Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 210018 AAA
AFDTWC

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TUCSON AZ
518 PM MST SUN JUL 20 2014

.SYNOPSIS...EXPECT ISOLATED TO SCATTERED THUNDERSTORMS MOSTLY EAST
AND SOUTH OF TUCSON THROUGH THE MIDDLE OF THIS WEEK. MUCH HOTTER
TEMPERATURES WILL OCCUR TUESDAY THROUGH THURSDAY...WITH NEAR RECORD
HIGHS POSSIBLE. AN INCREASE IN THUNDERSTORM ACTIVITY SHOULD OCCUR
LATE IN THE WEEK AND INTO THE WEEKEND.

&&

.UPDATE...BASED ON RADAR TRENDS AS WELL AS SPC STABILITY
DIAGNOSTICS...HAVE UPDATED THE OFFICIAL FORECAST TO CONFINE SHOWERS/
TSTMS THIS EVENING TO ABOUT THE SOUTHEAST HALF OF COCHISE COUNTY.
HAVE MAINTAINED ISOLATED SHOWERS/TSTMS ACROSS THE WHITE MOUNTAINS AS
WELL. 21/00Z KTWC SOUNDING DEPICTED A VERY STABLE AND QUITE DRY
REGIME...WITH LIFTED INDEX OF PLUS 2...AND TOTAL PRECIP WATER VALUE
OF 0.99 INCH. AT THIS TIME APPEARS THAT PRECIP-FREE CONDITIONS
SHOULD OCCUR AREA-WIDE BY ABOUT 10 PM TO MIDNIGHT MST.

&&

.DISCUSSION...WATER VAPOR IMAGERY AND 20/12Z UPPER-AIR PLOTS SHOW AN
UPPER LOW OVER SOUTH CENTRAL CALIFORNIA AND INTO CENTRAL NEVADA AND
MOVING NORTH. MEANWHILE...A RIDGE IS PARKED OVER THE GENERAL
VICINITY OF NEW MEXICO AND WEST TEXAS. THIS HAS RESULTED IN A STRONG
SOUTHERLY FLOW ALOFT IN THE MID TO UPPER LEVELS...WITH STEERING FLOW
AROUND 15 KNOTS.

THIS MORNINGS KTWC SOUNDING HAD THE LOWEST/DRIEST PRECIPITABLE WATER
VALUE THAT WE HAVE SEEN IN A WHILE...ESPECIALLY FOR A MORNING
SOUNDING WITH A VALUE OF 1.04 INCHES. CLIMATOLOGICALLY THIS PW VALUE
FALLS IN THE 25TH PERCENTILE FOR THIS TIME OF YEAR...WHICH IS PRETTY
DRY...RELATIVELY SPEAKING. THAT SAID...ISOLATED SHOWERS AND
THUNDERSTORMS HAVE DEVELOP AS EXPECTED OVER THE HIGHER TERRAIN OF
NORTHEAST SONORA AND NORTHWEST CHIHUAHUA. A FEW CELLS COULD MOVE
INTO SOUTHERN PORTIONS OF COCHISE COUNTY AND PERHAPS PARTS OF SANTA
CRUZ COUNTY AS WELL. U OF A 12Z WRF/NAM MODEL AND HRRR SHOW A
SIMILAR SCENARIO. THAT SAID...THINK THE POP FORECAST FOR THE
REMAINDER OF THIS AFTERNOON AND INTO THE EVENING SEEM TO BE ON
TRACK. HOWEVER...WILL BASE MY FORECAST FOR THIS EVENING LARGELY ON
SATELLITE AND RADAR TRENDS RIGHT BEFORE ISSUANCE TIME.

