20160630

Previous Day
As is typically the case when the model runs disagree, what was observed was somewhere between the two.  Tucson was able to recover somewhat as the sun came out by mid morning which led to a few strong storms by afternoon.  Less than the WRFGFS, more than the WRFNAM.  The same was the case around the Phoenix area where scattered strong late afternoon storms were able to generate enough outflows to trigger storms throughout the Phoenix area.  The WRFGFS also did well predicting the early morning storms around the Tucson area.

Initializations
Clouds cloud clouds.  The 12Z RR did a poor job initializing the morning clouds and showers.  The 12Z NAM isn't much better as it doesn't have nearly enough coverage over Pinal and Maricopa counties.  The 12Z GFS was similar.  I took a look at the 6Z runs and they are terrible too.  The GFS IPW initialization was the best of the three as it had only minimal errors.   The IT is located near the AZ/Sonora border southwest of Tucson and is initialized well.    Again, low confidence in the model forecasts due to the clouds with the WRFGFS looking the best.

Day 1
The WRFNAM from yesterday was correct with it's prediction of very high IPW for southern Arizona as 50+mm of IPW is present over much of SW Arizona.  Typically, a situation like this would result in very little precipitation due to the extensive clouds and modified air-mass, "too wet to rain".  The wildcard is the approaching IT.

The IT moves very slowly to the north and is somewhere over central Pima county during the afternoon.  Warm air at the mid levels, around -5C, is another negative today.

There are some areas of moderate CAPE thus if the sun can come out, some strong thunderstorms will form.  White Mountains and far western Arizona are the only clear areas at this time.

The areal coverage is probably overdone, but the favored areas look like northern and eastern Arizona.

Strong storms form out along the CO river valley and continue in eastern Arizona early this evening.  Again, these areas are likely to see more sun (especially far western Arizona) so this looks plausible.

Deep convection looks unlikely in/around Tucson and Phoenix.  Phoenix does have some CAPE, but without deeper mixing or strong outflows, deep convection is unlikely.  Tucson has a 'too wet to rain' profile with it nearly saturated and limited CAPE.

Day 2
The IT lifts northward thus winds become west or southwest over much of the state.  Some cooler air is present over western Arizona.

It's still very wet over central and eastern Arizona thus a chance for storms, but dry air is working in from both the south and the west.

With some dynamics in play (divergence aloft?, the model runs do fire off some storms over central Arizona during the morning hours.  Somewhat surprisingly, both the WRFGFS and WRFNAM are similar.

CAPE is quite high from central Arizona into SW Arizona as moisture remains high combined with cooling aloft.

Impressive CAPE over Phoenix tomorrow afternoon with 1700-2000 J/Kg.  Drier/warmer air advecting in from the west  at 700mb seems to be holding back widespread deep convection along with unfavorable wind profile.

Most of the activity moves into NM during the afternoon with a few strong storms forming around the Phoenix area.

Activity continues to the north of Phoenix during the evening with some storms drifting into the valley during the night.  With the CAPE present some storms could be very strong.

20160629 Day 2

It doesn't get any easier tomorrow.  The WRFGFS and WRFNAM both bring the IT into southwestern AZ with fairly strong southeasterly flow across southern and eastern Arizona.

Adding to the confusion, the WRFNAM is much(4-10mm) wetter than the WRFGFS over much of the southern 1/3 of the state.  It's certainly possible the IPW could be this high as very wet air is to the south in Sonora (60mm at Navojoa).

WRFNAM

Widespread morning showers and some storms are present which will again stabilize some areas thus putting a damper on later storms.  A "too wet to rain" situation where as little lifting will cause clouds to rapidly form and restrict further heating and deep convection.  The best chance for stronger storms look to be eastern Arizona and up over the White Mountains and Rim.

WRFNAM

With all the moisture, storms that do form will produce very heavy rain and wet microbursts as IPW is so high.  Is this really still June???  Looks more like August!

Big storms are possible during the early evening in and around the Tucson area as well as continuing up north.  It looks like Phoenix remains mostly quiet except for a chance early morning.

20160629

Previous Day
The late night/early morning storms did materialize as areas in and around Tucson saw storms after midnight.  The WRFRR handled this the best.

