056
FXUS65 KPSR 110019
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
519 PM MST Mon Jun 10 2024

.UPDATE...Updated 00z Aviation Discussion.

&&

.SYNOPSIS...
Near to slightly above normal high temperatures are expected across
the region today. Excessive heat will develop tomorrow across the
lower elevations of South Central Arizona as a ridge of high
pressure builds along the Arizona and New Mexico border through the
middle of the week. Excessive Heat Warnings will be in effect for
these lower elevation locations Tuesday through Thursday, before a
weather system traverses the region late this week and cools things
down by around five degrees on Friday.

&&

.DISCUSSION...
Current WV imagery and streamline analysis shows our region between
two upper level lows, one centered over East-Central New Mexico and
another cutoff low centered southwest of the Southern California
Coast. As heights aloft have not yet had time to build downstream of
the aforementioned cutoff low, temperatures today will only reach
near to slightly above normal values for the date. Highs will range
from the low to mid 100s across the lower deserts this afternoon.

By tomorrow, 500 mb heights over the region will have increased
upwards of 590 dam, and high temperatures in excess of 110 degrees
become possible across some of the hotter lower desert locations of
South-Central AZ. NBM probabilities for 110+ degree highs peak on
Wednesday, with values between 60-80% in the Phoenix Metro Area and
a 48% chance of at least tying the daily high at Sky Harbor. Due to
the proximity of the cutoff low which will linger offshore through
the middle of the week, a gradient in the high temperatures is
expected (particularly on Tuesday and Thursday), increasing from
west to east across the lower deserts. The coverage of Major
HeatRisk has consistently been highest on Wednesday through the past
several forecast packages, but since temperatures will be similar on
Tuesday and Thursday, Excessive Heat Warnings will be in effect for
all 3 days for portions of South-Central AZ.

Heading into the end of the work week, the WPC cluster analysis
shows great agreement between global ensemble members that the
cutoff low will begin to move inland across the Desert Southwest.
Ensemble and deterministic guidance show this occurring late
Thursday into Friday, which is expected to push temperatures back
down to near or slightly above normal readings on Friday. Guidance
shows mid-level moisture increasing into the region ahead of the
low Thursday, which may be enough for some weak shower development
across the AZ high terrain, but for now PoPs remain around 10-15%
or less for most places. Additionally, breezy conditions will
increase for the latter half of the week in response to the upper
low. The increase in winds combined with hot, dry conditions will
lead to enhanced fire weather conditions.

This weekend, cluster analysis reveals more disagreement on the
exact strength and positioning of a broad trough over the Pacific
Northwest. Flat ridging over the Desert Southwest is likely
following the passage of the cutoff low, allowing for above normal
temperatures to return on Saturday. Though uncertainty is still
moderate, latest NBM deterministic values have come up to 108-112
degrees for the highs on Saturday and Sunday across the lower
deserts. This would lead to widespread Moderate and isolated
pockets of Major HeatRisk developing, particularly in Southeast
California.

&&

.AVIATION...Updated at 0020Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
VFR conditions forecast through the TAF period. Wind pattern will
continue to follow diurnal tendencies, with speeds generally
remaining under 10 kts, although some occasional afternoon and
early evening gusts into the mid to upper teens can be expected.
Light easterly will develop overnight once again. FEW-SCT clouds
above 15 kft will prevail through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
VFR conditions forecast through the TAF period. FEW-SCT clouds
mainly aoa 20 kft can be expected. At KIPL, winds will generally
be out of the southeast through most of the period, with the
exception of a period of westerly winds during this evening. At
KBLH, winds will generally be out of the south. Wind speeds should
generally remain aob 10 kts at both sites.

&&

.FIRE WEATHER...
Hot and seasonably dry conditions will continue to support a high
fire danger across the area through the week. Near to slightly
above normal temperatures will continue today before heating up
once again heading into the middle part of the week. Winds will
continue to generally favor diurnal tendencies with occasional
afternoon breeziness of 20-25 mph expected across most of the
region. MinRHs ranging between 5-15% with poor to fair overnight
recoveries of between 20-45% are expected. Going into the end of
the work week, a weather system is expected to traverse the region
and bring widespread breeziness on Thursday and gusty winds over
the far eastern districts on Friday, along with a low (10% or
less) chance for dry thunder over the South-Central AZ high
terrain.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Tuesday to 8 PM MST Thursday
     for AZZ534-537>555-559-560-562.

CA...None.
&&

$$

DISCUSSION...Whittock
AVIATION...Young/95
FIRE WEATHER...Whittock/Smith