Scientific Forecaster Discussion
fxus65 kpsr 262032
Area forecast discussion
National Weather Service Phoenix Arizona
130 PM MST Wed Jun 26 2019
a high pressure system centered over New Mexico will continue to be
a strong influence for weather in Arizona and southeast California
through next week. This will result in mostly near normal
temperatures across Arizona to slightly below normal readings across
southeast California. The dry weather also looks to persist well
into next week for the bulk of the region with high terrain showers
and thunderstorms primarily relegated to far east central Arizona.
the region continues to be sandwiched between a deep upper level low
over the northwest U.S. And a modestly strong subtropical high
centered across southern New Mexico and western Texas. This synoptic
pattern will remain blocked through much of next week as the ridge
builds north into the Central Plains and several shortwaves in the
Pacific maintain the mean trough axis along the West Coast. This
orientation will keep much of the region under southwesterly upper
level flow sequestering any better quality deep moisture into
There is still good ensemble support that the subtropical high will
edge somewhat westward through the weekend with 500 mb heights reaching
a climatologically typical 590-594dm range. This should result in
temperatures warming a few degrees and highs hitting between 105f
and 110f regularly through early next week. However, there is some
minor forecast concerns over a remnant mid/upper tropospheric
moisture from tropical storm Alvin streaming into the Desert
Southwest over the weekend. Deterministic guidance has been
consistent with this outcome where a small jet streak and at least
one perturbation ripples into the southwest flow.
Model pwats increase dramatically across much of the region,
especially across Southern California and southwest Arizona. GFS
operational pwats seem to be on the high end of guidance around 1.5
inches with GFS ensemble mean and European closer to around 1 inch.
However, investigation of forecast soundings shows a majority of
this moisture packed above 12k ft with little more than 7 g/kg
mixing ratios below 600 mb. While virga (and maybe even a sprinkle)
seems a certainty, the greatest impact will be extensive cloud cover
over the weekend potentially narrowing the diurnal range
dramatically; and have cut into guidance output with this in mind.
Otherwise, some residual lower level moisture may seep into far
eastern Arizona as a result of outflows from convection in New
Mexico over the weekend leading to isolated storms potentially
clipping far eastern Gila County. With the prevailing SW flow, the
best odds point to any storms remaining over the White Mountains.
The most recent operational GFS iterations have been trending
towards the overall naefs ensemble mean with respect to the flow
pattern next week. It now shifts the subtropical high much farther
to the south into northern Mexico as the quasi-stationary Pacific northwest
low protrudes southward closer to our region. This keeps the vast
majority of the region under a dry southwesterly flow with better
boundary layer moisture only reaching central Sonora. On a positive
note, the influence of the upper trough should keep daytime highs
closer to 105 degrees through the bulk of next week.
Aviation...updated at 1725 UTC.
South-central Arizona including kphx, kiwa, ksdl, and kdvt:
timing of wind shifts and periods of gusty cross runway winds will
be the primary aviation challenges through Thursday morning under
period of passing high clouds. Confidence is moderate that some
measure of southerly winds will persist for much of the afternoon,
though directions may be quite variable (i.E. 150v210). Gusts 15-
20kt are possible though indications suggest these will be periodic
gusts rather than persistent through the afternoon. Better
confidence exists that the veering towards a west/SW component will
occur very late in the afternoon/early evening and more persistent
gusts near 20kt will prevail before decoupling late in the evening.
Southeast California/southwest Arizona including kipl and kblh:
strengthening winds this afternoon and evening will be the main
aviation challenge through Thursday morning with high clouds
clearing from the area. Steady 10-20kt southerly winds will impact
kblh through the evening before decoupling and trending towards
light and variable late tonight. Kipl should experience a brief
period of gusty west winds this evening, though confidence is only
moderate that speeds will reach anywhere above 20kt.
Aviation discussion not updated for amended tafs.
Saturday through wednesday:
seasonably warm and mostly dry weather will persist over all the
districts through the middle of next week. However, a slight
increase in moisture could lead to an isolated, non-wetting
thunderstorm across the far eastern Arizona high terrain Saturday
afternoon/evening. Ridge top and gap winds will occasionally be
breezy during the afternoon hours with SW gusts around 25 mph
common. Minimum relative humidity values will mostly fall into a 10-
15% range with generally poor (locally fair) overnight recovery. The
winds and humidity combined with very dry fuels will frequently
result in elevated fire weather conditions during this period.
Spotter information statement...
spotter activation is not expected.