Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 040953
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
253 AM MST TUE AUG 4 2015

.SYNOPSIS...DRIER AIR WILL CONTINUE TO BRING LITTLE IF ANY
THUNDERSTORM ACTIVITY TO THE REGION ALONG WITH ABOVE NORMAL
TEMPERATURES THROUGH THE MIDDLE OF THE WEEK. INCREASING MOISTURE
WILL THEN BRING SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS
THURSDAY INTO THE UPCOMING WEEKEND ALONG WITH A SLIGHT COOLING
TREND.

&&

.DISCUSSION...CLEAR TO MOSTLY CLEAR SKIES PREVAIL ACROSS ALL OF THE
CWA EARLY THIS MORNING THANKS IN PART TO THE GRADUAL TOP-DOWN DRYING
THAT WE STARTED BACK ON SUNDAY. A LOOK AT THE UPPER-LEVELS SHOWS AN
UNUSUAL PATTERN FOR EARLY AUGUST WITH A SW-NE ELONGATED 500 MB RIDGE
CENTERED SOMEWHERE JUST WEST OF BAJA CALIFORNIA AND A 300 MB HIGH
OVER WEST-CENTRAL CHIHUAHUA MEXICO. THE RESULTING UPPER-LEVEL SWLY
FLOW CONTINUES TO REINFORCE HIGH LEVEL DRY AIR...WHICH IS FURTHER
BEING AUGMENTED BY WLY/NWLY MID-LEVEL FLOW. THE END RESULT WAS A
PWAT VALUE OF 0.93 INCH ON THE 00Z KTWC SOUNDING WITH SIGNS OF
CONTINUED SCOURING OF MOISTURE FROM THE COLUMN ALL THE WAY TO THE
INTERNATIONAL BORDER PER THE CIRA LAYERED PW PRODUCTS.

BASED ON TRENDS ALONE...WE SHOULD SEE EVEN LESS CONVECTIVE ACTIVITY
THAN YESTERDAY. AT THIS POINT...AM DISCOUNTING THE RECENT HRRR RUNS
WHICH HAVE INSISTED ON DEVELOPING PRECIP IN THE WHITES ALL MORNING
LONG AND SUBSEQUENTLY INITIATING CONVECTION THIS AFTERNOON AS FAR NW
AS PINAL COUNTY. THAT SAID...DECIDED TO REINTRODUCE LOW-END SLIGHT
PRECIP CHANCES IN THE WHITE MOUNTAINS AND THE HIGH TERRAIN OF
EXTREME EASTERN COCHISE COUNTY WHERE WE MAY HOLD ONTO JUST ENOUGH
MOISTURE TO INITIATE A STORM OR TWO TODAY. THIS IDEA IS SUPPORTED BY
THE UNIV. OF AZ WRF RUNS AND THE EXPERIMENTAL HRRR (HRRRX) WHICH
HAS...AT LEAST QUALITATIVELY...BEEN OUTPERFORMING THE
OPERATIONAL HRRR RECENTLY.

WEDNESDAY WILL BE A TRANSITION DAY AS THE MID-LEVEL HIGH BEGINS TO
MOVE INTO NM. AS THIS OCCURS...A SMALL INCREASE IN MOISTURE MAY BE
ENOUGH TO SET OFF A FEW AFTERNOON/EVENING STORMS NEAR THE
INTERNATIONAL BORDER. THIS WILL STILL ONLY BE ISOLATED ACTIVITY. THE
BIGGER STORY DURING THE MIDDLE OF THE WEEK WILL BE VERY WARM
TEMPERATURES...SOME 8 TO 11 DEGREES ABOVE NORMAL ON TUESDAY AND
WEDNESDAY. OUR RECORD HIGH OF 108 (2009) MAY BE IN JEOPARDY ON
WEDNESDAY. FOR MORE ON THE POTENTIAL RECORD HEAT PLEASE SEE THE
CLIMATE SECTION BELOW.

ON THURSDAY AND FRIDAY WE SHOULD SEE A NOTICEABLE UPSWING IN
CONVECTIVE COVERAGE AS OUR MID-LEVEL HIGH ROTATES INTO EASTERN NM
AND THE SOUTHERN GREAT PLAINS. THE ENSUING SLY/SELY FLOW WILL DRIVE
MOISTURE BACK TO ABOVE-CLIMATOLOGICAL LEVELS ACROSS SE AZ. AT THIS
TIME...IT APPEARS AS IF WE`LL SEE THE HIGHEST PRECIPITATION COVERAGE
ON FRIDAY BUT THIS DOES PARTLY HINGE--AS WE SAW LAST
TUESDAY/WEDNESDAY--ON HOW ACTIVE THURSDAY IS. THAT SAID...NUDGED
POPS UP A BIT FOR CENTRAL AND EASTERN ZONES.

