Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/15/20

Area Forecast Discussion

National Weather Service Phoenix AZ

 452 PM MST Mon Sep 14 2020

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Slightly above normal temperatures are forecast this week with the
elevated haze from wildfire smoke gradually decreasing through at
least tomorrow evening. The warmest days will be during the
latter half of the week with high temperatures topping out between
106-109 degrees across the bulk of the lower deserts. Overall dry
conditions are expected, but slightly elevated moisture early this
week will support a slight chance of isolated afternoon showers
and thunderstorms mostly well east and south of Phoenix.

&&

.DISCUSSION...
A sprawling high pressure system has strengthened and shifted
further east and is now centered over the west-central US with a
~593 dam H5 center. A weak mid level closed low circulation and
thermal trough axis is positioned over E-NE AZ with light winds
aloft. Early afternoon ACARS sounding indicated a PW near 0.7" and
maintained slightly elevated moisture near 600 mb with easterly
component flow from the BL through about H5. Early afternoon
satellite imagery showed very substantial thinning out of the
regional smoke-haze layer aloft with less smoke advecting in.
Towering cu and very isolated showers were also seen across the
Mogollon Rim and the far outlining areas from Phoenix. With
abundant insolation today`s high has already reached 104 degrees
by early afternoon at Sky Harbor with regional temperatures
running a few degrees warmer than yesterday in the upper 90s to
low 100s.

A gradual increase in regional tropical moisture from the southeast
will continue from now through Tuesday morning with PWs climbing
just shy of 1" or slightly above seasonal norms. Combined with the
weak UL low pressure disturbance and weak vorticity expect a few
relatively modest isolated showers and thunderstorms across high
terrain areas and the distant deserts to the south today and possibly
Tuesday. The latest HREF CAMs guidance are in good agreement on
keeping most of the convection during those periods rather
isolated and short-lived. Isolated gusty afternoon and evening
outflow winds/dust and isolated dry lightning will be the main
concern.

Models remain in good agreement on maintaining the strong high
pressure system over the Southwest and West CONUS for much of the
week with the previously noted developing low centered east to
southeast of the region. Northerly and easterly flow aloft will
continue to help mitigate the smoke-haze at least in the next day
and a half or so. The persistent regional high pressure will also
combine with a drying trend beginning by midweek to support a
warm-up as models trend slightly warmer. Highs are expected to be
several degrees above normal for much of the week. Highs in and
around Phoenix could reach 106-109 by mid week and possibly a
couple of degrees warmer for SE CA to SW AZ and impose large areas
of moderate heat risk and isolated areas of high heat risk. The
wildcard could be the state of the haze-smoke layer for late
Wednesday through Friday.

Late this week and into the weekend a progressive low pressure
system passing to the north will flatten the ridge and shift it
east and south. Expect a slight cooling trend this weekend and
into early next week as heights gradually relax. Mostly dry west-
southwesterly flow aloft will also manage to keep conditions
mostly dry along with some occasional breeziness.

&&

.AVIATION...Updated at 2350Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Evening storm activity has remained over the Mogollon Rim and
southwestern Arizona with minimal impact to the terminal area.
Right now, winds are variable but headings continue to favor an
easterly direction, and should do so through tonight. There are
indications of possible LLWS tomorrow morning between 15/09Z and
15/14Z with nearly 80 degrees of directional shear and 20-25 kts
of speed shear between the surface and FL030. Otherwise, lofted
smoke is much less noticeable today compared to recent days.

Southeast California/Southwest Arizona including KIPL and KBLH:

There are no major aviation weather concerns as surface winds
transition to a westerly direction this evening. Speeds should
remain fairly light, AOB 6 kts. There may also be periods of a
very light/calm wind and variable directions. Lofted smoke is
considerably less noticeable today compared to recent days.

&&

.FIRE WEATHER...
Thursday through Monday:
A warm and dry weather pattern is anticipated during the period.
Above normal temperatures will gradually decrease to slightly
above normal from this weekend through early next week. Mainly
light to occasionally moderate winds will favor normal diurnal
patterns through most of the period. Daily min RH values near 10%
will improve slightly to the mid teens percent range by Saturday.
Overnight recovery around 25% will steadily improve every night
beginning on Friday night.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Sawtelle
AVIATION...AD
FIRE WEATHER...Sawtelle/Kuhlman