Initializations
This is going to be a tough day as the early morning activity has left behind lots of clouds and stable air in SE Arizona.  Bob has a excellent summary here.  The overnight runs have no clue regarding the modified air-mass as seen in the temperature plot below.

The 12Z NAM and GFS, while initializing too warm around Tucson, had a fair amount of clouds present.   There also appears to be a weak MCV over Santa Cruz county.   A large IT can be seen rotating over NW Mexico, similar to the WRFGFS from yesterday and this feature even shows up on the 12Z 500mb analysis.  The 12Z NAM  has it initialized well.

The 12Z RR struggled with the IPW initialization as much of Arizona was too dry and NW Mexico too wet.  The 12Z NAM and GFS were better with only minimal errors.

Confidence in the model runs, especially around Tucson is low due to the poor initialization of the rain cooled airmass and insufficient clouds.  However, clouds so seem to be dissipating which will allow some recovery. In other parts of the state, the model runs should be OK.  I'd say the best is the WRFNAM.

Day 1
Moisture continues to increase over all of the state with more than enough to support widespread activity this afternoon and evening.  With so much present, flash flooding potential with storms will be high.  The WRFNAM is a bit wetter as it has weak flow from the south while the WRFGFS has weak easterly flow over much of the eastern 1/2 of the state.

CAPE is moderate to high especially over the higher terrain of the Rim and White Mountains and as it's clear there this morning, storms should form rapidly and become strong.

Mid level winds continues to be somewhat favorable for propagation of storms into the lower elevations.  The direction is good, but the winds are weak.

The WRFGFS and NAM develop storms over far SE Arizona all along the Rim/Whites by early afternoon.  The big question is if deep convection will be present SE of Phoenix by late afternoon as that will be required for the generation of intersecting outflow boundaries needed for widespread Maricopa county storms.

WRFNAM

The afternoon Skew-T forecast indicates light easterly mid level steering, favorable upper flow, and a moderate amount of CAPE.  The issue is the PBL does not mix deep enough for convection, at least in the WRFNAM.

The WRFGFS has much more activity across SE Arizona by late afternoon than the WRFNAM.  I think the WRFGFS is overdone and is probably wrong.

WRFGFS

A big outbreak of strong/severe storms in Phoenix as predicted yesterday is now less likely as only one of the needed outflow boundaries is present by early evening.  The storms to the north of Phoenix did their part and a strong outflow moves south.

WRFNAM

As is so often the case, the actual events are many times somewhere in between the two model runs.  The WRFGFS has outflow boundaries moving in from the SE and N towards the Phoenix area.

WRFGFS

It's really a tough call for a major outbreak as Phoenix is primed and ready to go, even in the WRFNAM, as there is around 1500 J/Kg of CAPE.  I don't think a single strong outflow boundary is going to be enough to generate the lift needed, but if even a weak to moderate outflow boundary comes in from the SE, deep convection should initiate.

The WRFNAM does develop some activity in Pinal county during the evening.

The other extreme is the WRFGFS.  The wildcard is the IT that begins to eject into Arizona overnight.  The WRFGFS brings it into the state during the evening which helps organize convection.

Both runs continue activity into the early morning hours.

WRFGFS

Day 2 will follow later this morning

20160628

Previous Day
Most activity was restricted to SE Arizona and areas north of Phoenix.  A few weak storms managed to sneak into the east valley of Phoenix.

Model forecasts were pretty good in general and the weak outflow through Phoenix did verify.  They weren't quite strong enough with the activity north of Phoenix during the afternoon.

Initializations
For the first time in many days, Arizona is mostly clear and the model initializations have no problems with clouds.   IPW was initialized well by all three of the 12Z model initializations. Note that there are now no operational GPSMET IPW stations in the Phoenix area or in SE Arizona.  I haven't talked much about the Rapid Refresh this year as I am back to using the operational version's initial conditions, which at times, are quite poor.  Last year, I had access to the developmental version which is no longer the case this year.  Operational RR is supposed to be upgraded to the new version 'any day now'.   Very warm air is in the mid levels as seen at El Paso where it is -3C.  Also, the west Texas trough has sheared out and can no longer be identified.  Some of it may of sheared out to the SW across northern Mexico.  There is an inverted trough over the central Gulf of California in the initializations of all three 12Z models and an accurate initialization of this feature is critical for Arizona over the next few days.   The problem is the lack of a sounding at Guaymas which would be very helpful in this situation.  Satellite imagery does show some cyclonic circulation in that area along with an area of early morning storms so it does look like the feature is real.  Overall, initializations all look good with no favorite and model confidence is high.

