July 3 - Winds of Change - A shift to an excessive heat pattern is looming

 Overview: 

Hurricane Beryl is poised to impact Jamaica today as a major, but weakening, hurricane. Later this week/weekend, Beryl is expected to cross the Yucatan Peninsula and enter the Gulf of Mexico where some restrengthening is expected. Track guidance continues to shift northward increasing the potential for impacts along the Texas coastline. 

Closer to home, today will represent a transitional day as our weather shifts from south/southeasterly flow on the western side of high pressure in the Southern Plains to north/northeasterly flow on the eastern side of high pressure that will move into California this holiday weekend. While precipitable water values have decreased today, there is still enough moisture today to support isolated to scattered convection in southeastern Arizona. Convective allowing models are consistent in initiating isolated convective buildups starting along the higher terrain in the Catilina and Rincon mountains in the early afternoon with more widespread activity occurring in Cochise and in particular Santa Cruz counties near the Mexican border, just along and ahead of the afore mentioned wind shift at 500 hPa. By Thursday, the upper-level winds will have shifted to north/northeasterly and drier air will start moving into the region in earnest from the north. While surface dewpoints will likely continue to recover in shallow moisture surges overnight, mixing should result in significant dewpoints drops throughout the day as we head into the weekend. The combination of drier air and a hostile synoptic-scale environment should result in a shutdown of Monsoon activity through the weekend.

Beryl

As of 8 AM MST, the National Hurricane Center (NHC) has Beryl as a category 3 hurricane with winds speeds of 145 mph and a central pressure of 954 hPa. Below is the official forecast track from the NHC.

Forecast track of Beryl issued at 8 AM MST

(nhc.noaa.gov)

Note that Beryl is forecast to regain hurricane intensity over the Gulf of Mexico before making landfall along the western Gulf Coast. Ensemble guidance as of this morning continues to shift northward,

and the official forecast track is now along the southern edge of model guidance. Consequently, concerns along the Texas Gulf Coast should keep a close eye on forecasts of Beryl as we head into next week. This shift in track of Beryl to the north has diminished the likelihood of any positive contribution from Beryl to our Monsoon activity.

Today:

Big Picture

A region of cyclonic chear is evident in this morning's water vapor imagery between the southwesterly flow associated with the Southern Plains high and the notheasterly flow from the high pressure off of the West Coast. I have tried to highlight these flow features in the upper-level water vapor image below.

Upper-level water vapor valid at 8 AM MST

(weather.cod.edu)

In the image, you can see that moist conditions have become increasingly confined to the southeastern corner of Arizona. That corner of Arizona is demarcated by enhanced southwesterly flow in the upper-levels of the atmosphere as indicated by the 250 hPa flow map from the GFS below.

12Z GFS forecast 250 hPa winds valid at 11 AM MST

(tropicaltidbits.com)

This entension of the jet streak on the eastern side of the trough to our northeast should provide for some enhanced divergence, especially for regions close to the border with Mexico.

Zooming In:

This morning's sounding at Tucson shows drying in the mid to upper troposphere, although relatively moist conditions still remain below 500 hPa.

12Z Tucson sounding

(spc.noaa.gov)

The lower tropospheric moisture is enough to support precipitable water values over 1.5", which is still anomalously high. CAPE values range between 300-500 J/kg and are somewhat mitigated by a subsidence inversion just above 500 hPa. Downdraft CAPES of 1000 J/kg this morning should increase, but I am skeptical of the of the 1118 J/kg forecast CAPE values as surface dewpoints should drop throughout the day in response to a combination of mixing and advection. We can already see this starting to take place in the observations

Surface Observations from 10 AM MST

(rap.weather.edu)

as surface dewpoints as of 10 AM had dropped to 60 F at Tucson and are in the 50's across the greater Pheonix metropolitan area. This is in good agreement with the 12Z run of the UAWRF HRRR which shows a surface dewpoints of 58 F as of 10 AM MST

12Z UAWRF HRRR intitialization Forecast Dewpoint valid at 10 AM MST

(weather.arizona.edu)

Dewpoints should continue to drop into the mid 50's this afternoon at Tucson with the UAWRF show a value of 51F at Tucson by 2 PM MST.

12Z UAWRF HRRR intitialization Forecast Dewpoint valid at 2 PM MST

(weather.arizona.edu)

While the drying in the model may be slightly overdone, I think the overall trend is accurate and should limit CAPE this afternoon. The end result will be for convection to limited and widely scattered with the exception of areas along and just south of the border as indicated by the forecast reflectivity valid at 4PM today...

12Z UAWRF HRRR intitialization Forecast reflectivity valid at 4 PM MST

(weather.arizona.edu)

Overnight:

Expect surface moisture to recover due to a combination of moist outflow from the complex expected to develop over Sonora and a Gulf of California surge with dewpoints recovering to the 60's overnight

12Z UAWRF HRRR intitialization Forecast Dewpoint valid at 3 AM MST

(weather.arizona.edu)

However, this recovery is excessively shallow with the forecast sounding indicating the moist layer to be confined to the lowest 100 hPa of the atmosphere.

12Z UAWRF HRRR intitialization Forecast Sounding valid at 1 AM MST

(weather.arizona.edu)

Tomorrow:

Expect northerly or northeasterly at flow at 500 hPa to be established by early tomorrow.

12Z GFS forecast 500 hPa winds and vorticity valid at 11 AM MST

(tropicaltidbits.com)

Large scale descent should be occuring with warming and drying apparent in the forecast sounding for Tucson above 920 hPa.

12Z UAWRF HRRR intitialization Forecast Sounding valid at 11 AM MST

(weather.arizona.edu)

Forecast precipitable water values have dropped to less than an 1", and the "moist" layer remains confined to the lowest 100 hPa. By evening, a combination of subsidence and mixing has dropped the surface dewpoints into the 40's

12Z UAWRF HRRR intitialization Forecast Sounding valid at 5 PM MST

(weather.arizona.edu)

and obliterated any available CAPE.

The combination of drying and subsidence should preclude the development of any convection north of the border as supported by the HRRR ensemble, which shows a less than 10% chance of ANY measurable precipitation north of the border

12Z HRRR ensemble forecast probability of measurable precip valid at 5 PM MST

(tropicaltidbits.com)

Looking Ahead:

It will take several days for the high pressure system situated off of the West Coast to move inland over the Great Basin. Once this shift has taken place, we can hopefully expect a return to more normal Monsoon conditions. However, it will be a hot dry pattern until then as indicated by the ensemble 5 Day 500 hPa height anomalies valid next Wednesday....

12Z GFS ensemble forecast 5 day 500 hPa height anomaly valid at 5 AM MST July 10

(tropicaltidbits.com)

the 7 day ensemble 2m temperature anomalies

12Z GFS ensemble forecast 7 day 2m temp anomaly valid at 5 AM MST July 10

(tropicaltidbits.com)

and the 7 day precipitation anomaly

12Z GFS ensemble forecast 7 day precip anomaly valid at 5 AM MST July 10

(tropicaltidbits.com)