Area forecast discussion
National Weather Service Tucson Arizona
915 am MST Thursday Dec 12 2013
Synopsis...low pressure moving through Arizona will bring a chance
of valley rain and mountain snow to Southeast Arizona this afternoon
into early Friday...although most of the precipitation should be
east of Tucson. After slightly cooler temperatures today and
Friday...expect a warmup and dry conditions from this weekend into
early next week.
Discussion...main stream of deep moisture that passed over far Southeast
Arizona early this morning produced 0.15 inch of rain at Douglas and some
mixed precipitation in western New Mexico. Meanwhile upper low still churning
near San Diego...spawning a few thunderstorms in southern cal.
Already enough middle level instability in place here evident in
castellanus clouds out the window which shows up in model
fields...especially later today.
Current forecast generally on track with placement of chances for
showers and isolated thunderstorms developing later today...mainly NE
of a line from Tucson to Sierra Vista...although spotty showers
cannot be ruled out in both cities this afternoon. Just made minor
tweaks to delay the timing until middle afternoon for precipitation outside of
current cloud field until low gets closer to enhance convective
With sunshine a bit longer into the day than earlier expected...went
ahead and raised high temperatures a couple degrees in current sunny
Rrev discussion...satellite imagery this morning showed a stream of
mostly middle-high level clouds extending from southern Baja California California
NE toward southern New Mexico with parts of forecast area on northwest fringes
of this moisture plume. Water vapor imagery...as of 3 am...placed
upper low near San Diego. This upper low will lift NE across Arizona
later today into tonight. Precipitable water values this morning are
mostly around a half an inch...with models progging that values
later today will increase up to 0.60" west and 0.80" east. These
values are 1-2 Standard deviations above normal for December. Low
levels still on the dry side with best chances being in the
mountains. Might even see a rumble or two of thunder this afternoon
across the eastern areas. Highs today will generally be...depending
on location...2-7 degrees cooler than Wednesday. Snow levels will be
rather high with this system...mainly above 7000 feet.
Upper low will opens up tonight with trough axis moving into New
Mexico Friday morning. Trailing trough will move across the area late
Friday afternoon into Friday night. Might pop up a few flurries in
the whites Friday night.
Dry north-northwest flow aloft this weekend as strong high pressure builds into
California with this high being around into the first half of next
week. Slightly warmer this weekend with strong warmup Monday and
Tuesday. Made some slight adjustments up to highs for both Monday
and Tuesday which still may not be warm enough. Consensus guidance
still running too cool in my mind...with European model (ecmwf) guidance on the very
near record warm side. Plenty of time to make adjustments.
Aviation...sct-bkn cloud coverage 6-10k feet above ground level is expected mainly
east of ktus through about 13/06z with skies clearing thereafter from
west to east into Friday morning. As an upper low moves in from the
west today...there will be also be chance -shra/-tsra and mountain -shsn
from ktus eastward with the greatest coverage across the higher
terrain. Dry conditions are expected to prevail today west of ktus.
Gusty surface Ely/southeasterly winds this morning especially near ktus will
taper off by midday with surface wind generally less than 10 kts
thereafter through 13/18z. Aviation discussion not updated for taf
Fire weather...a low pressure system will move across the area...
resulting in a chance of valley rain and mountain snow showers from
Tucson eastward today into early Friday morning. There will also be
enough instability this afternoon for a slight chance of a few
thunderstorms as well. Expect near normal daytime temperatures
today through Sunday. Thereafter...dry conditions and above normal
temperatures are expected early to middle next week. Overall...winds
will generally be on the light side with the passage of this system
through this upcoming weekend...with sustained winds mainly less
than 15 miles per hour.
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