Day 1
Impressive early season moisture continues across much of the state extending all the way north to Las Vegas.  Easterly low level flow has become established across eastern Arizona with dry air over NE Arizona while SE Arizona remains wet.  By mid-day, the edge of the easterly flow is north-south of a line from Flagstaff to Tucson and will act as a focus for afternoon convection.

Warm air is present across southeastern Arizona and along with low level easterly flow, will restrict convection there.  Central and western Arizona are a bit cooler thus less hostile and along with moderate SE flow, storms that do form will be steered off of the higher terrain.

As usual, the WRFGFS has somewhat higher CAPE forecast for the afternoon.  Both runs have sufficient CAPE to support deep convection from SE Arizona up towards Flagstaff thus areas west of the windshift line should be quite active this afternoon.

By early afternoon, storms have developed from Nogales northward with some very strong/severe storms in the Flagstaff area.  The WRFGFS and WRFNAM are similar except the WRFGFS storms develop an hour or two later.  By late afternoon storms are winding down.

The WRFGFS diverges from the WRFNAM and WRFRR as the later two redevelop storms over eastern Arizona during the evening while the WRFGFS waits until later.  The question is if these storms continue and move into the lower elevations around Tucson and Phoenix later as was forecast by yesterday's runs.

Looking at the forecast Skew-T plot for Phoenix tonight, it certainly looks like the atmosphere will support big storms if they can propagate into the valley.  CAPE and moisture are high, much like the previous forecasts.

Tucson is also primed for late night activity as CAPE sufficient to support deep convection.

All of the 12 runs move/develop storms between Tucson and Phoenix during the late night and early morning.  There is quite a bit of uncertainty with timing, location, and intensity with the WRFRR have very strong storms in and around Tucson while the WRFGFS has storms around Phoenix after midnight and the WRFNAM has storms mostly in Pinal county.  In general, intensity has backed off compared to previous runs.  Still, some storms could be very strong producing isolated damaging winds, lightning, and heavy rain.

WRFRR

WRFNAM

WRFGFS

Day 2
There is the potential for a widespread strong/severe weather outbreak for many parts of the lower elevations during the late afternoon and evening.  Very wet air is present by early afternoon with most desert locations in the mid to upper 40mm range!   The low level easterly flow continues with the backdoor dryline/windshift front located again from about Flagstaff to Nogales.

WRFNAM

CAPE is forecast to be in the 1500 J/Kg range across much of Arizona which will support strong/severe storms.

There is disagreement between the WRFGFS and WRFNAM where the NW Mexico IT is located.  The WRFNAM moves it into far southern Arizona producing somewhat more favorable mid level winds while the WRFGFS keeps it stationary over the central GofC with weaker winds over the state.

WRFNAM 

WRFGFS

One issue is going to be how much overnight activity and morning clouds reduce heating.  If it's quite active, the atmosphere may not recover sufficiently to support widespread severe storms and we'll have to wait and see about that until the morning.   Both model runs develop strong storms by mid-afternoon over the higher terrain of southern Arizona and around Flagstaff.   The WRFNAM has storms farther east (in and around Tucson by late afternoon) as it did not move the backdoor front as far west as the WRFGFS.  What a complicated situation!

WRFNAM

A classic Phoenix outflow intersection/convergence situation is forecast for Phoenix as late afternoon thunderstorms to the south and north send strong outflows into the Phoenix area during the late afternoon and early evening.  CAPE is forecast to be in the 1100-1500 range which will result in strong/severe storms.

The WRFGFS has this outbreak just south of the Phoenix area while the WRFNAM is right over the valley.  Timing looks to be from 6-8pm.

WRFNAM

WRFGFS

The WRFGFS has storms developing back towards the Tucson area during the late evening.