textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- Temperatures will warm back into the normal range starting Tuesday, likely staying there for the rest of the workweek. Hotter temperatures with lower desert highs into the nineties look possible by the weekend.

- A weather system is likely to bring rain chances to portions of the region on or around Thursday, but the timing and potential rainfall amounts are still quite uncertain.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Tranquil weather conditions will continue early this week under quasi-zonal dry westerly flow. Large scale upper level troughing will persist across much of the Western U.S., but with no organized shortwaves moving within the trough. The post cold frontal air mass that only brought upper 70s for highs on Sunday will be slow to modify today with highs still only topping out in the upper 70s to maybe a few spots reaching the lower 80s under sunny skies.

A bump in upper level heights is expected for Tuesday as a Pacific low deepens well west of southern California allowing highs to warm into the mid 80s, or just within the normal range. This height pattern should carryover into Wednesday while the low picks up eastward motion toward northern Baja. The biggest change into Wednesday should be the increase in high clouds as moisture associated with a sub-tropical jet shifts northward into the southeastern 1/3rd Arizona. Temperatures should also nudge upward another 2 or 3 degrees with highs more into the upper 80s.

LONG TERM /THURSDAY THROUGH SUNDAY/

Thursday may be shaping up to be an interesting weather day across portions of Arizona if the Pacific weather system passes close enough or even across southern Arizona. Model uncertainty is still somewhat high with the GEFS indicating a slightly stronger system with more moisture getting pulled northward into our area compared to the EPS. Timing differences are also there with the EPS being around 12 hours behind the GEFS and CMCE, but for now sometime Thursday looks to be the best chance for any rain chances. The track of the low will also come into play as guidance shows the low center moving along the Arizona/Mexico border. Any shift toward the south would be detrimental for rain chances, while a shift more into Arizona would be more ideal.

Upper level moisture will advect into the region from the south southwest on Wednesday, with moisture gradually lowering with time as the disturbance nears our area on Thursday. Ensembles do mostly agree on PWATs increasing on Thursday to around 0.60-0.75", or 150-175% of normal with some members exceeding 1.00". Initially, some very high-based showers should become possible by Thursday morning from Phoenix and areas the east and southeast, but very dry air in the low levels is likely to prohibit any measurable rainfall. It should not be until the afternoon/evening hours when moisture improves enough within the low and mid levels and forcing reaches its peak for showers and potentially some thunderstorms to affect the area. So far moisture within the lower levels looks quite meager, but it would not be surprising to have enough moisture and instability in the mid-levels for some convective activity to occur. Some ensemble members are picking up on the convective potential indicating a potential of localized QPF amounts of a half an inch or more. Additionally, any thunderstorms that may develop could bring strong gusty winds with the potential for blowing dust. PoPs remain somewhat low due to the uncertainty with 10-20% across the western lower deserts, 25-40% over the south-central Arizona lower deserts to as high as 44-55% over the eastern Arizona high terrain.

Temperatures should dip again into or just below the normal range on Thursday due to the weather system skirting by to our south, but the slight cool down is likely to be short-lived. Once the system moves east southeast of the region by around Friday, upper level ridging should begin to filter in from the west. Whether the warmer temperatures move in already on Friday or wait until Saturday is still uncertain, but at the very least the lower deserts should reach into the low to mid 90s by Saturday. The 90s for highs are forecast to persist into Sunday and possibly into next Monday, but NBM guidance shows another slight cool down may occur early next week bringing temperatures back into the normal range.

AVIATION

Updated at 1751Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns through the next 24 hours under mostly clear skies. Winds will tend to follow typical diurnal tendencies, with some light variability during diurnal wind shifts and afternoon wind gusts up to 15-20 kts.

Southeast California/Southwest Arizona including KIPL and KBLH: Primary aviation impact over the next 24 hours will be gusty afternoon and evening winds at both terminals, with up to 20-25 kt westerlies at KIPL and up to 20 kt south-southwesterlies at KBLH. Wind directions will favor a westerly component through the TAF period at KIPL with a veering toward a NW/NW direction later Tuesday morning. At KBLH, directions will favor a S/SW component through this evening before shifting to a light NW/N tonight. both terminals can expect periods of light variability Tuesday morning. Mostly clear skies will prevail through tonight, followed by FEW to SCT high cirrus.

FIRE WEATHER

Drying conditions along with a slight warm up are expected through Tuesday. Look for MinRHs to fall to 15-20% this afternoon and 10-15% on Tuesday, while overnight recoveries transition from good to poor to fair (25-40%) by Tuesday night. Winds will be on the light side following diurnal patterns with only some occasional upslope breeziness during the afternoon hours. Another weather system is then forecast to move through the region during the later half of the workweek leading to increased RH and chances for rain and possibly some isolated thunderstorms.

PSR WATCHES/WARNINGS/ADVISORIES

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