July 7th - The heat was hot and the ground was dry.....

 Overview:

Dry and hot should continue to be the rule for at least the next 48 h. A somewhat unique (for July) pattern is setting up over the next couple of days. A shortwave disturbance on the western side of the trough in the Central Plains should act to increase the strength of the north to nothwestery flow over eastern Arizona. In response to the passage of the shortwave, a surface low-pressure system is expected to form over southwestern New Mexico as high pressure builds along the eastern slopes of the Rockies. The pressure gradient associated with this low-pressure system will act to disrupt the normal diurnal variation in surface winds in southeastern Arizona. With limited Sonoran convection and westerly winds overnight in response to the surface pressure gradient, expect minimal overnight dewpoint recovery. The lowest surface dewpoints are expected Monday afternoon/evening before the pattern begins to dissipate. Consequently, we will be left with a pattern characterized by steep lapse rates, wind shear favorable for convective organization, and precious little in the way of moisture to work with. Any clouds that can build over the higher terrain will be extremely high based and I would place to probability of measurable precipitation at less than 10% until at least Tuesday.

Meanwhile, what is currently Tropical Storm Beryl is slowly becoming better organized in the Gulf of Mexico as it encounters more favorable environmental conditions for intensification. Warm sea surface temperatures combined with wind shear values of 5-10 knots suggests that strengthening is likely and rapid intensification over the next 24 h cannot be ruled out. Beryl should move northward in response to the weakness in high pressure over the southern tier of the United Stated created by the Central Plains trough and landfall is expected early Monday morning near Galveston, TX. 

Beryl Update:

As of 7 AM MST, Beryl was still a tropical storm with a minimum central pressure of 992 hPa and maximum sustained winds of 55 knots. The storm is forecast to intensify to 75 knots before making landfall although concerns along the Texas coast should remain vigilant for rapid increases in intensity over the next 24 h as the storm moves over warm waters in a low shear environment. Current SST and shear estimates indicate that Beryl should be moving 

Beryl forecast track with SST's and wind shear

(tropic.ssec.wisc.edu)

over a region of 29 C water with wind shear values of 5-10 knots, which should be conducive to strengthening. Current satellite images as of 10 AM MST indicate convection attempting to enclose the center of circulation.

Beryl vis satelllite valid at 10 AM MST

(weather.cod.edu)

Chances for rapid intensification will be highly dependent on convection completely enclosing the center of circulation, isolating the storm from dryer environmental air. The latest official forecast track is below for reference.

Beryl forecast track

(nhc.noaa.gov)

Monsoon Forecast

This Morning:

The shortwave on the western side of the longwave Central Plains trough is evident in this morning's 500 hPa mesoanalysis and the trough axis is highlighted by the black line in the image.

500 hPa mesoanalysis valid at 9 AM MST

(spc.noaa.gov)

The tightening gradient between the West Coast high pressure and Centrqaal Plains trough should act to increase the strength of the mostly northerly 500 hPa flow over the next 24-36 h. At the surface, a low-pressure system can be seen in southwestern Colorado with a trough axis extending south through New Mexico. At the same time, a broad area of high pressure can be seen banked along the eastern slopes of the Rockies, with a sub-synoptic scale maximum situated in southeastern Colorado. These features are expected to propagate southward over time and will influence our surface wind pattern over the next 48 h.

12Z GFS MSLP and PWTR forecast valid at 11 AM MST

(tropicaltidbits.com)

Precipitable water values continue to run below seasonal norms with satellite estimates indicating values of less than an 1" over most of southern Arizona.

Satellite derived PWTR valid at 10 AM MST

(weather.cod.edu)

This morning's sounding from Tucson indicates a PWTR value of about an 1", although dewpoints decrease steeply above 800 hPa. Lapse rates are impressively steep, and would support significant CAPE values if we could avoid significant drying from a combination of advection and mixing as the afternoon progresses.

12Z KTUS sounding

(spc.noaa.gov)

The lifting condensation level at 5 AM was approximately 700 hPa and is expected to rise to 600 hPa by this afternoon.

12Z UAWRF HRRR KTUS forecast sounding valid at 2 PM MST

(weather.arizona.edu)

Winds at the surface will be from the Northwest in response to diurnal forcing, reinforced by surface low pressure forming in southern New Mexico.

12Z UAWRF HRRR surface wind valid at 2 PM MST

(weather.arizona.edu)

This should result in somewhat breezy conditions, particularly in mountain passes to the east of the Tucson metro area. Based on this morning's sounding, I would expect surface temperatures to max out near or just above 105 F this afternoon.

12Z UAWRF HRRR forecast surface dewpoints valid at 2 PM MST

(weather.arizona.edu)

The enhanced northwesterly and northerly flow on the back side of the surface low pressure in southern New Mexico results in the advection of impressively dry surface air with 2 m dewpoints of less than 25 F evident in in the yellow colors all extending into Chihauhau, Mexico. 

Summary:

In spite of steep lapse rates and surface heating, a lack of moisture should little in the way of cloud cover and precipitation today with HREF ensembles indicating a less than 10% chance of measurable precipitation over the all of forecast area.

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

(spc.noaa.gov)

Tonight:

The surface pressure gradient overnight will oppose diurnal forcing, and act to minimize dewpoints recovery overnight.

12Z HRRR MSLP valid at 12 Midgnight MST

(tropicaltidbits.com)

12Z UAWRF HRRR forecast surface dewpoints valid at 12 midnight MST

(weather.arizona.edu)

Tomorrow:

Monday may prove to be the bottom of the moisture curve as the trough of low pressure is "pushed" westward as high pressure surges southward along the eastern slopes of the Rockies behind the shortwave trough. 

12Z HRRR MSLP valid at 2 PM MST

(tropicaltidbits.com)

This results in impressive easterlies in southern New Mexico, with wind speeds exceeding 30 knots in favored passes. In our neck of the woods, northwesterly winds of 10-15 knots can be expected with values of over 20 knots in favored terrain in Cochise county.

12Z UAWRF HRRR forecast surface winds valid at 2 PM MST

(atmo.arizona.edu)

With the lack of an overnight surge, abundant sunshine, and a decent breeze, surface dewpoints should mix out to values in the lower 40's F by early afternoon.

12Z UAWRF HRRR forecast surface dewpoints valid at 2 PM MST

(weather.arizona.edu)

This should result in PWTR values of about .5" in and lifting condensation levels over 600 hPa. In other words, very little to no chance of precipitation.

12Z UAWRF HRRR KTUS forecast sounding valid at 2 PM MST

(weather.arizona.edu)

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

(spc.noaa.gov)