Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 181610
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
910 AM MST MON AUG 18 2014

.SYNOPSIS...AMPLE MOISTURE WILL PROVIDE SCATTERED TO NUMEROUS
THUNDERSTORMS THIS WEEK. SOME STORMS WILL PRODUCE GUSTY WINDS AND
HEAVY HEAVY RAIN THAT MAY PRODUCE FLASH FLOODING. DAYTIME
TEMPERATURES WILL BE BELOW AVERAGE BY MIDWEEK.

&&

.DISCUSSION...IR/VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS
INDICATE PARTLY CLOUDY SKIES ACROSS ERN SECTIONS TO CLOUDY SKIES
ACROSS WRN PIMA COUNTY. DEWPOINTS AT LOWER ELEVATIONS VALID 16Z
RANGED FROM THE UPPER 50S-MID 60S F...AND THESE TEMPS WERE NEARLY
IDENTICAL TO 24 HOURS AGO. SURFACE TEMPS WERE GENERALLY 2-6 DEGS F
COOLER VERSUS THIS TIME SUN.

18/12Z KTWC SOUNDING TOTAL PRECIP WATER VALUE WAS 1.51 INCHES. A
FAIRLY UNSTABLE ENVIRONMENT EXISTED WITH LIFTED INDEX OF MINUS 6 AND
UNMODIFIED SURFACE-BASED CAPE OF 1639 J/KG. HAVE NOTED THE
CONSIDERABLY STRONGER MID-LEVEL SELY STEERING FLOW FOR THUNDERSTORMS
VERSUS THE PAST 2-3 DAYS. 18/12Z UPPER AIR PLOTS DEPICTED A BROAD
RIDGE OVER THE SWRN CONUS WITH 591 DM HIGH PRESSURE CENTERED OVER
THE FOUR CORNERS REGION. LIGHT TO MODERATE GENERALLY ELY/SELY FLOW
PREVAILED IN THE SURFACE-400 MB LAYER WITH MODERATE WLY FLOW ABOVE
400 MB.

18/14Z RUC HRRR...18/12Z NAM AND 18/12Z UNIV OF AZ WRF-NAM WERE
SIMILAR WITH DEVELOPING SHOWERS/TSTMS BY EARLY THIS AFTERNOON MOSTLY
NEAR THE INTERNATIONAL BORDER ADJACENT SANTA CRUZ/COCHISE COUNTIES.
SHOWERS/TSTMS ARE THEN PROGGED TO MOVE NWWD INTO SOUTH CENTRAL AZ BY
AROUND MIDNIGHT TONIGHT. THIS SCENARIO SEEMS QUITE VIABLE GIVEN THE
AFOREMENTIONED STRONGER MID-LEVEL STORM STEERING FLOW AS OBSERVED
VIA THE 18/12Z KTWC SOUNDING.

BASED ON THESE SOLUTIONS AS WELL AS COORD WITH WFO PSR...HAVE OPTED
TO INCREASE THE INHERITED POPS FOR THIS AFTERNOON THRU TUE. BASED ON
THE COMP REFLECTIVITY/10M WIND SIGNATURES AS PER THE UNIV OF AZ
WRF-NAM...HAVE ADDED AREAS OF BLOWING DUST FOR SOUTH CENTRAL PINAL
COUNTY /AZZ505/ THIS EVENING. MAY OPT TO ISSUE A BLOWING DUST
ADVISORY LATER TODAY FOR SOUTH CENTRAL PINAL COUNTY IF SUBSEQUENT
RUC HRRR AND UNIV OF AZ WRF-GFS SOLUTIONS MIMIC THE UNIV OF AZ
WRF-NAM SOLUTION.

ALSO...BASED THUS FAR ON THE 18/12Z NAM...AM GIVING CONSIDERATION
TOWARD THE POTENTIAL ISSUANCE OF A FLASH FLOOD WATCH MAINLY FOR
LOCALES EAST OF TUCSON TUE. WILL ADDRESS THIS NOTION FURTHER IN THE
AFTERNOON DISCUSSION. OTHERWISE...HIGH TEMPS THIS AFTERNOON SHOULD
AVERAGE ABOUT 3-5 DEGS F COOLER VERSUS TEMPS ACHIEVED SUN.

PLEASE REFER TO THE ADDITIONAL SECTIONS FOR FURTHER DETAIL.

&&

.AVIATION...VALID THRU 19/18Z.
EXPECT SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP SOUTHEAST-TO-
SOUTHWEST OF KTUS BY EARLY THIS AFTERNOON. SCATTERED TO NUMEROUS
-TSRA/-SHRA WILL THEN OCCUR THIS AFTERNOON AND THIS EVENING. MVFR
VISIBILITIES AND BRIEF WIND GUSTS OF 45-50 KTS WILL OCCUR WITH THE
STRONGER TSRA. SCATTERED -SHRA AND ISOLATED -TSRA WILL PREVAIL LATE
TONIGHT INTO TUESDAY MORNING. OTHERWISE...CLOUD DECKS WILL MAINLY BE
AT 6-12K FT AGL AND SURFACE WIND GENERALLY BE LESS THAN 10 KTS THRU
TUESDAY MORNING. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED TO NUMEROUS THUNDERSTORMS WILL OCCUR THIS
WEEK AS AMPLE MOISTURE REMAINS ACROSS SOUTHEAST ARIZONA. THE
STRONGER THUNDERSTORMS WILL PRODUCE STRONG...GUSTY AND ERRATIC
WINDS. OTHERWISE...AFTERNOON MINIMUM RELATIVE HUMIDITIES ARE
FORECAST TO BE MOSTLY IN THE 25-50 PERCENT RANGE AT LOWER ELEVATIONS
FOLLOWED BY GOOD TO EXCELLENT OVERNIGHT RECOVERIES. 20-FOOT WINDS
WILL EXHIBIT NORMAL DIURNAL TRENDS AND BE MOSTLY LESS THAN 15 MPH.

&&

.PREV DISCUSSION...WEDNESDAY...UPPER LOW IS FORECAST TO BE ALONG OR
JUST OFF THE SRN CA CST. MOIST SOUTHERLY FLOW CONTINUES ACROSS SRN
AZ...BUT COULD ALSO SEE SOME DRIER AIR PUSH INTO THE SWRN PART OF
THE STATE. WILL CONTINUE CHANCE OF AFTERNOON/EVENING STORMS.
DEPENDING ON HOW MUCH RAIN FALLS ON TUESDAY WILL HAVE A PART IN
DETERMINING HOW WARM IT WILL GET. 00Z MOS GUIDANCE COOLER THAN WHAT
WE ARE FORECASTING. AGAIN WILL NOT MAKE ANY CHANGES HERE.

THURSDAY INTO THE UPCOMING WEEKEND...STILL SOME UNCERTAINTY OF WHEN
OR IF THE SRN CA UPPER LOW WILL LIFT THRU THE STATE. GFS SAYS
THURSDAY...ECMWF SAYS FRIDAY...CANADIAN KEEPS IT OFFSHORE. WITH SUCH
UNCERTAINTY...WILL MAINTAIN NEAR CLIMO POPS DURING THIS PERIOD.

OVERALL STILL SHAPING UP TO BE A WET WEEK ACROSS SE AZ WITH FLASH
FLOODING A CONCERN MOST OF THE WEEK.

&&

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

&&

$$

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

FRANCIS
PREVIOUS DISCUSSION...GLUECK




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