Scientific Forecaster Discussion
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Area forecast discussion...update
National Weather Service Tucson Arizona
1105 PM MST Thursday Apr 17 2014
Synopsis...a Pacific low pressure system will bring a slight
chance of showers and thunderstorms Friday afternoon into
Saturday. Cooler temperatures will also occur Friday followed by a
warming trend early next week. Gusty winds will return to the area
next Tuesday and Wednesday.
Update...ran out a quick update to the sky cover for the tonight
period as mostly cloudy conditions should prevail during this time
period. Made minor wording changes in aviation section also.
Discussion...shortwave trough just off the Southern California coast
this evening will continue to edge onshore. This will result in
increasing cirrus level clouds. The main vorticity lobe from this
system will slide into area from west to east during the middle
morning hours. This should increase in middle level cloud cover after
15z. By middle day there should be a few storms building though low
levels will remain dry as seen in multiple point sounding
inverted-v profile. Have updated the weather grid to only show
sprinkles with onset of the showers /prior to 00z/. Still best
shot for moisture look to be after 06z Saturday /and throughout
the day Saturday/ as another vorticity lobe pushes through the area. Only
other major change to the forecast was a lowering of snow amounts
as well as the onset of snow in the forecast for the white
mount ian. Otherwise...forecast in good shape.
Aviation...valid through 06z/19.
A weak upper level low pressure system near the Southern California
coast this evening will move into the area Friday. Expect broken to
overcast cloud decks mostly above 12k feet above ground level overnight and Friday.
Isolated-scattered -shra should develop Friday afternoon. There is also a
slight chance of -tsra Friday afternoon. Surface wind through
tonight will be mostly less than 10 kts. Surface wind Friday will be
southerly/southwesterly 12-18 kts with gusts to around 25 kts. Brief wind gusts to
near 40 kts may occur near thunderstorms. Aviation discussion not
updated for taf amendments.
Fire weather...a weak upper level low pressure system will move
east across the area Friday through Saturday. There appears to be
enough moisture to justify isolated to scattered showers Friday
afternoon through Saturday. There also appears to be enough
instability to support a slight chance of thunderstorms Friday
afternoon and Friday evening...and again Saturday afternoon.
Rainfall amounts are expected to be quite light.
However...the main concern will be for the potential of gusty and
erratic winds associated with any thunderstorms that occur. Dry
conditions will then prevail Saturday night through Wednesday.
Expect normal diurnal wind trends Sunday and Monday...with
occasional gusts during the afternoon hours due to daytime heating.
Critical fire weather conditions may return as early as Tuesday...
though more likely next Wednesday when stronger winds are forecast
to occur. The strongest winds will be across Greenlee...Graham and
Cochise counties east of Tucson.
Previous discussion... /issued 237 PM MST Thursday Apr 17 2014/
Discussion...a low pressure system approaching the Southern
California coast today will track through Arizona on Saturday.
Moisture associated with a weak impulse will move into the area
Friday ahead of the main system. Low level moisture will be
limited so any showers or thunderstorms that develop Friday
afternoon and early evening will produce very little rain. Models
showed deeper moisture moving into southern Arizona as the main
low pressure system moves through the state on Saturday. The cold
pool aloft will result in a little more instability Saturday
afternoon and evening for a better chance of thunderstorms
compared to Friday. A drop in daytime temperatures can also be
anticipated Friday and Saturday due to the affects of the system.
Thereafter...a ridge of high pressure will build over the region
for more dry conditions and warmer daytime temperatures. Medium
range models showed a significant change in the weather pattern by
the middle of next week as a large low pressure system enters the
western states. Moisture will be limited this far south so not
expecting any showers but wind and cooler temperatures for
southern Arizona will be the likely outcome.
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