Scientific Forecaster Discussion
fxus65 kpsr 221109
Area forecast discussion
National Weather Service Phoenix Arizona
409 am MST Tue Oct 22 2019
Update...updated aviation discussion.
dry conditions with mostly sunny skies will persist through the
weekend. High pressure over the eastern Pacific will result in a
warmup through midweek. Temperatures will peak today and
Wednesday with highs in the low 90s across the lower deserts.
Temperatures should cool slightly beginning Thursday through the
weekend in response to a trough passing by to the northeast. A
stronger trough pattern across the western U.S. Early next week
should bring the coolest temperatures of the season.
the synoptic weather pattern early this morning has seen little
change over the last 24 hours. A strong high pressure is still
positioned upstream over the epac just off the California coast and the
central U.S. Is dominated by a longwave trough and prominent
closed low. Between these features, deep northwest flow persists
across our area, maintaining very dry conditions with pwats below
the 25th percentile.
As the upper low near the Great Lakes continues shifting northeast,
the gradient over the western U.S. Will relax and 500 mb heights will
rise slightly today as the epac high nudges a little further east.
In response, a warming trend is expected today and again on
Wednesday with afternoon temperatures running 4-5 degrees warmer
than Monday. The Phoenix area will see highs around 90f, a few
degrees above the seasonal normal, and most of southwestern
Arizona/southeastern California will see highs reach the low to mid 90s. With
the very dry conditions, southern Arizona and California will be hard pressed
to see any clouds, but could see some distant lofted smoke in the
afternoons from any prescribed fires to the north, similar to
Thursday through the end of the week, a more amplified pattern
will develop with a strong 250 mb jet streak helping dig a trough
southward along The Rockies. The GFS and European model (ecmwf) still present
differing solutions. The GFS maintains an open progressive trough
while the European model (ecmwf) develops a cutoff low near The Four Corners
region and maintains it through Saturday. Despite the cooler
outcome of the Euro, the impact to temperatures across the lower
deserts is not too drastic, likely do to the fact that the epac
high is also expected to push further east to the California coastline.
The difference between GFS and Euro ensemble mean high
temperatures is ~5-8 degrees Thursday through Saturday. Still
leaning toward the warmer solution with the official forecast and
utilizing the National blend which has high temps in the mid to
upper 80s and lows around 55-60 degrees.
Regardless of the model solution for the end of the week, a
stronger gradient over region will lead to breezy conditions
Thursday, especially along the Colorado River valley, and again on
Friday across parts of southeast and southcentral Arizona following a
backdoor cold front.
Looking into early next week, long-range model guidance suggests
an active longwave trough pattern across the western U.S. With
multiple embedded shortwaves and much cooler weather. The first
such shortwave could even bring a very low-end precipitation
chance to AZ, but there is still too much uncertainty at this
Aviation...updated at 1110z
South-central Arizona including kphx, kiwa, ksdl, and kdvt:
Winds this morning may become very light at times leading to some
variability in direction, but overall, directions will favor
typical diurnal trends. Northerly winds aloft may advect smoke
from distant Forest fires into the terminal area producing some
slantwise visibility issues this afternoon.
Southeast California/southwest Arizona including kipl and kblh:
A mostly northerly wind will prevail for both terminals with
speeds mostly at or below 10 kts, although kblh may see a few
stronger afternoon gusts. Winds this evening and night will favor
a more northwesterly direction.
Aviation discussion not updated for amended tafs.
Thursday through monday:
Continued dry conditions with near seasonable temperatures and
periodic breezy conditions are expected through the period.
Slightly above normal highs near 90 on Thursday will settle into the
upper 80s by Friday and for most of the remaining period. Expect
breezy conditions each day across the region except for Saturday
when winds will be light and diurnal. Breezes with gusts of 15-24
mph will favor north-northeasterly and easterly directions on Thursday and
Friday, and south-southwesterly directions on Sunday and Monday.
Expect min relative humidity values to stay mainly in the 6-12 percent range across
the lower deserts through Saturday and then bump up into the teens by
Sunday. Mostly poor to fair overnight recoveries early in the period
will gradually improve by the weekend to become good to excellent by
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spotters should follow Standard reporting procedures.