Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 291621
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
920 AM MST FRI APR 29 2016

.SYNOPSIS...
EXPECT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS MAINLY NORTH
OF TUCSON THROUGH MONDAY. STRENGTHENING HIGH PRESSURE ALOFT WILL
THEN PROVIDE DRY CONDITIONS WITH A STRONG WARMING TREND BY THE
MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...VISIBLE SATELLITE IMAGERY DEPICTED SCATTERED TO BROKEN
CLOUDS NORTH TO NORTHEAST OF TUCSON. OTHERWISE...CLEAR SKIES
PREVAILED ACROSS SE ARIZONA. SURFACE WINDS WERE GENERALLY CALM
EXCEPT ACROSS THE UPPER GILA RIVER VALLEY WHERE WIND GUSTS TO NEAR
25 MPH WERE ONGOING. DEWPOINTS AT LOWER ELEVATIONS VALID 16Z RANGED
FROM THE MID 20S-MID 30S...AND THESE TEMPS WERE ABOUT 5-15 DEGS
HIGHER VERSUS 24 HOURS AGO.

MEANWHILE...SURFACE TEMPS VALID 16Z WERE ABOUT 5-15 DEGS COOLER
VERSUS THIS TIME THURSDAY. 29/12Z KTWC SOUNDING TOTAL PRECIP WATER
VALUE OF 0.43 INCH WAS 0.16 INCH HIGHER VERSUS 24 HOURS AGO. 29/12Z
UPPER AIR PLOTS DEPICTED A BROAD TROUGH OVER THE WRN CONUS...WITH
LOW PRESSURE CENTERED NEAR THE FOUR CORNERS...AND ANOTHER LOW
CENTERED OVER WRN MONTANA. MODERATE TO STRONG GENERALLY WLY FLOW
ALOFT PREVAILED ACROSS SE ARIZONA.

WATER VAPOR IMAGERY DEPICTED A CYCLONIC CIRCULATION SYSTEM MOVING
SEWD ACROSS WRN PIMA COUNTY AT THIS TIME. THIS SYSTEM WAS
INITIALIZED AS A VORT MAX VIA THE 29/12Z NAM/GFS...AND WILL SEWD
INTO NRN CHIHUAHUA BY THIS EVENING. THESE SOLUTIONS AS WELL AS
SATELLITE TRENDS SUGGEST THAT CLEAR SKIES OR JUST FEW CUMULOFORM
CLOUDS WILL PREVAIL FROM TUCSON SWD/WWD THRU THIS AFTERNOON.

MEANWHILE...SEVERAL HRRR SOLUTIONS FAVOR THE CONTINUATION OF CHANCE-
CATEGORY POPS MAINLY ACROSS THE WHITE MOUNTAINS INTO THIS EVENING.
THERE APPEARS TO BE ENOUGH PROGGED INSTABILITY TO SUPPORT A CHANCE
OF THUNDERSTORMS AS WELL. WLY/NWLY WINDS THIS AFTERNOON WILL BE LESS
VERSUS THUR AFTERNOON...THOUGH SOMEWHAT GUSTY ACROSS THE UPPER GILA
RIVER VALLEY. HIGH TEMPS THIS AFTERNOON WILL BE ABOUT 3-8 DEGS
COOLER VERSUS THUR.

&&

.AVIATION...VALID THRU 30/18Z.
NORTH TO NORTHEAST OF KTUS EXPECT ISOLATED TO SCATTERED -SHRA WITH
-TSRA THIS AFTERNOON. CLOUD DECKS WILL GENERALLY BE AROUND 8-12K FT
AGL INTO SATURDAY MORNING. KTUS VICINITY SOUTHWARD...CLEAR SKIES
THROUGH MUCH OF THE PERIOD WITH SCATTERED CLOUDS AROUND 10-15K FT
AGL MAINLY THIS AFTERNOON. SURFACE WIND THIS AFTERNOON AND EVENING
WILL BE WLY/NWLY AT 10-18 KTS WITH GUSTS TO NEAR 25 KTS. SURFACE
WIND DIMINISHING TO LESS THAN 10 KTS MOST LOCALES LATE TONIGHT...
THEN SURFACE WIND SATURDAY MORNING SELY TO SWLY AT 10-15 KTS WITH
GUSTS TO 20 KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS
MAINLY NORTH OF TUCSON THROUGH MONDAY. OTHERWISE...DRY CONDITIONS
WILL PREVAIL INTO THE MIDDLE OF NEXT WEEK. EXPECT AFTERNOON
BREEZINESS FROM THE NORTHWEST TO SOUTHWEST TO CONTINUE THROUGH THIS
WEEKEND FOLLOWED BY LESS WIND INTO THE MIDDLE OF NEXT WEEK.

