textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- Dry and tranquil weather conditions are expected through the workweek with temperatures gradually warming to slightly above normal by the end of the week.

- Next weather system could bring rainfall back to the area late next weekend.

SHORT TERM /TODAY THROUGH TUESDAY/

Upper level water vapor satellite imagery early this morning shows broad troughing stretching from the Desert SW into the Plains. Objective analysis and upper level water vapor satellite imagery show the closed low associated with the trough (and that brought rain to the region this past weekend) is now centered over eastern CO/western KS. With the desert SW on the back side of the trough there is an abundance of subsidence which has resulted in clear skies across the region. The lower levels are still holding onto moisture though which is evident in the current dew point temperatures, which range from the upper 40s to mid 50s across the lower deserts. Low temperatures this morning are forecasted to be very similar to the dew point temperatures which is an excellent setup, in conjunction with very light to calm winds, for the development of fog this morning. Looking at the nighttime microphysics satellite product areas of dense fog can already be seen in the valleys of the higher terrain areas north of the Phoenix Metro. Lighter fog can also be seen starting to develop across portions of SE CA and SW AZ. Fog will likely develop in low lying areas and river valleys. Models continue to show the potential for this fog to become dense, with visibilities falling below 1 mile at times. Drivers should exercise caution when encountering lower visibilities during the morning commute. Any fog that develops will burn off by 9-11am.

With broad troughing still influencing the region today, there will be one more day of below normal temperatures with afternoon high temperatures around 2-4 degrees below normal. Highs this afternoon are forecasted to be upper 60s to low 70s across the lower deserts and in the low to mid 60s across the higher terrain. Tomorrow temperatures will return to near normal. This is due to rising 500 mb heights, which is in response to high pressure building over the eastern Pacific. Afternoon high temperatures tomorrow will be in the the low to mid 70s across the lower deserts and in the mid 60s to low 70s across the higher terrain areas. In addition to warming temperatures the rising heights aloft will also promote dry and tranquil weather conditions across the region.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Models continue to be in good agreement that dry and tranquil weather conditions will continue across the region through at least the end of the workweek. Heights aloft will continue to rise as the aforementioned high pressure system continues to build and eventually moves and over our region during the middle of the week. Temperatures will peak during the middle of the week, when the high pressure is overhead. During this timeframe afternoon high temperatures will be 3-6 degrees above normal, with forecasted highs in the mid to upper 70s across the lower deserts and in the upper 60s to low 70s across the higher terrain. On Friday, a dry shortwave trough, out ahead of the next weather system, looks to move through the region cooling us off a couple degrees (but still near to slightly above normal). Morning low temperatures during the latter half of the workweek will be in the 40s across much of the CWA but more urban areas will see lows in the low to mid 50s.

By this weekend, global ensemble members all show a deep trough traversing the region by some point either during the weekend or early next week, but they differ on the exact timing. They are in good agreement that the trough will be moving down into our region from the Pacific NW (inland trajectory) and not move down along the eastern Pacific Ocean and then move inland like the last low pressure system did. With this trough taking an inland trajectory the system won't be bringing a lot of moisture to the region. PWATs currently look to only rise to a 0.5-0.7" range (the ECMWF and Canadian Ensemble have PWATs in a 0.5-0.7" range, but the GEFS has PWATs staying below 0.6"). This increase in moisture (in combination with forcing from the trough and terrain itself) would likely support showers across the higher elevations to the north and east of the Phoenix Metro. Showers across the lower deserts will likely be harder to come by with this amount of moisture and would need more help than that of the higher terrain areas. Nevertheless, another weather system will be moving through the region either late this weekend or early next week and would support showers across at least portions of the CWA along with cooling temperatures. With this weather system temperatures look to cool back off below normal. Stay tuned for future updates.

AVIATION

Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No weather concerns at the valley TAF sites through the forecast period. Winds will only show a weak duirnal trends, but overall light and variable.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concerns during the next 24 hours will be potential for fog redevelopment into KPIL again tomorrow morning. Have introduced VCFG for now from 10z-16z and continue to monitor. Otherwise, tranquil weather with with mostly clear skies and overall light and variable winds.

FIRE WEATHER

One more day of below normal temperatures is expected today before rising back to near to slightly above normal by the middle of this week. Dry and tranquil weather conditions return to the region today and will continue through the workweek. MinRHs will range from 40-60% with excellent overnight recovery of 80-100% for today. Drier air will filter into the region by the middle of the week with MinRHs bottoming out around 25-35% by Wednesday and Thursday. Even with the drier air overnight recoveries will still be in a 60-80% range. Despite a few upslope gusts in the teens to lower 20 mph range, winds will remain light and follow normal diurnal patterns.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.