ON SATURDAY AND SUNDAY...NWP SOLUTIONS ARE CONSISTENT IN MOVING A
SHORTWAVE TROUGH INTO THE GREAT BASIN WHICH WILL KICK THE HIGH A BIT
FARTHER TO THE SOUTH AND EAST. THIS WILL DRIVE THE BEST CHANCES OF
PRECIPITATION INTO EASTERN ZONES ON SATURDAY. SOME MOISTURE MAY
SLOSH FAR ENOUGH WEST ON SUNDAY TO BRING BETTER CHANCES BACK TO
CENTRAL AREAS. THE 04/00Z GFS/ECMWF STILL SHOW AN INVERTED TROUGH
POTENTIALLY IMPACTING THE REGION EARLY NEXT WEEK AS MENTIONED BY THE
PREVIOUS FORECAST SHIFT. TIMING THESE SUBTLE FEATURES AND THEIR
IMPACTS ON OUR WEATHER IS NOTORIOUSLY DIFFICULT--EVEN AT SHORT
RANGES. AS SUCH...FOR NOW MAINTAIN NEAR CLIMATOLOGICAL POPS THROUGH
THE END OF THE FORECAST PERIOD.

&&

.AVIATION...VALID THRU 05/12Z.
MOSTLY CLEAR SKIES THRU 04/16Z...THEN FEW-SCT CLOUDS AT 8-12K FT
AGL...MAINLY EAST OF KTUS THRU 05/05Z. MOSTLY CLEAR SKIES AGAIN
AFT 05/05Z. SFC WINDS GENERALLY LESS THAN 12 KTS WITH A FEW HIGHER
GUSTS DURING THE AFTERNOON/EARLY EVENING HOURS. AVIATION DISCUSSION
NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS ARE EXPECTED ACROSS MOST OF SOUTHEAST
ARIZONA TODAY...ALONG WITH ABOVE NORMAL TEMPERATURES...AND DAYTIME
MINIMUM RELATIVE HUMIDITY VALUES FALLING INTO THE 10 TO 20 PCT
RANGE. INCREASING PRECIPITATION CHANCES ARE THEN EXPECTED INTO THE
UPCOMING WEEKEND AS HIGH PRESSURE SHIFTS FROM NEARLY OVERHEAD...
EASTWARD INTO THE SOUTHERN PLAINS. OUTSIDE OF ANY THUNDERSTORM WIND
GUSTS...20-FT WINDS WILL GENERALLY BE TERRAIN DRIVEN AND LESS THAN
15 MPH. HOWEVER...THERE WILL BE SOME AFTERNOON AND EARLY EVENING
BREEZINESS...ESPECIALLY IN THE GILA VALLEY RIVER VALLEY NEAR SAFFORD.

&&

.CLIMATE...STRONG HIGH PRESSURE WILL BUILD OVER THE AREA TODAY INTO
WEDNESDAY...BRINGING HOT EARLY AUGUST TEMPERATURES TO THE
AREA...WITH A FEW SPOTS APPROACHING OR TYING RECORD HIGHS. NOT ALL
LOCATIONS IN SE AZ WILL GET INTO THE NEAR RECORD HEAT. BELOW ARE THE
SITES THAT WILL BE AT OR WITHIN THREE DEGREES TODAY AND WEDNESDAY.

DATE                     AUG 04           AUG 05
                       FCST RCD/YEAR     FCST RCD/YEAR
TUCSON INTL AIRPORT    107  109/1994     108  108/2009
FORT THOMAS            105  107/1995     106  109/2009
SAFFORD AG STATION     104  106/2009     105  108/1995

WITH A FORECAST HIGH OF 107 AT TUCSON AIRPORT TODAY...THIS WILL MARK
THE 7TH TIME SINCE 1895 THAT AUGUST HIT 105 OR HOTTER WHEN IT DIDN`T
OCCUR IN JULY. THE PREVIOUS SIX OCCURRENCES WERE IN
1914/1919/1945/1962/1975 AND 1977.

&&

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

&&

$$

PUBLIC...CARLAW
AVIATION/FIRE WEATHER...ZELL
CLIMATE...GLUECK

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON



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