&&

.PREV DISCUSSION /254 AM MST/...EARLY MORNING WATER VAPOR IMAGERY
CONTINUES TO REVEAL SLOW MOVING LOW PRESSURE OVER THE FOUR CORNERS.
THIS IS THE SYSTEM THAT BROUGHT STRONG WINDS TO PARTS OF THE AREA
YESTERDAY ALONG WITH A FEW LATE-AFTERNOON/EVENING SHOWERS NORTH/EAST
OF TUCSON. SINCE THEN IT HAS MOVED EAST AND TRIGGERED EARLY MORNING
CONVECTION ACROSS THE TEXAS PANHANDLE. IN ITS WAKE...NORTHWESTERLY
FLOW PERSISTS ACROSS THE AREA BUT A WEAK SHORTWAVE TROUGH IS NOTED
IN THE FLOW NEAR LAS VEGAS. CLOUDS ARE ON THE INCREASE ACROSS
CENTRAL ARIZONA BUT MUCH OF SOUTHEASTERN ARIZONA REMAINS CLEAR AS OF
09Z. TEMPS REMAIN SOMEWHAT MILD THIS MORNING...GENERALLY IN THE
MID/UPPER 50S GIVEN 5-10KTS OF WIND AT NEARLY ALL SITES.

THE AFOREMENTIONED SHORTWAVE TROUGH WILL SWEEP THROUGH THE AREA
TODAY BUT WILL REMAIN TO THE NORTH OF TUCSON. MODEST INCREASES IN
MOISTURE IMMEDIATELY AHEAD OF THE TROUGH COULD BE JUST ENOUGH TO
PRODUCE SOME LIGHT SHOWERS/SPRINKLES BUT THIS WOULD LIKELY BE
CONFINED TO THE HIGHER TERRAIN LOCATIONS NORTH/EAST OF TUCSON.
FORECAST SOUNDINGS ARE LARGELY UNIMPRESSIVE ACROSS THE LOWER
ELEVATIONS AND POPS WILL REMAIN BELOW 10 PERCENT. SHORTWAVE RIDGING
IS FORECAST ACROSS THE AREA LATE FRIDAY NIGHT INTO SATURDAY...THUS
THE WINDOW OF OPPORTUNITY FOR PRECIP IS NARROW.

ANOTHER...DEEPER LOW IS FORECAST TO DROP THROUGH ARIZONA ON SUNDAY
AND AT FIRST GLANCE IT MIGHT SEEM THAT PRECIP CHANCES WOULD BE
SIGNIFICANT...ESPECIALLY GIVEN H5 HEIGHT PERCENTILES SOMEWHERE ON
THE LOWER END OF THE SPECTRUM /BETWEEN 2-5 PERCENT/. HOWEVER...
MOISTURE /PWATS AND IVT/ IS FORECAST TO REMAIN WELL WITHIN
CLIMATOLOGICAL NORMALS FOR EARLY MAY. FORECAST SOUNDINGS ARE ONCE
AGAIN LARGELY NOT SUPPORTIVE OF PRECIPITATION ACROSS THE LOWER
ELEVATIONS AND ASIDE FROM A CHANCE OF SHOWERS IN THE WHITES...THE
MAIN IMPACT WILL BE IN THE FORM OF WINDS AND COOLER TEMPS. GEFS
PLUMES ARE DRY ACROSS THE LOWER ELEVATIONS AND NAEFS INDICATES 20-30
POPS WOULD BE WARRANTED ONLY TO THE NORTH.

LOOKING TOWARD NEXT WEEK...HIGH AMPLITUDE RIDGING WILL TAKE SHAPE
FROM TUESDAY THROUGH AT LEAST THURSDAY...RESULTING IN A RETURN OF
THE ABOVE NORMAL TEMPERATURES AND DRY CONDITIONS. THERE IS SOME
SUGGESTION FROM BOTH THE DETERMINISTIC AND PROBABILISTIC ECMWF AND
GFS THAT A LOW WILL DROP THROUGH SOUTHERN CALIFORNIA...POSSIBLY
DRAWING MOISTURE NORTHWARD INTO NEW MEXICO AND EASTERN ARIZONA. THE
AMPLITUDE OF THE TROUGH AND MAGNITUDE OF ANY MOISTURE ADVECTION IS
STILL UNCERTAIN AT THIS TIME BUT I FELT THAT HIGHER THAN CLIMO POPS
ARE WARRANTED IN THIS CASE ALONG WITH COOLER TEMPERATURES.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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