textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Another morning of patchy fog in low lying areas and river valleys will burn off by 9-11am LST.

- Dry and tranquil weather conditions are expected through the workweek with temperatures near to slightly above normal.

- Another weather system will bring much cooler temperatures and rain chances to the region late this weekend into early next week.

SHORT TERM /TODAY THROUGH THURSDAY/

Clear skies in combination with remaining surface moisture from this past weekend's rain has once again resulted in patchy fog across low lying areas and river valleys. Isolated areas of dense fog (visibility less than 1 mile) will be likely again this morning. Be prepared for sudden reductions in visibility and drivers should exercise caution when encountering any fog during the morning commute. The fog should burn off by 9-11am LST.

Water vapor satellite imagery and 500 mb streamline analysis early this morning show a ridge of high pressure over the eastern Pacific along with a trough in the upper Plains and another one entering the Midwest. The aforementioned ridge of high pressure will slowly move eastward over the next few days, becoming centered over our area by Wednesday night. As the ridge of high pressure moves overhead heights aloft will gradually rise, maxing out around 584-586 dm Wednesday into Thursday. This will result in gradually warming temperatures. Afternoon high temperatures today will be in the low 70s across the lower deserts and in the mid to upper 60s across the higher terrain. Temperatures will peak on Wednesday/Thursday, with afternoon high temperatures in the mid to upper 70s across the lower deserts and in the mid 60s to low 70s across the higher terrain. Morning lows will be in the mid 40s to low 50s, with the warmer temps in more urban areas. With the ridge moving through the region over the next few days, it will promote the continuation of dry and tranquil weather conditions.

LONG TERM /FRIDAY THROUGH TUESDAY/

On Friday a weak shortwave trough will move through the region. This will result in lowering heights aloft, with 500 mb heights will lower to around 575-577 dm. This will result in temperatures cooling a degree or two, but will remain above normal. Afternoon high temperatures will be in the mid 70s across the lower deserts and in the upper 60s to low 70s across the higher terrain. Dry conditions will persist on Friday.

By this weekend and into early next week, global ensemble members all show a deep trough traversing the region. They still differ a little on the exact timing, but tend to favor sometime in the Sunday- Tuesday window. They are in good agreement that this trough will be taking an inland trajectory down from the Pacific NW 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 has PWATs in a 0.5-0.7" range, the GEFS has PWATs staying below 0.6", and the Canadian Ensemble has PWATs only in a 0.3-0.4" range). 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 by early next week and would support showers across at least some 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 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period. Winds will be light with extended periods of VRB to calm conditions. Patchy fog can be seen on satellite imagery, but is mainly to the south and west of the Phoenix Metro. This fog may become dense (visibility less than 1 mile), however no impacts to the terminals is expected. Winds will follow their typical diurnal tendencies with speeds generally aob 6 kt. Extended periods of light and variable to calm winds are also expected, especially during diurnal transitions. Besides a FEW passing high clouds Tuesday afternoon, skies will be mostly clear.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concern will be the potential for FG to impact both sites. Reduced visibilities have already been observed at some point during the overnight hours at both terminals. But now the fog has moved SW of KBLH and dense fog is just north and east of the KIPL terminal. Therefore, VCFG remains in the TAFs at this time. The addition of a TEMPO group with VIS down to 5SM and BR has been added to the KIPL TAF between 13-15Z, which is when models show the denser fog trying to get into KIPL. Otherwise, winds will be light with extended periods of VRB to calm conditions through Tuesday morning before a N/NW component is established later in the forecast window. Other than the VCFG/FG this morning skies will be mostly clear.

FIRE WEATHER

Dry and tranquil weather conditions will continue through the workweek with temperatures slightly above average. MinRHs today will be around 30-50%, with overnight recovery around 60-80%. For the remainder of the workweek, minRHs will drop to 20-35% with overnight recoveries remaining in the 60-80% range. By this weekend and into early next week another weather system will move through the region cooling temperatures back off below normal and bringing another chance for showers and wetting rains to the region. Winds will remain light and follow their normal diurnal tendencies with only marginal upslope gusts into the upper teens to low 20s.

PSR WATCHES/WARNINGS/ADVISORIES

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