THE HIGH IS PROGGED TO MEANDER ACROSS THE GENERAL VICINITY THROUGH
MIDWEEK WITH A SIMILAR THREAT FOR ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS...MAINLY OVER THE MOUNTAINS...AS WELL AS ALONG THE
INTERNATIONAL BORDER EACH AFTERNOON AND EVENING. FROM WEDNESDAY AND
BEYOND I DID NOT MAKE ANY ADJUSTMENTS TO THE INHERITED POP FORECAST
DUE TO CONTINUED UNCERTAINTIES THIS TIME OF YEAR. I INHERITED AN
UPSWING IN THUNDERSTORM ACTIVITY FRIDAY...ESPECIALLY ALONG THE
INTERNATIONAL BORDER NEAR NOGALES AND DOUGLAS. HOWEVER...CONFIDENCE
ON THIS HAPPENING IS NOT AS HIGH SINCE THE LATEST MODEL RUNS SHOW
THE RIDGE BUILDING WEDNESDAY AND NEARLY OVERHEAD FOR THURSDAY AND
FRIDAY. PREVIOUS SOLUTIONS WERE SUGGESTING AN INVERTED TROUGH MOVING
WESTWARD ACROSS NORTHERN MEXICO...BUT NOW THIS FEATURE IS LESS
PRONOUNCED AND FARTHER SOUTH. THAT SAID...THE RAIN CHANCES FOR
FRIDAY MAY BE TOO HIGH. OVERNIGHT SHIFT WILL WANT TO TAKE A CLOSER
LOOK AT THIS AFTER RECEIPT OF 00Z MODEL RUNS.

THE BIG STORY HOWEVER IS THE EXPECTED HOT TEMPERATURES DURING THE
MIDDLE TO LATTER PART OF THE WEEK. HIGHS FOR TUCSON EXPECTED TO
POTENTIALLY REACH THE 110 DEG MARK...WITH SLIGHTLY HIGHER READINGS
FOR THE FAR WESTERN DESERTS. HIGH TEMPERATURES WILL BE ABOVE NORMAL
THROUGHOUT THE ENTIRE FORECAST PERIOD...WITH THE WARMEST DAYS
OCCURRING WEDNESDAY AND THURSDAY WHEN HIGHS WILL BE 10 TO 12 DEGS
ABOVE NORMAL...OTHERWISE HIGHS RUNNING ABOUT 4 TO 7 DEGS ABOVE
NORMAL EACH DAY. LOWS GENERALLY 3 TO 5 DEGS ABOVE NORMAL EACH
MORNING.

&&

.CLIMATE...NEAR RECORD HEAT EXPECTED TUESDAY THROUGH THURSDAY. THE
FORECAST EXCEEDS RECORD LEVELS ON WEDNESDAY AND THURSDAY WITH
TEMPERATURES AROUND 110 AT TUCSON INTERNATIONAL. THIS WOULD BE THE
FIRST 110 TEMPS OF THE YEAR AND HOTTEST JULY TEMPS SINCE 2011 (110
OR GREATER OCCURRENCES ARE MOST COMMON IN JUNE BEFORE THE MONSOON
ARRIVES).

&&

.AVIATION...VALID THRU 22/00Z.
ISOLD -TSRA/-SHRA SE OF KTUS AND MAINLY EAST OF KFHU EASTWARD TO
KDUG THIS EVENING. DRY CONDITIONS WILL PREVAIL ELSEWHERE INTO EARLY
MONDAY MORNING. BRIEF MVFR VISIBILITIES AND WIND GUSTS TO 40 KTS MAY
OCCUR WITH -TSRA. OTHERWISE SFC WINDS WILL BE LESS THAN 10 KTS
EXCEPT FOR THE GILA RIVER VALLEY IN THE VICINITY OF KSAD...WHERE
WLY/NWLY SURFACE WIND AROUND 15 KTS THRU EARLY EVENING. EXPECT ISOLD
-TSRA/-SHRA EAST AND SOUTH OF KTUS MONDAY AFTERNOON. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...THUNDERSTORMS REMAIN IN THE FORECAST NEAR THE
INTERNATIONAL BORDER AND IN THE EASTERN MOUNTAINS ALONG THE NEW
MEXICO BORDER EARLY THIS WEEK...BUT STRENGTHENING HIGH PRESSURE
ALOFT WILL TEND TO LIMIT OVERALL THUNDERSTORM COVERAGE AND BRING
NEAR RECORD HIGH TEMPERATURES BY THE MIDDLE OF THE WORK WEEK.
INCREASED MOISTURE AND BETTER CHANCES FOR THUNDERSTORMS ARE FORESEEN
AS THE WEEK DRAWS TO A CLOSE.

&&

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

&&

$$

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

FRANCIS
PREVIOUS DISCUSSION...MOLLERE
FIRE WEATHER...KD




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