon with the WRFGFS at the high end. Mixing ratio is from 11-12 g/kg. Steering flow is a bit weaker, but still OK with very optimal NE flow. Inflow is a bit weak but that isn't going to matter with such strong outflows and outflow intersections occurring in Pinal and Maricopa counties.
Strong to severe outflow winds blow through Phoenix around 6-9pm followed by strong to severe storms with very heavy rain, 2 inches/hour and continued high winds.
Strong to severe winds are possible all the way to Yuma during the night.
While I have not shown any figures from the 0Z runs, they should be relatively good since yesterday was a very suppressed day. The agreement among the full time-lagged ensemble is extraordinary for severe winds, though the details of when and where, along with how much precipitation is of course harder to pin down.
Day 2 will follow later once I catch my breath.
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